Carbon dioxide injection, either by huff and puff or displacement operations, results in a crude oil viscosity reduction at pressures below the miscibility conditions. Carbon dioxide miscibility occurs in reservoirs at miscible temperature and pressure, but these conditions are not possible in shallow reservoirs. Improved oil recovery in a shallow reservoir depends on the degree of viscosity reduction at the reservoir temperature and pressure. A recovery project's success depends on the interaction between the carbon dioxide and the reservoir system.
A research project carried out at Montana Tech to study the viscosity reduction and carbon dioxide solubility in Cut Bank crude oil at the reservoir's prevailing temperature and near fracture pressure shows a viscosity reduction ratio (crude-carbon dioxide mixture to original dead oil viscosity) of 0.22 at a pressure of 1000 psig and 90°F. An original mobility of 2 0 Md/cp improves to 91 Md/cp under a carbon dioxide recovery process at or near the reservoir's fracture pressure.
Based on our research, improved oil recovery operations in the Cut Bank Field, Montana, is viable when using a commercial on site carbon dioxide recovery or generating system to minimize the cost of CO2transportation. The major benefits ar oil viscosity reduction, mobility ratio improvement, gas drive, and crude oil swelling.