Conference Dates

June 22-27, 2014


Pressure pulse decay method is widely used for permeability tests for low permeability rock plug samples. This method can be used for crushed grain samples by removing the downstream chamber in standard pulse decay tests. Processes in pulse decay tests for low permeability crushed shale are investigated using numerical simulation. Both the Klinkenberg slip effect for gas flows in low permeability rock and the gas absorption/desorption in the porous matrix are considered. The complete mathematical model is set up to include the two effects. Deviation of the numerical pulse decay curve from the analytical one with an assumption that the pressure keeps a constant in the porous sample is investigated. The relative importance of gas absorption/desorption and gas compressibility is also investigated quantitatively. According to the present investigation, gas compressibility and adsorption both make negative contributions to the permeating process. A potential two-curve method is proposed to decide absolute permeability and the Klinkenberg coefficient when these two parameters cannot be distinguished using one pulse decay curve during the inverse fitting procedure. These two parameters can be determined at the same time only if the experiment is conducted under big initial pressure difference and the Klinkenberg coefficient has at least the same order of magnitude as the pressure.