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Using mercury intrusion porosimetry to identifying the sample size effect on pore structure characteristics of the Eagle Ford Shale

Abstract

Capable of working with different sample sizes, mercury injection capillary pressure (MICP) is a common technique used for characterizing pore structure (porosity, pore volume, and pore-throat size distribution) of reservoir rocks. Related to pore connectivity, a rock sample can exhibit sample size-dependent porosity; a poorly connected rock could have a larger porosity for a smaller-sized sample, and the porosity reaches a stable value at certain sample sizes. In this study, we focused on Eagle Ford Shale and used Atco Chalk, Del Rio Claystone, and Salmon Peak Limestone as comparisons. Our results indicate that when applying multiple sample sizes (1cm3 cube, crushed granular samples with sizes varying from 1.7-2.36 mm, 500-841μm, 177-500 μm, and 75-177 μm), the resultant porosity dramatically increases (accordingly at 2%, 3%, 6%, 9%, and 33%) for Eagle Ford Shale as an example. Comparing the MICP pore-throat distribution plots of cubic and granular samples, pore systems were generated and destroyed during sample crashing. The degree of pore systems’ generation and destruction is directly related to the sample sizes. The results suggested although the porosities of crushed samples may not have an obvious difference, the pore systems are different from non-crushed samples.