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Induced Seismicity RisksInduced Seismicity Risks

Maurice Dusseault

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EarthquakesEarthquakes

� Natural Earthquakes�Geotectonic Earthquake

�Ocean Earthquake → tsunami

�Volcanic Eruption Induced Seismicity

�Tidal Triggering of Earthquake

� Man-made Earthquakes�Underground Nuclear Explosion Related

Seismicity

� Induced Earthquakes (∆σ´, ∆p, ∆T…)

� Could O&G development be highly risky?

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A ReviewA Review

� Seismology Fundamentals� Exploration Applications� Induced Seismicity� Resource Management Applications� Public Relations Considerations

These slides ware from a public PPT file: GRC Exploration Workshop, Sept 28 - 29, 2007 Earth-

quake Monitoring. Some modifications were made.Thanks to those who make such things public!!

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Plate TectonicsPlate Tectonics

Earthquakes occur primarily along crustal plate boundaries, where the plates move past one another. That’s also where geothermal resources

are found.

DOE Geothermal Website

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How Earthquakes OccurHow Earthquakes Occur

The movement of the Earth's plates deforms the crust at the edges of the plates, stressing the rocks. When the stress exceeds the static frictional force across a fault, the fault ruptures and the rocks are

displaced, causing an earthquake.

Dr. R. Uhrhammer, UC Berkeley

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Seismic Wave GenerationSeismic Wave Generation

Dr. R. Uhrhammer, UC Berkeley

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The SeismographThe Seismograph

� Detects earthquake ground motions� Inertial reference� Clock� Sensitivity� Natural Period� Damping� Noise

This illustrates the principle of seismometer operation. Modern seismometers register motion

with a spring-mounted mass that moves inside a coil to induce an

electric signal.Dr. R. Uhrhammer, UC Berkeley

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Locating EarthquakesLocating Earthquakes

• Earthquakes are located based on timing of seismic wave arrivals at multiple synchronized stations.• It’s a 3D problem to resolve the hypocenter. The epicenter is the surface projection of the location.

• Need spread of stations (array aperture) to resolve locations. Poor resolution of earthquakes outside array or for depth > 0.5*aperture.

Dr. R. Uhrhammer, UC Berkeley

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The Richter ScaleThe Richter Scale……

� Distance to Epicenter� Maximum Amplitude on

SeismogramLogarithmic Scale� 10x Amplitude� 32x Energy

There is no “Richter-meter”. Magnitude is calculated using

measurements from seismograms at a number of

stations. After a large earthquake, magnitude

estimates will typically jump around as data are gathered

and analyzed.Dr. R. Uhrhammer, UC Berkeley

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Magnitude vs Frequency of OccurrenceMagnitude vs Frequency of Occurrence

10

y = -1.4x + 5.2

0.0

1.0

2.0

3.0

4.0

5.0

0.0 1.0 2.0 3.0 4.0 5.0

Magnitude

Log

cum

ulat

ive

num

ber

of e

vent

s

B-slope typically ~1: activity increases tenfold for each unit magnitude

decrease.

Extrapolate recurrence rates for large-

magnitude quakes

Magnitude threshold of seismic network

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The Modified Mercalli Scale The Modified Mercalli Scale

MMI Typical Effects

I Not felt

II Felt by persons at rest, on upper floors, or favorably placed.

III Felt indoors. Hanging objects swing. Vibration like passing of light trucks.

IV Windows, dishes, doors rattle.

V Small unstable objects displaced or upset. Doors swing, close, open.

VI Windows, dishes broken. Books off shelves. Weak plaster cracked.

VII Weak chimneys broken at roof line. Fall of loose bricks, stones. Some cracks in masonry C. Waves on ponds; water turbid with mud. Small slides.

VIII Some damage to masonry B, fall of stucco, some masonry walls and chimneys. Frame houses moved on foundations if not bolted down.

IX General panic. Masonry B seriously damaged. Frame structures, if not bolted, shifted off foundations. In alluvial areas sand and mud ejected, earthquake fountains, sand craters.

X Most masonry and frame structures destroyed. Large landslides.

