Simulation of Gas/Oil Gravity Drainage in a Stack of Interacting Blocks: Pseudo Relations for a Limited Number of Gridblocks

摘要

Naturally fractured carbonate fields contain a large portion ofrnthe world’s light oil reserves. A number of these fields whichrnare produced by gas/oil gravity drainage contain severalrnbillion barrels of oil.rnTo simulate naturally pervasively fractured fields, dualpermeabilityrnsimulation programs are used. To achievernreasonable simulation times for huge fields, the number ofrngridblocks has to be restricted. However, reducing the numberrnof gridblocks in vertical direction in a draining matrix columnrnin gas/oil gravity drainage simulations lead to systematicrnunderestimation of the oil drainage rate.rnThe simulation error due to limited number of gridblocks canrnbe quantified. Knowing the error, the error can be corrected byrnmodifying the (input) relation that links the oil drainage rate ofrna gridblock to its (average) oil saturation.rnIn this article, a procedure is presented to arrive at (pseudo)rnrelative permeability relations for gridblocks in gas/oil gravityrndrainage simulations. By assigning to each gridblock in arnstack a different pseudo relative permeability relationrndepending on its position in the stack, it is possible to largelyrnreduce and in some cases completely remove the simulationrnerror. This procedure enables using a very limited number ofrngridblocks in the vertical direction (in the extreme case onlyrnone gridblock).