Patent ID: 7634395

Claim:
A computer implemented method of generating in three dimensions a hybrid grid of a hydrocarbon reservoir crossed by at least one geologic geometric discontinuity for forming a model representative of fluid flows in the hydrocarbon reservoir in accordance with a numerical scheme, comprising: forming at least a first structured grid for gridding at least part of the hydrocarbon reservoir; forming at least a second structured grid for gridding at least part of the at least one geologic geometric discontinuity; providing a transition grid between the structured grids; using a computer for forming at least one cavity around the second grid so that cells of the transition grid providing a transition between the structured grids have an intermediate size between a size of cells of the first grid and a size of cells of the second grid, from the following steps: expanding the geologic geometric discontinuity using a local expansion coefficient α defined as a function of drainage radius r of the geologic geometric discontinuity, a local size δ reservoir of the cells of the first structured grid and a local size δ well of the cells of the second structured grid, wherein α is defined as: α = 1 + δ well + δ resevoir r determining cells of the first grid that intersect an image of the expanded geologic geometric discontinuity; defining a boundary of the at least one cavity by assigning sites to quadrilaterals bordering the cavity; forming the transition grid resting on the quadrilaterals bordering the at least one cavity by constructing a regular triangulation with respect to at least one constraint of admissibility constraints in a numerical scheme comprising conformity, convexity, orthogonality and self-centering of the cells; and optimizing the hybrid grid obtained by performing at least one of eliminating edges of a size below a value depending on at least one global parameter and on at least one local parameter and by eliminating and/or expanding the edges under control of quality criteria of the numerical scheme to change shape regularity of the hybrid grid; and displacing sites of the at least one cavity towards a center of mass thereof under control of quality criteria related to the numerical scheme.