Mathematical Simulation about Gas Transport in a Dual-Porosity Tight Gas Reservoir considering Multiple Effects

Abstract

Threshold pressure gradient, gas slippage, and stress sensitivity have important effects on the production of a tight gas reservoir. But previous studies only focused on one or two of these effects. In this study, a mathematical model considering these three effects was established to describe gas transport in a dual-porosity tight gas reservoir. Threshold pressure gradient, gas slippage, and stress sensitivity are simultaneously considered in the velocity term of continuity equation which is mainly different from the previous research results. The partial differential equation and definite solution condition are discretized by a central difference method. A finite difference procedure was compiled and applied to solve this numerical model and predict the productivity of a production well in a dual-porosity tight gas reservoir. The difference between the predicted and tested cumulative production is less than 10%, which indicates that the proposed mathematical model can be used to describe the characteristics of gas flow in the dual-porosity tight gas reservoir. Then, gas productivity of five different scenarios considering these effects was compared. Results show that both stress sensitivity and threshold pressure gradient are negatively correlated with gas production, while gas slippage is positively correlated with gas production. Among them, stress sensitivity has the greatest impact on the production of a dual-porosity tight gas reservoir. Overall, these three effects have great influence on the development of the dual-porosity tight gas reservoir, which should be considered in the production prediction.

Well-Testing Model for Dual-Porosity Reservoir considering Stress-Sensitivity and Elastic Outer Boundary Condition

“…Based on a combination of geomechanics and flow characteristics, Li et al [28] presented the production model for triple-porosity media, taking the adsorption and desorption of gas, slip flow, Knudsen, interfacial diffusions, and stress sensitivity into account. Chen et al [29] established the mathematical model for tight gas reservoirs considering threshold pressure gradient, gas slipping, and stress sensitivity, and Xue et al [30] conducted research on tight sandstone gas reservoirs with water produced and showed that strong stress sensitivity appeared as a result and increased with the water production. Zhao et al [31], Jabbari et al [32], Samaniego and Villalobos [33], and Zhang et al [34] carried out research on the stress-sensitivity of fracture reservoirs, and Wang and Wang [35] proposed the mathematical model considering the effect of slipping and stress sensitivity in fractured gas reservoirs.…”