High Resolution Sequence Stratigraphic Architecture and Reservoir Characterization of the Mississippian Burlington/keokuk Formation, Northwestern Arkansas

Abstract

The Upper Osagean Burlington-Keokuk Formation is a limestone and chert interval within the Mid-continent containing reservoir quality rock. Outcrop analogs in northwest Arkansas were studied in order to accurately characterize potential reservoir intervals in the subsurface of Kansas and Oklahoma. Using an integrated sequence stratigraphic approach combining thin-section analysis, high-resolution photography, and spectral gamma-ray logs, packages of coarsening and thickening upward successions of skeletal packstones and grainstones were identified. Accurate identification of cyclic stacking patterns allowed for the recognition and correlation of high frequency sequences across the outcrop, which enhance the predictability of potential reservoir and seal units. Within each sequence regressive skeletal grainstones exhibit abundant early syntaxial cement, occluding all effective pore space. Transgressive packstones contain little to no void-filling cement and exhibit varying degrees of silicification and dissolution, creating adequate reservoir rock in many cases. Facies associations suggest deposition occurred within a high energy skeletal shoal complex. Analysis of depositional analogs was utilized to provide first approximations of the scale of facies geometries and distributions in plan-view not provided by outcrop. Stochastic modeling allowed for integration of variables from analogs with the sequence framework and facies successions interpreted from outcrop in order to visually represent facies variability and potential reservoir distribution in the formation. Comparison of geostatistical models with two-dimensional rock data from outcrop allowed for the creation of multiple model iterations and identification of modeling parameters necessary for accurate subsurface representation and visualization.