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2Oilfield Review
Seismicity in the Oil Field
Vitaly V. Adushkin
Vladimir N. Rodionov
Sergey Turuntaev
Institute of Dynamics of Geospheres,
Russian Academy of Sciences
Moscow, Russia
Alexander E. Yudin
Ministry of Fuel and Energy of the
Russian Federation
Moscow, Russia
Much of this article originally appeared in the Schlumberger
Russian version of the Oilfield Review, Neftegasovoye
Obozreniye 5, no. 1 (Spring 2000): 4-15. For help in prepa-
ration of this English version, thanks to David Leslie,
Schlumberger Cambridge Research, England; and Yefim
Mogilevsky, Graphics International, Houston, Texas, USA.
Results in this article were based on data obtained by the
local seismic network of Stock Joint Company “Tatneft.”
The authors thank I.A. Iskhakov, head of the TNGF seismic
crew, and K.M. Mirzoev, chief of the Tatarstan seismic sur-
vey, who provided the catalogue of seismic events and the
produced and injected fluid volumes data. The support from
“Tatneft” and the Russian Foundation for Basic Research
(RFBR project # 98-05-64547) is gratefully acknowledged.
In some regions, hydrocarbon production can induce seismic activity. To help
understand how production affects seismicity, a recording network was installed
in a producing field in Russia. In a cooperative project between Schlumberger
and the Institute of Dynamics of Geospheres at the Russian Academy of
Sciences, scientists are analyzing the recorded data to help forecast seismic
events, understand reservoir properties and monitor water injection.
Scientists have observed that earthquakes can
be triggered by human action. Induced seismicity,
or seismic activity caused directly by human
involvement, has been detected as a result of
water filling large surface reservoirs, develop-
ment of mineral, geothermal and hydrocarbon
resources, waste injection, underground nuclear
explosions and large-scale construction pro-
jects.1It is important to understand the condi-
tions under which seismicity may be induced so
that these operations can be performed safely.
The notion that human activity can provoke
earthquakes is not new. In the 1870s, proposals
for impounding water in man-made lakes across
regions of southern California, USA, were
rejected because of concerns that this might trig-
ger earthquakes.2The hundreds of small earth-
quakes detected immediately after the 1936
filling of the Hoover Dam in Nevada and Arizona,
USA, provided the first definite evidence of such
an effect. Since then, more than 100 other cases
have been reported around the world.3In some
instances, the resulting seismic activity has been
severe. Within four years of completing construc-
tion in 1963, the reservoir area surrounding the
Koyna Dam near the west coast of India experi-
enced several significant earthquakes, the
largest being a major event of magnitude 7.0.4In
the nearby town of Koynanagar, masonry build-
ings were destroyed and 200 people died.
In the early 1920s, geologists in south Texas
noted faulting, subsidence and earthquakes in
the vicinity of the Goose Creek oil field. Houses
shook and faulting broke the earth’s surface.5A
direct relationship was proposed between oil
extraction and the onset of subsidence and seis-
mic activity. At the time, subsidence associated
with hydrocarbon extraction was considered
rare, and this case was thought to be a unique
occurrence in geological literature. Similar obser-
vations were then reported for the Wilmington
oil field in Long Beach, California, USA, where six
small earthquakes occurred between 1947 and
1955, and surface subsidence reached 9 m [30 ft]
in 1966 after 30 years of oil production.6
By the 1960s, it became clear that deep injec-
tion of fluid could also cause seismicity. Early in
1962, waste-water by-products from the Rocky
Mountain Arsenal near Denver, Colorado, USA,
were injected into a disposal well in fractured
Precambrian rocks at a depth of about 12,000 ft
[3660 m]. Earthquakes up to magnitude 4.3 began
occurring one month later, and continued for the
three-year injection period. The frequency of
earthquake occurrence was clearly related to the
rate and pressure of fluid injection.7
Summer 2000 3
Seismologists speculated that if the physical
basis for triggering earthquakes by injection could
be clearly established by field experiments, fluid
injection or extraction might become a means of
controlling earthquakes or preventing inadvertent
seismic activity. Geophysicists and hydrologists
designed an experiment to test the feasibility of
controlled earthquake generation in the Rangely
oil field in western Colorado. The field had been
on waterflood since 1957, and an array of seis-
mographs in the neighboring state of Utah had
been recording small earthquakes in the field
since its installation in 1962. In 1967, a portable
array of seismographs was installed directly over
the field. It began recording and locating seismic
events along a subsurface fault in two areas
where waterflooding had induced high pore
pressures.8The project successfully initiated seis-
mic activity by injecting even more water and
halted seismic activity by producing from near the
fault. The report suggested the technique might
be useful for controlling the timing and size of
major earthquakes, and noted that up to that
time, fluid injection for enhancing oil recovery had
not triggered any damaging earthquakes.
In all these cases, the result of human inter-
ference was to change the state of stress in the
surrounding volume of earth. If the stress change
is big enough, it can cause an earthquake, either
by fracturing the rock mass—in the case of min-
ing or underground explosions—or by causing
rock to slip along existing zones of weakness.
The situation in regions of hydrocarbon recovery
is not always well understood: in some places,
extraction of fluid induces seismicity; in others,
injection induces seismicity. In many areas where
the rock is not under large tectonic stresses, the
seismic energy released during induced events is
low—typically of magnitude 0 to 3—and not
even felt on the earth’s surface. However, if the
rock mass is already under large tectonic
stresses, the energy added by man’s endeavors
can have a destabilizing influence. Even minor
actions can trigger strong seismicity.9
Long-term hydrocarbon exploitation can dis-
turb conditions around oil and gas reservoirs in
several ways, causing significant stress changes
in the reservoir and the surrounding rocks.
Injected fluid can propagate or filter into cracks
and cause increased fluid pressure in pores
and fractures, serving as a kind of lubricant in
Induced by dams Induced by oil and gas recovery Induced by mineral-deposit exploitation
1. Nikolaev NI: “On the State of Study of Induced
Earthquakes, Related with Industrial Activity” in:
An Influence of Industrial Activity on the Seismic
Regime. Moscow, Russia: Nauka, 1977 (in Russian).
Gupta H and Rastogi B: Dams and Earthquakes. New York,
New York, USA: Elsevier Scientific Publishing, 1976.
Pasechnik IP: “Earthquakes Induced by Underground
Nuclear Explosions,” in: An Influence of Industrial
Activity on the Seismic Regime. Moscow, Russia:
Nauka (1977): 142-152 (in Russian).
Simpson DW: “Triggered Earthquakes,” Annual Review
of Earth and Planetary Science Letters 14 (1986): 21-42.
Nicholson C and Wesson RL: “Earthquake Hazard
Associated with Deep Well Injection—A Report to the
US Environmental Protection Agency,” US Geological
Bulletin vol. 1951, 1990.
Milne WG and Berry MJ: “Induced Seismicity in Canada,”
Engineering Geology 10 (1976): 219-226.
Grasso J-R: “Mechanics of Seismic Instabilities Induced
by the Recovery of Hydrocarbons,” Pure and Applied
Geophysics 139, no. 3/4 (1992): 507-534.
2. Bolt B: Earthquakes: A Primer. San Francisco,
California, USA: W.H. Freeman and Company, 1978.
