Improved Determination of Stress-Dependent Permeability for Anisotropic Formations

M. Bai; F. Meng; J.-C. Roegiers; S. Green
Presented at SPE/ISRM Rock Mechanics Conference, Irving, Texas, October 2002.


Qualitative determination of formation permeability is often obtained through laboratory flow tests on core plugs. However, the experimental determination of the permeability for anisotropic plugs (particularly the horizontal permeability) is difficult and less than perfect; generally relying on a highly simplified Darcy flow analysis. Numerical analyses could greatly improve the resolution, reduce the testing costs, and allow parametric investigations using sophisticated 3-D formulations. This paper reports such an analysis that interprets the analytical Darcy flow-pressure measurements, using numerical results to provide a “geometric factor”. A numerical iterative procedure correlates the core plug measured flow and pressures at the inlet and outlet boundaries for different boundary sources to derive the core plug anisotropic permeabilities. Since stress changes generally influence permeability, a conceptual model is developed – again via an iterative numerical method – that accounts for the effects of the solid deformations. From this, numerical schemes have been developed using “equivalent geometric factors” with embedded mechanisms for modifying core plug permeability based on the changes in the solid strains that simulate the coupled flow-deformation behavior of selected reservoir rocks.This is the first detailed 3-D numerical analysis iterative scheme that practically allows realistic determination of permeabilities in anisotropic core plugs.