GROUNDWATER FLOW MODEL OF FLUID INJECTION INTO THE ARBUCKLE GROUP, CENTRAL OKLAHOMA

The Arbuckle Group, a predominantly carbonate deposit throughout the Mid-Continent, is the main zone of injection for wastewater coproduced at oil and natural gas sites in Oklahoma. Despite the Arbuckle Group being a confined aquifer that is under stress from overburden pressure, it is able to easily accept large volumes of wastewater, a characteristic that is poorly understood. Recent research shows a coincidence between saltwater disposal wells in Oklahoma and the last decade increase in earthquake activity. The purpose of this study is to demonstrate injected fluid migration throughout the Arbuckle Group and adjacent strata by modeling pressure diffusion around injection wells in Oklahoma County. Monthly pressures and injected volumes were gathered from well operators and the Oklahoma Corporation Commission, and permeability of the Arbuckle was calculated from drill stem tests. MODFLOW was used to simulate pressure distribution and fluid migration in space and time under various geologic constraints. Preliminary results indicate that representing fault zones as no-flow boundaries versus vertically conductive zones drastically impacts pressure diffusion patterns within critically stressed fault zones. Fault zone connectivity between the Arbuckle injection zone and crystalline basement rock must be carefully defined to understand relationships between seismicity and deep saltwater disposal wells.