3. Guha SK and Patil DN: “Large Water-Reservoir-Related
Induced Seismicity,” in Knoll P (ed): Induced Seismicity.
Rotterdam, The Netherlands: AA Balkema Publishers
(1992): 243-266.
4. Earthquake magnitudes in this article are taken from
a variety of literature sources. Magnitudes are usually
calculated from the recorded amplitude of a seismic
wave of specified frequency and calibrated for the
distance from the earthquake and the magnification
of the seismograph.
5. Pratt WE and Johnson DW: “Local Subsidence of
the Goose Creek Oil Field,” Journal of Geology 34,
no. 7-part 1 (October-November 1926): 577-590.
6. Segall P: “Earthquakes Triggered by Fluid Extraction,”
Geology 17, no.1 (October 1989): 942-946.
7. Evans DM: “Man-Made Earthquakes in Denver,”
Geotimes 10, no. 9 (May-June 1966): 11-18.
8. Raleigh CB, Healy JH and Bredehoeft JD: “An
Experiment in Earthquake Control at Rangely, Colorado,”
Science 191, no. 4233 (March 1976): 1230-1237.
9. Simpson, reference 1.
Sadovsky MA, Kocharyan GG and Rodionov VN: “On the
Mechanics of Block Rock Massif,” Report of the Academy
of Sciences of USSR 302, no. 2 (1988): 193-197 (in Russian).
Rodionov VN, Sizov IA and Kocharyan GG: “On the
Modeling of Natural Objects in Geomechanics,”in:
Discrete Properties of Geophysical Medium. Moscow,
Russia: Nauka (1989): 14-18 (in Russian).
K A Z A K H S T A N
T U R K M E N I S T A N
U Z B E K I S T A N
Gazli
R U S S I A
T
U
R
A
N
P
L
A
T
E
>Location of the Gazli field, Uzbekistan.
fractured zones. Three types of forces help initi-
ate filtration-induced earthquakes as well as
other man-made and tectonic earthquakes by
causing motion of rock blocks along faults: First,
poroelastic forces can force displacement along
a fault in the surrounding rock mass. Second,
hydrostatic forces can transfer pore pressure
from an injection zone to a zone preparing for an
earthquake through a fault or other permeable
feature. Fluid migration in this case may be neg-
ligible. Finally, pressure differences can cause
fluids to migrate from injection zones to zones of
earthquake incipience.
Hydrocarbon field development always
induces at least minor changes in the stress state
of a reservoir. Sometimes this increases the level
of small, background seismic events. The energy
released depends on the properties of the reser-
voir and surrounding rocks, the level of hetero-
geneity and the rate at which they were
deposited. Some 40 examples are known in which
reservoir production caused significant changes in
the seismic activity of a neighboring region.
Comparison of data from these reservoirs with
measurements from 200 other fields around the
world shows which properties are most closely
related to production-induced seismicity (above).
Average reservoir depth and thickness appear to
be greater for oil fields with induced seismicity
than average depth and thickness values for
other hydrocarbon fields. Average porosity and
permeability are lower for hydrocarbon fields
with induced seismicity than for those without.
Initial reservoir pressure has the same distribu-
tion in both cases.
Although there are examples of significant
earthquakes related to reservoir development,
and it is sensible to consider triggered seismicity
as one of the possible hazardous consequences
of production, it is rare for reservoir development
to lead to earthquakes strong enough for people
to feel. More often, induced seismic events are
weak, and can be recorded only with the help of
a sensitive seismometer network.
These feeble seismic events, induced ones as
well as those caused by natural deformation pro-
cesses, carry important information about the
location of zones of weakness and seismically
active faults in the rock. They also contain infor-
mation about temporal changes in stress state
4Oilfield Review
>A comparison of probability distribu-
tions for some key variables in hydrocar-
bon reservoirs. The black line represents
data from 40 oil and gas fields with an
observed increase in seismic activity due
to hydrocarbon production; the red line
corresponds to random-sample data on
200 reservoirs located in various regions
around the world.
11000
0
0
0
2
4
4
6
8
10
200 400 500300 2 3 4
1
2
0
1
2
3
4
5
2000
0400 600 800 1000 1200
1
2
3
Reservoir thickness, m
Probability density x 10-3
Probability density x 10-4
Probability density x 10-2
Probability density x 10-3
Initial reservoir pressure, atm
Reservoir depth, km
Permeability, mD Reservoir porosity, %
5
4
3
3
2
1
0
00246810 20 40 60 80
Probability density x 10-4
Summer 2000 5
and other formation properties. Interpreting
records of production-induced seismicity allows
identification of active faults, delineation of fluid-
contrast fronts and estimation of time variations
of reservoir permeability and porosity. This infor-
mation, in turn, may help to optimize the schedul-
ing of hydrocarbon production, water injection
and enhanced recovery operations.
In the following sections, we examine the
relationship between recorded seismic events
and the evolution of hydrocarbon exploitation
parameters through two case studies. The first is
a study of earthquakes in the region of the Gazli
gas field in Uzbekistan. The second is an investi-
gation of temporal and spatial characteristics of
seismicity in the region of the Romashkino oil
field in Tatarstan, Russia.
Gazli Earthquakes
The Gazli gas field is located in Central Asia about
100 km [63 miles] northwest of Bukhara,
Uzbekistan (previous page, bottom). The field struc-
ture consists of Jurassic, Cretaceous, Paleocene
and Neocene formations overlapping Paleozoic
basement in an asymmetrical anticline with dimen-
sions 38 by 12 km [24 by 7.5 miles] (above). The
thickness of sediments is about 1000 m [3300 ft],
reaching a total depth of 1600 m [5200 ft].
The field has 11 accumulations—10 gas and
condensate, and one oil—all located in Creta-
ceous sediments. Producing horizons consist of
sandstone and clay beds. Porosity of the sandstone
is high and averages 20 to 32%. Permeability of all
but one producing horizons ranges from 675 to
1457 mD. Produced gas consists mainly of
methane (93 to 97%) with condensate in the lower
horizons (8 to 17.2 g/m3[67 to 144 lbm/gal]).
The gas field was discovered in 1956 and pro-
duction began in 1962. Over the next 14 years,
roughly 600×106m3of water, or 106ton per km2,
were injected. In spite of the water injection,
subsidence was detected at the surface. The
subsidence rates averaged 10.0 mm/a [2.5 in./yr]
in the period 1964 to 1968 and 19.2 mm/a
[5 in./yr] from 1968 to 1974. Subsidence was
observed to be associated with reduction in for-
mation pressure: when formation pressure
dropped by 1 atm [101 kPa], the central part of
the field subsided by 2 mm.10
Beginning in 1976, a series of large earth-
quakes was recorded. The first significant earth-
quake occurred on April 8, 1976 at a distance of
420
440
460
400
480
500
520
-560
-580
Section b
Section c
500 Isolines in meters
Wells
Tectonic discontinuities
Gas reservoir contour
Section b
Depth, m
Gas
Oil
Water
Clay
North 12 11 10 3
400
600
800
1000
Section c
24 15
400
600
800
1000
1200
Depth, m
North
Well no. South
Well no. South
1310118
35 23 14
5 km
3 miles
5 km
3 miles
5 km
3 miles
<
Structural map (top) and cross
sections from the Gazli gas field.
