A technical and economic evaluation of the applicability of the carbon dioxide immiscible process for heavy and medium oi1 recovery from Saskatchewan reservoirs has been performed.
A state of the art literature review on the CO2-heavy oil immiscible work, which includes displacement processes, laboratory pressure-volume-temperature (PVT) relationships, core displacement and scaled physical model studies, numerical simulation and the field test results is presented.
An economic analysis of the carbon dioxide immiscible recovery process, using reservoir and cost factors based upon the Lloydminster heavy oil area, has been carried out. The base case assumptions result in a total cost of $190 per produced cubic metre of oil. A sensitivity analysis investigating two main groups of variables--cast parameters and reservoir parameters--was performed. The results show that costs are relatively insensitive to formation thickness until thickness drops below three meters.
A reservoir screening study indicates that the CO2 immiscible flooding process could be applicable to most of the Saskatchewan heavy oil reservoirs. A reservoir pressure as low as 2.5 MPa and the existence of bottom water do not screen out the process.
The Lloydminster and Kindersley regions of Saskatchewan have a proven heavy oil resource of 1228 million cubic metres and a probable resource of 3400 million cubic metres. 1- 3 In addition to heavy oils, Saskatchewan has a proven medium oil resource of 397 mill ion cubic metres in the Swift Current region.! This vast resource presents a major economic opportunity for the Province of Saskatchewan and an important source of energy for Canada.
The heavy oil reservoirs are, however, characterized by thin pay, shaley sand, heterogeneity, low productivity and bottom water. 2–7 Primary and secondary methods together recover only about seven percent of the initial oil-in-place (IOIP). For the medium oi1 reservoirs, combined primary and secondary recovery averages about 23% of the IOIP. The development of appropriate enhanced oil recovery (EOR) techniques is, therefore, necessary in order to maximize the recovery potential of this resource.
Steam injection and in-situ combustion processes have been used for enhanced recovery of heavy oil from Saskatchewan reservoirs. Figure 1 presents a distribution of proven IOIP versus reservoir thickness which is a reworked version of lorsong's graphical tabulation of data8 collected from the Reservoir Annual 1984 published by Saskatchewan Energy and Mines. 9 This figure depicts several current thermal pilot projects as a function of net pay. It should be noted that all steamflooding pilots are in reservoirs having net pays of 10 m or greater. While steam injection has been successful for thicker reservoirs, usually greater than 15 m, it is expected that with technological advances this process may eventually be economically feasible for reservoirs which contain approximately 5% of proven initial oil-in-place.
Although in-situ combustion has been tested in the field for about twenty years, attempts are still being made to make it successful. Husky Oil Ltd. has shut down three in-situ combustion projects at their Golden Lake field.
