Probing oil recovery in shale nanopores with small-angle and ultra-small-angle neutron scattering

Neil, Chelsea W.; Hjelm, Rex P.; Hawley, M. E.; Watkins, Erik B.; Wu, Di; Mao, Yimin; Cheshire, Michael C.; Burger, Jon; Fischer, Timothy B.; Stokes, Martin

doi:10.1016/j.coal.2022.103950

Cited by 9 publications

(17 citation statements)

References 45 publications

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“…In our previous study of oil recovery from carbonate-rich shale, more than 90% of the ndecane-filled porosity was removable by methane pressure cycling, while for the kerogen and clay-rich shale, 20% was removable. 29 It thus seems likely that the removable decane in our Wolfcamp samples is located in mineral-hosted pores, rather than kerogen-hosted pores. It is possible that n-decane within the kerogen-hosted pores is irreversibly sorbed to kerogen molecules or that methane was unable to mix efficiently with decane within the kerogen pores.…”

Section: ■ Introductioncontrasting

confidence: 89%

“…Fluid at this minimal contrast condition is introduced into the porous matrix, minimizing scattering from pores which are open to the fluid relative to the significant scattering from the empty, inaccessible pores. Additional details on SANS theory as applied to geomaterials can be found in our previous publications. − …”

Section: Methodsmentioning

confidence: 99%

“…The fitting program makes two simplifying assumptions: first, that pores are spherical in shape, and second, that there is a two-phase system with scattering only from empty voids. As discussed in depth in our previous publications, these assumptions are not expected to significantly affect quantification, particularly as our focus is on relative changes in the apparent PDF, P A ( R ) P A ( R ) = normalΔ ρ 2 ( R ) ̅ ρ m 2 normalP normalR ( R ) where normalΔ ρ 2 ( R ) ̅ (cm –4 ) is the average squared contrast of pores relative to the local matrix environment and P R ( R ) and P A ( R ) are proportional to the Δρ 2 ( R ) V 2 ( R )-weighted probability densities of empty pores with radii between R and R + d R .…”

Section: Methodsmentioning

confidence: 99%

“…Unlike our previous study, 29 however, the Wolfcamp samples had more mineralogical overlap, with both samples containing kerogen, clay, and carbonate minerals. As a result, the "dark" sample, despite containing more clay and kerogen, had less removable decane than the previously tested clay-rich shale.…”

Section: ■ Conclusionmentioning

confidence: 99%

“…assumption is reasonable even though voids in shale are oblate ellipsoids, as our samples are cut approximately parallel to the bedding plane, making the view of the voids circular. 29 The scattering is thus a cross section of the squared Fourier transform perpendicular to the semimajor axis. While this approach, which is unavoidable using the Irena tool, might distort the reference pore size distribution function (PDF), it will not affect the change in R ( )…”

Section: ■ Introductionmentioning

confidence: 99%

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Small-Angle Neutron Scattering Investigation of Oil Recovery in Mineralogically Distinct Wolfcamp Shale Strata

et al. 2023

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Understanding and improving hydrocarbon yields during enhanced oil recovery (EOR) in unconventional reservoirs is complicated by the intrinsic mineralogical and geochemical heterogeneity of shale formations. In this study, we utilized small-angle neutron scattering (SANS) and ultra-small-angle neutron scattering (USANS) to investigate the degree of oil retention and its location in the nanoporous shale matrix for two mineralogically distinct shale samples. The two samples, dubbed “dark” and “light” based on their color, were taken from adjacent strata in a Wolfcamp shale core. While both samples contained kerogen, the dark sample contained more kerogen and clay (43.7 wt %) while the light sample contained more calcite (54.9 wt %). Samples were presaturated with decane, a model hydrocarbon, prior to pressure cycling with methane. Results showed significantly more retention of decane in 1.5–10 nm radius pores of both, likely indicating that oil is retained within kerogen nanopores. Although the dark sample had a higher porosity of 8.7%, versus 3.3% for the light sample, more pores were accessible to decane and a higher percentage of the imbibed decane was removable from the light sample compared to the dark sample. The majority of decane was not recoverable for the dark sample, indicating that EOR with methane can be challenging. These new findings can help to model expected recoveries of in-place oil from heterogeneous shale formations, as well as inform improved EOR strategies.

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Section: ■ Introductioncontrasting

confidence: 89%