人工裂缝逼近条件下天然裂缝破坏特征分析

发布时间：2018-08-29 13:00

【摘要】：通过水力压裂裂缝的诱导应力场打开远场天然裂缝,可改变储层应力场,易形成压裂主裂缝、分支缝、应力松弛缝相互连通的裂缝网络,从而提高了页岩气储层改造效率,因此在页岩气开采中具有广阔的应用前景。人工裂缝逼近条件下天然裂缝的破坏特征是人工裂缝诱导应力场激活远场天然裂缝的核心问题之一。应用位移间断法(DDM),建立了人工裂缝逼近条件下激活天然裂缝的力学模型。根据摩尔-库仑破坏准则,建立了不同天然裂缝破坏状态的约束条件,形成了天然裂缝破坏特征的计算方法,并通过算例验证其正确性。在此基础上,模拟了人工裂缝逼近条件下天然裂缝张开、滑移、闭合行为,并研究了其影响因素。结果表明,天然裂缝下表面处最大主应力呈双峰型分布,天然裂缝下表面处最大主拉应力随着天然裂缝与最大水平主应力方向夹角的增加而增大。当人工裂缝逼近天然裂缝时,天然裂缝的剪切型破坏长度大于张拉型。天然裂缝破坏长度随着天然裂缝与最大水平主应力方向夹角的增大而减小,随着缝内净压力的增大而增大。天然裂缝破坏长度随着人工裂缝尖端到天然裂缝的距离的减小而增加。天然裂缝剪切型破坏长度随着摩擦系数及黏聚力的增大而减小。研究结果对页岩气压裂技术具有理论指导意义。
[Abstract]:Through the induced stress field of hydraulic fracturing fracture to open the far-field natural fracture, the stress field of reservoir can be changed, and the fracture network of fracturing main fracture, branch fracture and stress relaxation fracture can be easily formed, thus improving the transformation efficiency of shale gas reservoir. Therefore, it has a broad application prospect in shale gas production. The failure characteristics of natural fractures under the condition of artificial crack approximation are one of the core problems of artificial fissure-induced stress field activating far-field natural fractures. The displacement discontinuous method (DDM),) is used to establish a mechanical model for activating natural cracks under the condition of artificial crack approximation. According to the Mohr-Coulomb failure criterion, the constraint conditions of different natural fracture failure states are established, and the calculation method of the natural fracture failure characteristics is formed, and the correctness of the method is verified by an example. On this basis, the behavior of natural crack opening, sliding and closing under the condition of artificial crack approximation is simulated, and the influencing factors are studied. The results show that the maximum principal stress at the surface of natural crack is a bimodal distribution, and the maximum principal tensile stress increases with the increase of the angle between natural crack and the direction of the maximum horizontal principal stress. When artificial cracks approach natural fractures, the shearing failure length of natural fractures is longer than that of tensile ones. The fracture length decreases with the increase of the angle between the natural fracture and the maximum horizontal principal stress direction, and increases with the increase of net pressure in the fracture. The damage length of natural crack increases with the decrease of the distance from the tip of artificial crack to the natural crack. The shear failure length of natural crack decreases with the increase of friction coefficient and cohesive force. The results are of theoretical significance for shale pressure fracture technology.
【作者单位】：中国石油大学(华东)石油工程学院;
【基金】：中央高校基本科研业务费专项资金资助(No.14CX06023A) 国家自然科学基金资助项目(No.51274230)~~
【分类号】：TE357.1

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