QUANTIFYING OIL- AND WATER-WETTABLE PORE NETWORKS OF THE BAKKEN, MANCOS, AND UTICA-POINT PLEASANT SHALES

Microscopic pore structure (both geometry and connectivity) characteristics control fluid flow and hydrocarbon movement in mudrocks. Considering the uniquely wide spectrum of pore sizes (nm to sub-mm), microscale mixed wettability, as well as the interplay of pore structure and wettability in organic-rich mudrocks, this work presents various approaches to quantifying the oil- and water-wettable pore networks for three leading American tight oil formations (Bakken, Mancos, and Utica-Point Pleasant) with a range of maturation and mineral compositions. The approaches include the utility of different wetting fluids (deionized water or API brine, n-decane and/or toluene, isopropyl alcohol or tetrahydrofuran or dimethylformamide), fluid pycnometry, fluid immersion porosimetry after vacuum saturation, mercury intrusion porosimetry, low-pressure gas physisorption isotherm, nuclear magnetic resonance, and field emission-scanning electron microscopy. In particular, (ultra-) small angle neutron scattering techniques, (U)SANS, are used to quantify the total (both edge-accessible and isolated) porosity and characterize pore size distribution in a pore length size from 1 nm to 10 mm; in addition, the employment of contrast matching technique of (U)SANS enables the discrimination of accessible (open) pores and inaccessible (closed) pores to a particular liquid fluid. Our results show that the Bakken samples have a relatively high total porosity (8.87-12.95%) with no more than 30% of the pores are accessible from sample surface, and are not preferentially wet by oil or water, while the Utica/Point Pleasant samples have a total porosity of 6.70-9.65% with over 80% of the pores are accessible ones and tend to be more oil-wet than water-wet.

Acknowledgements: Access to SANS NG7-30 and USANS BT5 instruments was provided by the Center for High Resolution Neutron Scattering, a partnership between the National Institute of Standards and Technology and the National Science Foundation under agreement No. DMR-1508249. A portion of this research used the USANS BL-1A resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory.