Large Scale Waterflood Performance Sprayberry Field, West Texas

Abstract

Abstract First response to large scale water flood in the fractured milli-darcy Spraberry sand has led to a new unique cyclic operation. Capacity waterinjection is used to restore reservoir pressure. This is followed by a few months production without water injection and the cycle repeated. Expansion of the oil, rock and water during pressure decline expels part of the fluids but capillary forces hold much of the injected water in the rock. Field performance has proved this cyclic operation is capable of producing oil from the matrix rock at least fifty per cent faster and with lower water percentage than is imbibition of water at stable reservoir pressure. Introduction The Spraberry Field of West Texas presents unusual problems for both primary production and water flooding. Extensive interconnected vertical fractures in the fractional-millidarcy sandstone permitted recovery of oil on 160-acre well spacing, but they made capillary end effects dominant; primary recovery by solution gas drive is less than 10 per cent of oil in place. The concept of displacement of oil from the sand matrix by capillary imbibition of water has led to field techniques which promise greatly increased oil recovery. Free exchange of laboratory research, reservoir information and results of field pilot tests among the various companies has been very important in development of this technology. Four units covering a total of 125,500 acres have been formed for waterflooding and eleven other areas covering an additional 220,000 acres are in various stages of unitization. Part of the Driver Unit reaching fill up first has demonstrated very unusual water flood behavior and indicated numerous operating problems that will develop within and among the various units.