Fracture Extension Law and Process Optimization of Lianggaoshan Formation Shale Reservoir in Sichuan Basin

Sichuan Basin is rich in shale oil resources. Resources is mainly distributed in Lianggaoshan Formation of Jurassic, which the reservoir lithology is shale and sandstone interbedding, Showing obvious lithological interbedding characteristics. (Young’s modulus of sandstone is 35.6–45.3 Gpa, Poisson’s ratio is 0.24–0.30, Young’s modulus of shale is 38–50 Gpa, Poisson’s ratio is 0.16–0.3). As a result, hydraulic fracturing is faced with the problems of complex hydraulic fracture extension law, unclear main control factors of fracture extension, and great difficulty in layer penetrating reconstruction. In this study, the outcrop of sand and shale interbedding in the field is selected to carry out the true triaxial physical model experiment. The experimental results show that the interface strength, stress difference and liquid viscosity are the main influencing factors; According to the geological engineering parameters of typical wells, the finite element+cohesive element is used to carry out the numerical simulation of fracture extension. The simulation results show that when the interface strength is lower than 4 MPa, the hydraulic fracture is easy to activate the bedding interface. When the inter-layer stress difference is greater than 6 MPa, the longitudinal extension of hydraulic fracture is blocked. The hydraulic fracture can be effectively extended longitudinally by using high viscous fluid combined with large displacement. This study has formed a through-layer fracturing process of large displacement+high viscous pre-fluid, The process has been applied for many times, and the microseismic monitoring results show that the vertical penetration is successful, and the length of the reconstructed fracture reaches 130–160 m, and the process effect is obvious.