Early CO2 Flood Experience at the South Wasson Clearfork Unit

Abstract

Early CO2 Flood Experience at the South Wasson Clearfork Unit D.E. Burbank D.E. Burbank Shell Western E and P Inc. Search for other works by this author on: This Site Google Scholar Paper presented at the SPE/DOE Enhanced Oil Recovery Symposium, Tulsa, Oklahoma, April 1992. Paper Number: SPE-24160-MS https://doi.org/10.2118/24160-MS Published: April 22 1992 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Burbank, D.E. "Early CO2 Flood Experience at the South Wasson Clearfork Unit." Paper presented at the SPE/DOE Enhanced Oil Recovery Symposium, Tulsa, Oklahoma, April 1992. doi: https://doi.org/10.2118/24160-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search nav search search input Search input auto suggest search filter All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE Improved Oil Recovery Conference Search Advanced Search SPE MemberAbstractThis paper describes the implementation and performance of the industry's first Clearfork CO2 flood - Shell's South Wasson Clearfork Unit (SWCU) located in the Permian Basin of West Texas. CO2 injection began in 1986 using a high water-alternating-gas (WAG) ratio (8:1), low volume (8% hydrocarbon pore volume) flood, or "CO2 augmented" waterflood. The intent of the flood was to increase our understanding of the Clearfork formation before committing to a larger scale CO2 flood.The performance of the "CO2 augmented" waterflood has met expectations. After 3-1/2 years of CO2 injection, enhanced oil production had increased to 450 BOPD, or 7 % of Unit production. CO2 injectivity was comparable to water injectivity, and no significant decrease in the WAG water injectivity was observed. Encouraged by the success of the CO2 augmented waterflood, a 2:1 WAG CO2 flood was approved and implemented in the northern half of the CO2 flood area in the spring of 1990.Through 1991, roughly 3 % of a hydrocarbon pore volume of CO2 has been injected at SWCU, and the cumulative enhanced oil recovery matches the original projections. The performance of the CO2 flood to date has been influenced by reservoir heterogeneity, injection pattern modifications, waterflood operating practices, and gas processing constraints.IntroductionBy 1985, large scale CO2 floods had been initiated in several Wasson area San Andres Units. The Wasson Clearfork reservoirs, though, differ in many respects from their shallower San Andres neighbors. The average porosity and permeability is lower, the gross interval is 4–5 times thicker, and pay is more discontinuous between wells. Also, waterflooding the Wasson Clearfork began only recently (1980), and no CO2 pilot has been run in the Clearfork. Accordingly, a more cautious approach was taken toward CO2 flooding a Clearfork reservoir. A high WAG ratio (8: 1) CO2 flood was initiated in January 1986 to gain experience in CO2 flooding a Clearfork reservoir before committing to a larger scale CO2 flood.During the CO2 augmented waterflood, many questions concerning the Clearfork reservoir were addressed. How would CO2 injectivity compare to water injectivity, and would water injectivity decrease after CO2 injection? How would EOR rates be calculated? What is the best injection pattern to maximize waterflood and CO2 flood recovery? How would CO2 breakthrough occur and how would it be handled?GEOLOGY AND DEPOSITIONAL ENVIRONMENTThe South Wasson Clearfork Unit is located along the southeastern edge of the North Basin Platform in the Permian Basin (Fig. 1) and produces from Permian Leonardian Clearfork reservoirs between 5900 and 7900 feet. During Permian time, cyclic changes in sea level (Fig. 2), it is suggested, caused cyclic depositional patterns. The Clearfork formation is primarily dolomite containing varying amounts of anhydrite, with intervals of clastic influx. The clastic intervals have been used to subdivide the Clearfork into three stratigraphic units, Upper (UCF), Middle (MCF) and Lower (LCF).P. 43^ Keywords: injector, fracture, augmented waterflood, breakthrough, south wasson clearfork unit, waterflood response, waterflooding, production rate, clearfork reservoir, enhanced recovery Subjects: Improved and Enhanced Recovery, Waterflooding This content is only available via PDF. 1992. Society of Petroleum Engineers You can access this article if you purchase or spend a download.