The structural map shows well
locations, contours of the uppermost
horizon in meters, tectonic disconti-
nuities, the locations of the cross
sections and the limit of the gas
reservoir. The cross sections show
gas, oil, water and clay layers.
[Adapted from Zhabrev IP (ed):
Gas and Condensate Deposits.
Moscow, Russia: Nedra, 1984
(in Russian)].
10. Piskulin VA and Raizman AP: “Geodesic Investigations
of the Earth Surface Deformation in Epicentral Zones
of Gazli Earthquakes in 1976-1984,” Proceedings of 7th
International Symposium on the Earth Crust Modern
Motion. Tallinn, 1986.
20 km [12 miles] from the Gazli gasfield boundary.
The earthquake magnitude measured 6.8. Just 39
days later, on May 17, 1976, another severe
earthquake occurred 27 km [17 miles] to the west
of the first one. The magnitude of the second
earthquake was 7.3. Eight years later, on March
20, 1984, a third earthquake occurred 15 km
[9 miles] to the west of the second earthquake,
with a magnitude of 7.2. The hypocentral depths
of all three were 25 to 30 km [16 to 18 miles], all
within the 32-km [20-mile] thick earth crust in the
region. Aftershocks occurred in a volume sur-
rounding the three hypocenters. These earth-
quakes are the strongest of all the known
earthquakes in the plain of Central Asia.
There was no clear relationship between the
location of the earthquake hypocenters and any
previously known active tectonic structures.
Closer investigation showed that the earth-
quakes had created new faults.11 Analysis of the
fine-scale structure of the aftershock zone indi-
cated an initial state of tectonic activation.12 The
orientation of the fault plane, the direction of
fault-block displacement and the trend of the
aftershock zone correspond to the regional stress
field and orientation of regional-scale faults.
Geodesic measurements were made after
each large earthquake (below). The area that had
previously subsided was found to have subsided
an additional 230±8 mm [9 in.] after the 1976
earthquakes (above).13 In the vicinity of the earth-
quake epicenters, an upward displacement of the
surface was detected: up to 830 mm
[33 in.] near the epicenter of the April 1976 earth-
quake, up to 763 mm [30 in.] near the epicenter
of the May 1976 earthquake, and up to 751 mm
[29.5 in.] near the epicenter of the March 1984
earthquake. Horizontal displacements of up to
1 m [3.3 ft] were detected and found to be
directed mainly away from the epicenters.
The amassed data indicate that the Gazli
earthquakes were triggered by exploitation of the
gas field.14 High tectonic stresses are typical for
border regions of young platforms such as the
Turan plate. These stresses cause accumulation
of significant tectonic energy. Depletion of the
gas field served as a trigger for the release of
accumulated tectonic energy in the form of sig-
nificant seismic events. Field production was
undertaken without consideration of the possibil-
ity of production-induced seismicity. Some geo-
physicists, including the authors of this article,
believe that if the natural tectonic regime had
been taken into account during the planning of
hydrocarbon recovery, the earthquakes might
have been avoided.15
6Oilfield Review
-100
+800
+500
+600
+200
0
+751
-100
0
+100
+400
0
Gazli
+830
+200
0
+100
+751
0
Chorbakty
Karakyr
Vertical displacement after the earthquakes in 1976, in mm
Vertical displacement after the earthquakes in 1984, in mm
A boundary of gas accumulation
Epicenters of the earthquakes on April 8 and May 17, 1976 and March 20, 1984
Tectonic faults
+100
+300
-100
Position of surface vertical displacement profile
+200
10 km
6 miles
<
Surface deformation following the Gazli
earthquakes of 1976 and 1984. Maximum
vertical displacements are shown as
black dots, and earthquake epicenters as
red dots. Dashed lines mark the vertical
displacement following the 1976 events;
and solid lines mark the vertical displace-
ment following the 1984 event. The gas
field is shaded in light red. Tectonic faults
are shown as thick black lines. The red
vertical line marks the position of the
cross section displayed (above). [Adapted
from Piskulin and Raizman, reference 10].
0
600
400
200
-200
South
Displacement, mm
010203040
North
Gazli fault Karakyr
fault
Distance, km
1964 to 1968
1968 to 1974
1974 to 1976
Measurement periods
800
>North-south profile of vertical displacement after the Gazli earth-
quakes. The region between the Gazli fault and the Karakyr fault
subsided, while north of the Karakyr fault, upward displacement
was measured.
Summer 2000 7
The Romashkino Oil Field
The Romashkino oil field is the biggest oil field
in Russia (right). It has a maximum dimension of
about 70 km [44 miles], a structural height of 50
to 60 m [164 to 197 ft] and a reservoir depth of
1600 to 1800 m [5200 to 5900 ft].16 The deposit is
a succession of 10- to 30-m [33- to 100-ft] thick
oil-bearing Devonian sandstones and carbonate
rocks (below). The main productive formation
contains thinly bedded sandstones and clays.
Permeability of the sandstone layers is 200 to
420 mD, porosity is 18.8 to 20.4% and oil satura-
tion is 69.4 to 90.5%. Initial reservoir pressure
was 160 to 180 atm [16.2 to 18.2 MPa].
Geological exploration in this region began in
1933. In 1947, exploration drilling commenced,
and in 1948 Romashkino produced its first oil.17
Water injection began in 1954, but for the first
several years, injection did not compensate for
fluid extraction. In 1958, for the first time, the vol-
ume of fluid injected that year exceeded the vol-
ume of fluid extracted, and by 1963 total injected
and extracted fluid volumes balanced. By 1975,
the total volume of fluid injected in the program
reached 2.13×109m3, or 104.7% of total
extracted fluid. Suggested maximum pressures
for water injection were 200 to 250 atm [20.2 to
25.3 MPa], but actual injection pressures some-
times were higher.
11. Shteinberg VV, Grajzer VM and Ivanova TG: “Gazli
Earthquake on May 17, 1976,” Physics of the Earth 3
(1980): 3-12 (in Russian).
12. Turuntaev SB and Gorbunova IV: “Characteristic
Features of Multi Fracturing in Epicentral Zone of
Gazli Earthquakes,” Physics of the Earth 6 (1989):
72-78 (in Russian).
13. Piskulin and Raizman, reference 10.
14. Akramhodzhaev AM and Sitdikov B: “Induced Nature
of Gazli Earthquakes, a Forecast of Earthquakes of
Gazli Type and Prevention Measures,” Proceedings of
Workshop on Experience of Gazli Earthquakes Study
Further Investigation Directions. Tashkent, Uzbekistan:
FAN (1985): 59-60 (in Russian).
Akramhodzhaev AM, Sitdikov BB and Begmetov EY:
“About Induced Nature of Gazli Earthquakes in
Uzbekistan,” Geological Journal of Uzbekistan 4 (1984):
17-19 (in Russian).
Volejsho VO: “Conditions of Gazli Earthquakes
Occurrence,” Proceedings of Workshop on Experience
of Gazli Earthquakes Study Further Investigation
Directions. Tashkent, Uzbekistan: FAN (1985): 65-66
(in Russian).
