The geothermal exploration of Campanian volcanoes: Historical review and future development

Abstract

Since Roman time, the heat produced by Neapolitan volcanoes was an appeal for people living in and outside the area, for the fruition of the famous thermal baths. This very large area, which spans from Campi Flegrei and Ischia calderas to Somma-Vesuvius volcano, is characterized by high temperature at shallow depth and intense heat flow, and is yet utilized for the bathing and spa treatment industry, while only in the middle of the 20th century a tentative of geothermal exploitation for energy production was performed. Pioneering researches of geothermal resource were carried out in Campanian region since 1930, until 1985, during which a large amount of geological data were collected. In this paper, we make for the first time a review of the history of geothermal explorations in the active Campanian volcanic area. By the analysis of a great amount of literature data and technical reports we reconstruct the chronology and the main information of the drillings performed since 1930 by the SAFEN Company an

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Reviews
16 (2012) 1004–
1030
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The
geothermal
exploration
of
Campanian
volcanoes:
Historical
review
and
future
development
S.
Carlino∗,
R.
Somma,
C.
Troise,
G.
De
Natale
Istituto
Nazionale
di
Geofisica
e
Vulcanologia-Sezione
di
Napoli,
Osservatorio
Vesuviano,
Italy
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
13
September
2011
Accepted
27
September
2011
Available online 21 October 2011
Keywords:
Geothermal
energy
Neapolitan
volcanoes
Magma
reservoirs
Heat
flow
Geothermal
gradient
a
b
s
t
r
a
c
t
Since
Roman
time,
the
heat
produced
by
Neapolitan
volcanoes
was
an
appeal
for
people
living
in
and
outside
the
area,
for
the
fruition
of
the
famous
thermal
baths.
This
very
large
area,
which
spans
from
Campi
Flegrei
and
Ischia
calderas
to
Somma-Vesuvius
volcano,
is
characterized
by
high
temperature
at
shallow
depth
and
intense
heat
flow,
and
is
yet
utilized
for
the
bathing
and
spa
treatment
industry,
while
only
in
the
middle
of
the
20th
century
a
tentative
of
geothermal
exploitation
for
energy
production
was
performed.
Pioneering
researches
of
geothermal
resource
were
carried
out
in
Campanian
region
since
1930,
until
1985,
during
which
a
large
amount
of
geological
data
were
collected.
In
this
paper,
we
make
for
the
first
time
a
review
of
the
history
of
geothermal
explorations
in
the
active
Campanian
volcanic
area.
By
the
analysis
of
a
great
amount
of
literature
data
and
technical
reports
we
reconstruct
the
chronology
and
the
main
information
of
the
drillings
performed
since
1930
by
the
SAFEN
Company
and
successively
in
the
framework
of
the
ENEL-AGIP
Joint
Venture
for
geothermal
exploration.
The
available
data
are
utilized
to
correlate
the
temperatures
measured
within
the
deeper
wells
with
the
possible
sources
of
geothermal
heat
in
the
shallow
crust,
down
to
about
8–10
km
of
depth.
Finally,
we
assess
the
geothermal
potential
of
the
hottest
areas,
Ischia
Island
and
Campi
Flegrei,
which
have
shown
the
best
data
and
favorable
physical
conditions
for
a
reliable,
and
cost-effective,
exploitation
for
thermal
and
electric
purposes.
© 2011 Elsevier Ltd. All rights reserved.
Contents
1.
Introduction
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2.
Geological
settings
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.1006
3.
The
Neapolitan
Volcanoes
in
the
history:
volcanology
and
natural
resources.
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4.
Geothermal
explorations
in
Italy
and
Campania
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.1009
5.
Campi
Flegrei.
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.1011
6.
Ischia
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.1015
7.
Vesuvius
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.1017
8.
Temperatures,
crust
rheology
and
magma
reservoirs
location
beneath
Campanian
volcanoes
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.1021
9.
The
assessment
of
geothermal
resource
of
Campanian
volcanoes
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.1025
10.
The
exploitation
of
geothermal
resource
in
Neapolitan
area
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.1027
11.
Conclusions
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.1027
Acknowledgments
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.1028
References
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.1028
1.
Introduction
The
geothermal
heat
supplied
by
the
active
volcano
districts
of
the
Campania
region
(Fig.
1)
was
an
appeal
since
Roman
time,
when
the
fruition
of
famous
thermal
baths
of
Ischia
island,
Baia
and
Lucrino
(Campi
Flegrei)
become
a
custom
for
people
living
∗Corresponding
author.
E-mail
address:
stefano.carlino@ov.ingv.it
(S.
Carlino).
in
and
outside
the
area
(Fig.
2).
Since
that
time
on,
visitors
to
Ischia
and
Campi
Flegrei
would
have
been
lured
and
connected
to
the
development
of
the
bathing
and
spa
treatment
industry
[1].
The
industrial
revolution,
started
on
the
XVII
century,
arose
the
needs
of
raw
material
for
energy
production,
coal
in
a
first
times
and
oil
in
recent
times.
In
this
framework
nowdays,
the
geother-
mal
renewable
energy
can
be
considered,
if
easily
available,
a
high
value
economic
resource
for
thermal
and
electric
energy
produc-
tion.
Pioneering
researches
of
geothermal
resource
were
carried
out
in
Campanian
region
since
1930.
More
recent
researches
were
part
of
the
National
Energy
Plan
[2],
aimed
to
better
constrain
the
1364-0321/$
–
see
front
matter ©
2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.rser.2011.09.023

S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030 1005
Fig.
1.
The
Campanian
Plain
and
the
active
volcanoes
area
of
Vesuvius,
Campi
Flegrei
and
Ischia,
with
main
tectonic
features.
geothermal
potential
in
the
volcanic
district
of
Campania
(Vesuvius,
Campi
Flegrei
caldera
and
Ischia
Island),
and
were
supported
by
a
Joint
Venture
between
ENEL
and
AGIP
Companies
[3].
The
explo-
ration
program
was
stimulated
also
by
the
interesting
results
on
geothermal
exploitation
obtained
at
Larderello
(Tuscany),
since
the
early
1900
[4].
From
1930
to
the
mid
1980,
a
total
of
117
wells
for
geothermal
exploration
were
drilled
down
to
a
maximum
depth
of
3046
m
(90
wells
at
Ischia,
26
at
Campi
Flegrei
and
1
at
Vesuvius).
The
results
of
such
investigations
were
particularly
encouraging
at
Campi
Flegrei
and
Ischia,
where
elevated
geothermal
gradients
were
recorded,
due
to
the
presence
of
high
enthalpy
fluids
(T
>
150 ◦C)
localized
at
shallow
depths
(hundred
of
meters)
and
both
vapor
and
water
dominated
[3].
Despite
these
interesting
results,
the
exploitation
of
the
campanian
geothermal
resource
was
never
started,
mainly
because,
after
the
mid
‘1980s,
the
oil
price
was
again
very
cheap,
Italy
was
starting
its
first
nuclear
plan
(abandoned
in
1986
after
the
Chernobyl
disaster)
and
there
was
not
yet
a
real
interest
for
renewable
energy
beyond
simple
economic
considerations.
The
drilling
program
at
Campanian
volcanoes
had
stimulated
not
only
the
geothermal
research
for
industrial
application,
but
also
the
researches
in
the
field
of
the
volcanolgy.
Important
information
such
as
temperatures
of
shallow
crust,
chemical
rocks
and
fluids
composition
at
depth
and
stratigraphy
have
been
utilized
for
the
reconstruction
of
the
eruptive
history
of
Vesuvius,
Campi
Flegrei
caldera
and
Ischia
and
to
constrain
physical
models
of
volcanic
activity
[14,36,58].
In
recent
time,
the
attention
posed
on
the
geothermal
potential
of
the
Campania
region
has
been
drawn
back
consequently
to
the
approval
of
the
“Campi
Flegrei
Deep
Drilling
Project”
(CFDDP),
in
the
framework
of
the
International
Continental
Drilling
Program
(ICDP)
(icdp-online.org).
In
this
paper
we
make
a
review
of
the
history
of
geother-
mal
researches
of
Campanian
volcanoes,
starting
from
the
earlier
volcanological
studies
at
Vesuvius,
Campi
Flegrei
and
Ischia.
We
analysed
the
historical
and
scientific
reasons
which
make
this
area
of
great
interest
for
geothermal
research;
by
the
analysis
of
a
great
amount
of
literature
data
and
technical
reports.
We
reconstruct
the
chronology
and
the
main
information
of
the
drillings
performed
since
1930
by
the
SAFEN
Company
and
successively
in
the
frame-
work
of
the
ENEL-AGIP
Joint
Venture
for
geothermal
exploration
[3].
Furthermore,
the
available
data
are
utilized
to
correlate
the
temperatures
measured
within
the
deeper
wells
with
the
pos-
sible
sources
of
geothermal
heat
in
the
shallow
crust,
down
to
about
8–10
km
of
depth.
Finally,
we
assess
the
geothermal
poten-
tial
of
Ischia
and
Campi
Flegrei,
which
have
shown
the
best
data
and
favorable
physical
conditions
for
a
reliable,
and
cost-effective,
exploitation
for
thermal
and
electric
purposes.
Our
studies
are
also
preparatory
for
the
realization
of
the
“Campi
Flegrei
Deep
Drilling
Project”
(CFDDP),
approved
by
the
International
Continen-
tal
Drilling
Program
(ICDP),
and
aimed
to
the
understanding
of
the
Campi
Flegrei
caldera
dynamics
and
to
the
accurate
geother-
mal
resource
assessment.
This
work
also
emphasizes
the
economic
importance
of
the
geothermal
electric
production,
for
Italy
and
mainly
for
the
Southern
regions,
also
as
an
alternative
to
the
nuclear
energy,
after
the
abandon
of
the
last
resource
decided
by
people
in
the
recent
general
consultation
(referendum).

1006 S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030
Fig.
2.
The
old
Roman
thermal
baths
of
Baia,
in
the
Campi
Flegeri
volcanic
area
(photo:
S.
Carlino).
2.
Geological
settings
The
Campania
volcanic
district
is
distinguished
by
the
pres-
ence
of
three
active
volcanoes,
Vesuvius,
Campi
Flegrei
and
Ischia
within
the
Campania
Plain.
This
structure,
located
on
the
Tyrrhe-
nian
margin,
at
the
west
of
the
Apennines,
is
characterized
by
a
general
tensional
tectonic
regime,
with
NE-SW
and
NW-SE
regional
faults
systems,
which
produced
faulted
graben
morphology
of
the
carbonate
basement.
The
structural
depression
is
mainly
filled
by
Plio-Quaternary
volcanic
rocks
and
sediments
(Fig.
1).
The
Cam-
pania
volcanoes
are
localized
along
the
NE-SW
and
N–S
regional
faults,
while
the
volcanism
of
this
area
seems
to
have
started
between
1
and
2
My
ago
[5–10].
The
Campania
volcanism
is
related
to
the
tensional
spreading
process
of
the
Tyrrenian
basin,
which
produces
the
thinning
of
the
crust
and
upwards
migration
of
magma,
generating
an
high
heat
flow
of
this
area
(>100
mW
m−2)
[11–13]
(Figs.
3
and
4).
The
Southesternmost
volcanic
edifice,
Mt.
Somma–Vesuvius,
is
a
strato-volcano
consisting
of
a
recent
cone,
Vesuvius,
which
evolved
within
the
older
Somma
caldera
[14,15]
(Fig.
5).
The
volcanic
com-
plex
rests
on
a
sequence
of
Mesozoic
and
Cenozoic
carbonates
overlain
by
Miocene
sediments
of
the
Campanian
Plain
[16,17].
This
thick
sedimentary
sequence
has
been
found
at
a
depth
of
about
1.5
km
[18],
and
in
seismic
profiles
in
the
Gulf
of
Naples
at
more
than
3–4
km
[6,19].
Volcanic
activity
in
the
area
near
Mt.
Somma–Vesuvius
extends
from
at
least
about
300
ky
BP
[18].
The
volcanic
history
(on
the
basis
of
the
outcropped
products)
started
about
25
ky
ago.
This
has
been
characterized
by
at
least
4
plinian
eruptions
(Pomici
di
Base,
18–20
ky;
Mercato,
8.7–9
ky;
Avellino
3.5–3.7
ky;
Pompei,
79
A.D.)
spaced
out
by
sub-plinian
eruptions
(Pomici
Verdoline,
15–16
ky,
Pollena,
472
A.D.;
1631
erution),
minor
eruptions
(effusive-strombolian
type)
and
by
qui-
escent
periods
[14,20–22].
In
recent
time,
from
1631
to
1944
the
Vesuvius
has
undergone
to
a
period
of
persistent
activity,
with
well
documented
effusive
to
volcanian
activity,
which
terminates
with
the
1944
moderate
eruption
[14,23].
During
the
history
of
the
vol-
cano,
the
magma
reservoirs
that
fed
the
eruptive
activity
migrated
from
8–9
km
to
3–4
km
depth
[24].
Mt.
Somma–Vesuvius
is
now
quiescent,
characterized
by
low
fumarolic
and
seismic
activity,
and
low
temperature
at
depth.
This
state
of
repose
has
been
associ-
ated
with
physical
and
chemical
modifications
affecting
a
cooling,
residual
magma
body
within
the
volcanic
conduit
[25].
The
pres-
ence
of
such
magma
body
is
supported
by
the
high
rigidity,
the
magnetized
character
of
the
crust
beneath
the
crater,
extending
Fig.
3.
Geothermal
areas
related
to
tensile
and
compressive
tectonic
processes.
After
AGIP
(1987).
Fig.
4.
Heat
flow
map
of
Italy.
After
Della
Vedova
(2001).

