基于分形方法的水力压裂分支裂缝分布模拟

发布时间：2019-08-03 16:27

【摘要】：对水力压裂裂缝分布位置的准确描述是进行压裂设计及压裂效果评价的重要前提,而在人工裂缝分支的描述方面,尚未开展有关裂缝位置和形态等描述研究。运用分形L-系统建立树枝模型,建立岩石天然薄弱面分布规律的平面模拟描述方法。应用分形相似原理,将天然薄弱面分级,得出各级天然薄弱面剪切、张开判别条件和天然薄弱面起裂后裂缝内压裂液压降梯度。依据天然薄弱面分布模型及裂缝剪切、张性断裂准则,提出水力压裂分支裂缝分布模拟计算方法。计算结果表明,水力压裂分支裂缝数量与井壁处缝内净压力、储层最大与最小主应力差值密切相关。主裂缝附近存在较多分支裂缝,分支裂缝数量随井壁处缝内净压力增加而增多;储层最大与最小主应力差值越小,细小分支裂缝开启数量越多,裂缝沟通面积越大。运用该计算方法能够模拟具有分形特征的裂缝平面形态和开启状况,并为复杂裂缝形成机理分析提供依据。
[Abstract]:The accurate description of the distribution position of hydraulic fracturing fracture is an important prerequisite for fracturing design and fracturing effect evaluation, but in the description of artificial fracture branch, the description of fracture location and shape has not yet been carried out. The fractal L-system is used to establish the branch model, and the plane simulation description method of the distribution law of the natural weak surface of rock is established. Based on the principle of fractal similarity, the natural weak surfaces are classified, and the conditions of shear and opening discrimination of natural weak surfaces are obtained, and the hydraulic gradient of fracture internal fracturing after fracture of natural weak surfaces is obtained. According to the distribution model of natural weak surface and the criterion of fracture shear and tension, the simulation calculation method of fracture distribution in hydraulic fracturing branch is put forward. The calculation results show that the number of fracture branches in hydraulic fracturing is closely related to the net pressure in the wellbore and the difference between the maximum and minimum principal stress of the reservoir. There are many branch fractures near the main fractures, and the number of branch fractures increases with the increase of the net pressure in the wellbore. The smaller the difference between the maximum and minimum principal stress of the reservoir, the more the number of small branch fractures are opened, and the larger the fracture communication area is. By using this method, the fracture plane shape and opening condition with fractal characteristics can be simulated, and the basis for the analysis of complex fracture formation mechanism can be provided.
【作者单位】：东北石油大学石油工程学院;
【基金】：国家自然科学基金“基于混沌理论煤层气井压裂孔裂隙分形演化与渗流特征研究”(51274067)和“煤层压裂复杂裂缝形成机理与压后裂缝导流能力评价研究”(51504068) 东北石油大学研究生创新科研项目“注采诱发地层水平断面滑移和套损规律研究”(YJSCX2015-008NEPU)
【分类号】：TE357.1

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