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AAPG Southwest Section Annual Convention

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Multiscale Pore Structure Study of Shales through Contrast Matching Technique in (U)SANS Measurements

Abstract

The investigation of multiscale pore structure for unconventional reservoir rocks (e.g., shales) is of critical importance to understand wettability, relative permeability, fluid migration, and ultimate recovery. In this study, (ultra-) small angle neutron scattering techniques, (U)SANS, are used to quantify the total porosity and characterize pore size distribution in a pore length size from 1 nm to 10 mm. The employment of contrast matching approach enabled the discrimination of accessible (open) pores and inaccessible (closed) pores as a function of rock pore size, and furthermore, was used to quantify total accessible porosity, hydrophobic porosity, and hydrophilic porosity by applying different wetting-fluids (e.g., isopropanol alcohol, n-decane, and water). This study examined the characteristics of oil-window Bakken Shale samples, oil/gas-window Utica/Point Pleasant samples, and gas- window Barnett Shale samples. Results showed that (1) the Bakken shales have a relatively high total porosity (8.87-12.95%) with no more than 30% of the pores are accessible pores and are not preferentially wet by oil or water; (2) the Utica/Point Pleasant samples have a total porosity of 6.70-9.65% with over 80% of the pores are accessible pores and tend to be more oil-wetting than water-wetting; (3) the Barnett shales have a total porosity of 6.15-9.19% and exhibiting oil-wetting to water-wetting characteristics in different samples. Overall, the application of contrast matching approach in (U)SANS techniques proves to an effective way of probing multiscale pore structure of tight rocks and provides a unique method of separating open porosity from total porosity.