Posted on May 1, 2015 by Mark Walker
Oklahoma has quietly earned the dubious distinction of earthquake capital of the Lower 48, having surpassed California last year. In 2014, Oklahoma had 585 earthquakes of magnitude 3.0 or higher compared to California’s 180. The cause of this dramatic rise in seismic activity, and whether it is induced by human activity, particularly by oil and gas operations, has been the subject of much discussion and scientific study.
When I last blogged about this subject (June 2014) the U.S. Geological Survey (USGS) and the Oklahoma Geological Survey (OGS) had just issued a joint warning of the increased risk of a M5.5 or greater earthquake in central Oklahoma, stating that the science suggests that a “likely contributing factor” to the increase in earthquakes is injection of oilfield wastewater into deep geologic formations. Despite several sensational articles implying that industry has exercised undue influence over the OGS and its scientific conclusions, on April 21, 2015, the OGS issued a statement in which it reiterated the view that “the primary suspected source of triggered seismicity is…from the injection/disposal of water associated with oil and gas production…the OGS considers it very likely that the majority of recent earthquakes…are triggered by the injection of produced water in disposal wells . . . .”
On April 23, 2015, the USGS released a new report which again noted the connection between earthquakes and certain deep disposal wells, but concluded that, “induced seismicity does not occur near every disposal well, so it is important that we continue to study and learn more about how these earthquakes are generated…These changes may be related to oil and gas exploration activity but they also may depend on physical processes, which are poorly understood…many questions remain”.
As the science develops, the Oklahoma Corporation Commission (OCC), which regulates oil and gas wastewater disposal wells in Oklahoma under the SDWA Underground Injection Control program, has taken an aggressive approach. The OCC has identified “areas of interest”, which are areas within 10 kilometers of any earthquake swarm. Eight areas of interest encompassing approximately 112 square miles have been identified. On March 12, 2015, the OCC sent letters to operators who dispose of oilfield wastewater into the deep Arbuckle formation within these areas of interest directing that they provide information from which it can be determined whether such disposal is in communication with the underlying crystalline basement rock. If it is, the OCC is requiring that disposal into the Arbuckle be discontinued. Failure to produce the information results in immediate curtailment of disposal by 50%.
With the downturn in crude oil prices, most companies have dramatically cut back on drilling and completing new wells. This downturn itself may provide a scientific opportunity to see if reduced oilfield activity produces fewer earthquakes in Oklahoma.