Abstract
Unconventional oil and gas from shale formations have emerged as some of the fastest growing energy resources in the United States, providing both cleaner energy to consumers and reducing the nation's reliance on energy imports. To properly harness these important natural resources, the nanopore structure of associated shales must be fully understood, particularly under hydraulic fracturing conditions, where they are exposed to both overburden compressive and hydrostatic fluid pressures. The current study uses small-angle neutron scattering (SANS) to characterize pore structure, including porosity, pore accessibility, and pore size distribution, in the 1-100 nm regime at elevated pressures for mineralogically distinct clay-and carbonate-rich shales from the Permian Basin. Unlike typical porosity measurement techniques, SANS is uniquely capable of characterizing both open and closed porosity, allowing measurement of how pore accessibility changes with pressure and determination of the size range of accessible versus inaccessible pores. The porosity of the clay-rich shale was 7.7%, compared to 0.51% for the carbonate-rich shale. However, only 2.6% of the nanopores in the carbonate-rich shale were inaccessible to water at 8 kPSI (55.1 MPa) compared to 7.8% for the clay-rich shale. Further analyses indicated that the closed pores fall within distinct size ranges, likely corresponding with the chemical nature of the pore host material. These results provide valuable insight into the effects of shale petrophysical properties on hydrocarbon extraction from unconventional reservoirs.
| Original language | English |
|---|---|
| Pages (from-to) | 8178-8185 |
| Number of pages | 8 |
| Journal | Energy and Fuels |
| Volume | 34 |
| Issue number | 7 |
| DOIs | |
| State | Published - Jul 16 2020 |
| Externally published | Yes |
Funding
This work was supported by the Chevron Energy Technology Company through a CRADA to the Los Alamos National Laboratory (LANL) (Project PIs: M. Rebecca Stokes and Hongwu Xu). LANL is operated by Triad National Security, LLC, for the National Nuclear Security Administration of the U.S. Department of Energy (contract no. 89233218NCA000001). Access to small angle neutron scattering instrumentation 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. Di Wu acknowledges the institutional funds from the Gene and Linda Voiland School of Chemical Engineering and Bioengineering and the fund of Alexandra Navrotsky Institute for Experimental Thermodynamics at Washington State University.