Improved Determination of Stress-Dependent Permeability for Anisotropic Formations

摘要

Qualitative determination of formation permeability is oftenrnobtained through laboratory flow tests on core plugs.rnHowever, the experimental determination of the permeabilityrnfor anisotropic plugs (particularly the horizontal permeability)rnis difficult and less than perfect; generally relying on a highlyrnsimplified Darcy flow analysis. Numerical analyses couldrngreatly improve the resolution, reduce the testing costs, andrnallow parametric investigations using sophisticated 3-Drnformulations. This paper reports such an analysis thatrninterprets the analytical Darcy flow-pressure measurements,rnusing numerical results to provide a “geometric factor”. Arnnumerical iterative procedure correlates the core plugrnmeasured flow and pressures at the inlet and outlet boundariesrnfor different boundary sources to derive the core plugrnanisotropic permeabilities. Since stress changes generallyrninfluence permeability, a conceptual model is developed—rnagain via an iterative numerical method—that accounts for therneffects of the solid deformations. From this, numericalrnschemes have been developed using “equivalent geometricrnfactors” with embedded mechanisms for modifying core plugrnpermeability based on the changes in the solid strains thatrnsimulate the coupled flow-deformation behavior of selectedrnreservoir rocks. This is the first detailed 3-D numericalrnanalysis iterative scheme that practically allows realisticrndetermination of permeabilities in anisotropic core plugs.