GEOLOGIC, PERMEABILITY, AND FRACTURE CHARACTERIZATION OF THE ARBUCKLE GROUP IN THE CHEROKEE PLATFORM, OKLAHOMA

Abstract

Permeability in the Arbuckle Group (Arbuckle) of central- Oklahoma is not well understood and may be key to understanding the relationship between fluids injected into subsurface formations and seismicity in the basement. Seismic activity from 2009 to 2016 far exceeded background seismicity in central-Oklahoma and motivated research in the Arbuckle and Timbered Hills overlying the Precambrian Basement. Movement of fluids in each formation must be understood, beginning with characterizing lithology, fracturing, and rock properties. Properties that help evaluate fluid movement in the Arbuckle and basement rock includes types of fractures, lengths of fractures, fracture aperture, lithology, and primary/secondary mineralogy. The different type of porosity and rock matrices affect fluid movement and can provide conduit for it. This research is important for understanding how and where saltwater disposed into the Arbuckle is migrating and whether individual formations act as fluid conduits, seals, or impermeable barriers. Arbuckle core was described to understand formation scale variability in rock properties affecting fluid migration. Small-scale permeability measurements from 165 locations within an Arbuckle core ranged from 0.22–387.2 mD. These values represent the smallest scale of the study and likely the lowest reasonable matrix permeability for Arbuckle subsurface materials in the study. Measurements were taken along fractures, but resulting values may underrepresent the upper limits of Arbuckle permeability. Analysis of observed solid earth tides yielded a range of permeabilities from 285.5–1304.7 mD from two wells over an open interval within the Arbuckle. This range is at the largest on the scale for permeabilities measured. By analyzing pressure monitoring data, injection response via a slug test method, drill-stem tests, small-scale permeability from core, describing the fracture pattern, and examining well logs, better hydrogeologic and geomechanical models will be developed to understand fluid or pressure propagation from the Arbuckle and into the underlying Precambrian Basement.