Integrated approach for closure correction of mercury injection capillary pressure measurements

Abstract

Closure correction is a key requirement for a reliable petrophysical evaluation using mercury injection capillary pressure (MICP). The available correction methods rely on identifying deflection points on capillary pressure curves which is often difficult and subjective and requires additional information for macropores that control the closure effect. The proposed approach in this study is novel in terms of integrating the pore-throat size distribution and incremental mercury intrusion data from MICP with porosity from routine core analysis as well as 2D visualization and watershed segmentation from thin section images. The proposed approach allows for lowering the uncertainty in closure correction by incorporating the pore-throat sizes and segmented porosity of the macropores from thin-section images. We tested this approach on samples of the Austin Chalk and Indiana Limestone. The effects of sample size and equilibrium time were also investigated. Identifying the closure pressure is demonstrated to be more difficult on small crushed samples due to the impact of mercury conformance associated with the increased specific surface area. The impact of increasing the equilibrium time is insignificant on relatively permeable Austin Chalk. However, for the tighter Indiana Limestone, conducting fast MICP experiments results in inconsistent and misleading results. We used rate-equilibrium testing at 0.001 μL/g to generate initial-residual curves and evaluate pores accessibility. We show that Austin Chalk pores are fully intruded below 10,000 psia whereas Indiana Limestone requires higher pressure to invade all the pore systems. This study emphasizes the importance of integrating additional information with the MICP data for the closure correction of complex pore systems.