The Palo Pinto Limestone (lower Canyon Series) of western Runnels County, Texas, is generally found at depths of 3,800-4,200 feet. The two productive porosity zones are in the upper 50 feet of the formation. The lower is by far the more productive. The Palo Pinto can produce from structural traps alone but the best producing fields are those in which stratigraphic pinchouts are associated with low-relief structures. Several of the presently productive fields produce 30-60 per cent water together with the oil; history now shows these fields to have considerably

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higher primary recovery rates, indicating that this produced water is not all connate, and that the fields are at least in part water-drive fields. Calcite-lined vuggy porosity commonly causes shows in drilling samples to be very difficult to detect in the lower porosity zone. Therefore, if the presence of porosity is indicated in this zone, a drill-stem test is certainly recommended. In many wells, 2½-inch tubing (as opposed to the 2-inch normally employed in this area) and 2¼-inch pumps are required in order to move enough total fluid to attain the oil allowables. However, indicated recovery rates in excess of 200 barrels per acre-foot more than justify the higher resulting production cost.

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