Laboratory investigation of the effect of the pore pressure on argillaceous siltstone permeability

The permeability of argillaceous siltstone is a critical parameter for the sustainable development of natural gas hydrates in the ocean beds. In the laboratory, the pressure pulse method is frequently used to measure permeability. However, the influence of pore pressure on permeability test results of argillaceous siltstone by pulse method is not established, resulting in inconsistencies between permeability test results in the laboratory and those in deep seawater (water depth >= 500 m). First, the effect of bound gas content in argillaceous siltstone on the rate of volume change in the test medium is considered, and the computation model of the pressure pulse method is validated. Next, the effect of pore pressure on the permeability of argillaceous siltstone is investigated while keeping the effective stress of the sample constant. The experimental results show that as pore pressure increases, the permeability of argillaceous siltstone increases gradually. The permeability measured in a 6 MPa pressure environment is two orders of magnitude greater than that measured in a 1 MPa pressure environment and the increased range is piecewise linear. The reasons for the increased permeability are investigated using the hydrophilicity of the argillaceous siltstone materials. Under high pressure, the hydrophobic properties of montmorillonite, quartz and kaolinite reduce the seepage resistance of argillaceous siltstone. The experimental results will serve as a foundation for future research, improving the accuracy of argillaceous siltstone permeability estimates.