Patent ID: 8073663

Claim:
A non-transient computer-readable medium storing instructions for performing a method for modeling the migration of reactant in a subsurface petroleum system, the method comprising: generating a mesh for a region of said petroleum system, the mesh comprising a plurality of elements, each element representing an enclosed volume and comprising a plurality of nodes, and each node representing a point in space in the region; calculating one or more variables representing one or more physical characteristics at each node in the region; and determining the migration of reactant in the petroleum system based on the one or more variables, wherein at least some of the nodes of the plurality of nodes are not spaced according to a three-dimensional orthogonal grid; the step of calculating one or more variables representing one or more physical characteristics at each node comprises at least: calculating densities and interfacial tension (â€œIFIâ€) for a node; computing back pressure for an element containing the node; computing capillary threshold pressure difference for the node; and computing maximum depth of reactant below the node; and wherein the back-pressure for an element is equal to the excess hydrostatic pressure in the element plus the reactant pressure in the element, where the reactant pressure in an element under review is calculated at each node of said element under review by: P node = âˆ« meniscus node â¢ G â¡ ( Ï water - Ï reactant ) â¢ â¢ â…† z where â€˜Gâ€™ is the gravitational acceleration in Newton's/kilogram, Ï water is the density of water and Ï reactant is the density of reactant in kilograms/cubic meter, and â€˜zâ€™ is integrated in meters between the depth of a water to reactant meniscus and the node depth.