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Moisture Equilibration and Permeability of Crushed Shale Samples



Shale cuttings and cores recovered from the subsurface and stored for hours to decades tend to dry out and lose moisture and hydrocarbons, leading to an increase in the effective matrix permeability. Moisture loss in shale sample is a fundamental sample preservation problem which can be solved by applying a standard moisture equilibration procedure to restore lost moisture. The objective of this study is to investigate the relationship between permeability and moisture content in as-received, as-received moisture equilibrated and saturated moisture equilibrated samples. Samples were crushed and moisture equilibrated at 97% relative humidity and permeability measured. Results show that moisture equilibration in the samples was achieved after 72 hours. The permeability of the saturated moisture equilibrated and as-received moisture equilibrated sample decreased exponentially with increase in moisture content. The high correlation coefficient between permeability and particle size (r = 0.96 and 0.97) for moisture equilibrated samples compared to 0.76 for as-received samples suggest that moisture equilibration improves permeability measurements in crushed shale samples. Furthermore, permeability measurements are repeatable for moisture equilibrated samples compared to samples that were not equilibrated (as-received). We conclude that moisture content affects permeability and moisture equilibration normalizes and improves the repeatability of permeability measurements in crushed shale.