Theoretical study of gas periodic oscillation method for low permeability testing in porous media

The high-precision gas steady-state method and the gas pulse decay method are widely used in the permeability measurement of tight porous media. However there is a lack of in-depth discussion and analysis of the gas periodic oscillation method (POM). The basic principle of POM is introduced, and three practical methods for simulating periodic pressure waves are proposed. Additionally, an experimental equipment scheme is recommended, which includes two adjustable gas storage containers on each side of the specimen. The theory proposed by Fischer regarding the periodic oscillation method is expanded in this study to include the scenario where the seepage medium is a compressible fluid, as opposed to only considering incompressible fluids. This extension allows for a wider range of applications for the periodic oscillation method. Additionally, the study examines the physical significance of this method and analyzes the relationships between different parameters involved. Based on the generic theoretical solution of POM, two special cases are analyzed and the treatment of some complex sub-terms is optimized. The calculation results of the theoretical and numerical solutions of POM are compared through a series of orthogonal cases, and the effects of permeability, porosity, downstream container volume, specimen diameter and length on the experimental process are discussed respectively. The numerical solutions are used to verify the accuracies and stabilities of the theoretical solutions, and to illustrate some shortages of the theoretical solutions. Based on the case study, a better design strategy of POM experiment is given.