Abstract: The weak formation energy and retained fracturing fluid in the normal-pressure gas shale formation tend to cause formation damage, resulting in a rapid decline in the production of shale gas wells and low ultimate recovery after hydraulic fracturing. In this research, the normal-pressure shale gas formation in southeast Chongqing is considered as the research object. A scientific conception of relieving fracturing fluid damage by subcritical or supercritical water stimulation is innovatively proposed after clarifying the formation damage mechanisms of fracturing fluid invasion and the solution to relievie such formation damage. This method can improve the aqueous phase mobility and the gas flow capacity in shale matrix. The engineering and geological characteristics of shale gas reservoirs after hydraulic fracturing are considered, so the scientific conception is qualified as practical. Furthermore, dissolving minerals/organic matter and inducing fractures in the shale matrix via sub-and supercritical water remediation are investigated through experiments. The results show that the porosity and permeability of shale samples are greatly enhanced due to a large number of submicron-micron intragranular and interparticle dissolution pores generated. A high-temperature thermophysical effect and a subcritical or supercritical water catalytic oxidative dissolution effect are considered as the main mechanisms of relieving aqueous phase trapping damage in a shale gas reservoir. The application prospect of subcritical or supercritical water remediation is forecasted from the aspects of synergizing with hydraulic fracturing and the green and low-carbon concept in shale gas development.

Key words: normal-pressure shale gas, retained fracturing fluid, formation damage control, multiscale, pore structure, subcritical or supercritical water