Research on data inversion process of gas pressure-oscillation method for low permeability testing in porous media

The pressure-oscillation method is a relatively new experimental approach for evaluating the seepage characteristics of porous media. It allows for simultaneous measurement of permeability and porosity, while offering several advantages, including flexibility, automation, and data re-peatability. However, there has been limited research on the data inversion process using this method. In this study, a data inversion process is proposed based on the theoretical solution proposed by Fischer (1992). The reliability and accuracy of the method are verified through synthetic signals and computation cases. The data inversion process involves two steps: processing the gas pres-sure data using fast Fourier transform and local extreme value locate to obtain the amplitude ratio and phase delay, and calcu-lating intermediate parameters that relate to gas apparent permeability and effective porosity using graphical and numerical root-finding algorithm. The calculation process is simplified by not calculating one complex intermediate parameter. The data inversion process is demonstrated using 11 computation cases, showing its intuitive nature, fast computation, deterministic results, and high accuracy. The impact of various factors on the gas pressure variations of downstream reservoir is analyzed through case analysis. This study can serve as a valuable reference for de-signing experiments using the gas pressure-oscillation method.