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A spatio-temporally constrained injection rate threshold for the mitigation of induced seismicity
Hollenbach, Andrew
Hollenbach, Andrew
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Abstract
The Cambrian-Ordovician Arbuckle Group is the primary disposal zone for Underground Injection Control (UIC) Class I and II wells across much of the U.S. midcontinent. Increases in wastewater disposal into the Arbuckle Group, linked with production from water-rich unconventional plays, is the inferred cause of a more than 40-fold increase in seismicity. Waste-water injection-induced seismicity has incited concerns about its potential impact on health and infrastructure, resulting in more than a decade of research on the subject. Nevertheless, mitigating earthquakes is a challenge for oil and gas operators and the regulatory community because a comprehensive understanding of operational factors (e.g., well spacing, injection rates, pore pressure diffusion in the Arbuckle and crystalline basement, etc.) and their relationship with seismicity is lacking. This study compares seismic events of magnitude 2.5+ with injection data from 4,366 brine disposal wells (Class 2) and 49 industrial waste wells (Class 1), from 2010 to 2017. A bi-variate Kernel Density Estimation method in R statistical software is used to construct a node lattice across the mapped data, and objectively compare the injected volumes, well densities, and earthquakes within a given radius from each node. The spatial scale of the analysis is varied by adjustment of the node lattice. The method identifies areas where the correlation between seismicity and nearby Arbuckle Group injection volumes are high, and also identifies areas where such a correlation appears to be diminished, or absent. The method tracks spatial distribution of injection volumes and seismicity, and can be used to monitor specific areas-of-interest or concern over time. The results can be referenced to inform rate-reduction calculations at the operational level.
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Date
2019-12-31
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University of Kansas
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Keywords
Geology, earthquake, induced, injection, seismicity