S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030 1007
Fig.
5.
Somma-Vesuvius
volcanic
complex.
The
location
of
Trecase
well
is
reported
(red
circle).
(For
interpretation
of
the
references
to
colour
in
this
figure
legend,
the
reader
is
referred
to
the
web
version
of
the
article.)
down
to
about
5
km
[26]
and
by
geochemical
data
[27].
Seismic
[28,29]
and
magnetotelluric
surveys
[30]
indicate
the
presence
of
a
large
magma
sill
located
under
the
volcano
at
about
8–10
km.
Notably,
a
deeper
magma
chamber
has
also
been
proposed,
perhaps
extending
to
20
km
[31],
where
the
crust–mantle
boundary
may
be
located
[32,33].
A
high
velocity
body
dipping
westward
from
65
km
down
to
285
km
was
interpreted
as
a
subducting
plate
within
the
mantle
[31]
which,
also
on
the
basis
of
deep
seismicity
(300
km)
detected
in
the
central
Tyrrhenian
Sea,
is
thought
to
indicate
an
actively
subducting
slab
[34,35].
Located
at
the
Northwestern
limit
of
the
Gulf
of
Naples,
the
Campi
Flegrei
caldera
(CFc)
is
roughly
12
km
wide,
with
its
centre
located
in
the
Bay
of
Pozzuoli,
about
15
km
to
the
west
of
Naples.
The
current
caldera
shape
is
thought
as
the
result
of
two
large
collapses,
the
first
of
which
was
probably
related
to
the
Campanian
Ignimbrite
(CI;
150–200
km3dense
rock
equivalent
[DRE];
age,
39
ky
BP),
and
the
second
to
the
Neapolitan
Yellow
Tuff
(NYT;
40
km3DRE;
age,
12–15.6
ky
BP)
eruptions
[22,36–39]
(Fig.
6).
The
volcanic
activity
has
continued
within
the
caldera,
with
phreatomagmatic
eruptions
and
lava
dome
emplacement
[36].
The
last
eruption
occurred
in
1538,
with
the
formation
of
the
Monte
Nuovo
crater,
roughly
in
the
centre
of
the
caldera.
Since
Roman
times,
the
CFc
area
has
been
characterized
by
slow
subsidence,
at
a
rate
of
about
1.1–2
cm
y−1[40,41],
which
has
been
interrupted
by
recurring
phases
of
rapid
uplift
that
are
generally
accompanied
by
intense
seismicity.
The
study
of
sea-level
markers
on
Roman
coastal
ruins
has
revealed
historical
ground
movements,
with
a
Roman
market-place
(Serapis)
that
was
uncovered
in
A.D.
1750
in
Pozzuoli
being
the
subject
of
many
studies
(see
for
a
review
[40,42,43]).
At
least
one
well
evident
phase
of
uplift
has
been
recognized
to
have
occurred
prior
to
the
last
Monte
Nuovo
erup-
tion
(A.D.
1538;
0.02
km3DRE)
[44].
More
recently,
two
phases
of
uplift
have
occurred,
during
1970–1972
and
1982–1984,
when
the
town
of
Pozzuoli
was
raised
by
1.7
m
and
1.8
m,
respectively.
During
the
1982–1984
unrest
episode,
more
than
15,000
shallow
earthquakes
(at
1–5
km
in
depth)
with
a
maximum
magnitude
of
4.0
were
recorded
by
the
seismic
stations
of
the
Osservatorio
Vesuviano
[45],
and
the
ground
uplift
occurred
at
an
average
rate
of
0.3
cm
d−1.
The
last
episode
of
unrest
indicated
the
possibility
of
an
imminent
eruption,
forcing
the
authorities
to
evacuate
Pozzuoli;
however,
the
unrest
virtually
ended
in
December
1984,
without
any
eruption
occurring
[31].
Studies
of
the
unrest
mechanism
and
caldera
dynamics
using
different
physical
approaches
are
useful
to
provide
assessments
of
the
volcanic
risks
of
this
highly
densely
populated
area.
The
caldera
of
Campi
Flegrei
is
characterized
by
the
occurrence
of
a
large
scale
hydrothermal
system,
at
a
depth
of
hundred
meters
to
few
kilo-
metre
of
depth,
whit
high
temperature
(>100 ◦C)
even
at
shallow
depth.
This
system
interacts
with
the
magma
reservoir
located
at
a
maximum
depth
of
8
km,
which
was
detected
by
the
seismic
tomography
experiments
[46].
At
shallower
depth,
the
eventual
presence
or
not
of
smaller
magma
batches
is
not
yet
clear.
A
large
number
of
studies
presented
different
models
to
explain
the
uplift
of
the
caldera
observed
during
the
1970–1972
and
1982–1984
unrest.
Same
of
these
relate
the
uplift
to
the
pressure
increases
in
a
shallow
magma
body
(3–4
km
in
depth)
located
below
Pozzuoli,
while
other
models
accounts
for
the
interaction
between
magma
and
overpressured
fluids,
which
supplied
the
main
contribute
to
the
uplift
[25,31,45,47–57].
Located
West
of
Campi
Flegrei
caldera,
the
Ischia
island
is
formed
by
volcanic
rocks
deriving
from
eruptive
centres
largely
destroyed
or
covered
by
subsequent
activity.
The
oldest
outcrops
date
back
about
150
ka
BP
while
the
most
recent
eruption
occurred
in
1301–1302
A.D.
The
central
sector
of
the
island
is
made
up
by
Mt.
Epomeo
(787
m
a.s.l.),
a
structure
uplifted
by
the
resurgence
of
the
caldera
formed
after
the
large
explosive
eruption
(55
ka
BP)
which
deposited
Mt.
Epomeo
Green
Tuff
(MEGT)
(Fig.
7).
The
resurgence
phase
started
about
33,000
years
ago,
producing
the
Mt.
Epomeo
structure
whose
edges
are
marked
by
a
NW-SE
and
NE-SW
and
N–S
system
of
faults
and
fractures
[37,58–65].
The
total
average
uplift
of
about
800
m,
inferred
from
the
present
height
of
marine
deposits
on
Mt.
Epomeo,
occurred
as
a
discontinuous
process
at
an
average
velocity
of
about
3
cm/year.
The
resurgence,
generally
interpreted
as
due
to
the
increase
in
pressure
of
a
shallow
magmatic
body,
was
accompanied
by
volcanic
activity
external
to
the
resurgent
block
with
dome
emplacement,
spatter
cones
and
tuff
rings
in
the
east-
ern
side.
This
evolution
culminated
with
the
dismantlement
of
its
southern
slope
by
avalanching
[58,64]
(Vezzoli,
1988;
Tibaldi
and
Vezzoli,
2004),
and
seismicity
since
1228
confined
in
the
north-
ern
sector,
while
moderate
volcano-tectonic
processes
occurred
in
the
western
slope
of
the
island.
The
supposed
trachytic
intrusion,
whose
top
is
located
at
about
2
km
of
depth,
is
responsible
of
the
active
hydrothermal
circulation
and
vigorous
surface
hydrothermal
manifestations,
with
maximum
temperature
of
the
surface
water
of
about
100 ◦C
[65–68].
3.
The
Neapolitan
Volcanoes
in
the
history:
volcanology
and
natural
resources
The
Neapolitan
volcanic
area
has
been
the
site
where
the
Western
Europe
civilization
was
born,
and
continued
for
over
25
centuries.
Cuma,
at
the
Northern
edge
of
Campi
Flegrei,
and
Ischia
volcanic
island
were
the
first
settlements
of
Greek
civilization
in
Italy,
dating
back
the
VIII
century
BC.
During
the
Roman
age,
Vesuvius
and
Campi
Flegrei
hosted
the
most
important
towns
of
the
Empire,
for
commercial
and
military
purposes
as
well
as
luxury
homes
of
the
Roman
aristocracy.
Baia,
west
of
modern
Pozzuoli,
hosted
the
largest
port
for
Roman
navy;
Pompeii,
close
to
Vesuvius,
was
a
leading
commercial
port,
whereas
Herculaneum,
located
just
below
Vesuvius,
was
a
rich
and
elegant
town
home
to

1008 S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030
Fig.
6.
Campi
Flegrei
caldera.
The
dotted
line
is
the
limit
of
the
caldera
inferred
from
the
Bouguer
anomaly
(after
Scandone
et
al.,
1991).
White
circles
are
the
location
of
shallow
wells
drilled
since
1939;
red
circles
are
the
deep
wells
drilled
during
the
AGIP-ENEL
Joint
Venture
until
1980.
(For
interpretation
of
the
references
to
colour
in
this
figure
legend,
the
reader
is
referred
to
the
web
version
of
the
article.)
Fig.
7.
The
island
of
Ischia.
The
dotted
line
represents
the
caldera
rim,
while
the
shaded
zone
is
the
area
which
undergone
to
the
resurgent
process
since
at
least
33
ky.
White
circles
are
the
location
of
shallow
wells
drilled
since
1939;
red
circles
are
the
deep
well
drilled
since
1954.
(For
interpretation
of
the
references
to
colour
in
this
figure
legend,
the
reader
is
referred
to
the
web
version
of
the
article.)

S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030 1009
political,
military
and
cultural
aristocracy.
During
the
Middle
Age,
and
the
modern
age
until
the
middle
of
the
19th
century,
this
area
continued
to
represent
the
focus
of
the
European
culture.
Most
of
the
historical
prosperity
of
Neapolitan
area
was
due
to
its
volcanic
nature
and
geothermal
resources.
The
fertility
of
the
volcanic
soils,
the
presence
of
thermal
hot
springs
particularly
appreciated
by
Romans;
the
variety
of
the
landscape,
marked
by
gentle
hills
look-
ing
at
sea,
represented
by
the
volcanic
cones
of
Campi
Flegrei;
the
round
and
deep
Gulfs,
formed
by
volcanic
collapses,
protecting
the
fishing
and
the
navigation;
all
these
elements
made
up
its
fortune
and
appeal
for
so
many
centuries.
The
spectacular
geothermal
activity
of
the
area,
visible
in
fumaroles
and
diffused
volcanic
gas
emissions,
shot
the
imagination
of
ancient
peoples,
loving
warm
and
healthy
water
in
‘Thermae’,
and
feeding
mythological
feelings,
like
the
Averno
lake
where
Roman
poets
located
the
Hell’s
gates.
Modern
geological
and
volcanological
research
was
also
born
in
these
areas.
The
unrest
of
the
Campi
Flegrei
caldera
recorded
by
marine
incrustations
and
shells
over
the
marble
columns
of
the
Serapis
temple
in
the
ancient
Roman
market,
attracted
the
attention
of
the
most
eminent
scientists
of
the
18th
century,
and
furnished
the
first
proof
that,
in
volcanic
areas
like
that
one,
the
ground
could
uplift
and
subside
of
tens
of
meters,
with
respect
to
the
sea
level.
Charles
Lyell
(1797–1875)
[69],
fascinated
by
the
proofs
of
impressive
ground
deformation
testified
by
the
columns
of
the
Serapis
temple,
put
them
on
the
cover
of
its
book
‘Principles
of
Geology’
(1830),
the
first
text
on
Geology
in
modern
sense,
and
a
benchmark
of
the
scientific
theory
of
‘gradualism’,
who
gave
rise
to
the
modern
geology.
A
decade
later,
in
1841,
the
Bourbon
Kings
of
Naples
started
to
build,
on
the
highs
of
Vesuvius,
the
first
volcanic
observatory
in
the
World,
aimed
to
apply
the
recent
discoveries
in
physics
and
electro-magnetism
to
the
study
of
volcanic
eruptions:
the
Osservatorio
Vesuviano,
inaugurated
in
1845
during
the
7th
International
Conference
of
Scientists
in
Naples.
In
recent
time,
the
attention
of
volcanologists
was
drawn
again
in
Neapolitan
area,
since
two
phases
of
uplift,
occurred
during
1970–1972
and
1982–1984,
when
the
town
of
Pozzuoli,
located
in
the
centre
of
Campi
Flegrei
caldera,
was
raised
by
1.7
m
and
1.8
m,
respectively.
During
the
1982–1984
unrest
episode,
more
than
15,000
shallow
earthquakes
(in
the
depth
range
1–5)
with
a
maximum
magnitude
of
4.0
were
recorded
by
the
seismic
sta-
tions
of
the
Osservatorio
Vesuviano
[70],
and
the
ground
uplift
occurred
at
an
average
rate
of
0.3
cm
d−1.
The
last
episode
of
unrest
indicated
the
possibility
of
an
imminent
eruption,
forcing
the
authorities
to
evacuate
Pozzuoli;
however,
the
unrest
virtu-
ally
ended
in
December
1984,
without
any
eruption
occurring
[31].
These
episodes
pushed
the
scientists
to
deepen
the
understand-
ing
of
the
Campi
Flegrei
caldera
behavior
by
using
physical
and
computer
modeling
[31,40,45–52,54–56,71–79].
The
strong
interest
for
the
volcanism
in
the
neapolitan
area
is
due
to
the
high
volcanic
risk
for
population;
in
particular,
since
the
end
of
World
War
II,
the
intense
urban
development
around
explo-
sive
volcanoes
exposes
some
millions
of
inhabitants
to
volcanic
risk.
Due
to
such
high
volcanological
and
civil
defence
interest,
in
recent
times
several
projects
have
been
funded
to
understand
Neapolitan
volcanism
and
to
mitigate
seismic
and
volcanic
risk.
Among
them,
the
Progetto
Finalizzato
Geodinamica,
which
was
launched
after
the
Irpinia
earthquake
occurred
on
November
23rd
1980
and
right
after
the
Campi
Flegrei
unrest
of
the
1982–1984.
This
project
also
provided
a
detailed
reconstruction
of
volcanic
activity
and
dynamic
of
Vesuvius,
Campi
Flegrei
caldera
and
Ischia
[14,36,58].
The
advancement
of
scientific
knowledge
on
these
areas
was
also
stimulated
by
the
application
of
innovative
exploration
tech-
nologies,
such
as
the
seismic
tomography.
At
the
end
of
1990s
two
international
projects
at
Vesuvius
(TOMOVES,
see
[29])
and
Campi
Flegrei
(SERAPIS,
see
[14,77])
allowed
the
reconstruction
of
the
shallow
crust
by
using
active
seismic
soundings.
An
important
result
was
the
detection
of
a
low
velocity
zone
beneath
Vesu-
vius
and
Campi
Flegrei
caldera,
in
the
depth
range
8–10
km,
which
was
interpreted
as
a
widespread
magmatic
reservoir
feeding
large
eruptions
in
the
area
[29,46,77].
Furthermore,
the
obtained
results
confirm
the
hypothesis
of
Moho
upwelling
below
the
Campanian
volcanic
district,
causing
the
migration
of
magma
in
the
shallow
crust
and
producing
an
anomalous
high
heat
flux
and
a
diffuse
shallow
hydrothermal
activity.
These
phenomena,
mainly
active
at
Campi
Flegrei
caldera
and
Ischia,
encouraged,
since
1930,
several
studies
aimed
to
assess
the
geothermal
potential
for
electric
and
thermal
energy
production.
4.
Geothermal
explorations
in
Italy
and
Campania
In
Italy,
just
from
the
19th
century,
it
became
clear
that
the
heat
supplied
by
the
Earth
interior
represented
an
energy
resource,
an
idea
that
was
put
into
practice
after
the
Industrial
Revolution,
for
the
first
time
at
Larderello
(Italy).
Here,
from
the
early
20th
cen-
tury,
a
number
of
wells
were
drilled
for
the
exploitation
of
thermal
energy,
and
later,
when
the
drilling
techniques
were
improved,
the
exploitation
was
extended
to
the
whole
geothermal
area.
In
1904,
the
Prince
Piero-Conti
Ginori,
performed
few
experiments
aimed
to
transform
the
thermodynamic
energy
of
the
vapor
into
electric
energy,
by
using
a
1
Hp
motor
matched
with
a
dynamo,
which
lighted
few
bulbs.
This
experience
lead
to
the
growth
of
geothermal
explorations
in
Italy,
as
an
alternative
to
the
conven-
tional
oil
industry,
which
involved,
at
the
early
1930s,
the
active
volcanic
areas
of
Ischia,
Campi
Flegrei
and
Vesuvius.
Starting
from
the
end
of
World
War
II,
a
relevant
technological
development
in
many
applied
fields
(i.e.
telecommunications,
transports,
mining,
geophysics,
etc.)
was
taking
place.
Such
a
development
in
turns
reflected
into
an
increased
amount
and
quality
of
data
on
earths
phenomena,
giving
a
strong
pulse
and
support
to
Earth
science
studies.
Geophysical
surveys
using
sophisticated
sensors
allowed
to
recognize
the
density
and
the
rheology
of
the
shallow
crust
down
to
few
kilometers
of
depth.
Moreover,
the
results
obtained
by
oil
exploration
were
used
for
the
geodynamical
interpretation
of
the
Italian
peninsula.
The
geological
studies
developed
in
Italy
until
the
20th
century,
and
particularly
those
related
to
the
volcanism,
char-
acterized
by
high
heat
flux
(Fig.
3)
as
a
consequence
of
spreading
of
the
Tyrrhenian
basin
occurring
since
2
My
ago
[3,7].
This
area
is
characterized
by
the
presence
of
NW–SE
volcanic
alignments
which
are
grouped
in
different
co-magmatic
province
of
Tuscany,
Latium
and
Campania.
The
attention
to
the
geothermal
exploration
was
also
stimulated
by
the
increase
of
energy
demand
and
by
the
1973
oil
crises,
which
culminated
with
the
oil
supply
interruption
provided
by
the
OPEC
(Organization
of
the
Petroleum
Exporting
Countries).
In
the
Campania
region
the
presence
of
hot
water
and
fumaroles
was
just
well
known,
since
the
16th
century,
due
to
the
spa
use.
At
Ischia,
from
the
mid
16th
century,
Giulio
Iasolino
(1538–1622)
[80],
a
doctor
from
Calabria,
professor
of
anatomy
at
Naples
University,
started
a
systematic
study
of
the
hot
springs
on
the
island,
which
he
introduced
into
curative
practice.
This
culminated
in
1588
with
the
publication
of
“De’
rimedi
naturali
che
sono
nell’isola
di
Pithecusa,
hoggi
detta
Ischia”
(On
the
natural
remedies
on
the
island
of
Pithecusa,
today
called
Ischia)
[80],
a
work
of
great
importance
and
editorial
success,
which
was
to
boost
Ischia’s
fame,
thanks
in
part
to
the
useful
map
of
sites
included,
engraved
by
the
mapmaker
Mario
Cartaro
from
Viterbo,
which
was
later
used
in
the
most
important
European
atlases.
Interest
in
Ischia
also
grown
due
to
the
eruption
of
the
nearby
Campi
Flegrei
in
1538
A.D.,
which
made
the
more
popular
thermal
baths
of
Pozzuoli

