--> Interpreting Permeability From Mercury Injection Capillary Pressure Data
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Interpreting Previous HitPermeabilityNext Hit From Mercury Injection Capillary Pressure Data

Abstract

Laminar flow theory predicts a strong correlation between Previous HitpermeabilityNext Hit and pore-throat distribution as revealed by Mercury Injection Capillary Pressure (MICP) data. Previous studies have developed relationships between MICP data and Previous HitpermeabilityNext Hit; however, the permeabilities predicted by different methods can differ substantially from the measured permeabilities and from each other, especially in low Previous HitpermeabilityNext Hit samples of interest for unconventional reservoirs. The purposes of this study are to evaluate why there is such large scatter, identify algorithms that best predict Previous HitpermeabilityNext Hit over a wide range of permeabilities, and evaluate what type of Previous HitpermeabilityNext Hit is actually measured by MICP data. Precision of Previous HitpermeabilityNext Hit predictions is low due to insufficient MICP pressure measurements, assumption of MICP curve shape, Previous HitpermeabilityNext Hit anisotropy of geological samples, and low precision and accuracy of Previous HitpermeabilityNext Hit measurement of tight rocks. Four methods for estimating Previous HitpermeabilityNext Hit from MICP data are found to have small bias and reasonable precision over a wide range of Previous HitpermeabilityNext Hit: the modified Purcell, the Katz-Thompson Lc, Katz-Thompson Lh, and the Swanson methods. A weighted average of these Previous HitpermeabilityNext Hit estimates corrects for accuracy problems and increases Previous HitpermeabilityNext Hit estimate precision. However, this MICP-predicted average Previous HitpermeabilityNext Hit still varies from measured Klinkenberg-corrected steady Previous HitpermeabilityNext Hit by an average of a factor of 2. This mismatch may be more apparent than real. Restoring reservoir stress prior to conventional Previous HitpermeabilityNext Hit measurement fails to remove completely the core damage caused by microfractures created during extraction, preparation, and storage of tight rock samples from deep boreholes. MICP permeabilities are estimated from the pore-throat distributions, which do not include the significant flow contributions from microfractures. Difference between MICP Previous HitpermeabilityNext Hit estimates and measured Previous HitpermeabilityNext Hit of tight samples may be caused by the inability of conventional Previous HitpermeabilityNext Hit analysis to remove damage effects by stress restoration. If so, MICP Previous HitpermeabilityNext Hit estimates are as good as or better than Previous HitpermeabilityNext Hit measured from tight, subsurface samples. MICP Previous HitpermeabilityNext Hit is either the ambient matrix Previous HitpermeabilityNext Hit or a stressed matrix Previous HitpermeabilityTop, depending on the relative magnitude of in situ reservoir stress and Hg pressure at threshold saturation.