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A new method
for
assessing fault seal integrity
by
using intersections between faults and gas chimneys
Abstract
TOTAL
~
Sutieng
H01,
2,
Jean-Philippe Blouet1,
3,
Martin Hovland1,
4,
Patrice Imbert5,
1,
Andreas Wetzel6 III!I
""
,,,
,,
~
1 Fluid Venting System Research Group, France, 20cean Center, National Taiwan University, Taiwan, 3Department of Geosciences, UniversitEi Libre de Bruxelles, Belgium, _
::::,,"'"
•••••
4Center for Geobiology, University of Bergen, Norway, 5Total-CST
JF,
France, 6Geological Institute, University of Basel, Switzerland
,-----------------~
Offshore Angola
II
Morpho-geometry & characteristics of Linear (planar) Chimneys in fault networks New method to assess fault permeability
•
Type
I =
Positive
high
amplitude
anomalies
above
pull-up
reflections
sw
NW o •
Type
II
=
Negative
bright
spot
columns
Counting numbers of different intersecting
positions between faults & chimneys
90/0
tnemlddle
1 %
From
the
e(>e.f).\"(I.~o\"l
of
PF
upper
tip
of PF
,~'IJ
9°(1.
upwardle~~ination~
~
%
IntouchwlthPF
~
upper tip 4%
No _ "
intersection 7"!.
Indeterminab~
3%
100m
UN
I
GAS
EL
Along the central axis of graben
Free
gas
accumu
la
tioo i
nthe
fractured
Qraben (Ho et a
I.
, 2016; 2018)
Positive high
amplitude anomaly
above
chimney
54% intersecting the lower
PF
footwall
or
the base below
@
~~~
•
Linear
Chimneys
occur
along
tectonic
faults
(in
non-polygonal
faulted
intervals)
@
Linear (planar) Chimneys have a lateral aspect rat i
o>
4:1. T hey often associate with
th
e linear depression &
linear seep carbonate at the top, or the linear gas column at the base. They occur
in
the Plioce
ne
aged
polygonal fault
(PF)
tier.
(3) Transversal
and
longitudinal secti
on
of a
Lin
ear Chimney shown
in
(4).
(4)
3D
view of a Linear (planar) Chimney unde
rl
ying a lin ear depression th
at
is
aligned parallel with
preferential orientated (anisotropic) polygonal
fau
l
ts
(PFs). (5) Chimney's linear planform shows
on
amplitude
and
dip overlay map .
•
Type
III
=
Positive
high
amplitude
anomalies
overlying
negative
bright
spots
@
(12) Amplit
ud
e map of
th
e
ho
ri
zon
i
nt
ersecting
the bases of t
he
Linear
Ch
imneys shows gas
accumulation exhibiti
ng
linear planform. The
downward terminat ions
of the c
hi
mneys
are
cha
ra
cterist
ic
of t
he
linear
gas
accumulati
on.
(13) A cross secti
on
shows the st
rat
igraphic
pOS
iti
on
of gas
accumulations
in
the
lower part of
ch
im
neys,
wh
i
ch
are
located in t
he
lower part of
PF
tier (6) 3D view of
Lin
ear
Ch
im
neys in Syncli
ne
-
3.
(7)-(8) Different sides of a
Li
near Chimney
in
(6), that is
composed
by
a
gas
column.
(9) Amplitude map shows
Li
near
Chi
mneys
(ye
ll
ow)
/POlygOnal
fault
(PF)
= Negative
bright
spot
column
(15) Nucleating positions of chimneys
in
f
au
lt blocks p
ro
vide
i
ns
ight
on
f
luid
transportati
on
efficiencies along faults.
If
ch
im
neys intersect the lower portions of
fau
l
ts
or root
in
strata
below t
he
f
au
l
ts,
it likely
in
dicates that fluid (gas) migrated vertica
ll
y, and cut
ac
r
oss
fau
lt planes.
If
fa
ul
ts
provide viable migration pathways, then fluid expulsi
on
and
ch
imney nucleati
on
would occur at the upper tip of the
fa
ult
(Ho
et al
..
2016) .
Permeable fault (
in
terpreted)
Chimney roots at the topmost tip of fault (1%)
_ 0 3
'C><,
c:::J
Low
pe<
me
abil
it
yl
ayer
E3
h,"""
r
me
able
barrie
r (Inlra·Plo l /
.:::~~:
parallel with aniso tropic
PFs.
In
terpretations. (16) Gas migrated along the f
au
lt
and
was expell
ed
from
the upper faul t t
ip.
(10) Gas accumulati
ons
where chimney nucleated. (17) Gas is compar
tme
n
ta
l
is
ed
by
impermeable faults
and
a
im
itate the
form
of PF blocks.
ho
ri
zontal barrier
in
the graben. Gas escaped
by
crea
tin
g a
ch
imne
y.
(18) Gas could not
100m
@
,.
+
--=
~
a.
(14) Kilometre-sca le
Li
near
Ch
im
neys
(blue arrows) deve loped
in
(11)
Seismic section across migra
te
further up t
he
upper fault plane,
so
it
created a
ch
i
mney
to escape. (19) Gas
•
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a
Dc~~!~~~!~~;6)f~~.
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:
e
s~nm:
~
y
of
~
f
oo
"
~
""
t
~r
i
n
t
Cf=oo~rn
r
~.
~h
Uoe~
C
~"'Y>:
a
ca
oe
,ttxly
~""
t
Oe
L
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Ba
,n
C ~oe
"
~
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.•
(21
Ho
. S.,
Homnd.
M
..
8~
~~
p~~~~~~~~~~
.
P
..
3
=rutoon
, D. (2018).
F~ma
t
oo
of
_
ar~
fOf
mm~y>
c
oott~~
by
..
o
~
ron
t
~h~
oca~
~~
e and
~
oo
n~
~
ro
=.
n
tau~
oo_
~
:c:~
~:t~:
:::~~~:~:~),~~:_i
,
~:
t:
~3~
p~~i?
r
~:i::
t~
I~;;)t~
~.=.:
~:~:~
:~~
r~t~
~::e:~We5
~R~~
~
U
'
mar
~n
~~
Goo~
~:~
I
=
Intersecting
th
e lower
footwall of fau lt
Cross cutting the fault plane
Free gas accumul
at
i
oo
i
nthe
strata at t
he
base
of
PF foot
wa
ll
(Hoeta
l.
,2016;2018)