Abstract

Although convective heat flux is neglected in classic steam-assisted gravity-drainage (SAGD) models such as the one derived by Butler, heat convection through the condensate flow into porous media can be very important. A key control on the condensate flow is the in-situ relative-permeability to water within the reservoir. To date there is no methodology that can calculate the in-situ relative-permeability to water in SAGD reservoirs during steam injection and progression of the steam chamber. The in-situ relative-permeability to water during steam injection can be different from laboratory and well-test results. The problem with the results from lab test is that they are mostly from disturbed cores or remolded samples. And the issue with results from both lab and well testing is that at the edge of the steam chamber, bitumen undergoes thermal expansion of some 15%; therefore, unless the water saturation increases by a similar amount, water mobility is quickly decreased by the expanding bitumen phase. A method is provided to calculate in-situ relative-permeability in oil sand reservoirs using the distance between pressure and temperature response at the same depth. The implementation of the concepts is tested for Underground Test Facility (UTF) project. The results suggest that the in-situ relative-permeability to water during steam in most SAGD projects is limited to 10-4 to 10-5 and having higher relative permeabilities is only possible at lean zones. This paper describes a new method for reservoir characterization based on water mobility for different oil sand projects.

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