Performance of a Propane Slug Pilot in a Watered-Out SandSouth Ward Field

Abstract

This pilot program was undertaken to determine if the process would be a successful tertiary method in a field that had already undergone a highly successful waterflooding. Recovery from the central, producing well of the closed five-spot indicated that the process of injecting propane, followed first by gas, then alternately by gas and water, definitely will bank up oil in a watered-out reservoir. Introduction The use of the propane slug process to miscibly displace oil from a reservoir has been discussed in the literature and used successfully in the field. The process, as generally used, entails the injection of process, as generally used, entails the injection of propane followed by gas, or gas alternating with propane followed by gas, or gas alternating with water, to drive the propane as a slug through the reservoir. Most applications of the process have been as a secondary recovery method. A special application of the propane slug process is as a tertiary method of oil recovery in a watered-out reservoir, the object being to recover the oil that remains as a residual to waterflooding. Laboratory tests indicate the feasibility of applying the process in this manner. To move the experiments from its research laboratory to the field, Atlantic Richfield undertook a pilot test of the propane slug process on the Yates Sand underlying its 320-acre W. D. Johnson lease in South Ward field, West Texas. This lease, which covers the E/2 of Section 9, BLK 34, H and TC RR CO. Survey, had been produced to primary depletion by solution gas drive and had been very successfully waterflooded. (Detailed analyses of waterflooding performance have been presented in two previous papers. At the time the experimental propane slug pilot was started in the summer of 1961, the lease was essentially depleted by waterflooding. Presented here are the results of the pilot test and a review of the reservoir and prior pilot test and a review of the reservoir and prior producing history. producing history. Geology and Reservoir Properties South Ward field is located in the southeastern paint of Ward County. It is one of a series of Yates Sand fields that form a trend along the west and south edges of the Central Basin Platform. The field is situated on an elongated anticline of low relief that is oriented in a general north-south direction. The W. D. Johnson lease is near the structural crest of the field, with the underlying Yates Sand having about a 1 degrees slope in a westerly direction. The field extends over approximately 14 sections, which means that the 320-acre W. D. Johnson lease constitutes a relatively small part of the field. The Yates formation is of upper Permian age and is composed of two sand bodies over most of South Ward field. The upper sand is referred to as the Grand Falls; the lower, the Penn Bennett. Both zones are productive of oil in the field. On the W. D. Johnson lease, however, a gas cap originally occupied a part of the Grand Falls zone; and whereas both zones part of the Grand Falls zone; and whereas both zones were produced under primary depletion, the original waterflooding and the propane slug were confined to the Penn Bennett. The Penn Bennett in the vicinity of the W. D. Johnson lease occurs at a depth of about 2,400 ft. It has a gross thickness of 60 to 80 ft, with about 30 ft of this being a clean, friable sand of good permeability and porosity. JPT P. 1209