GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 175-12
Presentation Time: 11:30 AM


CULLEN, Andrew, Norman, OK 73071

Since 1997, oil companies in Oklahoma have developed 3 different plays with large scale hydrogeological activity. These are: 1) Hunton de-watering 2) Mississippian Lime 3) Woodford-Meramec. Plays 1 & 2 required sustained high-volume injection of produced formation water, mostly into Cambrian carbonates near crystalline basement which resulted in an exponential increase in seismicity, including the 3 largest earthquakes ever recorded in Oklahoma (Mw >5.0). The delay for injection-related pressure fronts to reach critically oriented faults resulted in patterns of seismicity that did not fit the definition of induced seismicity; operators were slow to acknowledge their role in causation. In 2012, as seismicity continued to increase, the State and operators developed protocols to reduce seismic risk related to high volume disposal wells: reduce injection rates, improve monitoring of seismicity & fluid levels, plug perforations near the basement.

The Woodford-Meramec play relies on hydraulic fracturing and has been developed since 2006. Because these wells do not produce large water volumes after recovery of stimulation fluids, associated seismicity is minimal. In the last 2 years, however, seismicity associated with this play has increased. This uptick corresponds to increasingly intense completions: more water, more proppant, higher pump rates. Geologic and engineering analysis of completions-related seismicity indicates that critically oriented faults are prone to reactivation as stimulation intensity increases (classic induced seismicity). The State and operators responded to this new situation by developing additional risk management protocols that involve defined stage gate for modifications or cessation of completions in response to proximal seismic activity. As these protocols reduce the percentage of a well bore that is optimally stimulated, operators must account for this reduction in pre-production economic forecasts.

The cooperation of Oklahoma’s regulators and operators to reduce seismic risk offers important lessons for defining specifics risks for different plays, so that risk management protocols match the value-drivers of different stakeholders. Open discussion and getting the science right are key to enacting informed public policy and the license to operate.