David H. Crockett, Chevron Oil Company
The Kelly Snyder field is located in Scurry County, Texas, as shown on Fig. 1. This field is one of the major oil reservoirs in the United States. After discovery in 1948, the field was produced by solution gas drive until 1954 when a recommendation by the Scurry Area Canyon Reef Operators" Committee was implemented. The recommendation was to install a centerline water injection program to restore and maintain reservoir pressure above the bubble point. In March 1953 the SACROC Unit was formed and the proposed injection program was started in September 1954. Although this water injection program worked quite well, SACROC owners continued to look for ways to further improve recovery from the reservoir. In 1968, after careful study of several possible miscible displacement processes, a SACROC reservoir engineering committee recommended a miscible carbon dioxide injection program for the Unit to increase the ultimate recovery from the reservoir. The next three years were required to prepare for the carbon dioxide injection. The field was divided into 202 inverted nine-spot pattern areas and three phase areas which would be processed with CO2 on a separate time schedule consistent with the CO2 supply, as shown in Fig. 2. To commence injection it was necessary to install compression facilities and a CO, pipeline to transport 200,000 MCF/D of CO2 from several extraction plants in the Val Verde Basin area of southwest Texas and to prepare the Phase I area for injection by installing a field injection system, exposing the entire reef in the producers, and preparing the pattern injectors for injection. With the work completed, CO,injection began in January 1972. Downhole injection surveys were run frequently during the early life of the project, and poor profile coverage was discovered in many of the injectors. The problem became very critical when CO, breakthrough occurred during June 1972, more than a year before the CO2 removal facilities were complete, requiring curtailment of production. It became evident that correction of these poor profiles was necessary to avoid cycling the expensive CO2 and to avoid further production curtailments due to CO2 breakthrough. Since several methods are available for improving injection well profiles, the Unit Operator tested and evaluated several different methods. Open-hole packers were installed in several wells, but frequent failures occurred due to packer movement or CO, permeation of the packer rubber. Several types of polymer profile improvement jobs were performed with little success. The only control method which has proven to be consistently effective for controlling downhole injection profiles is the installation of a liner across the reef, followed by the installation of downhole flow control equipment.