A study of gas transport and production characteristics with non-Darcy flow in tight gas reservoirs

Tight gas reservoirs (TGRs) are important unconventional resources. In such reservoirs, the permeability is much lower than that in conventional gas reservoirs. While, the Klinkenberg effect is widely considered in gas reservoirs, it is not enough to depict complicated non-Darcy effects in certain TGRs including the nano-scale pores. It is also not clear that when complicated non-Darcy effects should be considered, and how strong these effects in TGRs. In this paper, a new model which couples both non-Darcy flow and stress effects was established. The flow regimes involve viscous flow, slippage flow, transition flow, and molecular-free flow. The impacts of stress effect on both the absolute permeability and non-Darcy flow regimes were incorporated as well. After that, the model was validated using experimental data. Finally, the model was employed to identify the critical conditions that Darcy flow, slippage flow, or complicated non-Darcy flow regimes should be accounted in different TGRs. The results show that when the permeability is lower than 10(-2) md, there is transition flow in TGRs, and the gas production will be underestimated if only viscous and slippage flows are considered; when the permeability is higher than 10(-1) md, Knudsen number is small which indicates that the slippage flow is slight, and the non-Darcy flow has very little impact on gas production.