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Fashing field, as presently defined, is 10 miles long and 2 miles wide. The field extends from the southeast corner of Atascosa County to the northwest corner of Karnes County, approximately 50 miles southeast of San Antonio, Texas. Lone Star Producing Company discovered gas in the Edwards limestone (Lower Cretaceous) at Fashing in July, 1956, when its No. 1-A L. T. Urbanczyk well reach the top of the Edwards at 10,210 feet and found 580 feet of productive section that had an initial potential of 26,000 MCFGPD plus 24 barrels of 50.6° gravity distillate per MMCF.
The Edwards structure at Fashing field is dominated by a simple, northeast-trending up-to-the-coast fault with effective closure against the high side. This fault has a maximum vertical displacement of approximately 700 feet at the Edwards level, which decreases to a maximum of 320 feet going up the section to the Carrizo Sand (Eocene) level. The fault is responsible for the Weigang field oil production at the Carrizo level. The fault dips northwest, with the angle of dip decreasing from 50° at the Carrizo to 38° at the Edwards.
Edwards gas production at Fashing comes from two separate zones called the "A" and "B" zones, respectively. The "A" zone has an average porosity of 15.5 per cent, an average permeability of 12.6 millidarcys, and an average connate water saturation of 28 per cent. The "B" zone has an average porosity of 13.2 per cent, an average permeability of 4.4 millidarcys, and an average connate water saturation of 24 per cent.
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