页岩储层各向异性对水平井坍塌压力的影响

发布时间：2018-04-22 05:17

本文选题：页岩储层 + 力学各向异性　；参考：《应用数学和力学》2017年03期

【摘要】：为揭示层理页岩强度各向异性对水平井井壁坍塌压力的影响规律,对取自四川盆地龙马溪组页岩钻井不同层理角度的岩芯,通过岩芯观测、偏光显微镜、扫描电镜试验分别从宏观和微观角度研究了页岩层理特征,并基于单轴抗压强度研究了页岩强度各向异性特征.层理结构发育导致页岩呈现出显著的各向异性特征,粗略地将页岩视为各向同性体及简单采用Mohr-Coulomb准则作为破坏判据,使得预测的维持井壁稳定的坍塌压力不能满足安全钻井的需要.该文在研究层理地层岩石力学特性的基础上,采用横观各向同性地层井周应力分析模型,研究了弹性模量及地应力各向异性比对井周应力的影响;并结合考虑中间主应力的Mogi-Coulomb判据,分析了井壁坍塌压力对弹性模量E和Poisson(泊松)比ν各向异性比值变化的敏感性.实例分析结果表明:弹性模量和水平地应力各向异性比值的变化会对井周应力产生较大影响;Poisson比各向异性对井壁坍塌压力没有明显影响,而弹性模量比值的变化对井壁坍塌压力影响较大;横观各向同性地层中井壁坍塌压力与储层水平和垂直方向的硬脆性强弱关系有关,弹性力学参数各向异性既有可能利于井壁稳定,也可能更易导致井壁的剪切破坏;在实际工程中应根据储层岩石水平和垂直方向的硬脆性强弱关系,确定安全钻井液密度窗口.该结果对现场施工具有很好的指导意义.
[Abstract]:In order to reveal the influence of anisotropy of shale strength on the collapse pressure of horizontal well wall, the core of shale drilling in Longmaxi formation, Sichuan Basin, with different bedding angles, was observed by core and polarized light microscope was used. The shale bedding characteristics were studied by scanning electron microscope (SEM) from macroscopic and microscopic angles, and the anisotropy of shale strength was studied based on uniaxial compressive strength. The development of bedding structure leads to the shale showing obvious anisotropic characteristics. Shale is roughly regarded as isotropic and the Mohr-Coulomb criterion is simply used as the failure criterion. The predicted collapse pressure to maintain the stability of wellbore can not meet the need of safe drilling. Based on the study of the rock mechanical properties of stratified strata, the influence of the ratio of elastic modulus and in-situ stress anisotropy on the stress around the well is studied by using the stress analysis model of transversely isotropic formation. Based on the Mogi-Coulomb criterion considering the intermediate principal stress, the sensitivity of collapse pressure to the variation of elastic modulus E and Poisson ratio v anisotropy ratio is analyzed. The results of practical analysis show that the variation of elastic modulus and horizontal anisotropic ratio of in-situ stress will have a great influence on the stress around the well. The Poisson ratio anisotropy has no obvious effect on the collapse pressure of wellbore. However, the variation of elastic modulus ratio has a great influence on the wellbore collapse pressure, and the sidewall collapse pressure in transversely isotropic formation is related to the hardness and brittleness of the reservoir in the horizontal and vertical directions. The anisotropy of elastic mechanical parameters may not only benefit the stability of wellbore, but also lead to shear failure of wellbore more easily. In practical engineering, the safe drilling fluid density window should be determined according to the relationship of hard brittleness in horizontal and vertical direction of reservoir rock. The results are of great significance for site construction.
【作者单位】：油气藏地质及开发工程国家重点实验室(西南石油大学);西南石油大学;
【基金】：国家自然科学基金石油化工联合基金重点支持项目(U1262209);国家自然科学基金(51274172) 四川省应用基础研究计划项目(2014JY0092)~~
【分类号】：TE243

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