Mavlyanov GA (ed): Gasli Earthquakes in 1976 and 1984.
Tashkent, Uzbekistan: FAN, 1986 (in Russian).
15. Akramhodzhaev et al, reference 14.
16. Bakirov AA (ed): Geological Conditions of Oil and Gas
Accumulation and Location. Moscow, Russia: Nedra,
1982 (in Russian).
17. Muslimov RH: An Influence of Geological Structures
Distinguish Features on an Efficiency of Romashkino
Oil Field Development. Kazan, Russia: KSU, 1979
(in Russian).
K A Z A K H S T A N
T U R K M E N I S T A N
U Z B E K I S T A N
Romashkino
R U S S I A
>Location of the Romashkino field, Russia.
1400
1450
1500
1550
1600
1650
Limestone
Clay
Oil reservoir
Basement
140 4811-88 518 519 14-91 27 33 30 627 19-553 18-552 16-551 8-550
Wells
Sandstone
NW SE
Depth, m
10 km
6 miles
>Geologic profile of the Romashkino field. [Adapted from Muslimov, reference 17].
For exploitation convenience, the Romashkino
oil field is divided into more than 20 areas. In
these areas, various methods of injection are
used: injection through a line of wells, local
injection wells and pattern waterflooding. In sev-
eral areas, well density is three to five wells per
km2. However, overall, the density of well cover-
age and geometry of well location appear to be
the result of a complicated development history
defined by objective factors as well as random
ones.18 Methods of nonstationary injection were
used in a number of areas. That is, water was
injected through one injection line for one month,
then the first line was switched off and water
was injected through another line, and so on.
Injected water migration velocity varies from
100 to 1500 m/a [330 to 4900 ft/yr].19
Characteristics of Romashkino Seismicity
According to seismic zoning maps, the southeast
part of Tatarstan in the region of the Romashkino
oil field is considered a seismically quiescent
area. But in 1982 and 1983, after decades of
production and injection, citizens in the vicinity of
the town of Almetjevsk began noticing moderate
seismic events. In 1985, the “Tatneftegeophysica”
seismic service installed a local seismic network
that recorded numerous earthquake epicenters in
the region of the Romashkino oil field (left). Most
of these are in the western part of the field on the
Altunino-Shunaksky depression, the structural
boundary between the Romashkino and Novo-
Elkhovskoye oil fields.
From 1986 to 1992, the network recorded 391
local earthquakes with magnitudes up to 4.0.
Three time intervals showed noticeable increases
in seismic activity—at the end of 1986, in the
middle of 1988 and at the end of 1991. The largest
episodes were an earthquake on September 23,
1986, with magnitude 3.8 and another with mag-
nitude 4.0 on October 28, 1991, in the region of
the town of Almetjevsk.20
8Oilfield Review
10 km
6 miles
Romashkino oil field
Almetjevsk
1
2
3
Leninogorsk
Novo-Elkhovskoye oil field
4
5
Seismic recording stations
Almetyevneft producing areas
Berezovskaja (B area)
Severo-Almetyevskaja (S area)
Almetyevskaja (A area)
Minibayevskaja (M area)
Limits of the Romashkino and
Novo-Elkhovskoye oil fields
Isointensity lines of the Sept. 23, 1986
earthquake
Cross section
Legend
3
Altunino-Shunaksky
depression structure
Energy classification of seismic events
510
>Seismic activity in the region of the Romashkino oil field.
Seismic recording stations are triangles, seismic epicenters
are dots or circles, with the size depending on the amount
of energy released. The dashed red ellipses are contours of
intensity of the September 1986 earthquake. The black line
positions the cross section displayed (previous page, bottom).
The four producing areas of the Romashkino field that
exhibit the most seismicity are delineated (B, S, A and M)
and discussed in later sections of the article. [Adapted from
Iskhakov et al, reference 20.]
N
1
50
100
500
1000
2000
Altunino-Shunaksky
depression structure
J/km2
1
/3
Quantified
seismic
activity,
10 km
6 miles
>Distribution of quantified seismic activity (color coded) in the
region of the Romashkino oil field. Quantified seismic activity is
the sum of the cube root of seismic-event energy occurring in one
square km2. The distribution of seismic activity is related to tectonic
faults (solid purple lines) and the Altunino-Shunaksky depression
structure (dashed lines).
Summer 2000 9
The recorded activity can be examined in sev-
eral ways to compare it to reservoir parameters.
A map of seismic activity in the region of the
Romashkino oil field shows spatial variations
in the level of activity (previous page, bottom).
A quantitative measure of seismic activity was
computed for each km2by summing the cube
roots of the energies in all earthquakes occurring
there during the 1986 to 1992 period of observa-
tions.21 Most of the seismic activity quantified
in this way is situated along the Altunino-
Shunaksky depression, with some corresponding
to mapped tectonic faults.22
Before the recorded seismic activity can be
used more quantitatively, the quality of the data
must be assessed. Seismic recording networks
have sensitivity limitations in the magnitude and
distance of events they can record. Extremely
small events can go undetected, as can distant
events. Also, since large events do not occur
often, shorter seismic recording intervals are less
likely to record the larger earthquakes. For all
earthquakes in a given region, a linear relation-
ship exists between the magnitude of seismic
events recorded in a time interval and the loga-
rithm of the number, or frequency, of events of
that magnitude. If the frequency-magnitude plot
shows deviations from a linear trend, the earth-
quakes being plotted are not representative of all
the seismic activity in the region. A deviation
from linear on the low-magnitude end indicates
that the seismic network is not sensitive enough
to weak events, while a deviation on the high-
magnitude end usually shows that the observa-
tion period was not long enough.
In the case of the seismic activity recorded
from the Romashkino network, the frequency-
magnitude plot is mostly linear (above). Only
those events that were listed in the 1986 to 1995
catalogs of instrumentally recorded seismic
events were plotted. Remote events with epicen-
tral distances of more than 70 km [44 miles] were
not considered. During the observation period,
different catalogs used different methods of seis-
mogram interpretation. To ensure consistency,
frequency-magnitude relations were plotted
separately for three different time intervals: 1986
through 1987, 1988 through 1992, and 1992
through 1995. Also, an average annual number of
events for these time periods was considered.
For the earlier time interval—up to 1987—
only the events with magnitude greater than
2 are representative for this particular seismic
network: not enough events with lower magni-
tude were recorded. After 1987, because of a
change in the seismic network, events with mag-
nitude 1.5 become representative, and so can be
included in further calculations.
For all three time intervals, the slopes of the
frequency-magnitude plots range from –1.02 to
–1.3, considerably more negative than the value
for natural seismicity, which is –0.75 to –0.9.23
The slopes of the Romashkino plots reach values
typical of induced and triggered seismicity, as
measured elsewhere in the world.24
Change in Quantified
Seismic Activity with Time
Quantified seismic activity is one of the most
useful parameters for characterizing seismicity.25
It provides a way to transform the display of seis-
mic events from a discrete system to a continu-
ous one: the point-by-point representation of
seismic events described by three spatial coordi-
nates plus the event time and energy converts to
a continuous plot in a different coordinate sys-
tem. The selected quantitative measure of activ-
ity was described earlier as the sum of the cube
roots of the energies in all events occurring in a
km2. To minimize the influence of an arbitrary
choice in the way the area is divided into squares
and in the selection of a beginning time interval,
activity values were computed for overlapping
areas and time intervals. The amount of overlap
depends on the smoothness of the obtained dis-
tributions of activity.
