This paper summarizes the response from foam injection in a pilot test conducted at the East Vacuum Grayburg/San Andres Unit (EVGSAU), including results of the reservoir characterization effort and an extensive monitoring program. The paper specifically presents (1) the positive injection-well response (documented with injectivity data and profile logs), (2) the positive production-well response, and (3) the economics of the foam test.
A pilot pattern (Fig. 1) in the EVGSAU, operated by Phillips Petroleum Co., was selected for a comprehensive evaluation of the use of foam for improving the effectiveness of a CO2 flood. This 4-year field trial was jointly funded by the EVGSAU working-interest owners, the U.S. Dept. of Energy (DOE), and the State of New Mexico. The Petroleum Recovery Research Center (PRRC), a division of the New Mexico Inst. of Mining & Technology, provided laboratory and research support.
Although the overall CO2 project performance at EVGSAU has been very encouraging, certain wells/patterns have shown anomalously high CO2 production. This has resulted in isolated cases of poor pattern sweep efficiency, inefficient CO2 utilization, and increased recycling costs and compression requirements. We suspected that these problems resulted from channeling of injected fluids through high-permeability zones, most likely exacerbated by dissolution of anhydrite in these zones.
The goal of the field trial was to investigate foam for conformance control to aid in suppressing this rapid CO2 breakthrough. Foam may improve injection conformance in two directions: (1) in a horizontal direction by increasing areal sweep efficiency and 2) in a vertical direction by diverting fluids to other, underinjected zones. Specifically, the prime directive of the trial was to prove that a foam could be generated and that it could change the mobility of CO2 in the reservoir. Proving or even determining economics or optimizing the size of the foam slug, while important, was not the original goal.
A geologic study delineated the major flow units and identified high-permeability layers that were channeling CO2 to a producing well in the pilot pattern. Production and injection logs were run in the producer and the injector and confirmed the channel. Laboratory work was performed at three different laboratories to determine which surfactant was most compatible with EVGSAU reservoir rock and fluids. Refs. 3 through 6 give details of that laboratory work, and Ref. 7 summarizes the work.