In-Depth Experimental Investigation of Shale Physical and Transport Properties

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Summary: URTeC 1582146 Natural gas produced from shale represents an important emerging energy supply not only in the United States but across the globe. Proper understanding of shale petrophysical properties is essential for accurate reserve estimations, recovery factor predictions, potential enhanced recovery techniques, and carbon sequestration. Due to matrix permeability in the range of a nanodarcy and porosity less than 10%, numerous challenges are faced to garner data in the laboratory regarding the physics and flow behavior of these shale rocks. The main question addressed here is the sensitivity of shale physical properties to the gas saturating the pore space. The paper presents apparent Klinkenberg permeability measurements at different pore and confining pressures. The advantage of using helium gas in this context is that it aids the study of slip flow without any complicating effects of gas sorption on permeability. Helium permeability and porosity are compared to nitrogen, methane, and carbon dioxide results for Barnett and Eagle Ford shale samples. The effect of sorption on permeability is inferred. Results show decreased permeability with increased sorption. Gibb’s excess sorption is measured utilizing the volumetric method and confirms the impact of sorption on the storage capacity and permeability of shale. Because of the small size of helium molecules, initial speculation suggested that helium measured porosity is greater than the effective methane porosity leading to overestimated shale pore volumes. Experimental results reported here for several shale samples, however, indicate otherwise.

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