Recovery of Oil by Steam Injection In the Smackover Field, Arkansas

Abstract

Steam injected into a 22-acre pilot area appreciably increased production and rates of recovery. The steam moved radially with an almost circular front through the gas cap above the oil zone. Conduction then carried the heat from the steam zone into the oil zone. For more than four years after the steam injection had stopped, the hot zone persisted, sustaining the production rate at about twice the primary rate. production rate at about twice the primary rate. Introduction This report describes the geology, lithology, and fluid saturation distribution in the Smackover field, Nacatoch sand reservoir, in the area of the Sidum steam injection pilot, and discusses the subsequent oil production and performance of the pilot. The production and performance of the pilot. The steam-injection pilot was started at a time when production under primary methods was approaching abandonment rates, and indeed many wells had already been plugged and abandoned. The viscous nature of the reservoir oil (75 cp at the reservoir temperature of 110 degrees F), the presence of a gas cap overlying a large portion of the oil-bearing zone, and the poor response to waterflood pilots on the periphery of the reservoir discouraged any further consideration of a waterflood. Although water encroachment in parts of the Nacatoch reservoir was believed to have increased recovery, it was concluded that waterflooding would not be economic. The Smackover field is in Townships 15 and 16 South, Ranges 15, 16, and 17 West, in Union and Ouachita Counties, Ark. (Fig. 1). The steam injection pilot is in the center of the Sidum lease, which is the SE/4 of Section 32, R-15-W, T-15-S (Fig. 2). There are two major geologic structures in the field, the Louann dome in the western part and the Norphlet dome in the eastern part; only the Norphlet dome was considered in this study. The first successful completion in the field was made on July 1, 1922, and the free gas cap was dissipated rapidly. By 1930, vacuum installations were operating and reservoir energy was essentially exhausted. Production thereafter resulted from gravity drainage and water influx. Geology and Lithology The Norphlet dome of the Smackover Nacatoch reservoir is a roughly circular anticline, approximately 5 miles in diameter, with 150 ft of structural relief. Fig. 1 is a structure map contoured on the top of the Nacatoch sand. The sand originally produced gas and oil at depths from about 1,900 to 2,040 ft. The formation can be segregated into three general zones, each having different lithologic and producing properties. The uppermost 30 to 50 ft of the Nacatoch sand consists of thin, highly permeable lenses separated by shale stringers and tight sandstone beds. The impervious beds are often only inches thick and look so much like the permeable lenses that it is difficult to detect them by simply looking at the cores. Only one shale bed (at a depth, of 1,974 ft in Sidum Well M-42, Fig. 4) can be correlated over much of the field. From the study of the Nacatoch sand in cores and at the outcrop it was concluded that the thin shale beds are often limited to only a few inches, and that the 2- to 3-ft-thick impermeable beds indicated by the spontaneous potential log probably are sections in which large quantities of shale are dispersed through the sand on both sides of the thin stringer. P. 883