Review of an Immiscible CO2 Project, Tar Zone, Fault Block V, Wilmington Field, California
- Allan Spivak (Allan Spivak PhD Inc.) | William H. Garrison (Long Beach Oil Development Co.) | John P. Nguyen (Long Beach Oil Development Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- May 1990
- Document Type
- Journal Paper
- 155 - 162
- 1990. Society of Petroleum Engineers
- 5.4.2 Gas Injection Methods, 5.2 Reservoir Fluid Dynamics, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.1.5 Processing Equipment, 4.3.4 Scale, 5.1.1 Exploration, Development, Structural Geology, 2.4.3 Sand/Solids Control, 5.4 Enhanced Recovery, 4.1.2 Separation and Treating, 5.3.4 Reduction of Residual Oil Saturation, 5.4.10 Microbial Methods, 6.5.2 Water use, produced water discharge and disposal, 5.8.5 Oil Sand, Oil Shale, Bitumen, 5.8.7 Carbonate Reservoir, 4.1.9 Tanks and storage systems, 5.4.1 Waterflooding, 5.2.1 Phase Behavior and PVT Measurements
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The Long Beach Oil Development Co. (LBOD) tertiary immiscible CO2 project began in March 1982 with the injection of a mixture of about 85% CO2/15% N2 into the Tar zone of Fault Block V in the Wilmington field, Los Angeles County, CA. The 330-acre [134-ha] project had been waterflooded since 1961, and the water cut was more than 95%. Gas was injected alternately with water for a period of about 5 years. This paper reviews project performance from inception to the end of 1987.
The Wilmington field, a major producing oil field in the Los Angeles basin, produces from seven zones at depths ranging from 2,000 to 7,000 ft [610 to 2134 m]. The Wilmington structure is a broad, asymmetrical anticline, broken by a series of transverse faults. The Tar zone, the uppermost producing zone, consists of a series of loosely consolidated sands with gross thickness ranging from 250 to 400 ft [76 to 122 m]. The Tar V CO2 injection project was begun in March 1982 to demonstrate the application of immiscible CO2 displacement as a tertiary recovery mechanism. The project area had been under waterflood since 1961. Table 1 gives basic reservoir data. The injected gas was not pure CO2, but an 85% CO2/15% N2 mixture. The gas source was stack gas from hydrogen-generation units at Texaco Inc.'s Wilmington Refinery in Los Angeles. Refs. 1 and 2 describe the transmission facilities from the refinery to the field. Ref. 3 describes the field surface facilities. All produced gas was compressed and reinjected. From the start of gas injection in March 1982 until the termination of gas purchase in Aug. 1986, 8.22 Bscf [233x 10-6 std m3] of gas was purchased and injected. Recycling of produced gas was continued after purchase of new gas was terminated.
Background on Immiscible CO2 Flooding in Heavy Oils
Several examples exist of the use of CO2 for immiscible flooding in heavy oils. U.S. Oil and Refining Co. conducted immiscible CO2 injection in the Ritchie field, Union County, AR, in 1969. In 1976, Phillips Petroleum Co. injected CO2 in the Lick Creek field, AR. Champlin Petroleum conducted a pilot project of immiscible CO2 injection in the Tar zone, Fault Block III of the Wilmington field, CA. in 1981. In 1982, Aminoil conducted CO2 huff `n' puff operations in the Huntington Beach field, CA. In 1986, Turkish Petroleum Corp. began conducting immiscible CO2 injection operations in the Bati Raman field, Turkey. As is often the case with EOR processes in the early years of field testing, the results of these projects are generally inconclusive.
The immiscible CO2 process is basically one in which CO2 dissolving in heavy oil reduces oil viscosity. In the case of an immiscible water-alternating-gas (WAG) process, CO2 and water are injected alternately until a certain predetermined amount of CO2 is injected, and then water is injected continuously. The subsequent water injection drives the reduced-viscosity oil, resulting in a water-flood with an improved mobility ratio. Additional recovery over waterflooding without CO2 results. For the Wilmington Tar V crude oil, laboratory measurements demonstrated that oil viscosity could be reduced by a factor of about 10 by saturation with CO2. In addition to reducing viscosity, the dissolved CO2 also swells the oil, so for a given fixed residual oil saturation (ROS), less stock-tank oil remains behind a waterflood. According to laboratory-measured swelling data, the effect of viscosity reduction is almost an order of magnitude greater than the effect of swelling. Ref. 10 discusses some of the mechanisms of the process as applied in the LBOD project. In this project, the presence of N2 is a complicating factor. On one hand, the N2 reduces the solubility of CO2 in the oil approximately according to the law of partial pressures (i.e., at a given pressure for x mol% N2 in the CO2/N2 mixture, the CO2 solubility in oil is reduced by about x%). On the other hand, the presence of N2, which is essentially insoluble in oil, results in trapping of free N2 by the injected water, which, in turn, can result in a lower residual oil to water. In addition to viscosity reduction and swelling, an additional mechanism can be described simply as the alteration of relative permeability characteristics in a manner that results in improved oil displacement characteristics. Khatib et al give background on early laboratory work and field tests that used CO2 to augment immiscible displacement of oil. They allude to the additional mechanism of relative permeability alteration and point out that this effect was observed in laboratory work more than 30 years ago.
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