Improved Determination of Stress-Dependent Permeability for Anisotropic Formation
M. Bai, TerraTek; F. Meng, SPE, Advantek International; J.-C. Roegiers,
SPE, The University of Oklahoma; S. Green, TerraTek
This paper was presented at the SPE/ISRM OilRock'02
Conference held in Dallas, Texas, 20-23 October 2002,
Copyright
2002, Society of Petroleum Engineers Inc.
Abstract
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.
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