Secondary propagation of hydraulic fracture in low-permeability reservoir after shut-in

It is significant for hydraulic fracturing design to accurately predict the secondary propagation pattern of hydraulic fracture after pump-off. Based on linear elasticing fracture mechanics, elasticing mechanics, finite volume method and Implicit Level Set Algorithm, a strongly nonlinear fluid-stress coupled planar fracture propagation model was established to simulate the secondary propagation and closure behavior of fractures after shut-in. The accuracy of the model was verified by the viscosity-dominated Penny fracture analytical solution. The effects of fracturing fluid viscosity, fracture toughness and barrier stress difference on the length of secondary propagation were studied. The results show that the fracture closure and secondary propagation coincide, and the distance of secondary propagation is much longer when there is a stress barrier. The displacement and barrier stress difference are positively correlated with the length of secondary propagation. The filtration coefficient, fracture toughness and fracturing fluid viscosity under engineering parameters have nonlinear and asymptotically linear negative correlations with the secondary propagation length of fracture, respectively. In hydraulic fracturing design, it is essential to consider the influence of secondary fracture propagation length for reservoirs with high stress difference barrier, low permeability and large displacement.