Correlation between Natural Seepage and Ionic Diffusion in Shales

The contact between fracturing fluid and shale reservoir induces water-rock reactions such as self-absorption, hydration damage, and ion diffusion, which leads to disturbed reservoir test results and makes it impossible to scientifically formulate extraction plans. Currently, there is a lack of interaction analyses, so we took the shale gas reservoir core in Fuling, Sichuan Basin, as the research object and carried out simultaneous tests of shale self-absorption and conductivity and the correlation between natural seepage and ion diffusion with the help of elemental geochemical measurements. The study concludes that self-absorption and ion diffusion have synchronous response characteristics, and self-absorption develops significantly in the early stage and then tends to stabilize gradually; the presence of cavities or clay-type hydrolysis-prone minerals in the shale pore space leads to a step-like pause in the absorption and conductivity curves at the specific self-absorption time.