关键词: 有限元-离散元法, FDEM-Flow, 水力压裂, 地应力

Abstract: With the proposed FDEM-Flow (combined finite-discrete element method considering fluid-solid coupling) method as a tool, we study the effects of in-situ stress on hydraulic fracturing. Through a numerical examples of an injection hole under the state of different in-situ stresses, the influence of in-situ stress on the direction and morphology of fracturing crack is studied. The results show that both the initiation pressure and direction of fracturing fractures are closely related to in-situ stress. When the vertical in-situ stress keeps constant and the lateral pressure coefficient ?>1, the initiation pressure and breakdown pressure are decreased. When ?>1 and its value is comparatively small, horizontal cracks are mainly produced with some oblique cracks generating. However, when ?>1 and the value is larger, cracks are strictly extended along the direction of the maximum principal stress and oblique cracks no longer occur. When ?<1, fracture pattern is dominated by vertical cracks. But when ?=1, the horizontal in-situ stress and vertical in-situ stress are equal, there is no advantage direction for crack extension. Under the conditions of different lateral pressure coefficients, the direction of crack propagation always coincides with that of the maximum principal stress. The fracture initiation and propagation are mainly controlled by the maximum principal tensile stress, and fractures are initiated in the concentration zones of tensile stress. These results agree well with the available experimental results and theoretical analysis, which demonstrate the effectiveness of FDEM-Flow method to simulate hydraulic fracturing.

Key words: finite-discrete element method (FDEM), FDEM-Flow, hydraulic fracturing, in-situ stress