A diagnostic approach to quantifying the stress sensitivity of permeability

Abstract

The sensitivity of core intergranular permeability to applied hydrostatic stress has been quantified through third-order polynomial fits to data from three loosely-to-moderately-consolidated sandstone formations from the same geological system. The derivatives of the fitted polynomials have allowed diverse permeability vs. stress behaviours to be identified and grouped as “stress facies”. This grouping is quantified using a composite stress-sensitivity parameter based on those polynomial regression constants that are retained during differentiation, in this case their root mean square. This composite parameter shows a sufficiently good correspondence to Leverett's equivalent circular pore diameter L p to define distinctive stress facies in terms of ranges of L p in these formations. A permeability-reduction factor from ambient conditions to effective reservoir stress is determined for each stress facies as a basis for correcting conventional core measurements. For a given formation, the resulting stress-corrected permeability data are more reliable than they would have been without any data partitioning. Although the results are formation- and stress-facies-specific, they are not exclusive: the approach has a more general validity and can be adopted for any appropriate permeability vs. stress function. Principal benefits include better reservoir characterisation and a sharper description of the change in permeability with stress as a basis for improved simulation models for development planning.