页岩地层水力裂缝剪切滑移机理研究

发布时间：2018-03-23 20:24

本文选题：页岩地层　切入点：水力压裂　出处：《西南石油大学》2015年硕士论文

【摘要】：水力压裂技术是低渗、致密和非常规油气藏增产的一项重要措施。在压裂过程中,地层内除了形成水力裂缝之外,常含有诸如天然裂缝、节理、断层等不连续面,所有这些结构面的力学行为都会对最终的裂缝形态和压裂效果产生重要影响。过去由于岩体的抗张强度一般小于剪切强度,因此裂缝的张性破坏研究地比较充分,而剪切滑移行为并未引起重视。近年来,随着页岩油气的开发,人们逐渐认识到裂缝的剪切滑移对地层的导流能力提升有重要的影响,但目前开展的定量研究并不多。本文首先讨论了剪切裂缝形成的力学条件,描述了裂缝剪切滑移的物理过程,然后以二维平面裂缝为研究对象,分别引入复变函数理论与位移不连续方法,建立了Ⅰ-Ⅱ型水力压裂缝应力及位移场计算模型和天然裂缝的滑移量计算模型。最终,基于滑移量计算结果,定量分析了由剪切滑移引起的裂缝导流能力的变化。理论分析表明,剪切滑移常发生天然裂缝或节理中,滑移过程中的剪切膨胀现象对裂缝的导流能力提升有重要影响；滑移量大小受力学参数和地层性质等控制,与裂缝半长和剪切应力成正比,与杨氏模量及摩擦系数成反比；天然裂缝面的剪切滑移存在阈值压力,低于该压力时天然裂缝的存在对应力分布没有影响,应力超过阈值后裂缝面从中部开始滑移。实验研究表明,裂缝发生剪切滑移后,导流能力会发生数量级的增加,但导流能力与具体滑移量之间并无明显联系。研究结果对页岩地层缝网压裂剪切滑移机制研究及压裂优化设计具有一定的指导意义。
[Abstract]:Hydraulic fracturing is an important measure to increase production in low permeability, dense and unconventional reservoirs. In the process of fracturing, in addition to forming hydraulic fractures, there are often discontinuous surfaces such as natural fractures, joints, faults, etc. The mechanical behavior of all these structural planes will have an important impact on the ultimate fracture morphology and fracturing effect. In the past, the tensile strength of rock mass was generally smaller than that of shear strength, so the tensile failure of fracture was studied more fully. In recent years, with the development of shale oil and gas, people have come to realize that the shear slip of fractures has an important effect on the enhancement of formation conductivity, but there are few quantitative studies carried out at present. In this paper, the mechanical conditions for the formation of shear fractures are discussed, and the physical process of shear slip is described. Then the theory of complex variable function and the method of discontinuity of displacement are introduced. The calculation model of stress and displacement field and the slip calculation model of natural crack are established. Finally, based on the calculation results of slip quantity, the variation of fracture conductivity caused by shear slip is quantitatively analyzed. Theoretical analysis shows that shearing slip often occurs in natural cracks or joints, the shear expansion phenomenon in the process of slip has an important effect on the enhancement of the conductivity of cracks, and the magnitude of slippage is controlled by mechanical parameters and formation properties, etc. It is directly proportional to the fracture half length and shear stress, and inversely proportional to Young's modulus and friction coefficient. There is a threshold pressure on the shear slip of the natural fracture surface, but the existence of the natural crack has no effect on the stress distribution when the pressure is lower. After the stress exceeds the threshold value, the fracture surface begins to slip from the middle part. The experimental results show that the conductivity increases by an order of magnitude after the shear slip occurs, but there is no obvious relationship between the conductivity and the specific slip. The research results have certain guiding significance for the study of fracturing and slip mechanism of fracture network in shale formation and the optimum design of fracturing.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE357.1

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