Interplay between permeability and compressibility in shale samples

Abstract

In this study, we present a new approach to evaluate shale permeability as a function of effective pressure using Mercury Injection Capillary Pressure (MICP) experiments. Traditional approaches to describe permeability from MICP data often use pore size distribution and porosity and ignore intrusion effects. However, recent studies suggest that significant misinterpretation of pore size distribution and porosity can be realized owing to ignorance of pore compressibility in shale samples. We evaluate permeability variation with pressure using MICP data while considering for pore compressibility and intrusion correction.A shale sample often undergoes three stages during MICP tests: conformance, compression and intrusion. By identifying different pressure regions associated with these stages, we characterize pore compressibility as a function of pressure using compression stage and re-evaluate pore size distribution and porosity based on intrusion stage. We then integrate intrusion correction and pore compressibility values to Katz-Thompson correlation to evaluate permeability as a function of pressure.Identifying true intrusion and applying pore compressibility allow us to alter key variables in Katz-Thompson correlation, thus significantly lowers the final estimation of permeability. We observe 10–30% permeability reduction in the samples analyzed after corrections.This paper improves the accuracy of permeability predictions from MICP data; the outcome can be further applied to improve predictions of reservoir performance.