Permeability of high-Kn real gas flow in shale and production prediction by pore-scale modeling

Abstract

Although shale gas has been commercially exploited, the gas transport mechanism in shale is still unclear. Because nanoscale pores are dominant in shale, the Knudsen number of the flow is relatively high so that the conventional Darcy's law fails. What is more, the shale gas in situ is under high pressure and high temperature so that the real gas (or non-ideal gas) effect is significant. Aiming at these two challenges, we did a pore-scale modeling by using lattice Boltzmann method in this work. We developed a pore-field-iteration (PFI) method to bridge up the pore-scale modeling results with the field-scale concerns, such as inflow performance relationship and decline curve analysis. Our results show that the high Knudsen effect leads to a higher gas flow rate, while the real gas effect causes lower gas flow rate. The gas production may be overestimated at early stage due to the real gas effect, while underestimated at late stage because of the high Knudsen number effect. These results may be very helpful for better understanding of gas transport mechanism in shale and for possible process optimization of shale gas developments in future.