Coupled Model of Multi-Mechanistic Gas-Water Transport Behavior in Tight Shale

In this work, the gas-water production period in a shale gas reservoir is divided into two stages: the gas-water twophase flow dominates at Stage I, while at Stage II, the flows are controlled by the desorbed gas and water in the adsorbed phase. The evolution models of porosity and permeability incorporate the swelling strains induced by the combined gas and water sorption. A coupled model of multi-mechanistic gas-water transport behavior in tight shale was proposed and numerically solved. Results show that at Stage I, rapid gas production is observed due to the flows of free gas and desorbed gas production, followed by a decline in the production profile toward the critical water saturation point. During Stage II, the gas production rate is influenced by the residual water content controlled by the flow of water in the adsorbed phase. The effect of sorption-induced matrix shrinkage strain will take the leading role at the late production stage. In addition, the effects of elastic properties, initial permeability, and diffusion time on the permeability ratio and gas/water production profiles are discussed. These results provide a framework for analyzing gas/water transport behavior and water retention behavior in tight shale.

Automated summary

In this study, the gas-water production period in a shale gas reservoir is divided into two stages: gas-water two-phase flow dominates at Stage I, while flows are controlled by desorbed gas and water in the adsorbed phase at Stage II. The evolution models of porosity and permeability consider the swelling strains induced by gas and water sorption. A coupled model of multi-mechanistic gas-water transport behavior in tight shale was proposed and numerically solved. The results provide insights into gas/water transport behavior and water retention behavior in tight shale.