Enhanced heavy oil recovery after solution gas drive by water flooding

Some heavy oil reservoirs in Canada and Venezuela show anomalous behavior under solution gas drive. However, although foamy oil can improve the performance of solution gas drive in heavy oil, only approximately 5-15% OOIP can be recovered during primary production. In this study, micromodel flood experiments and sandpack flood tests were performed to evaluate the potential of water flooding to enhance the recovery of heavy oil after solution gas drive. The micromodel test indicates connected gas channels were created in the micromodel when the pressure was lower than the pseudo-bubblepoint pressure during the solution gas drive; the injected water moves initially through low-viscosity gas channels and through the micromodel during subsequent water flooding. A large number of gas bubbles were found to be dispersed in the oil at the end of the solution gas drive. Heavy oil with dispersed gas bubbles was driven by injected water, forming a flow where water displaced the foamy oil present. The sandpack tests results show that the performance of the subsequent water flooding was significantly affected by the conversion pressure. The conversion pressure was the pressure at the end of the solution gas drive, and the subsequent water flooding was conducted when the pressure was reduced to the conversion pressure after solution gas drive. As the conversion pressure decreasing, the oil recovery of the solution gas drive increased, and the oil recovery of the subsequent water flooding decreased. The optimum conversion pressure of water flooding was found to be the pseudo-bubblepoint pressure. For the water flooding with the convertion pressure lower than the pseudo-bubblepoint pressure, most oil was produced in the high water cut period. Water imbibition caused by capillary forces was the main mechanism leading to the recovery of heavy oil at the high water cut period. The effect of water imbibition on the recovery was more significant at lower injection rate, leading to the higher recovery.