Induced earthquakes. Sharp increase in central Oklahoma seismicity since 2008 induced by massive wastewater injection

Science (Impact Factor: 33.61). 07/2014; 345(6195). DOI: 10.1126/science.1255802
Source: PubMed


Unconventional oil and gas production provides a rapidly growing energy source; however, high-production states in the United
States, such as Oklahoma, face sharply rising numbers of earthquakes. Subsurface pressure data required to unequivocally link
earthquakes to wastewater injection are rarely accessible. Here we use seismicity and hydrogeological models to show that
fluid migration from high-rate disposal wells in Oklahoma is potentially responsible for the largest swarm. Earthquake hypocenters
occur within disposal formations and upper basement, between 2- and 5-kilometer depth. The modeled fluid pressure perturbation
propagates throughout the same depth range and tracks earthquakes to distances of 35 kilometers, with a triggering threshold
of ~0.07 megapascals. Although thousands of disposal wells operate aseismically, four of the highest-rate wells are capable
of inducing 20% of 2008 to 2013 central U.S. seismicity.

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Available from: Matthew Weingarten, Jul 27, 2014
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    • "). In the U.S., seismic events have been associated with the development of oil and gas operations on numerous occasions (Davies et al., 2013; Ellsworth, 2013; van der Elst et al., 2013; Keranen et al., 2014 "
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    Science of The Total Environment 04/2015; 512. DOI:10.1016/j.scitotenv.2015.01.004 · 4.10 Impact Factor
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    • "To date, induced seismicity has been related to various anthropogenic applications such as dam impoundment, wastewater disposal, fluid extraction, overburden removal, enhanced geothermal systems, and hydraulic fracturing [e.g., Davies et al., 2013]. Recently, focus has shifted toward understanding induced seismicity in light of the growing concern over its potential for hazard [Ellsworth, 2013; Keranen et al., 2014; Atkinson et al., 2015]. "
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    03/2015; 42(8). DOI:10.1002/2015GL063455
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    • "Recent seismicity events likely related to disposal of waste fluid from hydraulic fracturing [1] have revived the concern that large-scale CO 2 injection will trigger earthquakes and that even small-to moderate-sized earthquakes may threaten the seal integrity of the injection zone (e.g., [2] [3] [4]). [3] stated that " Because of the critically stressed nature of the crust, fluid injection in deep wells can trigger earthquakes when the injection increases pore pressure in the vicinity of preexisting potentially active faults. "
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    ABSTRACT: Recent publications have suggested that large-scale CO2 injection could trigger earthquakes and that even small- to moderate- sized earthquakes may threaten the seal integrity of the injection zone, and potentially damage buildings and other surface structures. In this study, we compared seal thickness to estimated fault displacement due to a single hypothetical seismic event in a selected area of the Texas Gulf Coast comprising an offshore strip of state waters along two Texas counties. To evaluate the slip generated by a single seismic event, we compiled well log information on shale/sand sequences and seismic information on fault geometric characteristics of a section of Lower Miocene age. The section is thousands of feet thick and is overlain and underlain by marine shales (Amph. B and Anahuac, respectively) that are relatively easy to correlate between wells. The Amph. shale is the secondary and ultimate seal for all injection intervals in the Lower Miocene. Given its thickness, no realistic seismic event or small series of seismic events will offset it significantly. However, this may not be true of smaller local primary seals. An analysis of geophysical logs of a total of 71 wells yielded a total of 2,871 sand / shale binary intervals. An analysis of the dedicated 3D seismic survey counted 723 fault traces at five roughly horizontal horizons within the Lower Miocene Fault displacement estimated using the product of the fault length times an uncertain multiplier coefficient assumed to follow a triangular distribution with a 10-3 to 10-5 range and a mode of 8 × 10-5. We then compared estimated single-event fault displacements to seal thicknesses by means of a Monte-Carlo analysis. Only 1.8% of thickness/displacement pairs display a displacement greater than 20% of the seal thickness. Only 0.26% of the pairs result in a displacement of half the seal thickness and only 0.05% of thickness/displacement pairs result in a clear seal rupture. The next step was to compare the magnitude of the event generated by such a displacement to documented magnitudes of “large” earthquakes generated by waterflooding and fluid disposal. Based on this analysis, we conclude that seismicity that may arise from CO2 injection appears not to be a serious complication for CO2 storage integrity, at least in the Gulf Coast area.
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