Meeting growing energy demands while reducing reliance on energy imports necessitates strategies to improve the efficiency of current energy resources. Enhanced oil recovery (EOR) has been proposed as one strategy to improve hydrocarbon recovery from tight shale reservoirs through the injection of a substance following primary recovery to facilitate oil movement to a production wellbore. Typically, hydrocarbons remaining at this point are contained within the shale matrix rather than within fractures, where hydrocarbons are more mobile and quickly depleted. Implementation of EOR thus requires knowledge of fluid behavior in nano-sized pore spaces. To advance this knowledge, we established a new experimental method to observe decane movement <i>in situ</i> within the shale nanoporous matrix using high pressure small-angle neutron scattering (SANS), allowing us to mimic oil recovery utilizing methane as the injectant. Using this technique, we quantify the extent of decane saturation and recovery for samples of clay-rich strata and carbonate-rich strata (i.e., limestone) taken from a shale formation. The clay-rich sample has a much higher porosity of 5.6%, compared with 1.2% for the carbonate-rich sample. However, upon methane injection and withdrawal, decane is more easily removed from the carbonate-rich matrix, leading to similar hydrocarbon yields for the two samples. These new results demonstrate the ability of SANS to probe hydrocarbon behavior within shale nanopores during oil recovery, and can be used to assess viability of EOR injectants and develop models for field-scale recovery efficiency from different shale lithologies.

In situ</i> measurement of oil recovery from geologic nanopores using small-angle neutron scattering (SANS)

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