Small-angle Neutron Scattering (SANS) Characterization of Clay- and Carbonate-rich Shale at Elevated Pressures

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.

Thermal Evolutions and Resulting Microstructural Changes in Kerogen-Rich Marcellus Shale

“…Shale rock is at the forefront of fossil energy production, holding large storages of unconventional oil and gas, and thus is also at the center of environmental considerations, especially in terms of groundwater pollution. − Shale is a fine-grained sedimentary rock typically containing a mixture of clays (illite and smectite), quartz, feldspar, carbonates (calcite and dolomite), and pyrite, but most importantly, it also contains kerogen, a complex organic matter of highly linked heavy-molecular-weight carbons, including aromatic and aliphatic carbons. − Within a wide distribution of inorganic or organic macro-, meso-, and micropores of shale hold valuable oil and gas products. Current research focuses on industrially relevant issues associated with extraction of oil and gas, including measuring the pore structure of shale and modeling the behavior of its confined hydrocarbon fluids. − …”

Technical Aspects of the Pore Structure in Shale Measured by Small-Angle and Ultrasmall-Angle Neutron Scattering: A Mini Review

“…It is noted that PRINSAS allows one to choose a power law function to fit the data or to use a general size distribution ,− …”

Discovery of Gold Nanoparticles in Marcellus Shale

“…Shale formations have emerged as a major energy resource for unconventional oil and gas, and tremendous efforts were made to characterize the compositions and microstructures of various shales. 16,17 The occurrence of gold nanoparticles and associated opal nanospheres in shale may be direct evidence of the initial gold source contributing to the eventual formation of gold deposits via Au colloidal transport, likely facilitated by the oil/gas-generating organic media. Thus, this new observation provides important insight into the formation of "invisible" colloidal gold in various geological environments.…”

“…More recently, due to the advancement of various materials characterization techniques, gold nanoparticles have been increasingly recognized in geological environments such as volcanic fumaric vents, hydrothermal systems, supergene deposits, and black smoker. ,,, Here we report a new type of occurrence of colloidal gold nanoparticles in shales from the Marcellus Formation, a major shale play in Northern America. Shale formations have emerged as a major energy resource for unconventional oil and gas, and tremendous efforts were made to characterize the compositions and microstructures of various shales. , The occurrence of gold nanoparticles and associated opal nanospheres in shale may be direct evidence of the initial gold source contributing to the eventual formation of gold deposits via Au colloidal transport, likely facilitated by the oil/gas-generating organic media. Thus, this new observation provides important insight into the formation of “invisible” colloidal gold in various geological environments.…”