CO2 huff and puff for heavy oil recovery after primary production

In this study, micromodel tests were performed to investigate the microscopic flow behavior during primary production and the subsequent CO2 huff and puff. A series of 12 tests was conducted in sandpacks to evaluate the effects of the injection and production parameters on the displacement efficiency of the CO2 huff and puff. The micromodel tests and sandpack tests showed that the flow characteristics of CO2 huff-and-puff process was significantly affected by the pressure of converting the solution gas drive to the subsequent CO2 huff and puff. A foamy oil flow could be more easily formed in the production period of the CO2 huff and puff with a higher conversion pressure. Foamy oil can reduce the mobility of gas and provide tremendous energy to the system, thereby improving the performance of the CO2 huff and puff. The sandpack flood results show that the oil recovery of the solution gas drive decreased as the conversion pressure increased, whereas the oil recovery of the CO2 huff and puff increased as the conversion pressure increased. The highest total oil recovery was obtained at the pseudo-bubblepoint pressure. The oil recovery of the CO2 huff and puff increased as the CO2 injection pressure and pressure decline rate increased. The oil recovery of CO2 huff and puff increased with the soaking time, and it exhibits a significant change when the soaking time ranges from 10 h to 24 h; above this value, the increase become slight. (c) 2015 Society of Chemical Industry and John Wiley & Sons, Ltd