Oil Production in Shallow Reservoirs By Carbon Dioxide Injection

Abstract

ABSTRACT Currently there is a great deal of interest in carbon dioxide for the recovery of both heavy and light oils. This paper deals with the efficiency of gaseous carbon dioxide as a recovery agent for moderately viscous oils. The paper gives model results, and compares and contrasts the findings with laboratory and field test observations, pointing out the range of conditions over which carbon dioxide is likely to be effective. Also, the current status of carbon dioxide for light oils is considered. It was found that over the viscosity range of 1 to 1000 centipoises, carbon dioxide was superior to nitrogen injection, natural depletion, or waterflooding for oil viscosities above 70 cp. The gain over waterflooding was as much as 9 percentiles in oil recovery, being greater for the more viscous crudes. Oil saturation was an important variable as oil recovery decreased rapidly with a decrease in saturation. Another significant factor affecting ultimate oil recovery was the critical gas saturation. Viscous oils showed a 27% increase in recovery as the critical gas saturation varied from 0 to 10%. The blowdown recovery upon curtailment of carbon dioxide injection was about 1%; field values are as high as 4%. Reasons for this discrepancy are outlined. The amount of carbon dioxide left in the reservoir was used as a measure of the efficiency of the process; it was high for low oil saturations, especially for the more viscous oils. An economic analysis of the carbon dioxide injection process showed that the economics are tenuous; a variety of factors in addition to the oil price would determine the economic viability of the process.