Performance of an Alternate Repressuring and Producing Project

A reservoir which is being subjected to an alternate repressuring and producing mechanism is the Rincon field Frio D–7 sand lens located 16 miles northeast of Rio Grande City, Starr County, Tex., along the Vicksburg flexure and the southwestern edge of the Rio Grande embayment. As in most Frio fields in this area, numerous sand lenses are encountered and, in this instance, throughout 12 distinct strata. The subject reservoir, the D–7, was the seventh reservoir to be outlined in the D stratum. The D–7 reservoir shown in Fig. 1 is a 38 acre-ft, sand lens located at a subsea depth of - 3,230 ft on the west side of the Rincon structure. Only two wells, T. B. Slick HB No. 90 and 91, were drilled into the sand lens, encountering 12 and 16 ft of sand, respectively. Although Well No. 91 was cored, no analysis was obtained; therefore, 23 per cent porosity and an irreducible water saturation of 24 per cent, the average figures in Frio D sands in this area, were used. A fluid analysis is not available from the D–7 reservoir. Therefore, an analysis from the D–5 reservoir (sand) in proximity to the subject reservoir was used to obtain the assumed formation volume factor of 1.172 at 1,523 psi and 155°F. Primary Performance History In June, 1941, the T. B. Slick HB No. 91, the only well that produced during primary operations, was completed in the D–7 reservoir and potentialed for 166 B/D, no water, flowing through a 1 1/64 in. choke with a GOR of 311 cu ft/bbl, and tubing pressure of 320 psi. Flow valves were installed in Aug., 1944; in Feb., 1946, the well was shut in due to low productivity. The flow valves were repaired in Dec., 1947, and the well was re-potentialed for 45 B/D. The well then produced until Feb. 21, 1950, at which time it was permanently shut in due to low productivity. The primary production history of the reservoir is illustrated in Fig. 2. Cumulative production at the end of the primary life was 80,820 bbl of oil, no water and 159,872 Mcf of gas. Bottom-hole pressures taken in 1948, 1950 and 1951 are thought to be in error and probably represent gas-lift system pressures caused by a leaking valve. The gas-oil ratio increased from 311 to 52,800 cu ft/bbl, but the accuracy of the erratic gas-oil ratio history after 1946 is questionable and can probably be contributed to the inherent industry-wide problem of measuring injection gas during intermittent gas-lift operations.