1010 S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030
Fig.
8.
Exploration
leases
if
Italy
since
1977.
From
AGIP
(1987).
and
Baia
impracticable
([1]
and
reference
therein).
The
interest
for
the
extensive
geothermal
fields
at
Ischia
and
Campi
Flegrei,
turns
from
a
merely
spa
use
to
a
geothermal
exploitation
during
the
XX
century.
The
site
location
of
many
drillings,
particularly
at
Ischia,
was
chosen
very
close
to
the
shoreline,
since
the
sea
water
was
used
for
cooling
the
working
fluid
(C2H5Cl)
[81].
The
first
main
drillings
investigation
was
performed
at
Ischia
and
Campi
Flegrei,
from
1939
to
1943,
by
the
SAFEN
Company.
The
geothermal
surface
manifestations
of
these
areas
(hot
springs
and
fumaroles),
with
temperature
of
about
100 ◦C,
suggested
the
presence
of
a
high
geothermal
potential
in
the
shallow
crust
[81].
The
researches
continued
later,
in
the
framework
of
the
Joint
Venture
AGIP-ENEL
companies,
and
were
focused
in
the
Campi
Flegrei
area,
starting
from
1979.
Several
wells
reached
few
kilometers
of
depth,
with
a
maximum
depth
of
3
km
[3].
The
geothermal
researches
interested
also
the
Vesuvius
area,
starting
from
1952,
after
the
462
km2
“Ottaviano”
exploration
licence
issued
[3].
The
aim
was
to
test
under
which
conditions
high
enthalpy
fluids
(>150 ◦C)
could
be
commercially
produced
from
reservoirs
related
to
active
central
volcanoes
[82].
Thus,
a
2072
m
well
depth
was
drilled,
from
1980
to
1981,
in
the
south-east
sector
of
the
Vesuvius
(Trecase
well).
In
the
middle
of
1980,
thanks
to
the
results
obtained
by
vari-
ous
researches,
which
involved
different
areas
of
Italy,
a
reliable
picture
of
the
geothermal
potential
for
thermal
and
electric
uses
was
obtained.
The
exploration
licences,
at
that
time,
interested
a
global
area
of
8200
km2(Fig.
8),
about
2%
of
the
total
surface
of
Italy.
In
December
1983,
the
installed
geothermal
power
was
about
456
MW,
while
the
Italian
Energy
National
Plan
forecasted
an
increment
of
the
power
of
further
200
MW
during
the
incom-
ing
years
[2].
A
complete
report
of
the
geothermal
exploration
state
of
art
was
presented
during
the
“Workshop
for
the
Exploita-
tion
of
Geothermal
Energy
for
Production
of
Electric
and
Thermal
Power”
held
in
Florence
in
1984.
In
the
framework
of
ENEL
and
AGIP
activities,
the
report
identified
the
most
interesting
regions
of
Italy
for
geothermal
exploitation
in
the
range
of
both
low
and
high
enthalpy;
in
contrast,
at
the
moment
only
the
Tuscany
region
is
the
site
of
productive
geothermal
power
plants
[2].
The
main
identified
geothermal
areas
are
the
following:
-
Tuscany
(Larderello,
Travale-Radicondoli),
with
temperature
up
to
400 ◦C
at
3
km
of
depth;
-
Mount
Amiata
(Tuscany),
with
temperature
up
to
350 ◦C
at
3.5
km
of
depth;
-
Torre
Alfina
(Latium),
with
temperature
up
to
150 ◦C
at
2.2
km
of
depth;
- Cesano
(Latium),
with
temperature
up
to
150 ◦C
at
depth
of
about
1
km;
- Latera
(Latium),
with
temperature
up
to
170 ◦C
at
2.6
km
of
depth;
-
Sabatini
Mounts
(Latium),
with
temperature
up
to
290 ◦C
at
2.5
km
of
depth;
-
Lago
Patria
(Campi
Flegrei,
Campania),
with
temperature
up
to
420 ◦C
at
3
km
of
depth;
-
Vulcano
(Sicily),
with
temperatures
in
excess
of
400 ◦C
at
very
shallow
depths;
-
San
Donato
Milanese
(Po
Valley),
with
temperature
up
to
62 ◦C
at
2.2
km
of
depth;
-
Ferrara
(Po
Valley),
with
temperature
of
100 ◦C
at
1.3
km
of
depth.
The
above
results
show
that
the
Campania
region
is
the
area
characterized
by
higher
temperatures
at
shallow
depth,
which
are
useful
for
the
exploitation
of
geothermal
energy
in
the
high
enthalpy
domain.
Also
at
Ischia,
the
results
of
SAFEN
drillings,
showed
the
occurrence
of
high
temperature
(200 ◦C)
at
depth
of
few
hundreds
of
meters
[3].
On
the
other
side,
the
temperature
gradient
measured
within
the
Trecase
well
at
Vesuvius,
was
lower
then
expected
(about
30 ◦C
km−1),
although
the
rather
periferi-
cal
location
of
drilling
could
have
missed
the
geothermal
system,
which
from
indirect
considerations
would
be
much
more
con-
centrated
below
the
crater
area
[83].
The
data
obtained
after
the
explorations
in
Campania
also
allowed
a
better
knowledge
of
the
volcanic
processes
occurred
at
Ischia,
Vesuvius
and
Campi
Fel-
grei
caldera.
These
data
have
been
collected
in
various
technical
reports
of
AGIP
and
scientific
publications
representing,
nowadays,
an
important
database
for
geological,
geochemical,
volcanological
and
petrological
studies
[3,81,82,84–93].
The
increase
of
geother-
mal
energy
production
in
Italy,
as
forecasted
by
the
Italian
Energy
National
Plan,
was
not
followed,
and,
except
for
Tuscany
region,
the
project
of
geothermal
exploitation
was
abandoned
at
the
end
of
1980
years.
Nowadays,
the
geothermal
energy
in
the
world
is
harnessed
on
a
large
scale
for
space
heating,
industry
and
electric-
ity
generation.
The
geothermal
electrical
installed
capacity
in
the
World
was
7974
MWe
(year
2000)
and
the
electrical
energy
gen-
erated
was
49.3
billion
kWhy−1,
representing
0.3%
of
the
world
total
electrical
energy.
In
Italy
the
geothermal
electrical
installed
capacity
(year
2005)
is
about
800
MWe,
with
energy
production
of
about
5.6
GWh
per
year,
which
represents
1.7%
of
national
need-
ings,
while
for
direct
uses
the
capacity
is
about
300
MWt
[94,95]
In
recent
time,
the
interest
for
geothermal
exploitation
in
Campa-
nia
region
was
raised
by
many
converging
reasons.
The
strongest
pulse
towards
such
a
new
interest
was
due
to
the
“Campi
Flegrei
Deep
Drilling
Project”
(www.icdp-online.org),
which
raised
grow-
ing
interest
not
only
in
deep
volcanological
research
but
also
in
the
geothermal
exploration
and
exploitation.
In
the
following
sec-
tions,
we
describe
in
detail
the
main
results
obtained
during
the
50
years
of
geothermal
exploration
of
Campanian
volcanic
districts
(Campi
Flegrei
caldera,
Ischia
and
Vesuvius)
and
obtain
estimates

S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030 1011
of
geothermal
potential
for
industrial
use.
In
particular,
we
refer
to
the
research
leases
of
“Lago
Patria”
(Campi
Flegrei
caldera
and
Ischia)
and
“Ottaviano”
(Vesuvius)
and
to
the
drillings
performed
by
the
SAFEN
and
AGIP
Companies
and
the
related
data
obtained
during
the
pumping
tests
[3].
5.
Campi
Flegrei
The
first
geothermal
explorations
in
Campi
Flegrei
(Lago
Patria
lease)
were
carried
out
by
the
SAFEN
Company
during
1939
and
1943,
which
drilled
19
wells
(id:
LA,
CLV,
CMV,
A)
with
depth
from
few
meters
to
600
m
[81,84]
(Table
1
and
Fig.
9a
and
b).
The
investigated
area
was
characterized
by
a
vigorous
fumaroles
fields,
named
with
the
local
appellative
of
“mofete”.
The
drillings
showed
the
potentiality
of
this
area
(Mofete
area),
with
the
pres-
ence
of
a
water
dominated
system
at
temperature
of
about
200 ◦C
and
relative
high
pressure
(Fig.
10).
The
methods
and
the
technol-
ogy
adopted
during
that
time,
did
not
allow
the
complete
defining
of
physical
and
chemical
properties
of
geothermal
fluids
[85].
These
fluids
have
an
elevated
salinity
which
caused
problems
during
their
withdrawal.
For
instance,
within
the
CLV7
well,
which
produced
a
maximum
water
and
vapor
flow
rate
of
40th−1,
the
persistence
of
minerals
precipitation
generated
a
self-sealing
phenomenon
with
a
consequent
decreasing
of
flow
and
productivity
of
the
well.
Nev-
ertheless,
the
CLV7
and
CLV17
wells
were
initially
productive,
with
a
flow
rate
of
about
7
l
s−1and
temperature
of
water-vapor
mix-
ture,
at
well
head,
of
about
100 ◦C.
Furthermore,
the
temperature
measured
in
the
wells
showed
a
radial
decreasing
from
the
cen-
tre
of
the
caldera.
The
mid
term
productive
tests
(4
months)
also
demonstrate
that
the
superficial
water
level
in
the
wells
did
not
varied
significantly
during
the
fluid
withdraw.
In
the
early
1940,
a
new
well
was
drilled
within
the
crater
of
Monte
Nuovo
(CMV
well)
(Fig.
11).
This
was
the
result
of
the
last
volcanic
activity
(1538
A.D.)
occurred
in
Campi
Flegrei,
for
this
reason
the
experts
consid-
ered
that
a
sufficient
amount
of
heat,
for
high
temperature
vapor
production,
was
still
contained
in
the
shallow
magmatic
reservoir
which
fed
the
eruption
[84,96].
The
drilling,
lasted
about
5
months
by
using
a
direct
push
rig,
reaching
a
depth
of
667
m
and
a
maxi-
mum
temperature
of
78 ◦C,
lower
that
that
expected.
This
was
due
to
the
cooled
investigated
pyroclastic
deposits,
originated
by
the
Mt.
Nuovo
phreatic
eruption.
At
the
time
of
this
drilling,
the
knowl-
edge
of
volcanic
processes
was
not
clear.
At
the
present,
it
is
well
know
that
monogenic
volcanoes
are
supplied
by
dikes,
which
cool
rapidly
after
their
emplacement.
A
further
shallow
drillings
field
was
carried
out
in
1940,
at
Agnano
(A1,
A3,
A6
wells),
at
a
distance
of
1.5
km
from
the
Solfatara
crater.
Also
in
this
case,
the
results
of
the
drillings
were
not
satisfactory
and
the
exploration
of
this
area
was
temporarily
stopped,
when
a
depth
of
about
100
m
was
reached
and
a
temperature
of
30 ◦C
[84].
The
geothermal
exploration
of
the
whole
Campania
Plain,
was
also
suspended
for
the
World
War
II
occurrence,
in
September
1943.
Later,
from
1953
and
1954,
a
new
drilling
(CF23)
was
performed
at
Agnano
(Fig.
6),
with
a
depth
of
1840
m
and
a
maximum
temperature
of
about
300 ◦C
at
the
bottom.
The
high
temperatures
recorded
at
shallow
depth,
in
particular
in
Mofete
area,
stimulated
further
interest
in
the
geothermal
research,
calling
for
a
new
regional
drilling
program
carried
out,
since
1977,
by
the
established
AGIP-ENEL
joint-venture,
which
ended
in
1985.
Such
a
program
was
decided
by
the
Ministry
of
Industry
(AGIP
and
ENEL
were
at
the
time
State
companies)
in
search
for
alternative
energies
because
of
the
large
peak
of
oil
price
due
to
the
1973,
Israelo-Arab
war.
The
aim
was
both
to
test
the
exploitation
of
high
temperature
fluids
using
an
extraction/reinjection
system
and
to
monitor
the
perturbation
of
the
deep
geothermal
system
(pressure,
water
level
and
capacity)
induced
by
the
presence
of
active
wells.
Because
of
the
substantial
depth
of
the
wells
and
their
closeness
to
highly
urbanized
area,
particular
care
was
paid
to
the
protection
of
the
environment.
Many
surveys
of
micro-seismicity,
deforma-
tion,
soil
gas
emission
were
carried
out
before,
during
and
after
the
drillings
[85].
The
researches
were
extended
to
the
neighbor-
ing
area
of
S.
Vito,
to
the
north
of
Pozzuoli,
and
to
Licola
(L1
well)
located
outside
the
north-west
caldera
rim.
The
latter
was
planned
to
evaluate
the
area
extension
of
the
thermal
anomaly
observed
at
Mofete
(Fig.
6).
In
Mofete
area,
7
wells
(4
deviated
and
3
vertical)
were
drilled
(MF
1,
2,
3d,
5,
7d,
8d,
9d)
with
depth
ranges
from
800
to
2700
m.
The
deviation
allowed
to
intercept
the
possible
fractures
and
faults
zones
from
which
to
obtain
a
better
production,
avoiding
the
extension
of
the
wells
field
close
to
the
urbanized
areas
[89].
At
the
end
of
1985,
the
results
of
the
drillings
defined
the
following
picture:
no.
4
productive
wells
(1,
2,
7d,
8d);
no.
2
injection
wells
(3d,
9d);
no.
1
unproductive
well
(5).
The
results
at
Mofete
identified
three
main
aquifers
localized
within
the
tuffs
and
volcano-sedimentary
formations,
at
a
depth
of
500–1000
m,
1800–2000
m,
2500–2700
m,
respectively.
Only
the
two
shallower
layers
were
productive
for
geothermal
exploitation,
showing
maximum
temperatures
between
250
and
300 ◦C.
The
wells
are
characterize
by
a
vapor–water
mixture
with
a
well
head
temperature
of
180 ◦C–230 ◦C,
TDS
of
30–70
g
l−1,
20%
in
weight
of
non
condensable
gases.
The
flow
rate
of
the
shallower
aquifer
was
200th−1with
maximum
pressure
of
0.8
MPa
(8
bar).
The
intermedi-
ate
aquifer
was
characterized
by
a
lower
flow
rate
of
70th−1but
an
higher
content
in
weight
of
vapor
(40%),
thus
the
resulting
enthalpy
was
1100
kJ
kg−1for
the
shallower
aquifer
and
1600
kJ
kg−1for
the
intermediate
one.
The
characteristics
of
the
wells
and
productive
reservoirs
were
established
through
both
short
(2–3
days)
and
long
(3–4
months)
pumping
tests
[89].
In
the
former
case
the
fluids
were
collected
into
settling
tanks,
while
in
the
latter
case
the
flu-
ids
were
re-injected
into
a
well
that
was
also
utilized
to
study
the
behavior
of
the
geothermal
system.
At
the
end
of
the
investigations
was
established
a
potential
production
of
Mofete
wells
of
about
10
MW.
Also
from
the
geochemical
point
of
view,
the
Mofete
geothermal
field
indicates
a
multiple
reservoirs.
The
geochemical
survey
indi-
cates
that
the
thermal
waters
are
a
mixing
of
local
meteoric
waters
and
deep
hot
waters
of
marine
origin
with
indications
of
local
leak-
age
of
steam
[97].
In
particular
the
MF
1
indicate
the
presence
of
a
water
dominated
reservoir
at
500–900
m
in
fractured
volcanics
with
large
quantities
of
saline
water
(43,000
ppm
TDS,
correspond-
ing
to
30,000
ppm
TDS
at
reservoir
conditions)
with
a
temperature
of
247 ◦C.
Uncommercial
quantities
of
fluids
(65,000
ppm
TDS
at
surface
corresponding
395,000
in
the
reservoir)
were
produced
from
below
1223
m.
The
MF
2
has
encountered
in
fractured
volcano-sedimentary
rocks
(1300–1900
m
depth)
saline
fluids
(380,000
ppm
TDS,
corresponding
to
18,200
ppm
at
reservoir
conditions)
with
a
tem-
perature
of
337 ◦C.
The
MF5
produced
for
a
short
time
from
2700
m
very
hyper
saline
fluids
(over
500,000
ppm
TDS
about
150,000
ppm
in
the
reservoir)
at
a
bottom
hole
temperature
of
347 ◦C.
The
MF
3d,
7d,
8d
and
9d
tapped
the
Mofete
1
reservoir
between
500
and
1500
m
vertical
depth
with
a
bottom
temperature
of
230–308 ◦C
and
a
salinity
of
40,000–75,000
pmm
TDS
at
atmo-
spheric
conditions,
corresponding
to
28,000–52,000
ppm
in
the
reservoir.
Chemical
composition
of
the
brine
was
measured
at
atmo-
spheric
pressure
and
is
given
in
Table
2
and
3
ad
ppm.
From
the
above
values
is
possible
to
do
some
simple
considerations
con-
cerning
the
fluid
circulation
of
Mofete
field.
The
chemical
data
of

