INITIAL PIEZOMETRIC CONDITIONS OF THE ARBUCKLE GROUP

Literature has historically described the Arbuckle Group as being an underpressured reservoir. The high permeability of the formation and large storage capability resulted in it becoming the largest volume disposal zone in the world. This was both economically and environmentally beneficial as high volumes of mid-continent oil and gas production and fluid disposal within the Arbuckle Group reservoir coincided. In 2009, increases of induced seismicity events caused increased scrutiny of the hydrogeology of this reservoir. Initial potentiometric data for formations are critical for analyzing and managing pressure changes that may results in migration of injection fluids causing shallow impacts or inducing seismicity. An understanding of Arbuckle Group piezometric evolution over time will provide an understanding if changes in pressure condition in the disposal zone can be correlated to the stress conditions of faults located in crystalline basement rock below the Arbuckle Group in recent seismically active areas. Compiled pressure data from oil and gas drill stem tests completed within the Arbuckle Group or equivalent lithology (Texas-Ellenburger Formation) in Oklahoma, Kansas, and Texas indicate an underpressure reservoir with ~86% of the 101 well tests falling below the hydrostatic gradient (0.465 psi/ft) and an average deviation of -2.1 MPa below the hydrostatic conditions. These data will allow an understanding of changes in pressure distribution that may have occurred between aseismic and seismic periods. The understanding of pre-development pressure conditions can provide insight into current in situ pressure conditions, which can be input into models for evaluating disposal effects or seismicity.