China’s land has been affected by industrial development for a long time, and the pollution of low-permeability formations is very serious, so low-permeability contaminated sites need to be efficiently and quickly restored. Traditional ex-situ restoration technology has strong soil disturbance and slow restoration of the ecological environment, which is not enough to solve the current restoration dilemma. Therefore, the in-situ three-dimensional fracture network remediation technology needs to be studied urgently. At present, three-dimensional remediation of low permeability contaminated sites is faced with problems such as unknown mechanism of soil fracture propagation, easy settlement of existing proppant at the main fracture mouth and fracturing equipment fragmentation. Restricted by experimental conditions and mechanism research, further breakthroughs are needed into fracture network spreading mechanisms, multi-field coupling, new proppants and integrated fracturing equipment in a low permeability soil layer. This paper focuses on the mechanical behavior of low-permeability media under multi-field coupling and the progress and feasibility of fracturing equipment to improve the effective support of in-situ fractures. The key research points, such as the mechanism of soil fracture initiation and propagation, the fluid-solid-chemical multi-field coupling model, the new controllable mussel film-like proppant and gas-hydraulic driven fracturing technology and equipment, are put forward. It can guide the design of gas-liquid driven fracture network fracturing and infiltration enhancement repair of low permeability polluted formation, improve the transmission efficiency and placement range of agents, and realize the in-situ three-dimensional and efficient repair of low permeability contaminated sites.

The continental shale reservoirs of Jurassic Lianggaoshan Formation in Sichuan Basin contain thin lamina, which is characterized by strong plasticity and developed longitudinal shell limestone interlayer. To improve the production efficiency of reservoirs by multi-cluster fracturing, it is necessary to consider the unbalanced propagation of hydraulic fractures and the penetration effect of fractures. This paper constructed a numerical model of multi-fracture propagation and penetration based on the finite element coupling cohesive zone method; considering the construction cluster spacing, pump rate, lamina strength and other parameters studied the influencing factors of multi-cluster fracture interaction propagation; combined with AE energy data and fracture mode reconstruction method, quantitatively characterized the comprehensive impact of the strength of thin interlayer rock interfaces on the initiation and propagation of fractures that penetrate layers, and accurately predicted the propagation pattern of hydraulic fractures through laminated shale oil reservoirs. Simulation results revealed that in the process of multi-cluster fracturing, the proportion of shear damage is low, and mainly occurs in bedding fractures activated by outer fractures. Reducing the cluster spacing enhances the fracture system's penetration ability, though it lowers the activation efficiency of lamina. The high plasticity of the limestone interlayer may impact the vertical propagation distance of the main fracture. Improving the interface strength is beneficial to the reconstruction of the fracture height, but the interface communication effect is limited. Reasonable selection of layers with moderate lamina strength for fracturing stimulation, increasing the pump rate during fracturing and setting the cluster spacing reasonably are beneficial to improve the effect of reservoir stimulation.