18. Muslimov, reference 17.
19. Sultanov SA: A Control of Water Injection in Oil
Reservoirs. Moscow, Russia: Nedra, 1974 (in Russian).
20. Iskhakov IA, Sergeev NS and Bulgakov VYu, A Study of
Relation Between Seismicity and Oil Fields Development.
A report of OMP 50/81. Bugulma, Russia:
Tatneftegeophysica, 1992 (in Russian).
21. Energy is calculated through a formula based on the
square of the amplitude of seismic waves of specified
frequency content measured at a standard distance
from the event source.
<
Relationship between the
logarithm of the number of
seismic events and the magni-
tude of the events in the region
of the Romashkino oil field.
Nurec Dam,” in Seismological Investigations in the
Regions of Large Dam Constructions in Tajikstan.
Dushanbe, Tajikstan: Donish (1987): 101-119 (in Russian).
Turuntaev SB: “An Application of the Weak Seismicity
Catalog for Detection of Active Faults in Rock Massif,”
in The Monitoring of Rock Massif State During Long-
Time Exploitation of Large-Scale Underground Works.
Appatity, Russia: KFAS, 1993 (in Russian).
25. Ponomaryov VS and Tejtelbaum UM: “Dynamics
Interactions Between Earthquakes Focuses,” in:
Regional Investigations of Seismic Regime. Kishinev,
Moldova: Shtinitsa (1974): 79-92 (in Russian).
22. Belousov TP, Muhamediev ShA, Turuntaev SB, Junga SL,
Ischakov IA and Karakin AV: “Active Faults, Stresses
State and Seismicity of South-East Tatarstan,” Seismicity
and Seismic Zones of Northern Part of Eurasia, part 2.
Moscow, Russia: Nauka (1994): 90-108 (in Russian).
23. Sadovsky MA and Pissarenko VF: Seismic Process in
Block Media. Moscow, Russia: Nauka, 1991 (in Russian).
Isacks B and Oliver J: “Seismic Waves with Frequencies
from 1 to 100 Cycles Per Second Recorded in a Deep
Mine in Northern New Jersey,” Bulletin of the Seismo-
logical Society of America 54, no. 6 (1964): 1941-1979.
24. Mirzoev KM, Negmatullaev SH and Dastury TYu: “An
Influence of Mechanical Vibrations on Characteristic
Features of Seismic Energy Release in the Region of
Number of seismic events, N
0.1
1
10
100
1.0 1.5 2.0 2.5 3.0 3.5 4.0
Magnitude, M
1986 to 1987
1988 to 1992
1992 to 1995
Initially, the temporal and spatial components
of activity change were calculated separately.
The variation over time was examined on a
monthly basis by summing the cube roots of
energies of events that took place during a
month. The resulting temporal series was nor-
malized by the average value for that time period
(above, top). Two strong peaks and several
smaller ones are evident in this plot, but period-
icity, if it exists, is not obvious. The seismic activ-
ity also may be displayed in other ways to try to
extract any underlying periodicity. These meth-
ods involve transformation to phase coordinates
(see “Another Dimension in Seismic Activity,”
page 12). Looking at the data in the new coordi-
nate system led to the following results.
Over the observation period, seismic activity
in the Romashkino oil field occurs in two cycles.
Both cycles start with the strongest earthquakes
for this region and each cycle lasts for about
five years. The two cycles of activity variations
from 1986 to 1990 and from 1991 to 1995 can
be smoothed and superimposed so that their
first maximums coincide (above, near). An intrigu-
ing qualitative agreement of the curves appears,
presenting evidence of some kind of regularity in
seismic activity oscillations.
The existence of a regular component to the
sequence of seismic events carries information
about the energy state of the rock. It seems pos-
sible that when the level of energy accumulated
in the rock from both natural and human sources
reaches a certain value, energy is released by
seismic events that are structured in space and
time. This is similar to the behavior of a fluid
being heated: for certain values of the rate of
energy supplied to the fluid, its laminar move-
ment changes to a chaotic flow, and then to a
regular flow with convection cells.
In a rock formation undergoing oil production
and water injection, there is an increased possi-
bility of a large earthquake, regardless of the
release of natural tectonic deformation energy in
the form of seismic events. This is because the
energy transferred to the rock through hydro-
carbon exploitation will continue to increase.
The existence of quasi-periodic oscillations in
the level of seismic activity suggests that the
input energy is rather large. Understanding
this relationship between seismicity and
exploitation regimes may allow seismicity to be
controlled by a more careful scheduling of pro-
duction and injection.
Spatial Characteristics of
Romashkino Seismicity
The seismic behavior of the Romashkino oil field
exhibits an interesting characteristic: a high num-
ber of earthquakes occur in pairs, with a short
time between members of a pair. For example,
about 60 paired events with magnitude less than
1.0, or about 50% of the total number of events
with such magnitude, occurred within 24 hours of
one another. One can suppose that events
grouped in time are somehow also connected in
space. Examples of this can be seen in laboratory
studies of seismic signals generated during crack
growth in block models of rock.26 Under certain
conditions of crack development, a seismic
impulse is generated at the moment a crack
reaches the block boundaries. The locations of
the event pair define the limits of the episodic
movement along the crack, or fault.
Connections between epicenter pairs in the
Romashkino field generally show north-south
alignment, trending with the longitudinal
Altunino-Shunaksky depression (next page, top).
This direction also corresponds to the model of
the regional stress field.27
Correlating Seismic Activity with
Hydrocarbon Exploitation
It is always difficult to know whether seismicity
is the result of human modifications in the region
or if it is natural seismic activity related to tec-
tonic processes; timing could be the key to know-
ing the difference. In general, the answer might
be obtained if a regional seismic network had
been installed in advance of the hydrocarbon
development, dam construction or mining opera-
tion. The seismic network could record a back-
ground level of natural seismicity and quantify its
10 Oilfield Review
26. Turuntaev SB: “A Study of Various Model Waves
Sources in Application to Seismology,” PhD Thesis,
Institute of the Physics of the Earth, Moscow, Russia,
1985 (in Russian).
27. Belousov et al, reference 22.
28. Mirzoev et al, reference 24.
>Seismic activity variation in the Romashkino region. The
amplitude was calculated by summing the cube root of energies
from all events occurring in that month.
>Comparison of two cycles of seismic activity in the region of the Romashkino
oil field.
1986
0
3
6
9
Year
Seismic activity, normalized
1988 1990 1992 1994 1996
0
1
2
3
4
01224364860
Time, months
Seismic activity, normalized
1991 to 1995
1986 to 1990
Summer 2000 11
characteristics. If, after the beginning of human
action, a significant change in seismicity charac-
ter is recorded, it could reasonably be interpreted
as a seismic reaction of the rock formation to
man’s intervention.