XI Rails bent greatly. Underground pipelines completely out of service.

XII Damage nearly total. Large rock masses displaced.

A descriptive scale of observed effects at a given receptor site. Intensity depends on: earthquake magnitude, distance to epice nter, and local geology

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Risk Assessment StepsRisk Assessment Steps

• Regional Tectonic SettingIs the area near a plate boundary or other major tectonic feature?

What is the rate of slippage across the plate boundary?• Faults

Map surface faults, with attention to the long ones (10 miles or more).• Seismic history

Seismologic data: are there small quakes aligned along the fault?Historic (written or oral) accounts of earthquakes in the area.

Geologic evidence for recent (last few thousand years) displacement along the faults.

• Probabilistic Seismic Hazard AssessmentStatistically forecast earthquake magnitudes and locations

Model or extrapolate effects at receptor communitiesForecast recurrence intervals of shaking at receptor communities

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Reservoir Reservoir –– Hot Dry Rock SeismicityHot Dry Rock Seismicity

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Geysers Geysers –– Geothermal Geothermal -- CaliforniaCalifornia

Geysers Annual Steam Production, Water Injection an d Seismicity, 1960 - 2006

25 31 1232 23 26

SE

GE

P S

tart

up

SR

GR

P S

tart

up

0

250

500

750

1000

1250

1500

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Ear

thqu

ake

Cou

nt

0

50

100

150

200

250

300

Ste

am P

rodu

ctio

n an

d W

ater

Inje

ctio

n (b

illio

n lb

s)

Fieldwide Count M>=1.5

Fieldwide Count M>=3.0

Steam Production

Water Injection

• Prior to 1985, seismicity increased along with production and injection• Largest was magnitude 4.6 in 1972

• Since 1985, fieldwide earthquake count (M>3.0) has been stable.

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Seismicity Spread with DevelopmentSeismicity Spread with Development

Eberhart-Phillips and Oppenheimer (1984) noted spread of seismicity as development area expanded, and inferred expanding area of production-induced seismicity.

As seismicity spread toward residents, felt effects and community concern increased.

Anderson

WhisperingPines

Cobb

LakesForest

Hobergs

LomondLoch

SpringsAnderson

WhisperingPines

Cobb

LakesForest

Hobergs

LomondLoch

Springs

Reservoir Limit (red outer line), microearthquakes (brown dots) and developed areas (multicolored lines)

1978 1990

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isksNorth Geysers Microearthquakes (2002)

Activity extends beyond producing wells. Pressure observation data confirm that pressure drawdown extends to these areas.

0000 0.50.50.50.5 1.01.01.01.0 2.02.02.02.0

Scale (km)Scale (km)Scale (km)Scale (km)

BBBB

B'B'B'B'

AAAA

A'A'A'A'

Injection WellInjection WellInjection WellInjection Well

MicroearthquakeMicroearthquakeMicroearthquakeMicroearthquake

Depth Range:Depth Range:Depth Range:Depth Range:

0 -- 2.7 km subsea0 -- 2.7 km subsea0 -- 2.7 km subsea0 -- 2.7 km subsea

2.7 -- 5.2 km subsea2.7 -- 5.2 km subsea2.7 -- 5.2 km subsea2.7 -- 5.2 km subsea

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Geyers Induced SeismicityGeyers Induced Seismicity

Geysers Injection-Induced Seismicity

Local clustering of micro-earthquakes around most injection wells . Timing: seismicity lags injection by days, weeks, or a few months. Generally limited to M<3.0.

LF-15

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Geysers Timing of SeismicityGeysers Timing of Seismicity

0

5

10

15

20

25

30

35

40

20

02

20

03

20

04

20

05

20

06

20

07

Ea

rth

qu

ake

co

un

t

0

1

2

3

4

inje

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n (

mg

d)

or

ea

rth

qu

ake

m

ag

nitu

de

LF15

Monthly injection and NCSN seismicity in area around SRGRP injection well LF-15. Line with circles is monthly water injection. Dashed line is monthly count of earthquakes of M>=1.2. Solid line is monthly

count of earthquakes of M>=2.0. x’s show maximum magnitude each month.

