Department of Earth SciencesKFUPM

Introduction to Seismology

Reservoir Induced Seismicity (Reading Assignment: pp.384-386)

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Ali Onceloncel@kfupm.edu.

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Previous LectureReservoir Induced Seismicity •Earthquake Types•Volcanic Earthquakes•Humans Induced Seismicity

•Dam filling•Example: Koyna Dam, India (M6.3, 1967)•Triggered earthquakes at Koyna (1967-200)

•Waste water injection•Oil extraction and Seismicity

•Example: The Romashkino Oil Field of Russia•Example: Interrelationship between Seismicity and Gas Injection in Talco area.

•Hot water extraction•Mining•Nuclear tests

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• Dam Completed 1965• M 6.2 seven months later, after rapid filling to 80m

Kremasta Dam, GreeceIn

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Monticello Dam, South Carolina

• Reservoir for cooling of nuclear power plant• Seismometers in place since 1973

• Reservoir filled December 1977-Feb. 1978• Earthquakes start 3 weeks after filling starts

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Monticello seismicity concentratedunder reservoir

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Monticello: Filling vs. seismicityIn

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Filling curves & Seismicity RateIn

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Filling curves & large earthquakesIn

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• Earthquakes are associated with change in water level: with large scale filling of the dam, possibly with emptying• Seismicity often tapers off within ten years of water level stabilization• Variable time delays may occur between dam filling and earthquakes

General characteristics of reservoirtriggered seismicity

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Cause of reservoir triggered seismicity?

•Stress increase from weight of the water?•Stress at surface usually equal to 1-3 bars•Stress at earthquake depths much less than that•Earthquake stress drop is about 30 bars• Pore pressure increase reduces confining stress on faults?

Frictional stress = coefficient of friction x pressure of rock (pressure of water)

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• Gas extraction greatly decreases pore pressure• Subsidence/earthquakes occur• Many small earthquakes in the Lacq Gas Field, France• Gazli gas field, Uzbekistan. Gas withdrawal started 1966; max production 1968-71. 2. M 7earthquakes in 1976, one in 1984. Were they induced??• Some people have wondered about 1983 M 6.5 Coalinga earthquake, M 5.8

Does oil and gas extraction causeearthquakes?

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http://www.orfeus-eu.org/newsletter/vol3no2/ekofisk.html Mw=4.1-4.4

The May 7, 2001 Earthquake in the Ekofisk Oil Field Area, North Sea

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The seismic event was induced owing to stress changes caused by water injection (Ottemo¨ ller, et al., 2005, JGR, Vol.110)..

Conclusion for 2001 EQ(M=4.4)In

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Induced Event: Mmax: 4.3-1984In

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British ColumbiaIn

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Injection rate Seismicity

M max=4.3

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Location of the Valhall and Ekofisk oil fields are shown in a map of the southern Norwegian North Sea (a).A profile along line AA' illustrates the dome structure of the Valhall oil field (b).

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Microseismicity of Valhall Oil AreaIn

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Seismicity Induced by Petroleum and Geothermal Activities

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Carthage Gas Field, East TexasIn

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Two event sub-clusters each delineating the intersection of two planes. Looking along line of intersection (top) and face-on views (bottom).

Linear trends can be seen along fracture faces (bottom). The event sequences indicate earlyfluid invasion along linear trends.

Event rate changes correlate with production rate changes.

Seismic response lags production by 2–3weeks.

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Fracture planes are delineated by production-induced events occuring over a 6-month monitor period.

Composite fault plane solutions indicate thrust displacement along the mapped, low-angle fractures. Induced stress changes are very small (<0.1 MPa).

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Small magnitude events were detected above thereservoir by placing a downhole receiver array within the upper 800 feet of an abandoned well. Event occurrence terminates near the base of the serpentine unit.

WELL-BORE DEFORMATION

The Geysers, California

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Both the above reservoir and the deeper reservoir seismicity show correlations with reservoir injection activity in the study area.

WELL-BORE DEFORMATION

The Geysers, California

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