1012 S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030
Table
1
Synthesis
of
drilling
at
Campi
Flegrei
performed
from
the
1939
to
1943
(Penta
e
Conforto,
1951).
The
drilled
lithotype
are:
(a)
Trachitic
Tuffs
and
unwelded
pumices,
(b)
Yellow
Tuff;
(b’)
Grenish
Tuff
containing
small
white
pumices
and
lithics,
(c)
Gray
Tuff
sometime
lithified
with
layered
lavas.
Well
Head
well
elevation
(m
a.s.l.)
Depth
(m)
Water
table
(m
a.s.l.)
Encountered
soils
(formation
type)
Maximum
temperature
(◦C)
Data
of
drilling
Surface
temperature
(◦C)
pH
Other
technical
description
LA
1
35.5
72.7
1.49–2.3
0–14
m:
type
a;
14–72.7:
type
b’
111
March–April
1939
100–108
6.28–10
LA
2 23.7 93
0–1.5
0–16
m:
type
a;
16–86.4:
type
b’
104
August–September
1939
6.7–6.9
Rotary
drilling
LA
3
6.32
95.65
0–0.6
0–17
m:
type
a;
17–95.7:
type
b’
69
May
1939
69
Rotary
drilling
CLV
7
52.9
585.5
5.9–52
0–12.5
m:
type
a;
12.5–115:
type
b’;
115–518:
type
c
225
1939–1942
6.5–7.8
Casing
up
to
542.9
m
from
well
head.
Well
eruption
occurred
on
the
7th
April
1941
with
water
emission
up
to
the
5th
August
1942
LA
8
30.29
43.2
0.29–0.30
0–5.7
m:
type
a;
5.7–40.1:
type
b;
40.1–43.2:
b’
49
28th
November–12
December
1940
42–49
6–6.5
Wire
drilling
LA
9
38.96
49.5
0.04–0.3
0–7.2
m:
type
a;
7.2–49.5.
type
b
44
19–30
December
1940
32–40
7.5–8
LA
10
12.49
22.5
0.3–0.8
0–22
m:
type
b
85
7–29
January
1941
78–83
7–7.35
Wire
drilling.
Casing
up
to
21.30
m
from
well
head.
LA
11
72.5
80.8
0.7–1.4
0–44
m:
type
a;
44–80.8.
type
b’
107
7–29
January
1941
100–105
7–9
Casing
up
to
80
m
from
well
head.
LA
12
76.7
84.5
3.2–3.7
0–44
m:
type
a
44–80.8.
type
b’
102
7–21
February
1941
95–100
7.6–8
Casing
up
to
82
m
from
well
head
LA
13
57.37
92.4
1.3–2.37
0–53
m:
type
a;
53–92.4.
type
b’
75
1
March
–24
April
1941
70–73
7–8
LA
14
79.82
92.4
−1.4
to
(−1.27)
0–82
m:
type
a;
82–92.4.
type
b’
105
11–28
June
1941
90–100
7.4–7.5
LA
15
83.59
90.0
0.4–0.9
0–32
m:
type
a;
32–64:
sends
64–90:
type
b’
107
5–22
September
1941
101–106
7–8
CLV
16 64.10 400.0
0–4
0–40
m:
type
a;
40–146:
type
b’;
64–90:
type
b’
135
22
July
1942–1
April
1943
100
Casing
up
to
187.5
m
from
well
head
CLV
17
80.89
521.7
−7.5
to
6.0
0–51
m:
type
a;
51–145:
type
b’;
145–340:
type
c;
340–426:
altered
tuff;
426–521.7:
type
c
224
5
August
1942–24
April
1943
85
Wire
drilling.
Casing
up
to
357
m
from
well
head.
Well
eruption
occurred
on
the
3rd
July
1943
with
vapor
emission
mixed
with
tuff
material
from
the
wall
well
lasted
few
days.
CLV
20
39.7
252.5
0
0–17
m:
type
a;
17–38:
type
b;
38–121:
type
b’;
121–217:
type
c;
217–252.2:
altered
tuff
85
April
1943
and
interrupted
on
the
9th
September
due
to
the
War
World
II
45
CMV
13
676.9
−2.8
to
0
Lava
scoria
and
pumice
78
January
10th
–June
2nd
1942
60
7.2
A
1
17
107.7
n.a.
Altered
tuff
30
January
1940
18
@
4.25
m
Rotary
drilling.
Casing
up
to
100
m
from
well
head
A
3 n.a. 19.65
n.a.
Altered
tuff
and
send
19
December
1941
19
@
3.5
m
A
6
25
24.85
n.a.
Altered
tuff
21
February
1941
21
@
16.6
m
After
Penta
e
Conforto
(1951).

S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030 1013
Fig.
9.
(a)
Shallow
wells
(down
to
about
600
m)
of
Mofete
geothermal
area
(LA,
CLV)
and
Monte
Nuovo
(CMV).
(b)
Shallow
wells
(A)
of
Agnano
geothermal
area.
the
shallow
reservoir
for
the
MF1,
MF3d,
MF7d
and
MF9d
are
very
similar
at
the
same
depth.
An
increase
of
salinity
(i.e.
higher
Na/Li
and
Cl/B)
is
shown
in
MF1
and
MF3D
with
the
depth.
Such
increase
can
be
due
to
the
higher
formation
temperatures,
which
rise
with
depth
from
230
to
308 ◦C.
The
similar
Na/Cl
of
the
MF1
and
MF2
at
the
same
depth
points
to
a
common
origin
of
the
brines.
How-
ever
the
much
lower
salinity
of
MF2
intermediate
reservoir
at
a
short
distance
from
the
MF1
well
can
be
explained
by
considering
the
two
reservoirs
separated.
The
deep
reservoir
from
MF5
shows
a
completely
different
geochemical
composition
for
the
shallow
and
intermediate
reservoirs
(Table
3).
A
possible
model
of
how
the
Mofete
field
originated,
taking
into
account
the
above
discussed
fluid
chemistry
and
other
ele-
ments,
can
be
envisaged
as
follow:
in
a
first
deep
reservoir
(i.e.
MF5)
the
original
sea
water
brine
was
concentrated
to
the
present
values
because
of
evaporation
due
to
the
effect
of
the
high
tem-
perature
and
limited
recharge;
consequently
there
was
a
loss
o
steam
which
migrated
to
the
upper
reservoirs.
During
its
ascent
the

1014 S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030
Table
2
Chemistry
of
water
separated
at
atmospheric
pressure
(ppm).
Shallow
reservoir Intermediate
reservoir Deep
reservoir
MF1
(550–896
m)
MF1
(1273–1506
m)
MF3D
(430–665
m)
MF7D
(1110–1648
m)
MF3D
(552–907)
MF9D
(1339–1749
m)
MF2
(1275–1989
m)
MF5
(2310–2599
m)
Na 14320 20860 13790 14750 14590 21300 10600 85160
K 1760 3880 1122 2510 1526 4410 2467 43380
Ca 792 2124
714
790
752
3520
1005
53950
B 178 183 106 1440 90 288 295 231
Sr
49
58
43
26
41
54
30
1310
As 13 17 15 26 15 32 22
Li 36 46 34 56 37 56 28 480
Mn 10 28 4 10
8
55
52
5510
Fe 1 3 3 21 1 2 1 9450
SiO2568
590
425
639
454
578
938
210
Cl 25304 37800 23393 25650 25171 43897 21169 313850
HCO3116 77 110 195 98 73 85 Traces
SO472 7 156 70
82
14
12
Traces
TDS 42860 55509 39428 45997 42965 75695 37880 515902
Na/Li
398
453
406
264
394
380
379
177
Cl/B 142 207 221 185 280
152
72
1359
Na/Cl 0.57
0.55
0.59
0.55
0.58
0.49
0.50
0.27
ph 7.5
5.5
7.5
7.2
7.7
6.9
6
4.5
From
Carella
and
Guglielminetti
(1987).
Fig.
10.
1st
July
1943
well
eruption
at
Mofete
with
formation
of
a
geyser.
From
Penta
(1949).
Fig.
11.
The
Mt.
Nuovo
crater
formed
during
the
last
eruption
of
Campi
Flegrei
in
1538.
steam
entered
into
the
MF2
intermediate
reservoir
and,
condens-
ing
because
of
lower
temperatures,
caused
a
consistent
dilution
of
the
MF2
brine
which
again
one
must
suppose
poorly
connected
with
the
seawater
recharge
zone.
A
very
minor
quantity
of
steam
remained
to
alter
only
marginally
the
upper
reservoir
(MF1,
MF3d,
Table
3
Water
chemistry
for
selected
samples
calculated
at
reservoir
condition
(ppm)
(from
Carella
and
Guglielminetti,
1987).
Shallow
reservoir
Intermediate
reservoir
MF1
(550–896
m)
MF1
(1273–1506
m)
MF2
(1275–1989
m)
Na
10025
12589
5090
K
1230
2342
1180
Ca
555
1281
480
B
125
110
140
Sr
34
41
14
As
9
11
11
Li 25
28
13
Mn
7
17
25
Fe
1
2
1
SiO2398
417
450
Cl
17710
22310
10200
HCO381
46
41
SO450
4
5
TDS
30000
39500
18200
Na/Li 398
453
391
Cl/B
142
207
73
Na/Cl 0.57
0.55
0.50

S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030 1015
Fig.
12.
Temperature
profiles
measured
during
the
drilling
of
the
deepest
wells
at
Campi
Flegrei.
After
AGIP
(1987).
MF7d,
MF8d
and
MF9d)
better
connected
with
the
sea,
and
to
escape
at
the
surface.
In
December
1979,
a
new
drilling
program
was
started
in
S.
Vito
area,
few
kilometers
north
of
Pozzuoli
town,
with
3
wells
(SV1,
SV8d,
SV3)
(Fig.
6)
of
maximum
depth
and
temperature
of
3046
m
and
420 ◦C,
respectively.
During
the
production
tests
a
tempera-
ture
of
220 ◦C
and
pressure
of
70
kg
cm−2were
measured
at
wells
head.
The
SV1
well
crossed
the
caldera
rim
whose
collapse
was
esti-
mated
of
about
600–700
m
on
the
basis
of
stratigraphic
correlations
between
the
outcropping
Yellow
Tuff
close
to
the
Gauro
crater
and
its
depth
in
the
well.
The
highest
temperatures
(about
400 ◦C)
were
measured
by
using
a
zinc
alloy
with
melt
temperature
of
419 ◦C.
Before
starting
the
measure,
the
drilling
operations
were
stopped
for
some
time,
to
let
the
temperature
of
the
system
stabilize
[88].
In
order
to
evaluate
the
extension
of
the
thermal
anomaly
of
the
inves-
tigated
area
a
new
drilling
was
carried
out
at
Licola
(L1),
located
outside
the
caldera
rim,
close
to
Cuma
north
of
the
caldera.
This
choice
was
also
helpful
for
the
reconstruction
of
the
stratigraphic
sequence
which
was
not
affected
by
volcano-tectonics
events
due
to
caldera
formation.
The
recorded
temperature
in
the
L1
well
was
substantial
lower
than
those
measured
in
S.
Vito
zone,
highlighting
that
the
thermal
anomaly
is
confined
within
the
caldera
rim
[98]
(Fig.
12).
6.
Ischia
The
geothermal
resource
of
Ischia
Island
was
well
known
since
the
16th
century
and
was
utilized
just
for
thermal
baths
and
wellness
[80].
At
the
end
of
20th
century
more
than
180
spa
and
130
thermal
pools,
fed
by
200
wells,
were
operative
in
the
island
[92].
This
spa
activity
nowadays
represents
the
main
economic
resource
of
Ischia,
while
the
planned
exploitation
of
the
huge
geothermal
resource
for
industrial
uses
has
been
not
accomplished
yet.
Only
minor
use
of
this
resource
is
related
to
low
enthalpy
applications
for
buildings
heating.
The
first
geothermal
exploration
of
the
island
was
operated
since
1939–1943,
in
the
western
and
southern
sectors,
Cetara
(Forio)
and
Maronti
(Serrara
Fontana)
and
in
the
northern
sector
Mt
Tabor
(Casamicciola).
Such
exploration
consisted
of
84
drillings,
only
3
of
which
reached
more
than
100
m
of
depth.
Few
of
these
wells
were
used
for
irrigation
and
are
not
reported
here,
since
they
did
not
provide
useful
data.
From
1951
to
1954
the
SAFEN
Company
carried
out
further
6
drillings,
3
of
which
reached
a
depth
of
more
than
500
m.
Thus
a
total
of
90
drillings
were
performed
at
the
end
of
1954
[84]
(Figs.
7
and
13a–c).
Some
of
the
wells
were
utilized
to
check
the
water
table
changes
during
pumping
tests.
The
drillings
were
temporarily
stopped
during
1943,
due
to
the
war
events.
The
wells
were
drilled
in
the
western
and
southern
sectors
of
the
island,
where
the
most
vigorous
fumaroles
and
geothermal
manifestations
are
localized.
In
these
areas
the
surface
temperatures
can
reach
about
100 ◦C
[3].
In
the
eastern
sector
of
S.
Angelo
peninsula
20
drillings
(I,S,IFV)
were
performed
(Table
4)
(Fig.
13a),
only
3
are
deeper
than
100
m.
The
drilling
operations
lasted
from
1939
to
1943;
during
this
period,
despite
the
continuous
hot
fluids
withdrawal,
there
was
not
a
reduction
of
geothermal
manifestations
and
temperature
at
the
surface
[84].
The
geological
information
provided
by
these
wells
was
not
very
significant,
since
they
involved
just
the
surface
formations
of
reworked
tuffs
and
volcanic
breccia.
In
the
1939
second
half-year,
22
wells
were
drilled
in
the
southern
sector
of
the
island
(Maronti)
(Fig.
13b),
with
maximum
depth
of
few
tens
of
meters.
Six
wells
(IM),
with
diameter
of
310
mm,
were
utilized
for
the
pumping
tests,
13
(T)
wells,
with
diameter
of
245
mm,
were
exploited
as
monitoring-wells
and
3
(which
are
not
reported
here)
were
utilized
for
irrigation
(Table
5).
The
measures
of
the
water
table
highlighted
its
regular
oscillation
related
to
water
flow
seasonal
variations,
while
the
increase
of
water
level
was
generally
accompanied
by
a
decreasing
of
temperature.
This
evidence
was
ascribed
to
the
shallowness
of
the
wells,
where
the
water
table
is
rapidly
mixed
with
the
meteoric
one.
In
the
same
period
the
researches
were
extended
to
the
western
sector
of
the
island,
where
several
fumaroles
and
hot
springs
are
located,
with
maxi-
mum
surface
temperature
of
about
100 ◦C.
At
Forio
19
wells
(ICA)
for
the
pumping
tests
were
drilled
(
=
300
mm)
and
5
(S)
were
utilized
as
monitoring-wells
(
=
245
mm)
(Table
6
and
Fig.
13c).
A
number
of
the
deeper
wells
crossed
the
Mt.
Epomeo
Green
Tuff
formation,
whose
collapse
confirmed
the
presence
of
a
volcano-
tectonic
fault
with
vertical
slip
of
about
90
m
[84].
This
observation
supported
the
studies
of
Rittmann
(1930)
[99],
which
defined
the
structure
of
Mt.
Epomeo
as
a
volcano-tectonic
horst.
The
first
phase
of
exploration
was
completed
in
August
1943,
with
the
drilling
of
a
shallow
well
at
Casamiciola
(Mt.
Tabor)
in
the
northern
sector
of
the
island.
The
drilling
was
located
few
hundreds
meters
above
sea
level,
in
order
to
estimate
the
influence
of
the
sea
on
the
water
table
trend.
In
this
well
the
water
table
was
located
at
the
sea
level
with
temperature
of
100 ◦C
[84].
In
this
case
the
presence
of
hot
water
can
be
related
to
the
hydrothermal
circulation
through
a
N–S
faults
system
which
fed
the
most
recent
volcanic
activity
of
the
island
(last
10
ka)
[58].
The
geothermal
system
of
Ischia
is
also
charac-
terized
by
pressure
fluctuations,
which
were
evidenced
by
several
wells
eruptions
and
geyser
formation
occurred
during
the
drilling,
and
also
in
recent
time,
after
the
wells
closure
(Fig.
14a
and
b).
The
high
potentiality
of
the
geothermal
resource
of
Ischia,
pushed
the
SAFEN
Company
to
continue
the
exploration
drilling,
from
1951
to
1954,
furthers
wells
(Pc)
with
maximum
depth
of
about
1
km

