Kimberly B. Dollens, SPE, Phillips Petroleum Company, James C. Shoumaker, SPE, Phillips Petroleum Company, Burl W. Wylie, SPE, Cardinal Surveys Company, Phil Rice, SPE, Halliburton Energy Services, and Orjan Johannessen, SPE, Phillips Petroleum Company
Abstract
Two different methodologies were employed in obtaining injection profile surveys in two CO2 water-alternating-gas (WAG) horizontal injection wells in the South Cowden Unit (SCU) CO2 project. Both methods were used once during an initial water injection period to establish a baseline profile. Then, the first method was utilized on both of the horizontal injection wells during a CO2 injection period. The first method utilized a coiled tubing conveyed, memory-based logging system, including a correlation gamma ray and collar locator log; injection and shut-in temperature, capacitance, flowmeter and pressure gradient; and interface tag. The second method utilized a logging and injection program wherein coiled tubing and wireline were run in the injection well with a Y-block and coiled tubing side-entry assembly attached to the coiled tubing below the spot valve. The tool consisted of a positive and negative gamma ray and temperature tool, and utilized a slug of more than one gallon of radioactive gel rather than the standard injection volume of approximately 50 cc or 1 cc per station. Actual field results are reviewed. and the two methodologies discussed for application in CO2 WAG horizontal injection systems.
Introduction
The South Cowden Unit (SCU) is the site selected for one of three mid-term projects being conducted under the DOE Class II Oil Program for Shallow Shelf Carbonate Reservoirs. The project is being funded to demonstrate the technical and economic viability of an innovative CO2 flood project development approach, which utilizes horizontal water-alternating-gas (WAG) injection wells for centralization of production/injection facilities. The application of horizontal wells in South Cowden has reduced overall drilling and CO2 distribution costs, and is considered a key factor in the economic success of this project.
Figure 1 is a map of the Unit area indicating the location of the two horizontal injection wells. The drilling and completion operation for the horizontal CO2 WAG injector 6C-25H (the east well) began March 17, 1996 and was completed in 28 days. The drilling and completion operations for the horizontal WAG injection well 7C-11H (the northwest well) began April 14, 1996, and was completed in 24 days. The CO2 WAG injection well trajectories were planned to optimize reservoir performance, maximize sweep efficiency, and optimize injectivity performance. The wells were designed mechanically to optimize well injection performance and maximize the duration of their utility. Both wells were equipped with 9-5/8", 36 ppf, J-55 surface casing; 7", 20 ppf, J-55 production casing through the curve; and a 6-1/8" openhole injection interval. The production casing was sized at 7" to accommodate 3-1/2" production tubing. The 20 ppf casing weight was utilized for additional corrosion wear allowables rather than for withstanding the bottomhole pressures to be encountered during injection. The cased curve trajectory was designed to accommodate 125' of production casing within the San Andres producing interval. This was done to maximize packer setting depths while minimizing corrosion exposure of casing below the injection packer during workovers.
In order to maximize injection rates and volumes. 3-1/2" injection tubing was utilized. The entire downhole injection system was designed to resist the corrosive effects of CO2 injection alternating with water injection. P. 647^
