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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•Humans Induced Seismicity•What are the General characteristics of reservoir triggered seismicity?•What is the Physical Mechanism of reservoir triggered seismicity?•Does oil and gas extraction cause earthquakes?

•Dam filling•Example 1: Koyna Dam, India (M6.3, 1967 Triggered earthquakes at Koyna (1967-200))•Example 2: Miranda Reservoir: Event rate versus water level•Example 3:Kremasta Dam, Greece (M=6.2, 1965)•Example 4: Monticello Dam, South Carolina  Monticello: Filling vs. Seismicity

•Monticello seismicity concentrated under reservoir•Example 5: Filling curves & Seismicity Rate•Example 6: Filling curves & large earthquakes

•Oil extraction and Seismicity •Example 1: The Romashkino Oil Field of Russia•Example 2: Interrelationship between Seismicity and Gas Injection in Talco area.•Example 3: The May 7, 2001 Earthquake in the Ekofisk Oil Field Area, North Sea

•Conclusion for 2001 EQ(M=4.4)•Example 4: Induced Event: Mmax: 4.3-1984

•Seismicity rate/Stations/Oil Well in British Columbia•Example 5: Deep injection Rate versus Event Rate at Paradox Valley, Clorado- (Mmax=4.3)•Example 6: Microseismicity of Valhall Oil Area in Norway•Example 7: The 1993 M4.7 Kuwait earthquake: Induced by the burning of the oil fields?

•Gas extraction and Seismicity •Example 1: Carthage Gas Field, East Texas: Mapping Event Rate•Clustered Seismicity: Deep and Shallow•Cumulative production rate and microearthquake event rate•Fracture mechanics resolved by microseismicity

•Hot water extraction •Example 1: The Geysers, California

•Borehole Seismometer and resolved seismicity•Microeartquakes in Reservoir and above Reservoir

•Mining•Nuclear Tests

Review: Reservoir Seismicity In

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Recall: 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.

Recall

Event rate changes correlate with production rate changes.

Seismic response lags production by 2–3weeks.

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Recall

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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WELL-BORE DEFORMATION

The Geysers, California

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Rangely Oil Field experiments• Following the Rocky Mountain Arsenal episode, USGS scientists experimented with controlling earthquakes through fluid injection at the Rangely oil field• Experiments suggested that pore pressure increases, decreasing the normal stress on faults, was the controlling factor

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

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Mining and induced seismicity

• Quarry blasts may let off enough energy to be like an M 2 earthquake; many through California

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Mining seismicity

• Mining destabilizes rocks; causes rock bursts, small earthquakes

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Nuclear Explosions

An underground nuclear test can cause shaking likean M 5 earthquake.In

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A natural earthquake or a bomb?

• A lot of effort has gone into trying to being able to determine whether ground shaking is caused by a natural earthquake or a nuclear explosion• Establishment of the World Wide Seismic Network in the 1960s was actually funded based on the need to monitor bombs, not study earthquakes

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Earthquake or Bomb?

• Radiation pattern of seismic waves:

Bomb: compressional P wave first motion in all directions

Slip on a fault: P wavefirst motion compressional and extensional

How can we tell?In

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Earthquake or Bomb?• Nuclear tests are shallower than most earthquakes• Nuclear tests generally have weaker surface waves and stronger P wave arrivals

Nuclear test in China recorded in Oklahoma, vertical component

India’s nuclear bomb

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Can nuclear tests could trigger tectonic earthquakes?

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Some people take the connection between earthquakes and bombs a little too far?

Debate

• Some people believes such a relation since:Observation made at the Benham device at the Nevada nuclear test site (1968, 1.15 MT yield, M>6) triggered aftershocks lasting for at least several months• Gary Whiteford, University of New Brunswick, pointed out that there were nuclear tests in Nevada shortly before the 1992 Landers earthquake…..• The Hector Mine earthquake, 1999, occurred after testing had ceased…

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tectonic earthquakes?

•While other people do not given any credit for taking the connection between earthquakes and

bombs a little too far.

Could we induce earthquakes tomake a fault safe?

• People have thought about trying to induce many small earthquakes on a large fault; relieve the stress before a big one happens• Problem #1: It would take a lot of small earthquakes!• Problem #2: At present, there is no way of controlling the size of an induced earthquake!

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In one or two pages, respond to the questions given in below:

1. What are the General characteristics of reservoir triggered seismicity?

2. What is the Physical Mechanism of reservoir triggered seismicity?

3. Does oil and gas extraction cause earthquakes?

Homework, May 10In

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