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用提出的FDEM-Flow(考虑流固耦合的离散元-有限元耦合方法)方法作为工具,研究了地应力对水力压裂的影响。通过一个注水圆孔的算例,研究不同地应力状态对压裂裂隙的走向和形态的影响。研究结果表明,起裂压力的大小和压裂裂隙的方位均与地应力有密切关系。在竖向地应力v?保持不变的情况下,且侧压力系数?>1时,随着?的增大,起裂压力和失稳压力均减小;?>1时且取值较小时,主要产生水平向的裂隙,并有斜向裂隙产生;?>1时且取值较大时,裂隙严格按照最大主压应力的方向扩展,不再出现斜向裂隙;?<1时,主要产生竖向的裂隙;?=1时,水平地应力和竖向地应力相等,裂隙的扩展不存在优势方向。不同侧压力系数条件下,裂隙的扩展方向与最大主应力的方向一致,水力压裂裂隙的起裂和扩展主要由最大主拉应力控制,裂隙在拉应力集中的区域起裂。这些结果与已有的试验及理论认识是相符的,进一步验证了FDEM-Flow方法用于模拟水力压裂问题的有效性。
The proposed FDEM-Flow (Fluid-Solid Coupled Discrete Element-Finite Element Coupling Method) tool was used to study the effect of geostress on hydraulic fracturing. Through a numerical example of a water hole, the effect of different stress states on the strike and shape of fracturing fissures is studied. The results show that the magnitude of the initiation pressure and the orientation of fracturing fissures are closely related to the geostress. When the vertical stress v is constant and the lateral pressure coefficient is more than 1, the initiation pressure and the instability pressure decrease with the increase of σ, , Mainly produce horizontal fractures and oblique fractures; when> 1> 1 and the value is larger, the fractures expand strictly in the direction of the maximum principal compressive stress and the oblique fractures no longer appear; when <1, the main The vertical cracks are generated; when = 1, the horizontal stress and the vertical stress are equal, and there is no dominant direction for the crack propagation. Under the condition of different lateral pressure coefficients, the direction of crack propagation is consistent with the direction of maximum principal stress. The initiation and propagation of fractures in hydraulic fractures are mainly controlled by the maximum principal tensile stress, and the fractures initiate in the area where the tensile stress is concentrated. These results are consistent with the existing experimental and theoretical knowledge, which further validates the validity of the FDEM-Flow method for simulating hydraulic fracturing problems.