Installation of seismic recording networks and
assessment of background seismic activity are
already common practice in regions where the
level of natural seismicity is high.28 However, in
stable areas without a history of natural seismic-
ity and where no sizeable earthquakes are
expected, an advance seismic background study
usually is not performed. In the absence of an
advance study, the question may be resolved by
two methods: first, to compare characteristics of
the observed seismicity with those of known nat-
ural seismicity and those of induced seismic activ-
ity; and second, to look for correlation between
the natural seismic and human activities.
In the first method, as was shown above, the
slope of the magnitude-frequency plot for seis-
micity in the region of the Romashkino oil field
has a value more typical of induced than natural
seismicity. But the low number of recorded
events indicates this result may not have high
statistical significance.
The second method involves comparing the
recorded seismicity with the exploitation sched-
ule of the Romashkino oil field. The relevant pro-
duction data are the values of the monthly
volumes of fluid extracted and injected from 1981
to 1992 for the four most seismically active areas
of the Romashkino oil field: Almetyevskaja (A),
Severo-Almetyevskaja (S), Minibayevskaja (M)
and Berezovskaja (B).
With these values, a pseudocatalog was con-
structed to tabulate the monthly extracted and
injected volumes and the volume imbalance, or
the difference between the volumes of injected
and extracted fluids. These values were assigned
a date (middle of a month), time (middle of a day),
coordinates (approximate center of the consid-
ered area), and depth (1 km). Arranged in this for-
mat, the production data closely resembled the
standard form for seismic catalogs, but listed
fluid volume instead of seismic energy.
The previously described procedure for calcu-
lating quantified seismic activity was applied to
the volumes in the pseudocatalog, but this time a
“quantified exploitation activity” was calculated
(below). The quantified exploitation activity was
also analyzed using a 6-month moving average:
6-month averaged values of extraction, injection
and imbalance were calculated, then the interval
was shifted by a month and calculated again. The
results were normalized by the overall average.
N
1
50
100
500
1000
2000
J/km2
1
/3
Quantified
seismic
activity,
Altunino-Shunaksky
depression structure
Azimuth, degrees
Number of event pairs
12
10
8
6
4
2
0
-60 -30 60 90-90 30
0
10 km
6 miles
>Connections between pairs of Romashkino
seismic events. Black lines connect event pairs,
purple lines are mapped faults. The insert
shows azimuthal distribution of connections
between pairs of events.
(continued on page 14)
Seismic activity, normalized
3
2
1
0
-1
Production, injection and imbalance, normalized
3
2
1
0
9
8
7
6
5
4
3
2
1
0
4
3
2
1
0
Year
Production
Injection
Imbalance
Seismic activity
Year
Production
Injection
Imbalance
Seismic activity
Seismic activity, normalized
1981 1983 1985 1987 1989 1991 1993
1981 1983 1985 1987 1989 1991 1993
Production, injection and imbalance, normalized
>Top: Comparison of monthly values of seismic activity (red) with
variations in total volumes of injection, production and imbalance in
the four central areas (combined) of the Romashkino field. Bottom:
Comparison of smoothed values of seismic activity (red) with varia-
tions in volumes of injection, production and imbalance in the four
central areas of the Romashkino field.
12 Oilfield Review
For many natural processes, periodicity is evi-
dent from a simple plot of observation versus
time. For example, the periodicities of ocean
tides, phases of the moon, earth-surface tem-
perature, hours of daylight and several other
phenomena are easily recognized from observa-
tions or simple plots.
However, some processes may have so many
forces at work that periodicity is not obvious.
One way to analyze a time-varying observation
called A(t) is to write it as a sum of three
components
A(t) = Ap(t) + Ar(t) + At(t)
where Apdescribes the high-frequency random
oscillations of the activity, Aris the regular
component, and Atrepresents slow variations,
or a trend.
To find a regular component in the behavior
of the function A(t), we can change coordinates
from A(t) and tto phase coordinates A(t) and
its derivative, dA(t)/dt. The new coordinates
can be thought of as the activity and the rate
of activity variation.
For the seismic example, a point in the new,
phase-coordinate system defines a state of the
seismic process at some instant of time and the
velocity of change of this state. A set of points,
or a trajectory, defines a change of the system
with time.
It is known that if a system’s behavior can
be described with certain types of equations,
then special points, lines and areas in phase
coordinates exist that “attract” the neighboring
trajectories. These points, lines and areas are
called “attractors.”1
If the system is one of a monotonous decrease,
the corresponding attractor is known as a node
(below). For any starting time, the system
moves in a direct line toward that node in phase
space. In a system of damped oscillations, the
attractor is known as a focus, toward which the
system will move. A system of decreasing or
increasing oscillations will have a correspond-
ing, elliptically shaped, limit-cycle attractor in
phase space. Highly irregular oscillations can
still exhibit some regularity in phase space and
be drawn to multiple attractors.
When there is a change in the parameters
defining the system evolution, the set of possi-
ble solutions of the corresponding equations
can change too. That may result in a change
in the types of attractors in phase space. Such
a change in attractor type is called bifurcation.
The simplest examples of bifurcation are from
one node (or focus) to two nodes (or foci), a
bifurcation from focus to limit cycle, or bifurca-
tion from one limit cycle to two limit cycles.
Expressing seismic activity in terms of phase
coordinates is useful for several purposes:
• Two basic characteristics of the seismic pro-
cess (its activity and rate of activity variation)
are considered and transformed as indepen-
dent values.
• The resulting phase portrait, or map, is more
sensitive to procedures like smoothing and
trend removal, which simplifies the selection
of a time period for the calculation of activ-
ity, a smoothing type, or further coordinate
transformation.
Another Dimension in Seismic Activity
A(t)
dA/dt
a
t
A(t)
A(t)
dA/dt
b
t
A(t)
A(t)
dA/dt
d
t
A(t)
A(t)
dA/dt
c
t
A(t)
>Time-varying functions (left member of each pair) and corresponding types of attractors (right member
of each pair) in phase space. a) node; b) focus; c) limit cycle; d) limit cycle with multiple attractors.
Summer 2000 13
• The standard procedure of Fourier analysis
is not effective if applied to quasi-harmonic
oscillations with changing frequency and
amplitude. In phase coordinates, such changes
can still be analyzed in terms of attractors.
For example, an increase in the amplitude
of oscillations up to a constant value will look
like a growing limit cycle and a decrease in
amplitude to zero will look like a point-type
attractor.
• After transforming the phase portrait to a
form that allows a mathematical description,
one can carry out the reverse transformation
and obtain a mathematical description of the
regular component of the original seismic
process. This may allow estimation of future
seismicity. The statistical significance of this
prognosis depends on the value of the random,
or unpredictable, component of seismic activ-
ity and of rate of activity variation, and it also
depends on the ability to recognize bifurcation
points in phase trajectories (points of change
of seismic regime type).
Phase Characteristics of
Romashkino Seismic Activity
The time variation of quantified seismic activity
in the region of the Romashkino oil field (left,
part a) can be described by a phase portrait
(left, part b). At first glance, the activity-state
trajectory in phase coordinates looks chaotic.
However, the random component can be removed
by moving-window smoothing and the trend can
be removed by a linear transformation similar to
axes shift and rotation (left, part c).
The resulting phase trajectory (left, part d)
starts at an initial point then spirals in; at a
certain moment the trajectory comes back to
the outer part of the spiral and then spins in
again. All the while, the trajectory remains
within a certain area.
