Evaluation of Earthquake Potential Associated With the Injection of Wastewater Disposal Wells in Shale-Gas Resvoirs, Oklahoma, USA
Unconventional shale gas is a rapidly growing energy source in the Unites States. High producing states such as Oklahoma are facing earthquakes that are increasing at an unprecedented rate in quantity and magnitude. The space-time distribution of the increased seismicity, as well as numerous published studies indicate that the increase is due to anthropogenic origin. However, the traditional belief that induced seismicity is due to the fracking process has been reexamined. Studies now indicate that the increased seismicity is principally driven by injection of wastewater coproduced with oil and gas from tight formations. It is suggested that as fluid is injected into these wastewater wells the pore fluid pressure increases and propagates further away from the wells, thus disturbing a larger volume and increasing the probability that the fluid pressure will encounter a fault and induce an earthquake of high magnitude. This study utilizes data from Oklahoma Geological Survey's seismic monitoring system to test these claims by examining the geospatial relationships between saltwater disposal wells, earthquakes, and faults; as well as magnitude and frequency of earthquakes over the past 35 years in Oklahoma. The results of this work support recent studies that wastewater injection is the primary cause of the large change in seismicity observed in Oklahoma. Quantifying the frequency, magnitude, and geospatial relationships of earthquakes provides a deeper understanding of the physical processes and conditions that link perturbations to the earth system to its response in seismic events. Earthquakes increasing in quantity and magnitude create difficult challenges that will require new research into the physics of induced earthquakes and their mitigation. Investigation and mitigation of earthquake hazards from future-induced events will require a collaboration between industry, scientists, and regulators.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017