A large number of heavy oil reservoirs in Alberta and Saskatchewan are thin and marginal and thus unsuited for thermal recovery methods. For these reservoirs, immiscible gas displacement appears to be a very promising enhanced oil recovery technique for these heavy oil reservoirs. This process, if proven applicable, will access 90% of Saskatchewan's initial-oil-inplace. This paper discusses results of a laboratory investigation for assessing the suitability and effectiveness of three injection gases for heavy oil recovery. The gases investigated were a flue gas (containing 15 mol% CO2 in N2), a produced gas (containing 15 mol% CO2 in CH4), and pure CO2. The test heavy oil (14° API gravity) was collected from Senlac reservoir located in the Lloydminster area. The evaluation was based on PVT studies, coreflood experiments, scaled model tests, and numerical simulations. In this paper, the focus is on the first two.

PVT studies indicated that the important mechanisms for Senlac oil recovery by gas injection were oil viscosity reduction and oil swelling. Pure CO2 appeared to be the best recovery agent, followed by the produced gas. The coreflood results confirmed these findings. Nevertheless, produced gas and flue gas could be sufficiently effective flooding agents. They showed oil recoveries only 2 to 4 percentage points lower than those obtained with pure CO2 (exceeding 45% initial oil-in-place). Comparable oil recoveries in flue gas or produced gas runs were believed to be a combined result of two competing mechanisms – a free gas mechanism provided by N2 or CH4 and a solubilization mechanism provided by CO2. This latter predominates in CO2 floods.

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