摘要
The fracture initiation behavior for hydraulic fracturing treatments highlighted the necessity of proposing fracture criteria that precisely predict the fracture initiation type and location during the hydraulic fracturing process.In the present study,a Mohr-Coulomb criterion with a tensile cut-off is incorporated into the finite element code to determine the fracture initiation type and location during the hydraulic fracturing process.This fracture criterion considers the effect of fracture inclination angle,the internal friction angle and the loading conditions on the distribution of stress field around the fracture tip.The results indicate that the internal friction angle resists the shear fracture initiation.Moreover,as the internal friction angle increases,greater external loads are required to maintain the hydraulic fracture extension.Due to the increased pressure of the injected water,the tensile fracture ultimately determines the fracture initiation type.However,the shear fracture preferentially occurs as the stress anisotropy coefficient increases.Both the maximum tensile stress and equivalent maximum shear stress decrease as the stress anisotropy coefficient increases,which indicates that the greater the stress anisotropy coefficient,the higher the external loading required to propagate a new fracture.The numerical results obtained in this paper provide theoretical supports for establishing basis on investigating of the hydraulic fracturing characteristics under different conditions.
水力裂缝的起裂特性对水力压裂工程的顺利实施至关重要,因此,需要提出准确预测水力裂缝起裂类型和位置的断裂准则。在本研究中,将带有拉伸截断的摩尔-库仑准则引入有限元程序中,用来确定水力裂缝的起裂类型和位置。该断裂准则考虑了裂缝倾角、岩石内摩擦角和载荷条件对裂缝尖端应力场分布的影响。研究结果表明,内摩擦角能减弱剪切断裂发生的可能。此外,随着内摩擦角的增加,需要更大的外部载荷来使水力裂缝扩展。随着注水压力的增大,拉伸裂缝类型最终决定了水力裂缝的起裂类型。但随着应力差的增大,则优先产生剪切裂缝类型。最大拉应力和等效最大剪应力均随着应力差的增大而减小,说明应力差越大,裂缝扩展所需的外载荷越大。本文的数值计算结果为研究不同条件下水力裂缝的起裂与扩展特性提供了理论依据。
作者
TANG Shi-bin
DONG Zhuo
WANG Jia-xu
MAHMOOD Ahmad
唐世斌;董卓;王嘉旭;MAHMOOD Ahmad(State Key Laboratory of Coastal and Offshore Engineering,Dalian University of Technology,Dalian 116024,China;Department of Civil Engineering,University of Engineering and Technology Peshawar(Bannu Campus),Bannu 28100,Pakistan)
基金
Project(2017YFC1503102)supported by the National Key Research and Development Program
Projects(51874065,U1903112)supported by the National Natural Science Foundation of China。
