Geology of North Personville Field, Limestone County, Texas

Robert L. Zamboras

Mitchell Energy Corporation is currently active in the development of the Cotton Valley Lime reservoir at North Personville field, Limestone County, Texas. The complex nature of the reservoir has prompted the initiation of a study of the depositional-structural and diagenetic-burial history as related to hydrocarbon generation, migration, and entrapment.

In excess of 50 Mitchell Energy Corporation wells have been drilled in the North Personville field, Limestone County, Texas. In order to understand the variables that affect the ultimate reserves within the carbonate section, two conventional cores from Mitchell Energy Corporation wells were analyzed. The Mitchell Energy Corporation 1 Muse-Duke and 1 Ralph Spence limestone sections were studied to determine the relationship between log-derived reservoir parameters and the limestone lithologies for field wide application.

Production at North Personville field is lithology selective. Five distinct oolitic grainstone shoal "cycles" are identified and correlate field wide.

The sequence of events that led to the development of reservoir quality grainstones are (1) the infilling by oolitic grainstone shoals on an irregular Buckner Formation paleosurface. This surface was modified by pre-Cotton Valley limestone salt activity such that carbonate deposition did not take place or was eroded over structurally high areas, (2) Cotton Valley limestone deposition culminating with the deposition of a narrow belt of ooid grainstones, (3) nearly complete occlusion of primary porosity and permeability by the deposition of marine cements followed by "chalky" microporosity formation, (4) post-depositional salt and basement tectonics that pervasively fracture the more competent ooid grainstone facies producing additional secondary porosity and permeability, (5) hydrocarb n generation from the overlying Bossier marine shales migrates into the porous permeable Cotton Valley Limestone. The uppermost shoal cycle is preferentially charged due to their proximity to the source beds.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.