SPE Members
Abstract
A DOE-sponsored field test of the cycle CO2 injection process was conducted by members of Louisiana State University's Petroleum Engineering Department in conjunction with an independent operator. The test well was the Frank J. Bollich, et al. No. 5, located in Acadia Parish, Louisiana, and operated by Southwest Gas Producing, Inc. The well was drilled in December, 1987, and completed in the 4500 ft. Channel Sand of the Bayou Mallet Field. This reservoir has a 17 ft. oil zone overlying an 83 ft. water zone. Prior to CO2 injection, the well was producing on a pump at a rate of 17 BOPD and 160 BWPD.
Approximately 120 tons CO2 were injected into the well on July 1, 1991. After injection, the well was shut-in for a soak period, and production was resumed on July 29, 1991. The well produced only gas for three days, then production ceased and the well was placed on a pump. Fluid production has been impaired due to the formation of a CO2, oil, water foam/emulsion. Current production is 15 bbl fluid per day, with 10 STB oil and 5 bbl water.
Air emissions were monitored during CO2 injection and production. Atmospheric CO2 levels were elevated for only a short period of time during CO2 injection and during the first two days of production. After the second day of production, atmospheric CO2 levels returned to pre-test concentrations.
Introduction
Cyclic CO2 injection (or CO2 huff ‘n’ puff) was initially proposed as an alternative to cyclic steam stimulation for the recovery of heavy crude. Since 1984, the process has been applied to the recovery of light oil with encouraging results. The cyclic CO2 injection process has been investigated using laboratory corefloods, numerical simulation, and field tests.
Laboratory coreflood results indicate that overall process performance is adequate at near-miscible and immiscible conditions, but poor at miscible conditions. Process performance was benefitted by an initial gas saturation, larger CO2 slugs, gravity segregations, and water-in flux. A second cycle of CO2 injection recovered additional oil, but a decline in process performance was noted, and a soak period was required to maximize oil recovery. Computer simulations of the process indicate that the principal recovery mechanisms are oil swelling, oil viscosity reduction, and relative permeability alterations. Field tests have demonstrated that the process may be successfully implemented under diverse reservoir conditions, is economically feasible at moderate oil prices, and has a minimal impact on the environment.
State and federal agencies have been concerned since few EOR projects have been implemented in the State of Louisiana, and state oil reserves are being lost due to well closures. The scarcity of EOR projects can be attributed to financial and geological considerations. A majority of the state oil reserves are controlled by small oil companies with limited financial resources.
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