LABORATORY EXPERIMENTS AND RESERVOIR SIMULATION STUDIES IN SUPPORT OFCO2 INJECTION PROJECT IN MATTOON FIELD, ILLINOIS, USA

This paper describes the results of rock and fluid property measuremen ts and of the reservoir simulations associated with the demonstration of CO2-assisted oil recovery in the Cypress Sandstone reservoirs at Ma ttoon Field, Illinois. This work provided technical support for the fi eld project. Results from core flood tests indicate that oil recovery from immiscible displacement of reservoir crude oil with carbon dioxid e will increase with displacement pressure. Miscible displace ment of oil with CO2 from the Cypress Sandstone reservoirs at Mattoon field is not possible. As shown by the slim-tube experiments, the minimum misc ibility pressure (MMP) of Mattoon oil is close to the formation partin g pressure of the Cypress Sandstone at Mattoon field. Nevertheless, ph ase behaviour experiments show that dissolved CO2 significantly enhanc ed oil recovery through oil swelling and viscosity reduction at pressu res below miscibility conditions. Numerical simulations of CO2 injecti on into various reservoirs within the Sandstone were performed. A stra ight CO2-injection program and a water alternating gas (WAG) injection program were simulated and compared in both the A-sandstone of the Pi nnell Unit and E-sandstone interval of the Sawyer Unit. In the Pinnell Unit, the simulated results show an inefficient displacement of reser voir oil by CO2 and that neither of the two methods will be economical ly feasible because of the poor interwell communication and limited ar eal extent of the producing interval. This result is supported by the low oil recovery from the field CO2 injectivity tests in the Pinnell U nit. On the contrary, simulated results show that a significant amount of additional oil can be produced from the Sawyer Unit. The water-alt ernating-gas (WAG) injection program yielded more oil than water injec tion alone. The simulated results also indicate strategically-placed n ew wells will enhance the recovery of additional oil.