Quantitative characterization on dynamic methane flow in Chinese marine shales: An experimental study

Abstract

The dynamic characteristics of shale gas flow directly affect the high-efficiency exploitation of shale gas, which has attracted widespread attention. In this study, the flow rate and permeability of gas (methane and helium) under variable confining stress and gas pressure conditions were carried out based on six shale samples from the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation in the southeastern Sichuan basin. By performing the seepage experiments of non-adsorbed gas (helium) and adsorbed gas (methane) under the same test conditions, the controls of gas slippage, matrix shrinkage and effective stress on the methane permeability change during the flow process were quantitatively decoupled. It is concluded that the methane permeability change is the result of the superposition of three major geological effects including gas slippage, matrix shrinkage and effective stress. During the gas pressure depletion, the effective stress effect is the main factor leading to the permeability decrease, while the gas slippage is the main factor causing the permeability increase. The permeability change caused by matrix shrinkage is more complex, and is closely related to the shale composition. Based on the control mechanism of permeability change, a prediction model of the methane permeability change in Chinese marine shales is proposed and has a good match with experimental data. The model is suitable for the process of gas pressure reduction under a constant confining stress condition. This research is helpful to understand the characteristic and mechanism of dynamic flow process of shale gas.

Keywords

• Shale gas
• Dynamic flow
• Effective stress
• Gas slippage
• Matrix shrinkage