Oil/gas produced from shale and other low-permeability formations have become strategically important for the US domestic energy independence. Also, low-permeability geomedia may serve as confining layers of storage reservoir for CO2, hazardous materials, and other energy waste streams including nuclear waste. However, fundamental knowledge of processes that control fluids flow and propagation within nano-pore confinement is scarce, especially the lack of direct experimental observations. We have carried out laboratory investigations using small-angle neutron scattering (SANS) and inelastic incoherent neutron spectroscopy (IINS) to explore (1) Nano-pore characteristics of shale during hydrocarbon generation; (2) Pore features and water transport in clays for nuclear waste repository systems; and (3) Fingerprints of confined water molecular species and their dynamics in Permian salt. Our results on shale during laboratory pyrolysis show that smaller pores (&lt; 20 nm) change systematically as temperature increases during pyrolysis from 250 oC to 600 oC due to hydrocarbon expulsion. These results in combination with hydrocarbon fraction measurements during the same process provide a quantitative relation between pore characteristics and hydrocarbon generation. Our results on clays indicate that each clay shows an unique pore feature which can be influenced by water content, temperature, and pressure. This result also suggests that water absorption and transport behavior differ distinctly between clays. Our first-of-its-kind results of confined water molecular species in Permian rock salt using IINS demonstrate the significant variability in spectroscopic signatures of various forms of confined water (e.g., bound water in hydrous minerals, pore water as trapped in fluid inclusions) and their changes as a function of temperature. Intricacies of nano-pore confinement and properties of confined hydrocarbon, CO2, and water are the fundamental challenge across many applications in energy exploration and storage. Our work demonstrates that due to its sensitivity to light elements (e.g., H in H2O and hydrocarbon compounds) and flexible sample environments, neutron based elastic and inelastic scattering are the techniques of choice for in situ probing hydrocarbon and water behavior in nanoporous formations, providing insights into water-rock interaction and fluids transport in low-permeability geomaterials.

Neutron investigation of hydrocarbon and water in low-permeability geomaterials

249th National Meeting (2015)

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