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Geysers Spatial DistributionGeysers Spatial Distribution

Seismicity maps before and during injection at LF-15. Area shown is 4000’ box centered on midpoint of steam of injection well. NCSN seismicity data, magnitudes ≥ 1.2.

U 9/10

4.03.02.01.2

LF-15 Area Pre-injection, 8/22/02 -- 8/21/03

Earthquake Magnitudes

SONOMA SONOMA

U 9/10

FEET

LF-15 Area During Injection, 3/1/06 -- 2/28/07

0 1000 2000

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North Geysers Injection and Microearthquakes (2002)

0000 0.50.50.50.5 1.01.01.01.0 2.02.02.02.0

Scale (km)Scale (km)Scale (km)Scale (km)

BBBB

B'B'B'B'

AAAA

A'A'A'A'

Injection WellInjection WellInjection WellInjection Well

MicroearthquakeMicroearthquakeMicroearthquakeMicroearthquake

Depth Range:Depth Range:Depth Range:Depth Range:

0 -- 2.7 km subsea0 -- 2.7 km subsea0 -- 2.7 km subsea0 -- 2.7 km subsea

2.7 -- 5.2 km subsea2.7 -- 5.2 km subsea2.7 -- 5.2 km subsea2.7 -- 5.2 km subsea

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Cross-section B-B’ showing injection wells and MEQ’s

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This map shows earthquakes

recorded by USGS during 2002. Over 3,000 were located in The Geysers. Elsewhere, the quakes are

concentrated along linear fault zones,

such as the Rodgers Creek –Maacama faults in Sonoma County and the Bartlett Springs Fault in Lake County.

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This map shows regional

earthquakes of magnitude 4.5 or

greater recorded by USGS since 1967. Only one was located in The Geysers, and it

occurred in 1982. Elsewhere, the

quakes are again concentrated along the known fault

zones. The cluster south of Chico is related to the Oroville Dam.

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Conclusions Conclusions –– Recharge ProjectRecharge Project

24

• SRGRP is likely to increase the incidence of Intensity V shaking events (pictures move, small

unstable objects displaced or upset) by approximately 38%

• SRGRP will have little effect on incidence of Intensity VI shaking events (objects fall, dishes

and glassware broken)

• Maximum magnitude of Geysers induced seismicity tentatively assessed at 5.0

• Will not increase the risk of larger earthquakes on nearby faults

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Monitoring, Management, CommunicationMonitoring, Management, Communication

� Upgraded seismic network � Strong-motion stations� All data available to the public on the web.� Voicemail Hotline � Injection adjustments to minimize quakes� Regular public meetings and newsletters

• Written report to Santa Rosa every 6 months on the seismic

impact of SRGRP injection.• Lake County Seismic Monitoring

and Advisory Committee (SMAC).• Increased funding of community

projects

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Fault ReactivationFault Reactivation

� Pore pressure generation is a major natural trigger for fault motion, particularly thrusting, which needs high pressures

� The far-field stresses, either normal or tectonic, provide the energy for slip

� At yield, it is likely that a major valving event occurs along faults (spill-point)

� Faults may stabilize or be triggered by us� Stress change effects are vital as well� And – what are we doing to change p, σ′?� These are complex issues

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Induced EarthquakesInduced Earthquakes

Anthropogenically Induced Sources…

� Mining

� Tunneling

� Dam Reservoirs

� Injection (∆p, T)

� Exploitation (∆p)

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Induced Earthquake DistributionInduced Earthquake Distribution

[Adushkin, 2000]

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InjectionInjection--Induced SeismicityInduced Seismicity

� Injection: p↑→ ∆σ´, also, ∆V + ∆σ, and T effects

� σ transfer to faults, fracture zones?

