Comparative effectiveness of CO2 produced gas, and flue gas for enhanced heavy-oil recovery

A large number of heavy oil reservoirs in Canada and in other parts of the world are thin and marginal and thus unsuited for thermal recovery methods. Immiscible gas displacement appears to be a very promising enhanced oil re covery technique for these reservoirs. This paper discusses results of a la boratory investigation, including pressure/volume/temperature (PVT) studies and coreflood experiments, for assessing the suitability and effectiveness of three injection gases for heavy-oil recovery. The gases investigated we re a flue gas (containing 15 mol % CO2 in N-2), a produced gas (containing 15 mol % CO2 in CH4), and pure CO2. The test heavy-oil (14 degrees API grav ity) was collected from Senlac reservoir located in the Lloydminster area, Saskatchewan, Canada. PVT studies indicated that the important mechanism for Senlac oil recovery by gas injection was mainly oil viscosity reduction. Pure CO2, appeared to be the best recovery agent, followed by the produced gas. The coreflood res ults confirmed these findings. Nevertheless, produced gas and hue gas could be sufficiently effective flooding agents. Comparable oil recoveries in fl ue gas or produced gas runs were believed to be a combined result of two co mpeting mechanisms-a free-gas mechanism provided by Na or CH4 and a solubil ization mechanism provided by CO2. This latter predominates in CO2 floods.