1016 S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030
Table
4
Synthesis
of
drilling
at
Ischia
performed
from
the
1939
to
1943
at
Fumaroles
site
(southern
island
sector)
(Penta
and
Conforto,
1951).
The
drilled
lithotype
are:
(a)
Unwelded
Tuff
with
greenish
lithics,
(b)
Lavas
volcanic
breccias
with
tuffs
matrix
greenish-gray
with,
(c)
Gray
Tuff
sometime
greenish
with
layered
lavas.
(after
Penta
e
Conforto,
1951).
Well
Head
well
elevation
(m
a.s.l.)
Depth
(m)
Water
table
(m
a.s.l.)
Encountered
soils
(formation
type)
Maximum
temperature
(◦C)
Data
of
drilling
Surface
temperature
(◦C)
pH
Other
technical
description
I1
1.5
37.35
0.5
0–2
m:
sabbia
2-37.35:
type
a
142
June
1939
73
6.6–7.4
Rotary
drilling.
Persistent
geyser
activity
I2
5.2
83.75
−1
to
4.2
0–22.5
m:
type
a;
22.5–83.75:
type
b
160
Started
on
21st
August
1939
90–101
6.1–7.5
Rotary
drilling.
I3
12.52
14.30
2–3
0–14.3
m:
type
a
106
November
1939
95–100
6.2–7.1
Rotary
drilling.
I4 23.2
14.80
15.2–16.8
0–14.80
m:
type
a
103
January
1940
102
@
15
m
6.7–7.2
Rotary
drilling.
I5
29.5
20.80
0.4
0–20.80
m:
type
a
103
January
1940
70
6.4–7.5
I6 7
29.00
0.4
0–29.00
m:
type
a
120
July
1940
99
Wire
drilling.
Well
eruption
occurred
on
August
18th 1940.
Successively
closed
and
abandoned
I7
6.9
37.95
−3
to
2.3
0–30.00
m:
type
a;
30.00–37.95:
type
b
135
October
1940
77
7
I8
7.9
80.00
1.45
0–30
m:
type
a;
30–70:
type
b;
70–80.
type
c
153
19
October
1940–24
January
1941
91
6
February
3rd to
16th March
1941
persistent
geyser
activity
characterized
by
11
well
eruption
and
spontaneous
production
from
June
to
September
1943
I9
22.8
24.30
0.53
0–24.30
m:
type
a
100
March
1941
Wire
drilling
I10
30
16.5
7.5–9
0–30
m:
type
a
90
February
1941
81
@
8
m
7
Wire
drilling
I10A
–
17.00
–
0–17
m:
type
a
105
May
1941
89–100
@10
m.
7
Wire
drilling
I11
40.0
45.0
32–34
0–45:
type
a
110
March
1941
99
@10
m.
7
Casing
up
to
16
m
from
well
head
I12
not
localized
–
17
–
0–17:
type
a
71
April
1941
40
@
4.7
m.
7
Wire
drilling.
Casing
up
to
16
m
from
well
head
I12A
not
localized
–
20
0
0–20:
type
a
55
April
1941
70–80
Wire
drilling.
Casing
up
to
19
m
from
well
head
I13
not
localized
–
20
0
0–20:
type
a
55
April
1941
22–32
Wire
drilling.
Casing
up
to
19
m
from
well
head
S1
3.13
3.15
0.33
0–3.15:
type
a
67
January
1939
Inspection
well
S2
5.15
4.15
1.5–3.5
0–4.15:
type
a
100
April
1940
6.5–7
Inspection
well
IFV1 11.08
283.4
–
0–26.40
m:
reworked
tuff
(green);
26.40–69.30:
volcanic
breccias
and
reworked
tuff;
69.30–93:
gray
and
green
tuff;
93–110:
altered
tuff
with
breccia
110–263.4:type
c;
263.4–283.4:
green
tuff
with
breccia
175
June–December
1941
6.5–7
Casing
up
to
241
m
from
well
head.
Spontaneous
well
eruption
from
February
2nd to
end
of
September
1942
IFV2
24.6
330.0
2.6–3.6
0–23
m:
unconsolidated
tuff
23–78:
volcanic
breccia;
78–94:
gray-green
tuff;
94–132:
altered
tuff
with
breccia;
132–330:type
c
159
April
22nd
1942–20th
January
1943
7.2
Casing
up
to
153,3
m
from
well
head.
IFV4
25.5
140.0
–
–
–
Started
on
July
3rd
interupted
on
September
1943

S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030 1017
Fig.
13.
(a)
Location
of
shallow
wells
close
to
S.
Angelo
peninsula
(Ischia).
Red
circles
>100
m
of
depth,
white
circles
<100
m
of
depth.
(b)
Location
of
shallow
wells
at
Maronti
(Ischia).
Dotted
circles
are
the
monitoring
wells
used
to
measure
the
variation
of
the
water
table
during
the
pumping
tests.
(c)
Location
of
shallow
wells
at
Cetara,
Forio
(Ischia).
Dotted
circles
are
the
monitoring
wells
used
to
measure
the
variation
of
the
water
table
during
the
pumping
tests.
(For
interpretation
of
the
references
to
colour
in
this
figure
legend,
the
reader
is
referred
to
the
web
version
of
the
article.)
(ENEL,
1987)
(Fig.
7).
Such
drillings
allowed
a
detailed
reconstruc-
tion
of
the
geothermal
gradient
at
depth
to
better
constrain
the
geothermal
reservoir.
Within
the
Pc46
well
(Forio)
were
measured
the
highest
temperatures
(225 ◦C
at
1151
m
of
depth)
(Fig.
15).
The
data
obtained
by
the
SAFEN
researchers
highlighted
that
a
large
amount
of
potential
resource
is
related
to
vapor
dominated
systems
and
that
the
useful
temperatures
for
electric
production
can
be
generally
found
just
few
meters
below
the
sea
level
[100].
In
1950,
an
attempt
of
exploitation
of
the
geothermal
resource
was
developed,
with
the
installation
of
a
300
kW
binary
cycle
plant.
The
endeavor
was
abandoned
later,
due
to
practical
problems
related
to
the
wells
corrosion,
which
the
adopted
antiquated
technology
was
not
able
to
solve.
In
more
recent
time,
in
the
framework
of
“Progetto
Finalizzato
Geodinamica”
a
pilot
plant
of
500
kW,
which
utilized
fluids
at
temperature
of
150 ◦C,
was
planned
in
the
island
of
Ischia.
In
this
case,
the
failure
of
the
project
can
be
assigned
to
the
lack
of
interest
showed
by
the
local
communities,
concerned
by
a
hypothetical
negative
effect
that
the
presence
of
a
geothermal
plant
in
the
island
could
have
on
the
tourism
economy
[101].
7.
Vesuvius
The
attention
to
the
geothermal
resource
of
Campania
volcanoes
was
focused
on
Vesuvius
during
1980,
since
experts
thought
that
the
last
recent
eruption
of
the
volcano,
occurred
in
1944,
was
fed
by
a
still
hot
shallow
magma
chamber,
capable
of
producing
an
intense
heat
flow.
The
Trecase
1,
in
the
eastern
sector
of
volcano
well,
was
drilled
to
a
depth
of
2.072
m,
since
19
November
1980–13
March
1981
(Fig.
5).
During
the
drilling
five
bottom
cores
were
sampled
by
using
Christiensen
6
3/4 core
barrels.
The
well
was
later
closed
with
two
cement
plugs,
the
first
from
2003
m
to
1800
m
and
the
second
from
1156
m
to
890
m.
The
encountered
stratigraphy
was
Fig.
14.
(a
and
b)
8
April
1940
well
eruption
at
Cetara
(a)
with
formation
of
a
geyser
lasted
13
h;
(b)
4
August
1939
eruption
at
Fumarole,
lasted
with
intermittence
for
about
4
years.
From
Penta
(1949).

1018 S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030
Table
5
Synthesis
of
drilling
at
Ischia
performed
from
the
1939
to
1943
at
Maronti
site
(southern
island
sector).
Well
Head
well
elevation
(m
a.s.l.)
Depth
(m)
Water
table
(m
a.s.l.)
Encountered
soils
(formation
type)
Maximum
temperature
(◦C)
Data
of
drilling
Surface
temperature
(◦C)
pH
Other
technical
description
IM1
2.5
11.5
0.1–1.8
0–6
m:
sands
6–11.5:
tuff
68
August
1939
60
@
1.68
m
Casing
up
to
7.7
m
from
well
head
IM2
1.9
13.5
0.2–1.5
0–13.5
m:
sands
68
August
1939
61
@
31
m
6.5–8
Casing
up
to
6.15
m
from
well
head
IM3
1.9
12.0
0.2–1.7
0–12
m:
tuffs
69
August
1939
6.8–7.5
Casing
up
to
5.14
m
from
well
head
IM4
2.9
16.5
0.2–1.7
0–16
m:
tuffs
72
September
1939
72
@
0.73
m.
6.8–7.5
Casing
up
to
5.76
m
from
well
head
IM5
2.3
13
0.1–1.6
0–13
m:
tuffs
84
September
1939
75
@
6.9
m.
6.6–7.4
Casing
up
to
6.9
m
from
well
head
IM6
6.6
17.3
3.5
0–17.3
m:
clay
and
tuffs
60
September
1939
7
T1
4.7
5
0.1–1
62
6.9–8.4
Casing
up
to
5
m
from
well
head
T2
4.47
5
0–1.5
46
7–8.3
Casing
up
to
5
m
from
well
head
T2A
5.9
6.20
0.1–1.8
55
7–8
Casing
up
to
6.2
m
from
well
head
T3
4.6
6.20
0.1–2
58
7–8.4
Casing
up
to
6.2
m
from
well
head
T3A
5.7
6.10
0.1–1.9
64
7.3–8
Casing
up
to
6.1
m
from
well
head
T4
4.3
4.95
0.1–2.2
64
7–8
Casing
up
to
4.96
m
from
well
head
T5
4.7
4.9
0.1–1.8
70
6.8–7.5
Casing
up
to
4.9
m
from
well
head
T6
4.2
4.6
0–1
70
6.8–7.5
Casing
up
to
4.6
m
from
well
head
T7
6.7
8
0–1.6
89
6.7–7
Casing
up
to
8
m
from
well
head
T8
10.0
10.75
0–1.5
80
6–7.5
Casing
up
to
10.7
m
from
well
head
T9 7.8
8.15
0.1–1.8
80
6.3–7.5
Casing
up
to
8.2
m
from
well
head
T9A 8.2
8.5
0–4.8
90
6.7–7
Casing
up
to
8.5
m
from
well
head
T10
10.24
11.5
0.1–1.5
81
6.6–7.6
Casing
up
to
10.9
m
from
well
head
Penta
and
Conforto
(1951).
Fig.
15.
Temperatures
versus
depth
measured
during
the
deep
drilling
at
Ischia.
After
AGIP
(1987).
mainly
represented
by
a
succession
of
lavas,
tuffs,
pumice,
sand-
stones,
siltstone
and
clay
[87].
From
1890
m
to
the
well
bottom,
dolomite
rocks
were
encountered.
The
drilling
allowed
to
identify
different
evolution
stages
of
the
volcano
during
Quaternary,
with
a
new 40Ar/39 Ar
dating
of
the
oldest
volcanic
activity
which
was
estimated
about
400
ky
B.P.
The
volcanic
activity
since
this
period
was
also
characterized
by
volcanic
quiescence
and
marine
sedi-
mentation
[18].
The
whole
emergence
of
the
shoreline
occurred
about
37
ky
B.P,
mainly
due
to
the
sea
level
change
during
the
last
glacial
period
and
deposition
of
the
60
m
thick
Campania
Ign-
imbrite
deriving
from
the
39
ky
B.P.
Campi
Flegrei
eruption.
The
Trecase
1
drilling
represents
the
only
example,
in
the
Campania
Plain,
in
which
the
Mesozoic
basement
carbonatic
rocks
have
been
encountered
(Brocchini
et
al.,
2001).
Unfortunately,
the
expected
temperatures
for
geothermal
exploitation
were
not
found,
in
fact
the
measured
geothermal
gradient
was
lower
than
the
earth’s
average
one
(30 ◦C
km−1),
with
bottom
well
temperature
of
51 ◦C
(Fig.
16).
Furthermore,
the
absence
of
hydrothermal
alterations
within
the
sampled
rocks,
demonstrate
that,
around
the
volcano,
is
not
present
a
significant
circulation
of
hydrothermal
fluids.
The
low
thermal
gradient
measured
within
the
Trecase
1
well
was
most
likely
due
to
the
magmatic
system
type,
probably
com-
posed
by
a
series
of
shallow
vertical
dikes
(2–4
km)
which
rapidly
loose
the
heat
by
conduction
and
by
water
circulation.
Relatively
low
temperature
was
also
found
during
the
more
recent
deviated
drilling
at
Unzen
active
volcano,
performed
on
2004,
just
9
years
after
its
last
eruption.
A
dike
was
sampled
at
1.3
km
of
depth,
within
the
0.5
km
wide
volcano
conduit,
a
zone
consisting
of
multiple
lava
dikes
and
pyroclastic
veins,
where
temperature
was
less
than

S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030 1019
Table
6
Synthesis
of
drilling
at
Ischia
performed
from
the
1939
to
1943
at
Forio
site
(southern
island
sector)
(Penta
and
Conforto,
1951).
Well Head
well
elevation
(m
a.s.l.)
Depth
(m) Water
table
(m
a.s.l.)
Encountered
soils
(formation
type)
Maximum
temperature
(◦C)
Data
of
drilling Water
temperature
(◦C)
above
sea
level
pH Other
technical
description
ICA0 6.9
19.3
0.7–1
0–19.3
m:
sands
and
tuffs
100 April
1939 95
@
4.8
m 6.4–7 Rotary
drilling.
Casing
up
to
13
m
from
well
head
ICA1 7.2
22.20
0.4–1.4
0–22
m:
tuffs
120 October
1939 86–88
@
1
m.
6.7
Wire
Drilling.
Casing
up
to
17.3
m
from
well
head.
Spontaneous
geyser
activity
April
1940
ICA2 4.4
96.0
0.3–1.4
0–4
m:
soil;
4–90:
gray
unconsolidated
tuffs;
90–86:
green
tuff
128 October
11th
1939–June
8th
1940
60
@
0
m 6.7
Wire
Drilling
Casing
up
to
27.75
m
from
well
head.
ICA3 5.8
15.5
0.1–0.9
0–15.5
m:
sends
and
tuffs
103 October
1939 93
@
1
m 6–8 Casing
up
to
15.15
m
from
well
head.
Capacity
during
pumping
test
6–1
l
s−1
ICA4 9.7
14 0.1–1
0–14
m:
sends
and
tuffs
95 October
1939 93
@
1
m 6–7.5
Casing
up
to
bot
Capacity
during
pumping
test
3–4
l
s−1
tom
well.
ICA5 2.5
13.0
−0.9
to
1
0–13.00
m:
sends
and
tuffs
113
October
1939
110
@
0
m
6–7
Casing
up
to
botto
Capacity
during
pumping
test
15–20
l
s−1m.
well.
ICA6 2.1
10 0–0.7
0–10.0
m:
sends
and
tuffs
76
November
1939
6.5–7.5
Casing
up
to
bottom
well.
ICA7 2.2
13 −0.1
to
1
0–30
m:
type
a;
30–70:
type
b;
70–80.
type
c
60 November
1939 6.8–7.1 Casing
up
to
bottom
ICA8
11.4
19
0–0.80
0–24.30
m:
type
a
99
April
1940
95
@
0
m
6–7
Wire
Drilling.
Casing
up
to
17.5
m
from
well
Capacity
during
pumping
test
6–7
l
s−1
ICA9
9.3
16.2
0.3–0.8
0–16.2
m:
sends
and
tuffs
104
December
1941
Wire
Drilling.
Casing
up
to
17.5
m
from
well
Capacity
during
pumping
test
0–1
l
s−1
ICA10
6.12
20.0
0–0.8
0–20
m:
sends
and
tuffs
111
June
1940
92
@
0
m
Wire
Drilling.
Casing
up
to
17.3
m
from
well
Capacity
during
pumping
test
7–9
l
s−1
ICA11 11.94
19 0–0.9
0–45:
type
a
100 June
1940 96
@
0.5
m Casing
up
to
18
m.
ICA12 7.02
14.25
0.3–0.9
0–17:
type
a
100
June
1941
71
@
0.5
m
Casing
up
to
13.5
m.
Capacity
during
pumping
test
10–15
l
s−1
ICA13
6.55
15.8
0–0.8
0–20:
type
a
97
Novembre
1941
77
@
0
m
Casing
up
to
14.5
m.
Capacity
during
pumping
test
4–8
l
s−1

1020 S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030
Table
6
(Continued)
Well
Head
well
elevation
(m
a.s.l.)
Depth
(m)
Water
table
(m
a.s.l.)
Encountered
soils
(formation
type)
Maximum
temperature
(◦C)
Data
of
drilling
Water
temperature
(◦C)
above
sea
level
pH
Other
technical
description
ICA14
7.05
18.6
0.2–0.6
0–20:
type
a
116
August
1942
Casing
up
to
17.7
m.
Capacity
during
pumping
test
14
l
s−1
ICA15 7.19
20 0.4–0.8
0–3.15:
type
a
100
August
1942
Casing
up
to
15
m.
Capacity
during
pumping
test
11–15
l
s−1
ICA16
7.14
20
0.5
0–4.15:
type
a
102
October
1942
Wire
drilling.
Casing
up
to11.1
m.
Capacity
during
pumping
test
13–14
l
s−1
ICA17
7.19
19.60
–
0–26.40
m:
reworked
tuff
(green);
26.40–69.30:
volcanic
breccias
and
reworked
tuff;
69.30–93:
gray
and
green
tuff;
93–110:
altered
tuff
with
breccia;
110–263.4:
gray-green
tuff
with
lava
and
pumice;
263.4–283.4:
green
tuff
with
breccia
October
1942
Casing
up
to
16
m.
ICA18 4.5
19
0.2–2.7
0–23
m:
unconsolidated
tuff;
23–78:
volcanic
breccia;
78–94:
gray-green
tuff;
94–132:
altered
tuff
with
breccia;
132–330:
gray-green
tuff
with
lava
and
pumice
100
June
1940
79
@
−0.5
m
6–7
Capacity
during
pumping
test
7–8
l
s−1
S8
3.83
5.5
−0.2
to
1.2
40
Novembre
1939
7–8
Casing
up
to
the
well
bottom
S9
3.89
5.5
−0.2
to
1.3
45
Novembre
1939
7–8
Casing
up
to
the
well
bottom
S10
3.33
5.5
−0.3
to
0.8
88
Novembre
1939
6.7–7.8
Casing
up
to
the
well
bottom
S11
2.95
5.5
−0.2
to
0.8
85
Novembre
1939
6.5–7
Casing
up
to
the
well
bottom
S12 1.14
4.5
−0.1
to
1
32
Novembre
1939
Casing
up
to
the
well
bottom

