Onshore Unconventional Hydrocarbon Development Induced Seismicity and Innovations in Managing Risk–Day 2: Proceedings of a Workshop (2018) / Chapter Skim
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2 Understanding Induced Seismicity and Managing Risk
2 Understanding Induced Seismicity and Managing Risk
Pages 5-12
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From page 5... ...
However, the rate of earthquakes is controlled by the deformation rate of the crust, not just the stress level. The fact that the load from water reservoirs behind major dams around the globe has caused induced seismicity indicates that very small pore pressure perturbations in the crust are possible, even in intraplate ("tectonically stable")
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From page 6... ...
along the plane is reached and the block jumps forward, releasing the stress. In an analogous way, when stress in the Earth's crust reaches its frictional strength along a fault such as the San Andreas where two tectonic plates are moving relative to one another, the fault slips, causing an earthquake, and then the process of building stress along the fault begins again.
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From page 7... ...
The most common triggering mechanism for induced earthquakes from fluid injection is related to the disposal of produced water from oil and gas operations. Produced water may be generated either from conventional oil and gas wells or from wells that have been developed with unconventional technologies (the combination of horizontal drilling and hydraulic fracturing)
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From page 8... ...
The third situation may involve hydraulic fracturing itself, which has in rare situations in the United States generated earthquakes that could be felt at the Earth's surface. The best-studied case of hydraulic fracturing causing positive magnitude earthquakes in the United States was near Youngstown, Ohio where a potentially active fault in crystalline basement2 was accidentally drilled; when the operators pressurized the zone during hydraulic fracturing, the fault slipped, causing several earthquakes ranging between magnitude 1.7 and 2.2 (Friberg et al., 2014)
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From page 9... ...
The earthquake hazard, Zoback indicated, depends on whether or not the injection of wastewater for disposal in the sedimentary rock is potentially going to activate faults in the underlying basement. He referred to the work of Horton and colleagues in Arkansas where fluid injection into sedimentary units, related to disposal of wastewater from oil and gas production, generated earthquakes in the underlying basement, the largest of which was M4.7 (Horton, 2012)
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From page 10... ...
He also underscored the importance of having adequate and accurate fault maps; the M5.8 Pawnee earthquake in Oklahoma in 2016 occurred on a previously unidentified basement fault whose existence and orientation were only determined after analyzing the radiated seismic energy from the main earthquake shock. Zoback said that the software he and colleagues used to conduct this kind of analysis has been put online to allow geomechanical analysis of a particular area, including its faults, based on knowledge of the local stress field.3 Zoback concluded by discussing additional approaches for managing the risk of producing induced seismic events from fluid injection activities.
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From page 11... ...
A participant raised the point of the importance of mapped faults as boundary conditions to help refine local pressure changes in the vicinity of fluid injection. Zoback agreed and explained further that the models he discussed are based on the idea that fluid pressure in the Arbuckle is primarily displaced laterally and some of that fluid pressure finds a permeable fault in the basement.
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