Correlation between sandstone permeability and capillary pressure curves

The effective permeability in a hydrocarbon pay zone is normally estimated based on well pressure transient test. If well test data is not available, permeability normally comes from measurements on core plugs. Correlations between core plugs and well logs can be used to estimate permeability in uncored intervals. In cases where the direct measurement of permeability is not available, capillary pressure curves measured from small rock samples, such as portions of sidewall core samples or drill cuttings, can be used for estimating rock permeability. Swanson's parameter (S-nw/P-c)(A) has traditionally been utilized to estimate permeability from capillary pressure Curves. Different correlations between permeability and the Swanson's parameter have been found in literature for sandstone cores with permeabilities ranging from 23 to 1150 md and sandstone cores with permeabilities between 0.002 and 0.1 md. A new parameter called Capillary Parachor (S-nw/P-c(2))(max) was derived in this study, and excellent correlations between permeability and the capillary parachor have been found. Mercury-air and air-water capillary pressure curves were used to develop the correlations. Core permeability was found to be proportional to the mercury-air capillary parachor with a proportionalinity factor equal to 0.054. The permeability is proportional to the air-water capillary parachor squared with a proportionalinity factor of 0.00007. Analytical methods were developed to determine Swanson's parameter and capillary parachor for hyperbola-shaped capillary pressure curves. (C) 2004 Elsevier B.V. All rights reserved.