� Hydraulic fracturing

� Density-driven loading (gas…)

[Sminchalk, 2002]

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[McGarr, 1991][Segall, 1989]

ExploitationExploitation--Induced SeismicityInduced Seismicity

� p↓ → poroelastic stress transfer

� HC withdrawal → isostatic imbalance

� Regional stress transfer (reservoir scale x 5)

� Mass transfer and fluid circulation

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IdentificationIdentificationof Induced Seismicityof Induced Seismicity

� Spatiotemporal correlation between injection-production history and seismicity

� The relationship between frequency and magnitude of earthquakes (b-value)

� The relationship between the magnitude of the main shockand maximum aftershocks

� Magnitude-time decay of after-shocks

� The model of preshocks and aftershocks

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Zagros Sedimentary BasinZagros Sedimentary Basin

� An example of a study in Iran…

[Alsharhan, 1997]

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Oil and Gas Fields Oil and Gas Fields

distribution in Zagros distribution in Zagros

BasinBasin

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KuhKuh--e Mond Heavy Oil NFCRe Mond Heavy Oil NFCR

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Data GatheringData Gathering

The seismic data were gathered from different source such as

� International Institute of

Earthquake Engineering

and Seismology (IIEES)

� Building and Housing

Research Center (BHRC)

� Institute of Geophysics of

University of Tehran (IGUT)

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Data AnalysisData Analysis……

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(including the Shiraz local seismic network)(including the Shiraz local seismic network)

Annual seismicity of Zagros BasinAnnual seismicity of Zagros Basin

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M M ≤≤ 2.02.0

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M M ≤≤ 3.03.0

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M M ≤≤ 4.04.0

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M M ≤≤ 5.05.0

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M M ≤≤ 6.06.0

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Focal Depth Focal Depth ≤≤ 5 km5 km

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Focal Depth Focal Depth ≤≤ 10 km10 km

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Focal Depth Focal Depth ≤≤ 20 km20 km

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Focal Depth Focal Depth ≤≤ 50 km50 km

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Zagros Region Seismic ParametersZagros Region Seismic Parameters

� Gutenberg-Richter Frequency-Magnitude Distribution(1941)

N: cumulative earthquake

number with magnitude

greater than M

A, b: constants (A>0, b>0)

bMAN −=10log

AA = 6.888= 6.888

bb = 0.985= 0.985

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The bThe b--value Contour Map value Contour Map

� Zagros region was divided into different blocks � 1×1 degree blocks (110×110 km2)

� 0.5×0.5 degree blocks (55×55 km2)

� b-value was calculated for each block

1×1 0.5×0.5

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bb--Value Contour MapValue Contour Map

110×110 km2 blocks

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bb--Value Contour MapValue Contour Map

55×55 km2 blocks

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Case Study: Oil Field BCase Study: Oil Field B

� Field: 65 by 8 km2

� Discovery: 1928� Production: 1937� Injection: 1977� Cumulative (2001)

�8.34 BBL Oil�4.35 TCF Gas

� Injection Rate (2001)�6.13 TCF Gas

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Seismicity of Oil Field BSeismicity of Oil Field B

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Seismicity & Fault LocationSeismicity & Fault Location

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Seismicity vs. Injection & ProductionSeismicity vs. Injection & Production

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ConclusionsConclusions

� 2674 earthquakes (0.3<ML<6) 1974-2005 in the Zagros region were gathered.

� Uncertainty remains in event locations (z)

� Contours of b-values at different scales�1×1 degree blocks (110×110 km2)

�0.5×0.5 degree blocks (55×55 km2)

� b-value contour maps indicate active regions, suitable areas for more detailed investigations

� Oilfield B: most seismicity increase in 1976, 1983, 1989 induced by injection, exploitation

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RecommendationRecommendation

� Local seismic networks on Iranian O&G fields are advised for several reasons…

� assess risk of induced seismicity

� obtain more information… geology and dynamic behavior of reservoirs

� use as a source functions to help refine the velocity models

� potentially, tracking processes over time

� Large-scale damaging earthquakes seem highly unlikely from O&G activity

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Overall IssuesOverall Issues

� Seismic risk assessment in O&G requires:�Historical and background data

�A commitment to monitoring locally

�A sufficient system of sensors, reasonable analysis

� In many regions, stress criticality exists

� In general, risks of generating a large and destructive earthquake are small�Stressed volumes are small

�Depths are shallow (local shaking)

� But, monitoring, coupled analyses are vital