Objective The Chang 7 tight sandstone reservoir in Ordos Basin is characterized by tight rock, strong heterogeneity and poor pore throat sorting and connectivity. In the early stage, the conventional fracturing technology transformation

Methods are single, and the transformation effect of tight reservoirs with underdeveloped fractures is poor.

Methods According to the dimensional analysis method (π theorem), the design idea of similarity criteria for physical simulation experiment was optimized, and the simulation system of fracture initiation and extension with equal proportion reduction was designed. Using the large scale true triaxial simulation test system, 30 cm × 30 cm × 30 cm tight sandstone outcrop sample hydraulic fracturing physical simulation experiment was carried out. According to the experimental pump pressure peak value during rock mass fracture, the three-dimensional scanner was used to quantitatively evaluate the fracture reconstruction area and reveal the fracture initiation and extension rules.

Results The simulation experiment has quantified the fracturing fracture initiation pressure and reconstruction area under the conditions of fracturing fluid type, stress difference, natural fracture and weak surface and construction displacement. It has revealed the influence rule of geological engineering factors on the fracturing fracture extension behavior, and clarified the influence degree of geological engineering parameters on the fracturing fracture extension and complex fracture network formation.

Conclusions The research showed that low stress difference, weak surface development of natural fractures and low viscosity slippery water were favorable factors for obtaining complex fracture morphology, which provided experimental evidence and theoretical basis for the study of block volume fracturing technology tests. It is suggested to adopt the volume fracturing idea and technology of "large fluid volume, large displacement and expanded swept volume" to achieve the transformation goal of complex fracture network.