S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030 1021
Fig.
16.
Temperature
versus
depth
measured
during
the
drilling
at
Vesuvius
(Tre-
case
well).
After
AGIP
(1987).
200 ◦C.
In
this
case
the
feeding
dike
of
the
1991–1995
eruption
had
cooled
from
850 ◦C
to
200 ◦C
in
nine
years
(72 ◦C
y−1),
mainly
due
to
the
hydrothermal
circulation
[102].
In
the
case
of
Vesuvius,
the
sit-
uation
could
be
different
because,
if
there
is
not
large
hydrothermal
circulation,
the
central
part
just
below
the
crater,
down
to
several
km
of
depth,
could
be
still
hot
because
representing
the
large
vol-
umes
of
intruded
magma
leading
to
recent
eruption
[103].
Such
central
plug
below
the
main
crater
is
marked
in
fact
by
very
high
rigidity,
which
should
indicate
magma
solidification
in
the
main
rising
conduits.
However,
by
conduction
alone
such
a
solidification
cannot
be
explained
in
terms
of
significant
cooling,
and
it
has
in
fact
been
interpreted,
by
De
Natale
et
al.
(2004)
[103],
as
mainly
due
to
marked
gas
exholution
from
magmas,
with
only
modest
decrease
of
temperature.
If
this
model
is
true,
the
low
temperatures
encoun-
tered
in
the
Trecase
wells
are
simply
explainable
because
the
site
is
too
far
from
the
crater,
below
which
should
be
concentrated
the
thermal
anomaly
due
to
rising
magmas.
8.
Temperatures,
crust
rheology
and
magma
reservoirs
location
beneath
Campanian
volcanoes
The
intermediate
to
deeper
structure
beneath
the
Campania
volcanoes
has
been
investigated
since
1970
by
seismic,
gravi-
metric
and
aeromagnetic
surveys
[5,9,29,46,104–106].
At
regional
scale
the
Bouguer
gravity
anomaly
data
show
a
minimum
cen-
tred
over
the
Campanian
Plain,
in
the
Campi
Flegrei
area
[26].
This
is
due
to
the
refilling
of
low
density
pyroclastic
deposits
and
to
the
occurrence
of
altered
rocks
of
the
Campi
Flegrei
caldera
and
surroundings.
In
this
volcanic
area
no
evidences
of
the
magma
emplacement
at
shallow
level
have
been
detected
by
the
seismic
survey,
while
an
extensive
partial
melt
zone
at
a
depth
of
about
8
km
beneath
the
Campi
Flegrei
caldera
has
been
identified
by
the
high-resolution
seismic
reflector
in
the
Bay
of
Naples.
This
low
velocity
layer
has
probably
an
extension
not
less
than
30
km2,
with
a
thickness
of
about
1
km
[46,77].
Evidence
of
deep
low
density
body,
located
at
a
depth
of
8–10
km
beneath
Campi
Flegrei
area,
was
just
inferred
from
gravity
and
aeromagnetic
data
by
Rapolla
et
al.,
1989
[9].
A
similar
magma
body
was
recognized
by
the
TOMOVES
experiment,
beneath
the
Vesuvius,
at
about
9–10
km
of
depth
[29],
while
shallower
magma
reservoirs
did
not
detected.
Otherwise,
the
method
used
in
the
seismic
investigations
does
not
allow
the
detection
of
magma
bodies
with
a
volume
less
than
1
km3.
At
Ischia,
a
relative
maximum
Bouguer
anomaly
in
the
south-
western
sector
of
the
island
was
observed
on
the
basis
of
gravimetric
data
[104,105].
An
intense
magnetic
anomaly
was
also
measured
in
the
western
of
Ischia.
On
the
other
hand,
at
local
level,
a
low
value
of
magnetic
susceptibility
was
recorded
in
the
cen-
tre
of
the
island
and
this
was
interpreted
to
be
the
consequence
of
high
temperatures
due
to
the
presence
of
hot
magmatic
bod-
ies
at
shallow
depths
[65,105].
Despite
the
numerous
geophysical
investigations
performed
since
1970
in
the
Campanian
volcanic
area,
the
presence
and
location
of
possible
shallow
magma
bod-
ies
(<8
km),
which
could
supply
the
large
heat
flow
measured
at
Ischia
and
Campi
Flegrei,
has
not
yet
univocally
defined.
Otherwise,
the
measured
temperatures
at
different
depth
can
furnish
further
important
constrains
to
understand
the
rheology
of
the
shallow
crust
and
possible
magma
batches.
The
data
recorded
during
the
geothermal
exploration
fields
at
Campi
Flegrei,
Ischia
and
Vesu-
vius,
have
been
utilized
by
various
authors
to
provide
a
geological
and
geophysical
structure
of
campanian
volcanoes
shallow
crust.
These
data
have
also
been
employed
for
the
calibration
of
geophys-
ical
surveys,
particularly
for
the
correlation
between
seismic
wave
velocity
and
rocks
density
at
different
depth
[29,46,65,74,76,107].
The
integration
of
the
temperatures,
measured
within
wells
that
go
deeper
than
1
km
[3],
with
the
seismic
and
gravimetric
data
represents
a
reliable
constrain
for
crustal
dynamic
and
rheology
assessment.
In
fact,
the
deviation
of
temperature/depth
profile
from
the
average
Earth
one
(30 ◦C
km−1)
depends
on
different
conditions
such
as
the
thickness
of
the
crust
and
its
thermal
conductivity,
the
heat
production
at
depth,
the
fluids
circulation,
the
age
and
tec-
tonic
history
of
the
lithosphere.
In
active
volcanic
area
is
generally
observed
an
increase
of
temperature
variation
with
depth
and,
of
course,
an
increase
of
the
heat
flux
in
respect
to
the
average
for
all
continents
(65
±
1.6
mW
m−2)
[108].
This
is
due
to
the
upward
migration
of
the
Moho
and
to
the
magma
rising
within
the
crust
at
shallow
levels
(few
kilometers).
In
the
south
of
Italy,
at
regional
level,
the
temperature
distribution
with
depth
show
that
the
heat
flow
and
the
crust
temperatures
increase
from
Adriatic
to
Tyrrhe-
nian
Sea
direction
(Fig.
17)
[13].
According
to
the
interpretation
of
volcanic
activity
of
the
western
Tyrrhenian
margin
(which
start
about
2
My
ago)
[7],
this
is
due
to
the
mantle
upwelling
and
sea
floor
spreading,
which
produce
a
thinning
of
the
crust
and
the
increasing
of
the
heat
flow
from
east
to
west.
Heat
flow
at
Campi
Flegrei
was
calculated
by
Corrado
et
al.
(1998)
[109],
who
show
very
high
val-
ues
at
Mofete
(160
mW
m−2),
S.
Vito
and
Mt.
Nuovo
(80
mW
m−2)
and
Agnano
(120
mW
m−2).
At
Ischia
we
calculate
the
heat
flow
(q
=
k
×
T/l)
considering
the
temperature
measured
within
deep
wells
(Pc
46,
Pc
47
and
Pc
48)
located
in
the
south-western
sec-
tor
and
setting
the
thermal
conductivity
(k)
for
shallow
volcanic
environments
equal
to
1.5
W
m−1
◦C−1[110].
The
results
show
that
also
this
sector
is
characterized
by
a
very
high
heat
flow
equal
to
588
mW
m−2(Pc
46),
620
mW
m−2(Pc
47)
and
560
mW
m−2(Pc
48).
At
regional
level,
the
shallow
thermal
plume
which
is
located
in
the
western
part
of
Campanian
volcanoes
is
also
highlighted
by

1022 S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030
Fig.
17.
Temperature
versus
depth
measured
in
the
deep
wells
along
a
section
from
Adriatic
to
Tyrrhenian
sea.
The
geothermal
gradient,
except
for
anomalous
low
temperature
at
Vesuvius
(Trecase),
decrease
from
Adriatic
towards
Tyrrhenian
sea.
Modified
after
Della
Vedova
(2001).
the
temperature
distribution
with
depth,
along
the
section
which
crosses
the
Ischia
island,
the
Campi
Flegrei
caldera
and
the
Vesuvius
(Fig.
18).
In
fact,
the
isotherm
of
200 ◦C
is
located
at
a
depth
of
about
1–1.5
km,
going
from
Ischia
towards
Campi
Flegrei,
and
deepen
towards
Vesuvius
down
to
about
6
km
close
to
the
volcano.
Local
hot
plumes
have
been
observed
at
Ischia
and
Campi
Flegeri
depend-
ing
of
the
local
geology
and
fluids
circulation
(Fig.
19a–c).
Fig.
19a
shows
a
temperature
high
below
the
Mofete
geothermal
field.
At
Ischia,
in
the
south-western
sector,
a
possible
doming
structure
caused
by
lava
intrusion,
after
the
MEGT
eruption
(55
ky),
pro-
duced
bending
of
the
upper
layers
and
the
rising
of
the
isotherm
at
shallow
depth
(Fig.
19b).
Also
the
southern
sector
is
characterized
by
a
constant
high
temperature
at
the
surface
(80–100 ◦C)
along
the
Maronti
shoreline
(Fig.
19c).
Thus,
short
wave-length
variation
of
the
isotherms
(hundreds
of
meters)
can
be
related
to
shallow
magma
batches
and
hot
fluids
upwelling,
while
long-wave
vari-
ations
(tens
to
hundred
of
kilometers)
can
be
linked
to
the
heat
provided
by
deeper
and
larger
magma
bodies
and
to
the
rising
of
the
Moho
discontinuity.
As
described
above
and
in
the
previous
sec-
tions,
the
investigated
volcanic
areas
are
characterized
by
different
dynamics
and
shallow
structure.
Ischia
and
Campi
Flegrei
caldera
have
been
marked
during
the
volcanic
history
by
large
ground
uplift.
Starting
from
about
55
ky,
the
island
of
Ischia
has
undergone
an
uplift
of
about
800
m,
at
a
rate
of
about
3
cm
y−1,
which
formed
the
present
Mount
Epomeo
resurgent
block,
in
the
centre
of
the
island
[37,58,65,68,99].
At
Campi
Felgrei,
different
periods
of
uplift
have
been
identified
during
Roman
times,
before
the
1538
erup-
tion,
and
in
recent
times,
during
the
1970–1972
and
1982–1984
unrests
(with
rate
of
few
millimeter
per
day),
with
a
total
uplift
of
some
tens
of
meters.
These
periods
are
superimposed
to
a
general
subsidence
trend
at
a
rate
of
1.1–2
cm
y−1.
In
both
volcanic
areas,
and
mainly
at
Ischia,
there
is
the
presence
of
a
vigorous
hydrother-
mal
system,
with
maximum
surface
temperature
of
about
100 ◦C.
Furthermore,
at
Ischia
and
Campi
Flegeri
the
seismicity
recorded
in
historical
time
is
located
in
the
first
2
km
and
4
km
of
depth,
respectively,
probably
reflecting
the
transition
form
brittle
to
duc-
tile
behavior
of
rocks
at
these
depths
[31,65,111–113].
All
these
elements
are
distinguishing
of
the
dynamic
of
shallow
magma
bod-
ies.
Conversely,
the
Vesuvius
is
characterized
by
the
presence
of
a
Fig.
18.
Sketch
of
the
shallow
crust
beneath
Campanian
volcanoes
along
a
section
from
Ischia
to
Vesuvius
deduced
from
gravity,
seismic
and
wells
data.
It
is
reported
the
regional
200 ◦C
isotherm
and
the
depth
of
the
brittle
to
ductile
transition
(T
>
350 ◦C).

S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030 1023
Fig.
19.
(a)
Isotherms
beneath
the
Mofete
geothermal
field
deduced
from
wells
data.
It
is
also
reported
the
startigraphy
and
productive
zones
(modified
after
AGIP,
1987).
(b)
Isotherms
beneath
the
south-western
sector
of
the
Ischia
island
and
stratigraphy
deduced
from
wells
data.
The
heat
plume
is
possible
related
to
the
local
shallow
trachytic
intrusion
occurred
after
the
MEGT
eruption
(55
ky)
which
deposited
the
Epomeo
Green
Tuff.
(c)
Isotherms
beneath
the
south
sector
of
the
island
and
stratigraphy
deduced
from
wells
data.
A
stable
temperature
zone
is
identified
along
the
Maronti
shoreline.
shallow
(1–2
km)
cooled
dikes
system
and/or
small
magma
batches
which
fed
the
last
volcanic
activity
since
1944
[31,83,103].
For
this
reason
the
residual
heat
is
concentrated
just
along
the
crater
axis
(roughly
a
cylinder
with
300
m
of
diameter)
where
hydrothermal
circulation
occurs.
The
lack
of
a
large
radius
hydrothermal
system
is
confirmed
by
the
very
low
temperature
measured
in
the
Trecase
well
(3.8
km
far
from
the
carter
axis).
Larger
and
hotter
fluids
circu-
lation
probably
occurs
deeper
than
about
2
km
[83].
The
absence
of
shallow
(1–2
km)
large
scale
hot
groundwater
motion
at
Vesuvius,
probably
produce
a
mostly
conductive
regime
(instead
of
advec-
tion)
of
the
heat
supplied
by
the
deep
reservoir.
In
this
case
is
not
surprising
to
find
very
low
temperature
at
shallow
depth,
while
an
increase
of
temperature
is
expected
closer
to
the
magma
reservoir.
A
theoretical
demonstration
of
such
statement
can
be
performed,
firstly
for
Vesuvius,
by
using
the
relation
showing
the
increase
of
temperature
with
depth
and
time,
for
the
simplified
assumption
of
one
dimensional
unsteady
heat
conduction
in
an
infinite
region
[108].
This
assumption
is
suitable
for
the
case
of
a
sill
intrusion
having
heat
content
per
unit
area
(Q)
equal
to:
Q
=
[c(Tm−
T0)
+
L]2b
(1)

1024 S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030
Fig.
20.
Comparison
between
the
conductive
curve
obtained
by
Eq.
(2)
for
a
sill
intrusion
8–9
km
depth,
at
a
time
t
=
25
ky
and
the
measured
shallow
temperature
profile
at
Vesuvius.
where

is
the
rocks
density,
c
is
the
specific
heat
of
magma,
Tm
is
the
magma
temperature,
T0is
the
temperature
of
surroundings
rocks,
L
is
the
latent
heat
of
fusion
and
b
is
the
thickens
of
the
sill.
The
last
value
is
inferred
by
the
results
of
the
seismic
tomography
at
Campi
Flegrei
and
Vesuvius
and
by
the
gravity
data,
which
provide
an
average
thickness
of
about
1
km
[9,29,46,106].
Furthermore,
we
consider
an
initial
condition
of
undisturbed
crust,
with
geothermal
gradient
of
30 ◦C
km−1.
After
the
sill
intrusion,
at
depth
of
8–10
km,
the
temperature
distribution
varies
with
time,
perpendicular
to
the
sill.
The
temperature
distribution
T(y,t)is
given
by
the
following
equation
[108]:
T(y,t)=Q
2c√t e−y2/4t (2)
where
k
is
the
thermal
diffusivity,
t
is
the
time,
y
is
the
distance
from
the
sill.
For
the
calculation
of
Q,
from
Eq.
(1),
we
set
an
aver-
age

