Carbonate Diagenesis and Porosity Evolution of the Council Grove Group, (Upper Pennsylvanian-Lower Permian), Hugoton Embayment, Anadarko Basin, Southwest Kansas

Nicholas J. Pieracacos

The Hugoton Embayment of southwestern Kansas is a large, shelf-like extension of the Anadarko Basin of Oklahoma. Shallow-shelf carbonates of the giant Hugoton-Panhandle gas trend form the largest gas producing field in North America. The Council Grove Group is a major reservoir within this trend.

Lithologies identified in core include siltstones, dolostones, mud stones, wackestones, and packstones that are developed in somewhat variable repetitive sequences of shallow subtidal shelf to peritidal sabkha depositional environments. A shallowing-upward cycle generally consists of thin transgressive marine limestones overlain by thicker progradational and aggradational subtidal-supratidal limestones, which is succeeded by nearshore siltstones and paleosols.

Petrographic analysis of carbonates from several wells indicates a complex diagenetic pattern, characterized by numerous stages of diagenetic modification and alteration. Most original textures have been destroyed, obliterated, or masked by regional diagenetic processes, which have severely altered the original fabric of most reservoir quality carbonates within the Council Grove Group. Precipitation of evaporites (anhydrite), silicification, dolomitization, secondary calcite cementation, and stylolitization have extensively altered the original depositional fabric.

Diagenetic environments recognized include marine phreatic, freshwater phreatic, mixing zone, and deep burial. Porosity types include: 1) major amounts of late stage dissolution porosity, 2) intercrystalline porosity related to dolomitization, 3) interparticle and intraparticle porosity, and 4) microporosity associated with silicification and dolomitization. Diagenetic modifications appear to be facies selective and are manifested in varying degrees throughout the Council Grove Group. Reservoir quality appears best in the subtidal-supratidal depositional environments which are characterized by wackestones and packstones.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995