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Multiple Approaches to Pore Structure Characterization of Self-Sourced Shales


Ultra-small and small-angle neutron scattering (USANS/SANS) techniques have increasingly been applied to study the pore structure of sedimentary rocks - especially shales. Total porosity and pore-size distribution results obtained from applying a polydisperse spherical pore (PDSP) model to (U)SANS curves are compared against results from mercury injection capillary pressure (MICP) analysis as well as N2 and CO2 adsorption isotherms for shale samples from Bakken/Three Forks in North Dakota and Utica/Point Pleasant in Ohio with different mineralogy and maturation. This study focuses on shale samples from self-sourced shale reservoirs. Variation in total porosity and pore size distribution are observed between organic-rich source rocks and organic-lean reservoir rocks, and the correlation between pore size distribution and mineralogy is also conducted. Total porosity obtained from (U)SANS, MICP and gas adsorption are varyingly consistent, and the deviations between the methods are discussed. Across all methods, porosity is larger in source rocks than in reservoir rocks - a phenomenon attributed to the unique geometry of organic pores in kerogen. The organic pore structure and volume changes in source rocks are also discussed together with potential migration mechanisms and routines from source rocks to reservoir rocks in self-sourced shale system.