=
2300
kg
cm−3,
c
=
1
kJ
kg−1K−1,
L
=
350
kJ
kg−1,
Tm=
1000 ◦C
(1273
K)
and
T0is
300 ◦C
(573
K)
close
to
the
sill
at
the
initial
condition
[29,31,74,75,103,107,108,110,114].
Thus,
the
value
of
Q
is
equal
to
6
×
1012 J
m−2.
Setting,
in
the
Eq.
(2),
k
=
10−6m2s−1
[108],
we
estimate
the
change
of
temperature
as
a
function
of
the
distance
from
the
sill.
In
Fig.
20
we
show
an
example
of
the
tem-
perature/depth
profile
obtained
from
Eq.
(2),
by
setting
t
=
25
ky,
which
corresponds
to
the
time
of
the
oldest
emerged
volcanic
activ-
ity
of
Somma-Vesuvius
volcanic
complex.
This
is
compared,
just
for
the
first
2
km
of
depth,
with
those
obtained
from
the
temper-
ature
measured
within
the
Trecase
1
well,
showing
a
generally
reasonable
fit.
The
obtained
result
supports
the
hypothesis
that
the
shallow
structure
of
Vesuvius
is
formed
by
a
cooled
dikes
system
or
small
magma
batches
and
that
the
hydrothermal
shallow
system
(0–2
km)
is
characterized
by
relative
low
temperature.
Within
and
below
the
carbonatic
layer,
down
to
2
km
of
depth,
an
isolated
cell
hydrothermal
system
with
higher
temperature
could
exist
[83].
At
Ischia
island
and
Campi
Flegrei,
the
persistence
of
a
large
hydrothermal
system
produces
a
perturbation
of
temperature
dis-
tribution
within
the
shallow
crust,
with
very
high
geothermal
gradients
(150–200 ◦C
km−1).
This
indicates
that
possible
magma
bodies
induced
the
observed
large
scale
groundwater
motion,
but
also
in
these
volcanic
areas
is
not
yet
definitely
clear
the
pres-
ence
of
shallow
magma
reservoirs.
Recent
studies
of
Ischia
island
volcano
dynamics
agree
with
the
presence
of
a
laccolith
beneath
the
centre
of
the
island,
whose
top
is
locate
at
about
2
km
below
the
surface
[65,67,68].
The
magma
intrusion,
which
started
from
55
to
33
ky
ago,
produced
the
uplift
of
the
central
block,
and
the
partial
exhumation
of
the
active
magmatic
hydrothermal
system
[68].
At
Ischia,
the
measured
geothermal
gradients
within
the
deep
wells
show
a
rapid
increment
down
to
about
200
m,
and
a
steady
temperature
zone
between
about
200
and
900
m
(Fig.
15).
This
sta-
ble
reservoir
has
a
temperature
of
about
180 ◦C
(Pc
48
well)
and
130–140 ◦C
(Pc-46-47
and
IFV2
wells).
In
this
case,
since
the
tem-
perature
distributions
at
depth
are
certainly
dependent
on
the
hot
fluid
circulation,
we
can
study
the
upwelling
flow
above
the
intru-
sion,
by
using
the
approximation
of
one-dimensional
advection
of
heat
in
a
porous
media.
In
the
hypothesis
of
heat
advection
by
the
groundwater
motion,
the
temperature
as
a
function
of
depth
is
depending
on
various
factors
such
as:
temperature
difference
between
reservoir
and
surface
(Tr−
T0),
fluid
density
(f)
and
its
specific
heat
(cf),
Darcy
velocity
of
the
fluids
in
the
porous
media
(v),
solid
matrix
thermal
conductivity
()
and
depth
(y).
Thus,
the
temperature
distribution
with
depth
(T)
is
given
by
the
following
analytical
solution
[115,108]:
T
=
Tr−
(Tr−
T0)
·
exp fcfv
y(3)
As
reported
above
by
the
analysis
of
the
geotherms
within
the
deep
well
at
Ischia,
we
set
the
steady
temperature
of
the
shallow
reservoir
equal
to
180 ◦C
(Pc
48
well)
and
140 ◦C
(Pc-46-
47
wells),
respectively,
and
f=
1000
kg
m−3,
cf=
4.185
×
103J
kg−1,

=
3.35
W
m−1C−1and
v
=
6.7
×
10−8m
s−1.
The
two
latter
val-
ues
are
the
ones
generally
utilized
for
volcanic
environment
[108,116,117].
The
average
surface
temperature
(T0)
at
Ischia
is
evaluated
at
about
60 ◦C.
The
comparison
of
the
obtained
theoret-
ical
curves
with
the
measured
gradient
is
shown
in
Fig.
21.
The
good
agreement
of
the
curves
confirms
the
occurrence
of
geother-
mal
advection
beneath
the
island.
Furthermore,
if
the
flow
is
driven
by
the
buoyancy
of
the
hot
water,
we
can
also
use
the
Darcy
veloc-
ity
(v)
to
estimate
the
permeability
(K)
of
the
system,
assuming
that
the
flow
is
laminar
and
the
amount
of
pressure
gradient
in
excess
of
the
hydrostatic
value
is
negligible
in
the
upwelling
flow.
This
indirect
method
is
very
useful
to
estimate
the
large
scale
perme-
ability,
when
the
analysis
is
performed
over
a
dimensional
space
that
is
larger
than
the
dimension
of
the
porous
or
spacing
fractures
through
which
the
fluid
flows.
The
permeability
K
as
a
function
of
Darcy
velocity
is
given
by
[108]:
K
=
v
˛ffg(Tr−
T0)(4)
where
,
˛fand
fare
the
viscosity,
the
coefficient
of
ther-
mal
expansion
and
the
density
of
the
fluid,
respectively.
The
obtained
values
of
permeability
are
6
×
10−16 m2and
2
×
10−15 m2
for
the
reservoir
temperature
of
180 ◦C
and
140 ◦C,
respectively.
The
results
are
in
agreement
with
the
average
permeability
val-
ues
inferred
from
theoretical
fluid-dynamical
models
of
ground
deformation
data
at
Campi
Flegrei
and
other
volcanic
environments
[57,118].
In
addition
to
the
heat
in
the
crust
maintained
by
hot

S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030 1025
Fig.
21.
Comparison
between
advection
and
conductive
curves
with
the
tempera-
tures
measured
in
the
deep
wells
at
Ischia
(see
text
for
details).
fluids
circulation
beneath
the
island
of
Ischia,
we
have
to
consider
also
the
conductive
heat
due
to
magma
intrusion
at
shallow
depth,
by
using
Eqs.
(1)
and
(2).
The
heat
content
per
unit
area
(Q)
is
evalu-
ated
considering
that
initial
conditions
are
those
that
followed
the
great
eruption
of
the
Mount
Epomeo
Green
Tuffs
(55
ky),
which
certainly
produced
a
large
amount
of
heat
in
the
shallow
crust.
Thus,
we
set
the
difference
of
temperature
between
the
reservoir
and
the
surroundings
(Tm−
T0)
to
roughly
100 ◦C
(373
K),
while
the
density
of
rocks
is
assumed
as
2100
kg
m−3,
obtaining
a
value
of
Q
=
1.6
×
1012 J
m−2.
By
Eq.
(2),
we
evaluate
the
temperature
distri-
bution
as
a
function
of
depth
and
time,
setting
t
=
33
ky,
which
is
the
time
of
resurgence
onset
in
the
island
indicating
the
occurrence
of
shallow
magma
intrusion,
at
about
2
km
of
depth
[58,63,65,68,119].
This
magma
body
is
nowadays
partially
cooled,
with
temperature
at
the
top
probably
above
350 ◦C.
The
obtained
curve
(conductive
curve)
is
compared
with
the
measured
temperature
within
deep
wells
(Fig.
21).
The
result
is
interesting,
since
the
curve
fits
well
the
deeper
part
of
the
geothermal
gradients
of
Pc48
well.
This
lower
part,
which
is
characterized
by
a
linear
increase
of
the
tempera-
tures
can
be
hence
assumed
as
due
to
a
conductive
regime.
With
this
assumption,
the
difference
between
the
Pc46
well
tempera-
ture
curve
and
the
conductive
curve
could
represent
the
average
increment
of
temperature
due
to
the
hydrothermal
circulation.
At
Campi
Flegrei,
the
temperature
versus
depth
distribution
measured
in
deep
wells,
show
a
different
pattern
with
respect
to
Ischia,
which
is
probably
associated
to
the
presence
of
various
permeable
layers
[3].
The
lack
of
a
unique
shallow
fluid
reser-
voir
does
not
allow
the
occurrence
of
steady
temperatures
within
Fig.
22.
Comparison
between
conductive
curves,
for
different
time
of
sill
emplace-
ment,
with
the
temperatures
measured
in
the
deep
wells
at
Campi
Flegrei
(see
text
for
details).
a
consistent
interval
of
depth
and
thus
Eq.
(3)
is
not
applicable.
Several
models
of
geothermal
circulation
and
resurgence
in
the
Campi
Flegrei
caldera
highlight
that
hot
fluids,
which
have
been
partly
responsible
of
the
uplift
recorded
during
the
1970–1972
and
1982–1984
unrests,
circulate
mainly
within
the
inner
caldera
rocks
[31,50,54,120].
This
is
also
supported
by
the
higher
temper-
ature
gradients
recorded
in
wells
located
inside
the
caldera
itself
(MF1-2-5,
SV1-3-8d
wells),
with
respect
to
the
lower
and
roughly
linear
gradient
of
L1
well,
that
is
located
outside
of
the
caldera.
For
this
reason,
we
assume
that
the
temperature–depth
profile
of
L1
is
mostly
due
to
a
purely
conductive
transport
of
the
heat
provided
by
the
magma
reservoir
and
only
in
minor
part
to
hot
fluids
circu-
lation.
Assuming
the
same
parameters
of
the
deep
magma
source
adopted
for
the
case
of
Vesuvius
(Q
=
6
×
1012 J
m−2),
located
at
a
depth
of
8
km,
we
calculate
the
conductive
temperature–depth
curve
for
different
times
which
correspond
to
15
ky
(NYT
erup-
tion),
39
ky
(CI
eruption),
150
ky
(older
Ignimbrite
eruptions),
1
My
(older
volcanic
activity
of
Campania
volcanism),
[7,22,36,38,121]
(Fig.
22).
Comparison
of
the
obtained
curves
with
the
measured
temperatures–depth
profile
of
the
wells,
shows
that
a
conductive
heat
transport,
also
acting
at
the
longer
time
scale,
is
not
sufficient
to
get
the
nowadays
thermal
state
of
the
shallow
crust,
also
assum-
ing
a
shallow
magma
source
(4
km).
This
result
is
in
agreement
with
the
Campi
Flegrei
caldera
thermal
model
proposed
by
Wohletz
et
al.
(1999)
[107].
Only
for
the
L1
well,
the
measured
temperatures
are
similar
to
those
obtained
by
conductive
heat
transport
after
1
My.
Then,
the
thermal
state
outside
the
caldera
could
be
mainly
linked
to
the
long
term
conductive
heat
propagation
from
the
deep
source,
while
the
higher
gradients
within
the
caldera
are
related
to
hot
fluids
circulation.
9.
The
assessment
of
geothermal
resource
of
Campanian
volcanoes
A
preliminary
evaluation
of
geothermal
resources
was
made
during
the
AGIP-ENEL
drilling
at
Campi
Flegrei
(AGIP,
1987).
It
did
not
take
into
account
the
whole
geothermal
potential
of
the
area,
but
considered
the
available
electrical
energy
for
the
productive

1026 S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030
Table
7
Data
from:
Penta
and
Conforto
(1951),
AGIP
(1987),
Schon
(2004),
Smith
(2006).
Area
(m2)
Layer
thickness
m
(depth
interval)
Volume
(m3)

(kg
m−3)
Tiaverage
(K)

Mofete
2
×
1061
500
(500–1000)
1091759
503
0.28
2 200
(1800–2000)
0.4
×1092459 613
0.1
3 200
(2500–2700)
0.4
×
1092459
613
0.1
S.
Vito
3
×
1064
500
(0–500)
1.5
×
1091759
351
0.3
5
500
(100–1500)
1.5
×
1091759
411
0.25
Ischia
17
×
1066
600
(300–900)
10
×
1092000
273
0.3
wells
of
Mofete
area
(Mofete
1,
2,
7d
and
8d),
which
amounted
to
some
tens
of
MWe.
Further
evaluation
of
the
geothermal
poten-
tial
at
Campi
Flegrei
and
Ischia
is
reported
by
Marini
et
al.
(1993)
[101],
taking
into
account
the
well
temperature
profiles
and
the
geochemical
fluid
composition.
The
results
of
the
above
analy-
sis
highlighted
the
feasibility
of
geothermal
exploitation
at
Campi
Flegrei
and
Ischia,
but
this
possibility
was
abandoned
for
both
tech-
nical
and
political
reasons.
The
development,
in
recent
time,
of
new
technologies
for
geothermal
energy
production,
allows
the
exploitation
also
of
medium
enthalpy
resources
(T
<
150 ◦C).
For
this
reason
we
consider
appropriate
a
new
assessment
of
the
geother-
mal
potential
of
Campi
Felgrei
and
Ischia,
as
stored
into
the
shallow
crust.
We
use
here
the
classical
and
most
commonly
used
method
for
geothermal
potential
estimation,
the
volume
method
proposed
by
Muffler
and
Cataldi
(1978)
[122].
This
requires,
in
the
first
step,
the
calculation
of
the
heat
stored
in
a
certain
volume
of
the
crust
to
a
specific
depth.
The
subsurface
volume
is
sub-divided
in
several
units
based
on
hydrogeological
and
geothermal
consider-
ations,
taking
into
account
the
temperature
and
porosity
trends
with
depth.
The
amount
of
total
geothermal
heat
stored
into
a
cer-
tain
volume
(Et)
is
equal
to
the
sum
of
heat
stored
in
the
rocks
(Er)
and
in
the
fluids
(Ew),
following
the
relationships
[122]:
Er=
Vi·
(1
−
i)
·
ri ·
Cri ·
(Ti−
T0)
(5)
Ew=
Vi·
i·
wi ·
Cwi ·
(Ti−
T0)
(6)
where
Viand
iare
the
volume
and
the
average
porosity
of
the
ith
unit,
ri and
Cri are
the
density
and
the
specific
heat
capacity
of
the
rocks
of
the
ith
unit,
wi and
Cwi are
the
density
and
the
specific
heat
capacity
of
the
fluids
contained
in
the
ith
unit,
Tiis
the
average
temperature
of
the
ith
unit,
and
T0is
the
reference
temperature,
which
is
taken
to
298
K
in
this
example.
Moreover,
only
a
fraction
of
the
geothermal
heat
stored
in
the
subsurface
can
be
extracted.
This
is
strictly
correlated
to
the
characteristics
of
the
geothermal
reservoirs,
which
are
difficult
to
evaluate
by
numeri-
cal
models
[123],
thus
the
fraction
of
actual
extractable
energy
(Ee)
can
be
known
only
upon
completion
and
discharge
of
geothermal
wells.
Empirical
data
show
that
a
recovery
factor
Rf
=
Ee/Et
can
be
adopted
to
avoid
this
limitation.
Muffer
and
Cataldi
(1978)
[122],
after
a
review
of
heat
extraction
from
geothermal
systems,
argued
that
the
value
of
Rf
ranges
from
0.05
to
0.15
(5–15%),
and
that
this
value
increases
from
liquid-dominated
to
vapor-dominated
systems,
respectively
[124,125].
Furthermore,
the
volume
method
considers
only
the
status
quo
underground
[122],
without
evalu-
ate
the
heat
recharge
coming
from
higher
depths,
where
magma
reservoirs
are
located.
Nevertheless,
several
modelings
of
geother-
mal
systems,
as
well
as
experimental
results,
have
shown
that
the
recovery
of
heat
during
few
tens
of
years
of
exploitation
gener-
ally
does
not
exceed
10–20%
of
the
heat
extracted
from
the
storage
alone
[122,125].
Since
the
volume
method
considers
a
recovery
factor
of
5–15%,
in
general,
the
replenishment
of
the
geothermal
resource
could
be
guaranteed
by
the
10–20%
of
the
heat
resup-
ply.
By
using
Eqs.
(5)
and
(6)
we
evaluate
the
geothermal
potential,
for
Campi
Flegrei
and
Ischia,
while
this
evaluation
is
neglected
for
Vesuvius
were
the
geothermal
gradient,
down
to
2
km
of
depth,
is
not
relevant
for
our
purpose.
For
Campi
Flegrei,
we
consider
two
main
areas
(Mofete
and
S.
Vito)
for
which
the
parameters
of
deep
geological
reservoirs
(temperature,
porosity
and
density)
are
available
[3,74,76,126].
Three
formations,
with
hot
fluids
circula-
tion,
have
been
identified
at
Mofete:
500–1000
m
with
20%
vapor;
1800–2000
m
with
40%
vapor;
2500–2700
m
probably
vapor
dom-
inated.
The
surface
area
has
been
delimited
by
the
extension
of
the
well
fields
and
is
assumed
equal
to
2
km2.
At
S.Vito
(SV1
well),
we
recognize
that
the
temperature
gradient
with
depth
(dT/dh)
is
very
low
at
the
depth
interval
of
0–500
m
and
100–1500
m,
where
is
rea-
sonable
to
suppose
the
occurrence
of
more
permeable
layers
with
fluids
circulation,
which
accounts
for
the
homogeneous
tempera-
tures.
The
S.
Vito
area,
where
the
wells
are
located,
is
considered
of
about
3
km2.
At
Ischia,
the
high
temperature
gradients
of
150–220 ◦C/km−1,
measured
in
the
wells
of
the
south-western
sector
of
the
island
[84],
and
the
intense
surface
thermal
activity
(springs,
fumaroles)
reveal
the
presence
of
a
vigorous
hot
hydrothermal
system
at
shallow
depth.
Fractured
lava
layers
could
represent
the
main
hydrothermal
aquifer,
which
is
likely
developed
until
a
depth
of
2
km
(Chiodini
et
al.,
2004)
where
temperatures
exceed
the
critical
point
of
the
water
(374 ◦C).
Furthermore,
the
temperature
data
of
Pc46-47-48
wells
reveal
a
steady
temperature
with
depth
from
300
to
900
m,
where
fluid
circulation
occurs.
Also
according
to
the
stratigraphic
and
geochemical
data
[3,127],
we
consider
that
the
shallow
hot
fluids
reservoir,
at
Ischia,
has
a
minimum
vertical
extension
of
about
600
m.
In
addition,
the
distribution
of
fumaroles
and
hot
springs
at
the
surface
(with
pCO2>
0.10
bar)
suggests
that
the
areal
extension
of
geothermal
reservoir
is
about
17
km2[101,127].
The
specific
heat
capacity
of
Ischia
rocks
inferred
from
literature
is
Cr
=
0.9
kJ
kg−1K−1[110];
while
for
fluids
we
consider
the
value
of
the
water
Cwr
=
4.19
kJ
kg−1K−1and

