Abstract
The fracture propagation simulation is extensively studied analytically and numerically since the hydraulic fracturing is widely used for the exploitation of unconventional reservoir resources. Especially, the fracture propagation in natural fractured reservoirs often behaves twist and curved trajectories, so the fracture orientation and propagation path determination need more computational work in fracture tip stress field analysis in current finite element models. This paper describes a new finite element approach solving hydraulic fracture propagation by triangular gird split method (TMSM). This approach uses interaction integral to compute the mix-mode (opening and sliding modes) stress intensity factors, and the vector cross-product is applied on the split element position. The arbitrary fracture propagation angle is obtained through the maximum tangential stress criterion. Thus, the fracture dynamic propagation simulation can be achieved by the local unit of the fracture tip through mesh split or node movement. Because the fracture can grow along the mesh boundary or split one element, so this approach allows the fracture propagation path without the initial pre-determined meshes control. In the cases of classical fracture propagation and fracture interference analysis between adjacent fractures, the efficiency and accuracy of this approach was validated comparing the existing mesh reconstruction method. The results show that this approach can simulate fracture growth exactly at more complex stress circumstances with the advantage of no singular element construction and local mesh refinement at fracture tips. The relative computational efficiency makes this approach can be applied for better description of fracture propagation problems in complex naturally fractured reservoirs.
1. INTRODUCTION
Hydraulic fracturing is a widely applied engineering technology. It plays an important role in many fields, such as petroleum stimulation, rock burst prevention, in-situ stress measurement and geothermal development et al. Especially, with the development of shale gas reservoirs, the novel concept of SRV (Stimulated Reservoir Volume) has been put forward, which aims to form a complex fracture network rather than single elliptical fracture [1, 2]. Thus, the hydraulic fracture design not only describes hydraulic fracture propagation accurately but also should be computationally efficient for engineering. However, the fracture propagation mechanical law and the intercoupling mechanisms between fracturing fluid and rock matrix in hydraulic fracturing treatment under complicated geological conditions remains a research challenge in current technology [3,4,5].
