A radial differential pressure decay method with micro-plug samples for determining the apparent permeability of shale matrix

We propose a radial differential pressure decay (RDPD) method to measure the apparent permeability in shale matrix. The experimental design extends the upper limit of pressure in conventional methods. The experimental error caused by the dispersiveness of sample size and the irregularity of particle shape is reduced by utilizing precisely prepared micro-plug samples with highly uniform diameters, and the reliability of the result is improved substantially. The late-time approximate solution for cylindrical samples based on the experimental configuration is presented for data interpretation and verified with the numerical simulation. The experiments based on shale matrix samples are demonstrated. The results reveal that the RDPD method can capture a differential pressure decay curve precisely, which can be closely fitted through the late-time solution. It also has great potential for various tight porous media. This method sets the stage for the accurate investigation of gas transport mechanisms in tight porous media in future work.