Real Gas Transport Through Complex Nanopores of Shale Gas Reservoirs

Abstract

Abstract A model for real gas transfer in nanopores of shale gas reservoirs (SGRs) was proposed on the basis of the weighted superposition of slip flow and Knudsen diffusion, where the ratios of the intermolecular collisions and the molecule-nanopore wall collisions to the total collisions are the weighted factors of slip flow and Knudsen diffusion, respectively. The present model takes account of slip effect and real gas effect, additionally, the effects of cross-section type and its shape of nanopores on gas transport are also considered in this paper. The present model is successfully validated against existing molecular simulation data collected from different sources in literature. The results show: (1) the present model is reasonable to describe all of the gas transport mechanisms known, including continuum flow, slip flow and transition flow in nanopores of SGRs; (2) cross-section type and shape of nanopores both affect gas transfer capacity: at the same cross-sectional area, gas transfer capacity of nanopores with a circular cross-section is greater than that with a rectangular cross-section, and gas transfer capacity of nanopores with a rectangular cross-section decreases with an increasing aspect ratio; compared to cross-section type, the effect of cross-section shape on gas transfer capacity is stronger; (3) a real gas effect improves gas transfer capacity, which becomes more obvious with an increasing pressure and a decreasing pore size; (4) and compared to nanopores with a circular cross-section, the effect of real gas effect on gas transfer capacity of nanopores with a rectangular cross-section is stronger, and the effect increases with an increasing aspect ratio. The proposed model can provide some theoretical support in numerical simulation of reservoir behavior in SGRs.