Measurement of threshold capillary pressure for seal rocks using the step-by-step approach and the residual pressure approach

Abstract

Measurement of threshold capillary pressure and evaluation of the sealing efficiency for caprocks are essential to assess the long-term CO2 storage in deep saline aquifer. These measurements are quite standard for permeable rocks but more challenging for very low permeability rocks in terms of accuracy and measurement time. We applied three approaches to measure threshold capillary pressure for 3 caprock samples in this study. One approach is the step by step approach: Stepwise pressure increase by gas at inlet is conducted to measure the threshold capillary pressure. Next approach is the residual pressure approach: High gas pressure gradient is instantaneously imposed across the rock samples and monitor pressure changes to measure residual capillary pressures. Last approach is mercury porosimetry approach: Estimate threshold capillary pressure from mercury-air capillary pressure curve. We report the results of these threshold capillary pressure measurements and the comparison to each other.