Heavy Oil Production 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 an investigation of the efficiency of gaseous carbon dioxide as a recovery agent for moderately viscous oils. The paper gives numerical 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. The carbon dioxide injection simulator used simulates three- phase flow, and was checked out for numerical dispersion grid effects, material balance, etc. It was then employed for a variety of carbon dioxide injection simulations. The base cases were in qualitative agreement with the reported experimental data. It was found that over the viscosity range of J 10 1000 mPa.s, carbon dioxide was superior to natural depletion, inert gas injection or water flooding, jar oil viscosities above 70 mPa. s. The gain over water flooding was as much as 9 per cell· tiles 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 blow down recovery on curtailment 0/ carbon dioxide injection was about 1 percentile; field values are as high as 4 percentiles. 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. Introduction Although there is little debate that a significant amount of oil remains held in the ground by current technical and economic constraints, opinion is widespread as to the proper recovery technique or techniques to unlock these reserves. (Infill drilling and a handful of alternative recovery methods, such as thermal, miscible and improved mobility floods, compete for the over 52 billion cubic metres of United States and Canadian oil (<980 Kg/m3) that remains in place. Carbon dioxide injection, as one of these processes, has long been thought of as a miscible process best applied in light oils with densities less than 930 Kg/m3. However, immiscible carbon dioxide flooding as part of the suite of enhanced oil recovery methods being tested may be promising in the case of heavy, moderately viscous oils where carbon dioxide injection improves recovery by lowering oil viscosity and promoting swelling. Deposits of heavy oil total over one-half trillion metres3 in the U.S., Venezuela and Canada. In the U.S. alone, there are over 2,000 heavy oil reservoirs occurring in 1500 fields in 26 states.