Coalinga Nose Pressure Maintenance Project

Abstract

A large gas injection program in this unitized field in California has improved gravity drainage, resulting in an ultimate recovery approaching half the oil in place. Deliberate water production has reduced a natural water influx that would have reduced recovery if not checked. Few "giant" oil fields can match the performance of the Coalinga Nose field. Introduction The Gatchell pool of the Coalinga Nose field provides a 34-year case history of a gravity drainage reservoir. The field is approximately 6 miles northeast of the town of Coalinga in Fresno County, Calif. After 12 years of competitive operations, the field was unitized in 1950. The most unusual feature of the Gatchell pool's production history is that since unitization, it pool's production history is that since unitization, it has been operated in a manner to maximize the gravity drainage potential and arrest natural water encroachment. Crestal gas injection was begun in 1950 and has continued to the present. A pilot waterflood was attempted but was short lived because it proved less efficient than gravity drainage. Further, large volumes of water have been produced from edge wells to prevent natural water encroachment from reducing recovery. In 1969, the gas injection was supplemented with a large-scale program of nonindigenous-gas injection. More than 58 Bcf of natural gas has been injected under this program. Cumulative oil production exceeds 425 million bbl, or 42.7 percent of the production exceeds 425 million bbl, or 42.7 percent of the original oil in place, and the current production is about 10,000 BOPD. An ultimate recovery of 470 million bbl, or 47.2 percent of the oil in place, is expected; this is an increase of 79 million bbl over the calculated primary recovery. Development History and Method Of Operation The pool was discovered with the completion of well Gatchell No. 2 (now 1-18F) on June 26, 1938. Development progressed rapidly until Dec. 1941, at which time 157 wells had been drilled. Most of the field was developed on 20-acre spacing, but some closer spacing along the east flank and the southwest area has reduced the average spacing. A total of 192 wells had been completed as of July 1, 1972. In June of that yea, 75 of those wells were active producers, 21 were used for gas injection, 15 had been abandoned, and 81 were idle. During World War II the maximum efficient production rate (MER) for the pool was set by the production rate (MER) for the pool was set by the Petroleum Administration for War (PAW). Petroleum Administration for War (PAW). Controversy between the PAW and the operators developed over what the proper production rate should be to minimize pressure decline. MER's set during this period ranged from 15,000 to 50,000 B/D. To meet period ranged from 15,000 to 50,000 B/D. To meet the wartime demand, production in excess of the MER was permitted to as high as 59,000 bbl. The MER was 30,000 B/D when the PAW was dissolved on Sept. 30, 1945. MER recommendations were made by the Conservation Committee of California Oil Producers as the successor of the PAW. From 1945 until 1953 the operators produced at rates ranging from 43,000 to 54,000 B/D. The production history for the pool is shown graphically in Fig. 1. JPT P. 1147