Hydraulic fracturing is generally necessary to achieve economically viable production rates during exploitation of shale reservoirs. Polyacrylamide‐based fracturing fluid is commonly used in shale fracturing. Polyacrylamide (PAM) becomes adsorbed in the shale micro‐fractures, decreasing the permeability of the reservoir. For improving the production of shale after being stimulated, the adsorption behavior and adsorption mechanism between the PAM and shale are studied. An ultraviolet spectrophotometer is used to obtain the amount of adsorption. To observe the adsorption morphology, a scanning electron microscope is employed. The action force between the PAM and shale rock is analyzed through Fourier transform infrared spectroscopy, zeta potential instrument, and X‐ray photoelectron spectroscopy. The results indicate that hydrogen bonding is the key force between the PAM and shale. A kind of shale micro‐fractures model is designed to determine the recovery of permeability. Urea breaks the hydrogen bonding and keeps the molecular of HPG stretch which can decrease the amount of adsorption on the shale surface and effectively recover the permeability of shale micro‐fractures up to 72.46% after being damaged. In conclusion, it is believed that the competitive adsorption is a new approach for remediation of the permeability damage by PAM‐based fracturing fluid and has great potential in oil field application.

It is challenging to get water-based fracture fluid to flow back into low-pressure gas reservoirs. In order to solve the problem, supercritical CO2 is a novel type of non-aqueous fracturing technique with a wide range of applications prospect in low-pressure tight sandstone. In order to determine whether supercritical CO2 fracturing with low-pressure tight sandstone is feasible tight sandstone cores from the Jinqiu Gas field in the Sichuan Basin were used to evaluate the influence of supercritical CO2 on the formation sensitivity of sandstone reservoirs. Supercritical CO2 was used to interact with tight sandstone samples under formation conditions, and then the changes in velocity sensitivity, water sensitivity, salinity sensitivity, alkaline sensitivity, acid sensitivity, and stress sensitivity of tight sandstone were observed. Velocity sensitivity damage decreased by 5.4%, water sensitivity damage decreased by 13.3%, salinity sensitivity damage decreased by 16.6%, alkaline sensitivity damage decreased by 2%, acid sensitivity damage decreased by 14.4%, and stress sensitivity damage increased by 8% after the interaction between tight sandstone and supercritical CO2. This finding provides a quantitative assessment of the impact of supercritical CO2 on formation sensitivity, and it can be used to build a supercritical CO2 fracturing scheme for low-pressure water-sensitive tight sandstone.

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Due to the brittleness of the shale and tight reservoir and the development of natural fractures and horizontal beddings, complex fractures will be built by shear slip and tensile failure during multistaged horizontal well fracturing. Whether proppant can enter complex fractures and form effective support in main fractures and branch fractures determines conductivity of the complex fracture and stimulation effect of multistaged horizontal well fracturing. By means of discretization of disordered complex fractures, the orthogonal three-dimensional physical model of complex fractures is obtained and the complex fracture experimental device for simulating fracture complexity is developed and a complete set of proppant transport characteristic experimental device in unconventional reservoir complex fractures is formed. Combined with field parameters and lab experiments, the influence of proppant performance parameters and discharge capacity to proppant transport characteristics in complex fractures of the unconventional reservoir is studied. And on the basis of experimental results and analysis, the sensitivity analysis method is applied to analyze the influence degree of proppant transport characteristics in complex fractures of the shale or tight sandstone reservoir. The sensitivity order of influence factors is fracture morphology, proppant performance, liquid viscosity, displacement, and proppant concentration. The experimental device and research results can provide strong experimental support for the optimisation of shale or tight sandstone fracturing materials and field parameters.

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