CALIBRATED MODELING OF PRESSURE PROPAGATION IN THE ARBUCKLE GROUP FROM SALTWATER DISPOSAL IN OKLAHOMA

Oklahoma’s increased seismicity is attributed to large volumes of saltwater disposal (SWD) injected into a geologic zone, the Arbuckle Group. Since August 2016, fifteen inactive SWD injection wells with open intervals in the Arbuckle Group have been instrumented with pressure transducers to collect high-resolution pressure data every 30 seconds. The wells are in northwest Oklahoma, a location of high SWD and seismicity. These data have been analyzed to characterize the hydraulic properties of the Arbuckle Group, which are needed to properly represent the subsurface system. Next, the creation of a four-dimensional (x, y, z, time) hydrogeologic model calibrated against downhole pressure data will simulate SWD effects on pressure in the Arbuckle Group and underlying basement rock and the potential contribution of injection to pore pressure and seismicity.

Utilizing MODFLOW, a groundwater flow model will be designed to have boundary conditions within the sub-regional area with instrumented wells. Input parameters for the model include reservoir properties and hydraulic parameters (transmissivity, storage coefficient, permeability) calculated through solid Earth tide analysis from the collected pressure data and core characterization. The model will simulate pressure within the Arbuckle Group before injection (steady-state conditions) and after the effects of injection (transient conditions).

Scientific models calibrated and verified against observed data are more accurate and useful. Previous attempts to quantify the influence of SWD injection on pressure within the Arbuckle Group by modeling lacked real-time data. Once simulations have been run, the model will be calibrated against the pressure data collected from the instrumented SWD wells. This model can be used as a tool for decision-making regarding SWD in Oklahoma.