Flowback rule experiment and micromechanical mechanism analysis for shale gas wells

In view of problems that the understanding on the flowback law of fracturing fluid from shale gas wells is unclear, as well as that the unclear understanding affects optimizing the working system of actual shale gas production wells, by using the core flow experiments and the analysis on microcosmic force among gas, water, and reservoir rocks, the flowback rules and mechanisms of fracturing fluids were studied. The research results show that the differences in reservoir mineral composition are the main factors affecting the flowback speed and flowback rate of fracturing fluids. Reservoirs with high clay mineral content have slow flowback speed and low flowback rate, while the flowback pressure difference only affects the initial flowback speed. By analyzing the microscopic molecular force of the fracturing fluid in the organic and inorganic pores in the reservoir, the flowback pressure difference corresponding to different pore diameters was given, and then reasonable flowback pressure difference can be calculated according to the total pore size distribution. Finally, the method for calculating cumulative flowback volume based on single-pore model was established. The research results have practical significance for analyzing the flowback rule of fracturing fluid and determining a reasonable production system.