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Abstract: Petrography and Petrology of the Wilds Sand, Wildsville Field, Concordia Parish, Louisiana

Maureen K. Corcoran, Danny W. Harrelson, Gary W. Hennington

Wildsville field, discovered in 1953, has produced approximately 325 million bbl of oil from the Wilds Sand (C-6) member of the Eocene Wilcox Formation. The discovery well flowed 110 bbl of oil per day from perforations between 5089 and 5090 ft, and ultimately produced over 190 million bbl of oil before being plugged and abandoned in 1962. Field development later extended the reservoir to over 600 ac, with the drilling of eight additional wells by 1955. The reservoir sand was found to average about 8 ft of net pay sand, and over 880 million bbl of recoverable oil was calculated to be in place.

In 1991, Oilwell Acquisition drilled the 1 Mary T. Smith et al. well in an updip portion of Wildsville field as an attempt to reestablish production in the Wilds Sand. A conventional core was cut from 5050 to 5100 ft, recovering a total of 38 ft from 5050 to 5088 ft. Subsequent core analysis indicated porosities as high as 34.7%, permeabilities up to 1990 md, and possible "flushed zones." Pipe was run and the well was completed with perforations from 5067 to 5070 ft. The production history of the well did not reflect the favorable core analysis and currently the well is shut-in.

To better analyze the production history of the Smith well, 38 thin sections were taken at one-foot intervals from the core for complete petrographic analysis of the reservoir materials, the source rocks, and the flushed zones. This analysis indicated that, in general, the Wilds Sand can be interpreted to be a fluvial-deltaic unit composed of fining-upward sand sequences and silts interspersed with shales and lignites. The member is believed to be self generating, i.e., the shales are the source rocks for the hydrocarbons that were emplaced by short-range migration. Petrographic analysis of additional samples from various other Wilcox fields in the trend indicates deposition of the formation is influenced by sea level fluctuations. Base-level changes of channels during the Eocene cont olled depositional rates and to some extent depocenters. Deposition as a result of these sea level fluctuations produced numerous "sand packages" such as the Wilds, Nichols, Artman, Turner, etc., that are vertically stacked but often have a limited lateral extent. The individual channel sands are often very erratic as a result of being deposited by streams meandering through the delta during a minor sea level rise.

The Wilcox trend in the southeast is a relatively shallow trend that has proven to be both profitable and problematic. Although the majority of the reservoirs have yielded smaller reserves as compared to deeper trends, the formation will continue to attract independent oil producers because of low drilling and completion costs. In the future, horizontal drilling and improved completion techniques will insure continued exploration of this profitable trend.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994