Reservoir Description by Simulation at SACROC - A Case History
Authors: Brummett W.M. , Emanuel A.S. , Ronquille J.D. 
Published: December 2007

To determine areal distributions of pore volume and transmissibility in an effort to control a large CO2-assisted recovery project, a 24-year history match of more than 1,500 wells was conducted with a two-dimensional, black-oil simulator. A good quantitative match resulted, which provided the necessary parameter distributions. Subsequent performance has largely supported the results of the study.

Introduction

The Canyon Reef reservoir in Scurry County, Tex., is about 25 miles long and from 4 to 7 miles wide. It is the largest of 15 news that lie along the eastern flank of the giant Horseshoe Atoll, which accumulated in the Midland basin during late Paleozoic time.

The structure is a limestone reef ranging in thickness from about 100 ft on the flanks to about 750 ft on the crest, with an aver-age of about 213 ft. The average producing depth is 6,700 ft. Initial pressure was 3,122 producing depth is 6,700 ft. Initial pressure was 3,122 psig at -- 4,300 ft subsea. Initial temperature was 132 degrees F. psig at -- 4,300 ft subsea. Initial temperature was 132 degrees F. The porosity is primarily intercrystalline and effectively ranges from about 2.5 to 14 percent. Effective permeability ranges from about 0.1 to 51. 0 md. permeability ranges from about 0.1 to 51. 0 md.The reservoir was discovered in Nov. 1948 when Chevron Oil Co. completed its Jessie Brown No. 2-1 well at a depth interval of 6,334 to 6,414 ft for an initial flow of 22 BOPD of 43.5 degrees API oil. This discovery was named the Kelly-Snyder field. Soon afterward, other operators discovered the Diamond "M" and Sharon Ridge Canyon fields to the south.

Development drilling revealed that the three fields merged to form one continuous reservoir. Subsequent development was rapid and essentially complete by Nov. 1951, when 1.617 producing wells had been drilled by 88 different operators. There was also extensive Canyon Reef development to the north of Kelly-Snyder in the Cogdell field, but early performance indicated that it was not connected.

The reservoir pressure declined by 50 percent after producing only 5 percent of the oil. This indicated that producing only 5 percent of the oil. This indicated that solution gas dove was the primary producing mechanism. It was apparent from the rapid pressure decline that a pressure-maintenance program would be required to prevent excessive loss of reserves. It was estimated that only 19 percent of the original oil in place could be recovered by primary depletion.

Unitization agreements in the Diamond "M" and Sharon Ridge Canyon fields were approved and water injection was initiated into Diamond "M" in late 1951. As a result of reservoir studies and information derived from the Diamond "M" project, the operators and royalty owners in the Kelly-Snyder field agreed to unitize to begin pressure maintenance.

In 1953, the Texas Railroad Commission approved formation of the SACROC (Scurry Area Canyon Reef Operators Committee) Unit, which encompasses about 98 percent of the Kelly-Snyder field. SACROC contains 49,895 acres. (There were 1,258 wells as of Jan. 1973.) The unit was first operated in three segments by Standard Oil of Texas (now a part of Chevron Oil Co.), Sun Oil Co., and Mobil Oil Corp. under a joint unit-manager's office. Chevron was elected operator for the entire SACROC Unit in May 1962.

Water injection in SACROC began in Sept. 1954 into 53 wells located along the longitudinal axis of the crest of the reef. This unique pattern is often referred to as the "center-line" waterflood at SACROC. To minimize migration, the SACROC operators established an injection-row "fence" of wells along the boundaries of Diamond "M."

JPT

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