=
1000
kg
m−3[128].
All
the
other
parameters
of
Eqs.
(5)
and
(6),
for
Campi
Flegrei
(Mofete,
S.
Vito)
and
Ischia,
are
reported
in
Table
7.
The
results
of
application
of
Eqs.
(5)
and
(6)
are
shown
in
Table
8.
We
apply
a
recovery
factor
Rf
to
the
total
energy
for
each
area
equal
to
0.1,
which
represents
an
average
estimation
of
the
realistic
val-
ues
based
on
world-wide
experience
[122].
The
total
heat
energy
stored
in
the
Mofete
geothermal
reservoir
is
equal
to
1.08
×
1017 J,
while
the
recoverable
energy
(Ee)
is
equal
to
3.7
GWy.
A
value
of
7.8
×
1017 J
(Ee
=
2.7
GWy)
is
obtained
for
S.
Vito
area.
The
total
heat
energy
(Et
=
6.4
GWy)
is
not
all
recoverable
for
electrical
produc-
tion.
Usually,
a
cut
off
of
fluids
temperature
is
posed
at
130 ◦C
[128],
above
which
it
is
generally
assumed
a
good
efficiency
of
geothermal
plants
for
electrical
production
(although
the
actual
lower
limit
for
our
climates
is
around
90 ◦C).
Thus,
subtracting
the
contribution
of
fluids
with
temperature
T
<
130 ◦C,
we
obtain
a
value
of
5.7
GWy.
These
values
are
similar
to
that
calculated
by
Chiodini
et
al.
(2001)
[129]
for
the
neighboring
crater
of
Solfatara,
using
the
surface
thermal
flux
method.
The
former
authors
find
that,
on
the
basis
of
CO2/H2O
ratio
measured
in
high-temperature
fumaroles
inside
the
degassing
area
of
Solfatara
(roughly
in
the
centre
of
Campi
Flegrei
caldera),
the
total
thermal
energy
flux
is
1.19
×
1013 J
d−1.
The
investigated
area
has
an
extension
of
about
1.4
km2[129,130].
The
obtained
energy,
allowing
for
a
recovery

S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030 1027
Table
8
Evaluation
of
recoverable
energy
at
Campi
Flegrei
and
Ischia.
Mofete
Erlayer
1
(J)
Erlayer
2–3
(J)
Ewlayer
1
(J)
Ewlayer
2–3
(J)
Ei-tot
(J)
Ei-tot
(kWh)
Ei
recoverable
(GWy)
2.34
×
1017 5.01
×
1017 2.40
×
1017 1.06
×
1017 1.08
×
1018 3.00
×
1011 3.7
S.
Vito
Erlayer
4
(J)
Erlayer
5
(J)
Ewlayer
4
(J)
Ewlayer
5
(J)
Ei-tot
(J)
Ei-tot
(kWh)
Ei
recoverable
(GWy)
8.81
×1016 2.01
×
1017 1.76
×
1017 3.12
×
1017 7.77
×
1017 2.16
×
1011 2.7
Ischia Erlayer
6
(J)
Ewlayer
6
(J)
Ei-tot
(J)
Ei-tot
(kWh)
Ei
extractable
(GWy)
1.70
×
1018 1.67
×
1018 3.40
×
1018 9.44
×
1011 11
factor
of
0.1,
corresponds
to
5
GWy.
This
result
is
interesting,
since
the
values
of
extractable
energy
related
to
similar
geothermal
areas
(for
size
and
geological
features)
within
the
Campi
Flegrei
caldera,
show
that
the
volume
method
is
roughly
comparable
with
the
sur-
face
thermal
flux
one.
At
Ischia,
the
total
thermal
energy,
which
is
related
to
a
shallow
reservoir
whose
temperatures
are
above
130 ◦C,
is
equal
to
3.4
×
1018 J,
corresponding
to
11
GWy
of
recov-
erable
energy.
Finally,
the
obtained
results
for
the
total
energy
stored
in
the
geothermal
reservoirs
are
compared
with
the
values
of
the
heat
content
per
unit
area
(Q)
previously
calculated
for
the
magma
reservoirs
of
Campi
Flegrei
(Q
=
6
×
1012 J
m−2)
and
Ischia
(Q
=
1.6
×
1012 J
m−2),
taking
into
account
the
related
surface
areas
(total
surface
for
S.Vito
and
Mofete
=
5
km2;
total
surface
Ischia
17
km2).
We
obtain
a
value
for
both
the
area
Q
=
∼3
×
1019 J.
This
is
one
order
of
magnitude
larger
then
the
values
calculated
with
the
volume
methods.
Assuming
that
the
evaluation
of
heat
content
per
unit
area
is
corrected,
the
lower
values
obtained
with
the
vol-
ume
methods
can
be
ascribed
to
the
variation
of
the
entropy
of
the
whole
thermodynamic
system.
10.
The
exploitation
of
geothermal
resource
in
Neapolitan
area
The
most
important
result
coming
from
the
analyses
performed
in
the
former
paragraph
is
the
large
amount
of
recoverable
energy
computed
for
Campi
Flegrei
and
Ischia.
It
totals
about
16
GWy
of
recoverable
‘thermal’
energy
(16
GW
of
available
power).
Consider-
ing
a
minimum
estimation
for
the
efficiency
of
geothermal
electric
power
plants
of
0.1
(which
is
a
minimum
value
obtained
for
very
low
temperatures
around
100 ◦C,
while
for
dry
steam
high
enthalpy
power
plants
it
can
be
higher
than
0.4)
we
got
a
minum
power
estimation
of
1.6
GW,
which
is
about
double
than
the
installed
electrical
power
in
the
Tuscany
geothermal
areas.
This
means
that
the
potential
of
Neapolitan
volcanic
area
is
about
the
same
order
of
magnitude
with
respect
to
the
actually
exploited
part
of
Tus-
cany.
Neapolitan
volcanic
areas
are
however
characterized
by
high
urbanization,
land
value
and
huge
geothermal
potential,
with
high
enthalpy
resources
often
found
at
few
hundreds
meters
of
depth.
The
results
from
drillings
at
Mofete
area
show
that
high
enthalpy
resources
can
be
found
starting
from
depths
as
low
as
400
m,
whereas
minimum
temperatures
exploitable
for
power
genera-
tion
(T100◦)
can
be
found
also
at
few
tens
of
meters
of
depth
in
areas
like
Campi
Flegrei
and
Ischia,
and
at
few
hundreds
meters
of
depth
in
most
of
Neapolitan
area.
Although
high
urbanization
rep-
resents
an
obvious
problem
for
a
geothermal
exploitation
based
on
large
power
plants
like
in
Tuscany
Region
(Larderello-Amiata),
other
exploitation
models
can
fit
better
the
features
of
the
area.
Firstly,
the
presence
of
a
large
urbanization
just
in
the
site
of
abun-
dant
and
shallow
low
enthalpy
resources
naturally
call
for
the
direct
use
for
heating
and
cooling.
In
fact,
the
availability
of
shallow
resources
practically
at
any
site
of
the
urban
area
makes
very
prof-
itable
the
direct
use
of
geothermal
heat,
which
does
not
need
the
building
of
long
and
costly
pipelines.
Furthermore,
the
best
model
of
electrical
energy
production
at
this
area
should
be
with
diffuse
networks
of
small
to
medium
plants
with
almost
negligible
emis-
sions
and
total
reinjection.
For
medium
enthalpy
resources,
this
can
be
obtained
by
the
use
of
binary
power
plants
(with
ORC
or
Kalina
cycle)
which,
for
the
climate
conditions
of
this
area
can
work
well
with
water
down
to
about
100 ◦C,
allowing
efficient
conden-
sation
of
the
binary
fluid
at
local
wet-bulb
temperature.
For
high
enthalpy
resources,
exploitation
should
be
made
with
dry
steam
or
flash
plants
(depending
from
the
balance
water/steam
in
the
flu-
ids)
with
recondensation
of
steam
out
of
the
turbines,
and
almost
total
re-injection
in
the
reservoir.
The
recondensed
fluid,
before
the
reinjection,
could
be
driven
in
a
further
binary
cycle
(hybrid
plants,
see
De
Pippo,
2005
[131])
or
into
a
pipeline
for
thermal
co-generation.
Both
of
such
cycles
help
to
improve
the
efficiency
of
exploitation.
An
appropriate
size
for
such
a
diffused
system
of
small
power
plants
would
be
in
the
range
1–10
MW.
The
modern
technology
for
geothermal
exploitation
has
also
reduced
the
impact
of
small
to
medium
size
plants
on
the
landscape;
for
instance,
the
binary
power
plant
located
in
Nevada,
with
a
net
power
of
14
MW,
has
a
dimension
less
than
200
square
meters
[131].
The
exploita-
tion
of
reservoirs
located
at
very
shallow
depth,
as
largely
present
at
Campi
Flegrei
and
Ischia,
would
also
make
completely
negli-
gible
any
risks
of
induced
seismicity
which,
however,
is
already
practically
negligible
during
exploitation
of
natural
hydrological
reservoirs.
At
Campi
Flegrei,
in
particular,
there
is
evidence
for
almost
complete
absence
of
seismicity
in
the
first
kilometers
of
depth
except
some
very
small
seisms
(ML
<
1)
generally
ascribed
to
geothermal
system
perturbations.
11.
Conclusions
The
history
of
geothermal
researches
in
the
Campanian
volca-
noes
shows
that,
from
1930
to
the
middle
1980,
a
strong
pulse
was
given
to
the
exploration
by
using
drillings
and
geophysical
sur-
veys.
Although
the
main
goal
of
the
drillings
was
the
assessment
of
the
geothermal
resource,
in
order
to
understand
the
feasibility
of
its
exploitation
for
thermal
and
electrical
uses,
after
the
aban-
don
of
exploitation
plans
in
the
mid
1980s,
the
main
use
made
of
geothermal
data
and
drillings
has
been
for
volcanological
pur-
poses.
The
period
of
geothermal
explorations,
for
such
reason,
was
characterized
by
a
great
pulse
to
the
volcanologicalstudies,
driving
a
hugeimprovement
of
knowledge
about
volcanic
processes
and
related
risk
of
eruptions
in
the
highly
urbanized
area
of
Naples
and
neighborings.
The
risk
problem
emerged
particularly
after
the
two
unrests
episodes
occurred
at
Campi
Flegrei
caldera,
in
1970–1972
and
1982–1984,
which
indicated
the
possibility
of
an
imminent
eruption,
pushing
the
local
authorities
to
evacuate
the
town
of
Pozzuoli
[31].
The
temperatures
measured
in
the
wells
(down
to
a
maximum
depth
of
about
3
km),
joined
with
the
stratigraphy
and
the
geophysical
data
inferred
from
the
drillings,
provided
impor-
tant
information
to
evaluate
the
rheology
of
the
crust
and
the
depth
of
magmatic
sources.
Scientific
results
highlight
the
presence
of
a
high
heat
flow
area
(>100
mW
m2)
in
the
western
sector
of
Campa-
nia
and
Tyrrhenian
basin,
which
is
linked
to
the
rising
of
the
Moho
at
about
20
km
of
depth
and
to
the
migration
of
magma
at
shallower

1028 S.
Carlino
et
al.
/
Renewable
and
Sustainable
Energy
Reviews
16 (2012) 1004–
1030
levels.
This
process
occurred
since
1–2
millions
years
[3,9,13,109].
We
have
remarked
that
the
fluid
circulation
(advection)
supplies
the
main
contribution
to
the
heat
transmission
to
shallow
lay-
ers
(1–2
km
of
depth).
Advection
processes
are
mainly
developed
at
Ischia
and
Campi
Flegrei,
which
show
geothermal
gradients
of
150–200 ◦C
km−1,
while
they
are
less
vigorous
at
Vesuvius,
where
the
gradient
is
roughly
30 ◦C
km−1.
This
fact
is
mainly
dependent
on
the
different
types
of
magmatic
feeding
systems
at
individual
volca-
noes.
The
dynamic
of
Campi
Flegrei
and
Ischia,
with
uplift
and
sub-
sidence
periods,
and
their
high
geothermal
gradients,
can
be
related
to
the
presence
of
shallower
(2–4
km)
and
still
hot
magmatic
sources
[56,65,107].
This
feature
is
better
constrained
by
the
results
of
geological
and
geophysical
analysis
at
Ischia,
while
at
Campi
Fle-
grei
the
presence
of
shallow
magma
bodies
(less
than
7
km)
is
still
debated.
On
the
other
side,
the
shallow
magmatic
structure
of
Vesu-
vius
is
characterized
by
a
cooled
system
of
dikes,
which
supplies
a
negligible
amount
of
heat
at
the
surface.
The
heat
propagated
by
efficient
convection
is
possibly
concentrated
close
to
the
crater
axis,
while
the
larger
hot
fluids
circulation
is
mostly
confined
in
the
carbonatic
layer.
Despite
the
high
temperatures
recorded
at
shal-
low
depth
and
the
occurrence
of
both
water
and
vapor
dominated
systems,
at
Campi
Flegrei
and
Ischia,
the
research
for
geothermal
exploitation
was
abandoned,
after
1985,
for
some
technical
prob-
lems
and,
much
more,
for
social
and
political
reasons.
The
reason
why
exploitation
was
not
pursued
despite
the
recognized
high
potential
is
likely
due
to
the
fact
that,
at
that
time,
geothermal
energy
was
not
seen
as
an
‘alternative’
(renewable)
energy,
but
rather
as
one
of
the
energy
sources,
at
the
same
level
of
gas
and
oil,
with
which
it
should
be
economically
competitive,
without
any
added
value
related
to
its
‘cleaner’
and
‘renewable’
character.
Anoher
problem
was
probably
to
ascribe
to
the
fact
that
Mofete
and
San
Vito
areas,
in
that
period,
were
becoming
much
more
urbanized,
so
that
it
would
have
been
problematic
to
adopt
a
large
plant
model
development
like
in
Tuscany.
Nowadays,
the
technical
problems,
related
to
the
high
fluids
salinity
of
the
hot
reser-
voirs,
are
overcome,
thanks
to
the
innovative
technology
applied
to
the
geothermal
plants
[131].
Furthermore,
now
to
geothermal
energy,
like
the
other
renewable,
is
recognized
a
high
added
value
with
respect
to
more
polluting,
hydrocarbon
sources,
overcoming
purely
economic
considerations.
The
option
to
invest
on
geother-
mal
energy
in
the
high
heat
flow
area
of
south
Italy
and
Campanian
volcanic
district
will
obviously
depend
on
the
policy
of
the
future
national
and
regional
plans
for
energy,
which,
at
the
moment,
is
not
well
defined
yet.
We
have
shown,
anyway,
the
very
high
poten-
tial
of
Ischia
and
Campi
Flegrei
geothermal
areas,
by
using
the
volume
methods,
whose
reservoirs
have
a
total
potential
recov-
erable
energy
(thermal
and
electric)
of
about
17
GWy.
Taking
into
account
the
extension
of
the
urban
settlements
of
the
investigated
areas,
the
features
of
natural
landscape,
and
the
characteristics
of
the
geothermal
reservoirs,
the
planning
of
small
size
power
plants
(1–10
MW)
would
be
appropriate
both
from
a
cost-effective
and
from
an
environmental
point
of
view.
The
Campi
Flegrei
area
will
be
target,
in
the
next
years,
to
CFDDP
(Campi
Flegrei
Deep
Drilling
Project).
The
project
will
consist
of
two
drillings
located
in
the
east-
ern
sector
of
the
caldera,
the
first
(pilot
hole)
reaching
500
m
of
depth
and
the
second
down
to
3.5
km
deep.
This
large
international
drilling
project
will
further
improve
both
scientific
information
on
volcanic
mechanisms
at
Campi
Flegrei
caldera,
and
the
knowledge
about
related
geothermal
systems
for
the
whole
depth
extension
of
aquifers,
down
to
the
supercritical
temperature
layers.
Acknowledgments
We
thank
two
anonymous
referees
for
reviewing
the
manuscript.
This
work
has
been
supported
by
EU-VIIFP
GEISER
Project
(ENERGY:2009.2.4.1).
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