AN EVALUATION OF POSSIBLE SEISMICITY INDUCED BY DEEP WASTEWATER INJECTION IN OHIO: COMPARISONS BETWEEN ACTIVE WELLS AND THE 2011 YOUNGSTOWN EARTHQUAKE SEQUENCE

The 2011 Youngstown Earthquake Sequence (YES) in eastern Ohio has been linked to the injection of wastewater derived from oil and gas well completion and production activities in the Appalachian Basin. The YES is thought to have occurred due to reactivation of an ancient basement fault system as injection-related pore-fluid pressure reduced the effective normal stress along the fault. Key to this interpretation is that the Youngstown injection well was drilled ~200 feet into the Proterozoic crystalline basement and was completed “open hole” thus providing a direct pathway for injection fluids into the basement fault zone.

The purpose of this study is to identify possible seismicity in Ohio induced by injection into wells that are similar to the Youngstown well. State records indicate there are currently over 210 Class I and II injection wells in Ohio, with 34 drilled into Precambrian igneous/metamorphic rocks. Of these, 23 have been completed “open hole”. The locations of the 34 deep wells were compared with locations of seismic events catalogued by the Ohio Seismic Network. Excluding the 2011 YES, we have identified only 5 earthquakes located within 10 km of 6 of the 34 basement wells. These earthquakes were located between ~1.7 and 8.3 Km from an active well and had similar magnitudes to the YES (M 2.5 to 3.0), but with recurrence intervals and event spatial distributions that are dissimilar to the YES. In addition, 4 of the 5 events occurred in areas that experienced historical earthquakes within 2.5 km of the well prior to injection. In the case of the one event that occurred in an area with no historical seismicity, the nearby injection well was completed to isolate injected fluids entirely within lower Paleozoic sedimentary rocks.

Collectively, we have been unable to demonstrate with confidence that the active injection wells drilled to the Precambrian basement have induced earthquakes in Ohio. This does not, however, preclude the possibility of induced seismicity associated with shallower injection horizons. Moreover, close attention needs to be given to future seismic events occurring near any injection wells in the state given projected increases in injection volumes due to expanding oil and gas operations in the Appalachian Basin.