SEISMIC MOMENT VERSUS WATER: A STUDY OF MARKET FORCES AND REGULATORY ACTIONS

Evidence is mounting that there is a relationship between saltwater disposal (SWD) and seismic activity in Oklahoma, especially from disposal into basal sedimentary strata (i.e., Arbuckle Group). Oklahoma’s statewide (excluding Osage County) Class II Underground Injection Control (UIC) SWD volumes ranged from about 849 million barrels (MMbbl) in 2009 to more than 1.54 billion barrels (Bbbl) in 2014. Volumes of saltwater being disposed into wells completed in the Arbuckle increased from about 434 MMbbl in 2009 to more than 1.05 Bbbl in 2014.

A series of events have led to an apparent decline in seismic moment, a measure of rate of energy released in dimensions of N-m/day, in Oklahoma. Firstly, oil prices dropped substantially in mid-2014 and concomitant declines in SWD started about October 2014. Then (2014–present) operators, at the request of the Oklahoma Corporation Commission (OCC), plugged back SWD wells that were potentially penetrating basement rock. In mid-2015, OCC began directing operators to reduce disposal rates for Arbuckle SWD wells in the northern and central Oklahoma area of interest (AOI), which at present includes about 700 wells. When evaluating the statewide seismic moment, we observe an increase in seismicity in Oklahoma over the 2009–2015 timeframe, but the statewide seismic moment started to decline in early 2016. It is critical to continue synthesizing oil price, oil production, co-produced water volumes, and the resulting 30-day (i.e., monthly) SWD volumes versus 30-day seismic moments so that the effect of market forces versus OCC-driven measures can be quantified. In this research, we are working to prove or disprove three hypotheses including (1) plugging back of SWD wells from basement rock resulted in an increase in seismic moment, (2) OCC-driven volume reductions resulted in a decline in the seismic moment, and (3) market forces resulted in lower rates of saltwater production and disposal, hence, decreased seismic moment. Preliminary results indicate that market forces strongly affect production of oil, gas, and (co-produced) water; therefore, the change in oil prices is largely responsible for decreases in seismic moment in the early part of 2016. When evaluating relationships at a regional-scale in Oklahoma, regions exhibit different temporal trends in SWD and seismicity.