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Potosi (Jennings Lime) Field, Taylor County, Texas

Johnny Bill Hailey

The Potosi (Jennings lime) field in Taylor County, Texas, opened up Strawn production in an area that previously had only very shallow pays (Wolfcamp) and established viable reserves in an area that historically had been characterized by limited reservoir size and economic returns. The field was discovered in late 1984 and presently has 14 wells and a cumulative production exceeding 80,000 bbl of oil. Development of the field is ongoing, with well potentials of 150-200 BOPD being recorded. The pay is from a high-energy, offshore bar of gray to pinkish-tan grainstone that has been leached and recrystallized then abraded into rounded grains. The fusulinid genus Beedina dates the zone as late Strawn.

The reservoirs are narrow and elongate with a maximum observed pay of 30 ft. The moderate drilling depth (3,800 ft) and estimated per-well reserves of more than 50,000 bbl of oil make this a viable exploration target. Because of the very limited Strawn control in the area, an inconclusive assessment of the areal extent of the field reservoir is not possible at this time. The closest comparable Strawn production is approximately 20 mi away. Careful subsurface work, using isopach studies and environment of deposition models, will determine conditions conducive to reservoir formation and will probably lead to other fields being discovered in this newly established trend.

AAPG Search and Discovery Article #91034©1988 AAPG Southwest Section, El Paso, Texas, 21-23 February 1988.