Cessford Basal Colorado A ReservoirCaustic Flood Evaluation

Abstract

This paper discusses a laboratory study to determine the feasibility of caustic flooding in the Cessford Colorado A reservoir in southeastern Alberta. Preliminary tests indicated that the crude contained sufficient organic acids to make it interfacially active with caustic solutions. A program of core displacement tests on preserved reservoir core and Berea sandstone then was carried out with encouraging results. Introduction Caustic flooding is being considered as an alternative to waterflooding in portions of the Cessford Basal Colorado A pool. The reservoir is located in southeastern Alberta and is currently in an advanced stage of primary production. A waterflood is scheduled to commence in Dec. 1980.Screening of oil reservoirs operated by Hudson's Bay Oil and Gas Co. Ltd. for enhanced recovery prospects was initiated in 1976. At that time the subject pool was chosen as a caustic flood candidate, based on the acid number of the crude and the relatively low concentration of multivalent ions in the formation and proposed injection waters. The fact that the reservoir had not been waterflooded added to the attractiveness of the project.Several articles on the research and field testing of caustic flooding for improved oil recovery have been published since as early as 1917. In 1976 Johnson reviewed the mechanisms involved, the conditions required for successful application, and the results of several field tests. More recently, McAuley has reported on an 80-acre pilot in the Wainwright field in Alberta; Raimondi et al. have published results on a 5-acre pilot in Texas; and the City of Long Beach and Aminoil U.S.A. Inc. have undertaken separate projects to evaluate alkaline flooding in California in cooperation with the U.S. DOE.This paper discusses the laboratory study to determine if oil recovery can be enhanced by adding caustic to the waterflood in the Cessford Basal Colorado A pool and to determine the apparent recovery mechanism. The application of the laboratory results for predicting field performance and the ongoing meld and design work are discussed briefly. Reservoir Description The Cessford Basal Colorado A pool was discovered in 1958 with original oil in place (OOIP) of approximately 12 × 10(6) m3. Projected primary recovery is estimated at 1.2 × 10(6) m3. A peripheral waterflood is scheduled to begin in 1980. It is proposed to inject caustic in the five 80-acre inverted five-spot patterns (Fig. 1) to augment the waterflood.Table 1 gives the reservoir and crude properties. The sandstone is described as fine grained and loosely consolidated with an average porosity of 24% and an average permeability of 354 md. X-ray diffraction analysis shows an average clay content of 4%, almost all kaolinite. The oil is a medium-gravity crude with a relative oil density of 0.912 g/cm3 and a viscosity at current reservoir conditions of 24 mPas. Its acid number is 0.5 mg KOH/g.The formation and proposed injection waters are relatively low in calcium and magnesium as shown in Table 2. The proposed injection water is produced from the Viking sand approximately 65 m above the Basal Colorado formation. JPT P. 2103＾