This phase portrait resembles the limit cycle
displayed on the previous page, part c for an
oscillator under the action of an external force.
An outward motion of a spiral trajectory gen-
erally corresponds to an increase in amplitude
of seismic-activity oscillations, while an inward
motion corresponds to a decrease of activity
oscillations. Shape and dimensions of the
obtained cycles can yield additional information
about the seismic process, and should be stud-
ied further. One observation already is that
oscillations of the seismic activity are not
strictly sinusoidal; the period tends to oscillate
with an average value close to 12 months.
1. Haken H: Advanced Synergetics. Instability Hierarchies
of Self-Organizing Systems and Devices, Springer series
in Synergetics. Vol 20. New York, New York, USA:
Springer-Verlag, 1983.
1986
Year
1988 1990 1992 1994 1996
Year
0
3
6
9
Seismic activity, normalized
Seismic activity, normalized
dA/dt
dA/dt
Seismic activity, normalized
Seismic activity, normalized
0
0
1
1
-1
-1
-1
-2
-4
0
0
12
2
4
3456789 2-2
0
-1
-2
1
2
d
c
a
b
1986 to 1990
1991 to 1995
1986 1988 1990 1992 1994 1996
>Seismic activity variations in the Romashkino region. Amplitude of seismic activity (top left)
was calculated by summing the cube root of energies from all events occurring in that month.
These data were displayed in phase coordinates (bottom left) to see if periodicity could be
identified. The seismic activity data were then smoothed and detrended (top right) to extract
a regular component. The phase portrait (bottom right) of the smoothed, detrended regular
component shows some similarities to the phase portrait of a limit cycle on previous page, part c.
An injection effectiveness, or ratio of pro-
duced fluid to injected water volumes, was cal-
culated for the four most seismically active areas
(right). Comparing these to the quantified seismic
activity in the region of the Romashkino oil field
shows an inverse relationship in the oscillations
of seismic activity and effectiveness of injection.
In 1986, the time at which the seismic activity
data become available and show a marked drop
from extremely high to low, the character of time
variation of the production parameters changes
considerably.
In Area A, injection effectiveness begins to
oscillate with significant amplitude opposite to the
oscillations of seismic activity. In Area S, the onset
of injection-effectiveness oscillations is also
observed, but they are less synchronized with the
seismic-activity oscillations. In Area B, even
clearer, quasi-harmonic, injection-effectiveness
oscillations are observed with a period close to
12 months and a regular amplitude. In Area M,
a trend of decreasing injection effectiveness
changes in 1986 to an increase with oscillations,
roughly opposite in sign to the oscillations of
seismic activity.
To some extent, the features observed in the
temporal variations of injection effectiveness are
related to a change to a new fluid-injection tech-
nology in 1986. One of the results of such a
change was a decrease of the injected volume in
summer. In winter, injection was maintained to
avoid freezing in the flow lines. This introduced a
seasonal component to the effectiveness oscilla-
tions and more economical water injection in
general. At the same time, it is impossible to
assert that all the variations are due to injection-
technology differences.
The injection effectiveness for the A, S, M and
B areas can be compared with the variation in
quantified seismic activity in each area (left). For
completeness, the seismic activity changes are
also compared with the extracted and injected
fluid volumes.
A notable feature is the increase of injection
volumes that took place four months before the
two most considerable increases in seismicity—
at the beginning and at the end of the studied
time period in Area A. It is also remarkable
that production decreased in these periods of
increasing seismic activity, even when injection
14 Oilfield Review
Injection effectiveness Injection effectiveness
Injection effectiveness
0.8
0.9
1.0
1.1
1.2
0
1
2
3
4
Injection effectiveness Seismic activity
0.6
0.8
1.0
1.2
0
1
2
3
4
0.7
0.8
0.9
1.0
0
1
2
3
4
0.6
0.8
1.0
1.2
1.4
0
1
2
3
4
Seismic activity
Berezovskaja
Severo-Almetyevskaja Almetyevskaja
Minibayevskaja
Seismic activity Seismic activity
YearYear
YearYear
1981 1983 1985 1987 1989 1991 1993 1981 1983 1985 1987 1989 1991 1993
1981 1983 1985 1987 1989 1991 19931981 1983 1985 1987 1989 1991 1993
>Comparison of overall Romashkino seismic activity with variations of injection effectiveness for
the four different areas of the field. In each case, the scale of the left vertical axis is injection
effectiveness and the scale of the right vertical axis is normalized seismic activity.
Year
1986 1988 1990 1992
0
2
4
6
8
10
12
14
16
18
20
Seismic activity, normalized
Ratio of volume of produced fluid to volume of injected water
Imbalance x 10
3 m3
Volumes of production and injection normalized on average values
0
0.2
0.4
0.8
1.0
1.2
1.4
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
-200
200
0
400
600
800
1000
0.6
Year
1986 1988 1990 1992
Injection
effectiveness
A
M
B
S
Seismic activity
A
M
B
S
Imbalance
A
M
B
S
Production
A
M
B
S
Injection
A
M
B
S
>Comparison of seismic activity variations (bottom left) with injection effectiveness
(top left), production and injection (top right) and volume imbalance (bottom right)
for the four most seismically active areas of the Romashkino field.
Summer 2000 15
increased. Later on, even weaker increases of the
seismic activity are always accompanied by a
decrease in total fluid production in Area A. It is
also interesting that, for example, during the 1991
to 1992 increase of seismic activity in Area M,
both injection and production increase, but injec-
tion effectiveness decreases at the same time.
Regression analysis shows a statistically sig-
nificant relationship between the seismic-activity
variations in the four studied areas and produc-
tion and injection regimes for these areas. The
confidence level of the relationship is 99%.
Crosscorrelation coefficients were computed
to help understand the relation between seismic
activity in the four most seismically active areas
of the Romashkino oil field and some character-
istics describing the exploitation process, such as
extracted and injected fluid volumes, imbalance
and injection effectiveness. During the period of
study, the volume of injected fluids and the vol-
ume of produced fluids both decreased for eco-
nomic reasons. For completeness, correlations
were computed between the seismic activity and
detrended values—removing a linear trend from
the values—of injected and produced volumes.
Correlation between the exploitation parame-
ters in one area and the seismic activities in all
four areas can be shown graphically (right). The
correlation with the seismic activity of each
region is depicted as a horizontal bar. Longer bars
indicate better correlation, and bars to the left
show negative correlation.
It is remarkable how well the seismic activ-
ity and exploitation parameters correlate, not
only within an area but also between areas. The
injected and produced volumes in every area
and their detrended counterparts correlate pos-
itively with the seismic activity in all four areas,
with few exceptions (correlations between seis-
mic activity in Area A and production in every
area are negative). The injection effectiveness
(produced/injected) in every area correlates
negatively with seismic activity in all four areas
while imbalances correlate positively. The high-
est absolute values of correlation are observed
between the detrended production in Area A
and the seismic activity in Areas A and M
(which is near A); and between the imbalance in
Area M and the seismic activity in Areas S and
B. Absolute values of these correlation coeffi-
cients are greater than 0.7.
