AAPG Annual Convention and Exhibition

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Oil Recovery Potential From Organic Nanopores in Source Rocks

Abstract

Over the past decade there has been significant progress in production from unconventional resources such as shale oil. However, the oil recoveries are characteristically low. The production rate declines rapidly as the fractures are depleted and the production is controlled increasingly by the formation. Resource shales are organic-rich “black” shale. They hold up large volumes of hydrocarbons within the nanopores of the organic matter. It is not clear, however, whether the declining production contains any fluid that has been released from the organic matter. In this presentation the authors answer this question at a fundamental level using a new molecular simulation approach by numerically measuring the rheological properties of the hydrocarbon mixtures in model organic pores with sizes varying in between 1-20nm and counting the released hydrocarbons during their differential liberation. It is found that the apparent molecular weight, viscosity, and the mean free path of the hydrocarbon mix is sensitive to organic nanopore size. Under the same formation pressure and temperature conditions, the mixture becomes heavier and more viscous as the pore size decreases. The effect is significant in pores with size less than 10 nm. During pressure depletion, the fluid in nanopore gets heavier. However, interestingly, the mean free path of the molecules does not increase as predicted by the kinetic theory of ideal gas. The results indicate that the mobility of hydrocarbon fluid is significantly reduced in nanopore due to amplified pore wall-fluid molecular interactions and to the level of nano-scale confinement. Consequently, we predict hydrocarbon recoveries much less than 20% for both light and heavy hydrocarbons produced.