Breakthrough Pressure Model of Shale Gas in Water-Saturated Nanopore-Throat Systems: Insights from Molecular Simulations

The abundant nanopore throats of shale formations significantly influence the transport of gas in shale reservoirs. The critical pressure of shale gas to transport through water-saturated pore-throats is a key parameter to evaluate gas transport properties and is crucial for the production of shale gas and preservation of conventional gas reservoir. Due to the strong confining effects of abundant nanopore throats of shale formations, the mechanism for gas breakthrough pressure has yet to be fully revealed, and thus, it is hard to predict the breakthrough pressure of gas transport in nanopore-throat. To learn more, we employed both equilibrium and nonequilibrium molecular dynamics simulations to investigate the methane transport behavior during the gas breakthrough process in nanopore throats filled with brine under reservoir conditions. The results suggest that the critical pressure driving fluid transport through pore-throat systems is precisely determined by the confinement effects of the pore-throat. In addition, we discussed the correlations of breakthrough pressure with the size and geometry of pore-throat. Furthermore, a gas breakthrough pressure model was proposed to describe the breakthrough mechanism of shale gas transport in pore-throat systems, which may provide a new perspective on shale gas breakthrough pressures.