ABSTRACT: Relationship of Pore Geometry to Reservoir Properties: Smackover Formation, Walker Creek Field, Arkansas

BLIEFNICK, DEBORAH M., and JOHN G. KALDI, ARCO Oil and Gas Co., Plano, TX

Walker Creek field in southern Arkansas produces hydrocarbons from carbonates of the Jurassic Smackover Formation. The relationships between pore geometry and reservoir quality in these rocks were evaluated using petrographic methods (thin sections and pore casts) and mercury injection capillary pressure (MICP) analyses. Results indicate that reservoir quality is controlled by pore geometry, which in turn is determined by depositional and diagenetic processes.

Rocks at Walker Creek formed as prograding ooid grainstone shoals in a shallow water, high energy environment. Diagenetic processes, including early calcite cementation, compaction, and a late stage episode of dissolution, modified the original pore system. Interparticle porosity is the dominant effective pore type and is most important in terms of reservoir performance. Microporosity is also abundant, comprising a significant percentage of total porosity, but is generally ineffective.

The rocks were subdivided into lithofacies based on their depositional and diagenetic origin. Within each lithofacies, reservoir, marginal reservoir, and nonreservoir rock types were broken out as a function of their pore geometries. Each of these rock types has a characteristic capillary pressure curve. There is a close correlation between MICP curve shape and aspects of pore geometry such as pore throat size, pore throat size distribution, and pore interconnectivity. In addition, MICP analysis provides guidance in evaluating overall reservoir quality by rock type, as well as answering specific questions regarding net pay criteria as a function of height above free water level.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)