Five-Spot vs. Crestal Waterflood Patterns, Comparison of Results in Thin Reservoirs

Abstract

Abstract This paper presents a comparison of results for two different waterflood patterns which were utilized in separate reservoirs of the same producing horizon. The El Javali field is located in South Texas, about 30 miles north of Rio Grande City on the Jim Hogg County-Starr County boundary. The field is composed of two separate reservoirs separated by a shale-out. The production from the El Javali field is obtained from the O'Hern sand of Eocene age at approximately 2,300 ft. The field was discovered in Oct., 1951. Porosities are good, permeabilities are low, connate-water content in average and the sand thickness is thin. The oil gravity is 32°API and the viscosity is relatively low. Studies of secondary possibilities were initiated in early 1955 to conduct waterflood operations in the north reservoir. Water injection was commenced in this reservoir in May, 1956, by utilizing a crestal, or line, flood pattern in two injection wells and five producers. Primary recovery in this reservoir amounted to 297 bbl of oil/acre-ft. Secondary recovery, as of July, 1959, for the north reservoir was 102 bbl of oil/acre-ft. It is anticipated that the total secondary recovery from this reservoir will be about 157 bbl of oil/acre-ft. In Sept., 1957, water injection was begun in the south reservoir by injection into 10 injection wells forming three modified 20-acre five-spots. Primary production from this reservoir was 316 bbl of oil/acre-ft. Water flood recovery in the reservoir, as of July, 1959, was 81 bbl of oil/acre-ft; the ultimate secondary recovery is estimated to be at least 200 bbl/acre-ft. Secondary increases in production in the north reservoir were experienced in one well at a time. The secondary "kicks" in production for the south reservoir have been more or less simultaneous for all of the producers. From the data presented, it can be seen that the five-spot project will ultimately recover some 21 per cent more secondary oil per acre-foot than the crestal pattern flood.