Imbalance
Injection detrended
Production detrended
Production/injection
detrended
Production/injection
Production
Injection
-
0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Severo-Almetyevskaja
Imbalance
Injection detrended
Production detrended
Production/injection
detrended
Production/injection
Production
Injection
Almetyevskaja
Imbalance
Injection detrended
Production detrended
Production/injection
detrended
Production
Injection
Production/injection
Berezovskaja
Activity of all areas
Imbalance
Injection detrended
Production detrended
Production/injection
detrended
Production
Injection
Production/injection
Severo-Almetyevskaja
Almetyevskaja
Berezovskaja
Minibayevskaja
Correlation
-
0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Minibayevskaja
>Correlation between exploitation parameters and seismic activity for
the four production sectors. The exploitation parameters are listed at the
right. The correlation with seismic activity in each of the four areas is
shown as a colored horizontal bar. For example, at the top, the correlation
coefficient between the production/injection ratio in the S sector and the
seismic activity in the A sector (blue bar) is –0.12.
The correlation between seismic activity and
hydrocarbon exploitation means the two are
related, but it does not indicate which one is the
cause, which one is the effect, and how long it
takes the cause to create the effect. Shifting the
data series in time relative to each other, recom-
puting the correlation, and tracking the lag that
results in the best correlation gives the best sta-
tistical estimate of the time lag between cause
and effect (right and next page). Positive lags cor-
respond to positive time shifts of the seismic-
activity series relative to other data series. The
most interesting are the plots for Areas M and A,
which indicate that changes in exploitation param-
eters precede changes in seismic activity. For
these areas, maximum correlation is observed
when lags are positive and equal to one to two
months. Correlation coefficients reach 0.8 for
Area M (correlation between seismic activity and
injection) and 0.7 for Area A (correlation between
seismic activity and imbalance, and between seis-
mic activity and production).
The maximum correlation for Area B corre-
sponds to zero or negligible time shift.
It was a surprise that for Area S, the maxi-
mum correlation occurs when the time shifts of
seismic activity relative to most parameters are
negative and equal to six to seven months. This
means that the change in the seismic activity
precedes the change of exploitation parameters.
Exploiting Seismicity
Few will deny that there is a relationship
between hydrocarbon recovery and seismic activ-
ity, but exactly how strong a relationship exists
has yet to be determined. Furthermore, what can
or should be done about it sparks another debate.
In regions of high tectonic potential energy,
hydrocarbon production can cause severe
increases in seismic activity and trigger strong
earthquakes, as in Gazli, Uzbekistan. In regions of
lower tectonic stress, earthquakes of that magni-
tude are less likely, but relatively weak earth-
quakes could occur and damage surface structures.
16 Oilfield Review
Activity with Injection (detrended)
Lag, months
-25 -15 -5 5 15 25
-1.0
-0.6
-0.2
0.2
0.6
1.0
Crosscorrelations
Activity with Production (detrended)
-25 -15 -5 5 15 25
-1.0
-0.6
-0.2
0.2
0.6
1.0
Crosscorrelations
Activity with Injection Effectiveness
-25 -15 -5 5 15 25
-1.0
-0.6
-0.2
0.2
0.6
1.0
Crosscorrelations
Activity with Imbalance
-25 -15 -5 5 15 25
25
-1.0
-0.6
-0.2
0.2
0.6
1.0
Crosscorrelations
-25 -15 -5 5 15
-1.0
-0.6
-0.2
0.2
0.6
1.0
Crosscorrelations
-25 -15 -5 5 15 25
-1.0
-0.6
-0.2
0.2
0.6
1.0
Crosscorrelations
-25 -15 -5 5 15 25
-1.0
-0.6
-0.2
0.2
0.6
1.0
Crosscorrelations
-25 -15 -5 5 15 25
-1.0
-0.6
-0.2
0.2
0.6
1.0
Crosscorrelations
Severo-Almetyevskaja area
Berezovskaja area
Lag, months
Lag, months Lag, months
Lag, months Lag, months
Lag, months Lag, months
Activity with Injection (detrended) Activity with Production (detrended)
Activity with Injection Effectiveness
Activity with Imbalance
>A change of correlation coefficients (between seismic activity and detrended production,
injection, imbalance and injection effectiveness) due to shift of data series in time relative
to each other. A positive lag, as seen in the cases of the A and M areas, indicates that the
changes in field exploitation parameters precede changes in seismic activity. A negative lag
indicates that changes in seismic activity precede changes in exploitation parameters.
Summer 2000 17
Analysis of data on temporal and spatial char-
acteristics of seismic activity can provide useful
information on the deformation processes occur-
ring in reservoirs and surrounding rocks. Zones of
active faulting that also have high permeability can
be delineated. If acquired over sufficient periods of
time, this information may help forecast hazardous
increases of seismic activity and evaluate recovery
methods. For example, in the Romashkino oil field,
water-injection effectiveness decreased during
periods of increased seismic activity and increased
during periods of low seismic activity. It may be
that faults that become activated during periods of
seismic activity also develop higher permeability.
This could decrease injection effectiveness.
Installing a local permanent seismic network
in advance helps quantify the level of background
seismicity so that changes can be detected. This
helps unravel the mysteries of the relationship
between production and seismic activity.
Experience shows that to estimate the values of
temporal and spatial parameters of seismic
deformation processes in the region of hydrocar-
bon fields, it is advisable to record the data for
one or two years in advance of any production.
However, more recording and analysis should
provide further insight. The results published
here are the preliminary findings of the coopera-
tive project between Schlumberger and the
Institute of Dynamics of Geospheres in Moscow.
Other groups are also actively pursuing surface
monitoring of seismic activity that may be related
to hydrocarbon exploitation. For example, the
Koninklijk Nederlands Meteorologische Instituut
(KNMI) has a program to monitor seismicity in
The Netherlands. Several other groups are
monitoring seismic activity with borehole sen-
sors. All of these efforts will improve the indus-
try’s understanding of the effects of production
on our surroundings. —LS
Lag, months Lag, months
Lag, months Lag, months
Lag, months Lag, months
Lag, months Lag, months
Activity with Injection (detrended) Activity with Production (detrended)
Activity with Injection Effectiveness
Activity with Imbalance
Activity with Injection (detrended) Activity with Production (detrended)
Activity with Injection Effectiveness
Activity with Imbalance
-25 -15 -5 5 15 25
-1.0
-0.6
-0.2
0.2
0.6
1.0
Crosscorrelations
-25 -15 -5 51525
-1.0
-0.6
-0.2
0.2
0.6
1.0
Crosscorrelations
-25 -15 -5 515 25
-1.0
-0.6
-0.2
0.2
0.6
1.0
Crosscorrelations
-25 -15 -5 5 15 25
-1.0
-0.6
-0.2
0.2
0.6
1.0
Crosscorrelations
Almetyevskaja area
Minibayevskaja area
-25 -15 -5 51525
-1.0
-0.6
-0.2
0.2
0.6
1.0
Crosscorrelations
-25 -15 -5 5 15 25
-1.0
-0.6
-0.2
0.2
0.6
1.0
Crosscorrelations
-25 -15 -5 515
25
-1.0
-0.6
-0.2
0.2
0.6
1.0
Crosscorrelations
-25 -15 -5 5 15 25
-1.0
-0.6
-0.2
0.2
0.6
1.0
Crosscorrelations
