ABSTRACT: Reservoir Description, Walker Creek Field, Arkansas

Deborah M. Bliefnick, Susan M. Bissmeyer, Karen M. Frey, Thu-Thuy Dang

A multidisciplinary reservoir description of Walker Creek field in southern Arkansas was conducted to evaluate the field's potential and determine the best method of increasing recovery. The reservoir is within a 100-ft-thick section of the ooid grainstone facies of the Jurassic Smackover Formation. The reservoir is currently under partial pressure maintenance by reinjection of produced gas at the crest of the structure. One of the goals of the study was to evaluate reservoir management options for effecting significant incremental oil recovery.

The reservoir was originally divided into five producing zones (1-5). Of these, zones 2 and 4 account for nearly 95% of the production. The grainstone facies in zones 2 and 4 consist predominantly of ooids, but also contain peloids, oncolites, and intraclasts. Calcite cement creates discontinuous tight streaks throughout the reservoir. Porosity is predominantly intergranular and ranges from 1% to greater than 20%. Permeability also varies widely, ranging from 0.1 to > 5000 md. Five percent porosity and 0.6 md permeability, as determined by log analysis, were used as a net pay cutoff.

Data from lithologic and log analyses were used to construct cross sections across the field. These sections and grainstone isopach maps illustrate that the two main reservoir zones represent two generations of prograding ooid shoal development. Calcite cemented intervals within the zones cannot be correlated beyond two or three wells. The local extent of these intervals does not justify using them to further subdivide the reservoir zones. Gross pay, net pay, and ^phgrh maps indicate that development of porosity followed the trend and distribution of the ooid shoals. Production data (pressure plots, gas-to-oil-ratio maps, and tracer studies) suggest that individual reservoir zones are in communication across the field. These results led to a decision against infill drilling in the fie d. Studies on methods of repressurizing the reservoir are in progress.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990