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Petrography and Petrology of the Wilds Sand, Wildsville Field, Concordia Parish, Louisiana
Maureen K. Corcoran (1), Danny W. Harrelson (1), Gary W. Hennington (2)
Wildsville field, discovered in 1953, has produced approximately 325 million barrels of oil from the Wilds Sand (C-6) member of the Eocene Wilcox Formation. The discovery well flowed 110 barrels of oil per day from perforations between 5,089 and 5,090 ft and ultimately produced more than 190,000 barrels of oil before being plugged and abandoned in 1962. Field development later extended the reservoir to more than 600 acres with the drilling of eight additional wells by 1955. The reservoir sandstone was found to average about 8 ft of net pay, and more than 880 million barrels of recoverable oil was calculated to be in place.
In 1991, the No. 1 Mary T. Smith et al. well was drilled in an updip portion of Wildsville field as an attempt to reestablish production in the Wilds Sand. A conventional core was cut from 5,050 to 5,100 ft, recovering a total of 38 ft from 5,050 to 5,088 ft. Subsequent core analysis indicated porosities as high as 34.7%, permeabilities up to 1,990 millidarcys, and possible "flushed zones." Pipe was run, and the well was completed with perforations from 5,067 to 5,070 ft. The production history of the well did not reflect the favorable core analysis, and currently the well is shut in.
In order to better analyze the production history of the Smith well, a total of 38 thin sections were taken at 1-ft intervals from the core for complete petrographic analysis of the reservoir materials and the flushed zones. The cored interval is interpreted to be a fluvial-deltaic unit composed of upward-fining sandstone sequences and siltstones interspersed with shales and lignites. Petrographic analysis of additional samples from various other Wilcox fields in the trend indicates deposition of the formation is influenced by relative sea-level fluctuations. Base level changes of channels during the Eocene controlled depositional rates and to some extent depocenters. Deposition as a result of these relative sea-level fluctuations produced numerous sandstones units, such as the Wilds, Nichols, Artman, and Turner, that are vertically stacked but commonly have a limited lateral extent.
The Wilcox trend in southeast Louisiana is relatively shallow and has proven to be both profitable and problematic. Although the majority of the reservoirs in this trend have yielded smaller reserves as compared to deeper trends, the Wilcox 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 ensure continued exploration of this profitable trend.
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