【作者】 张帆；

【导师】 孟英峰； 刘厚彬；

【作者基本信息】 西南石油大学 ， 油气井工程， 2018， 硕士

【摘要】 随着页岩气资源开发的持续进行,层理性地层的井壁稳定性问题日益突出,原有的基于各向同性假设的均质模型无法真实反映层理性地层的井壁稳定性问题。为揭示层状页岩井壁岩石垮塌失稳诱因,探索井壁垮塌主要控制因素,将层状页岩简化为横观各向同性材料,应用室内力学实验测试方法,采用龙马溪组井下岩心开展直接剪切和三轴实验。基于实验数据,通过考虑井下环境中页岩横观各向同性特征、力学强度各向异性,并考虑了层状地层各向异性的渗流特征,建立了层理性页岩井周应力分布模型,计算了地层井壁坍塌压力,结合实际钻井情况,分析了不同层理条件对井壁岩石垮塌失稳及井壁崩落的影响规律。主要研究工作有:(1)开展了岩石力学室内实验,实验结果表明,龙马溪页岩岩体平行层理极为发育,层理面间力学强度弱,沿层理走向的页岩剪切强度远低于垂直层理走向;页岩具有较强的力学参数各向异性,页岩的力学参数变化与取心方向密切相关,当取心方向与层理法向夹角β满足β=O0和β=900时,页岩力学强度较高,β=60°时,页岩力学强度较低。该研究成功解释了龙马溪组页岩水平钻井井壁岩石垮塌失稳的力学主控因素。(2)研究了层状地层的各向异性渗流特征,并揭示层理产状对水平井井周渗流应力的影响规律,综合分析了不考虑渗流,考虑渗流各向同性,渗流各向异性的井周渗流能力的分布规律。(3)研究了横观各向同性条件下,弹性参数、层理产状对水平井井周应力的影响规律,并研究了层状地层层理产状与水平井井周主应力的角度变化关系,建立了考虑最大主应力和中间主应力的水平井坍塌压力计算模型,揭示了最大主应力和中间主应力对坍塌压力的影响。结果表明,本文模型计算的坍塌压力随着井斜角先增加后减小,且与实际情况吻合。(4)分析了层状地层条件下考虑各向异性渗流的井壁失稳问题,基于此建立了考虑中间主应力的Mohr-Coulomb准则和弱面准则的井壁坍塌压力计算模型,研究了不同的弱面特征下,井壁坍塌压力的分布规律。发现:当同时考虑弱面和渗流时,坍塌压力高于只考虑一种因素时的坍塌压力。(5)基于井壁坍塌压力计算结果,建立了层状地层井壁崩落模型,研究了当井壁发生垮塌失稳时,不同层理条件下井壁失稳的方向及井壁崩落特征,发现了不同层理产状对井壁崩落形态的影响规律。本文研究成果为层理性地层水平钻井井身结构及工程参数优化设计奠定基础,具有较高的现场应用价值。更多还原

【Abstract】 With continuous development of shale gas resources,the rational formation layer of borehole wall stability problem increasingly prominent,the original homogeneous model based on isotropic hypothesis cannot reflect the rational formation of sidewall stability problem.To reveal the collapsed wall rock instability of stratified layers cause,explore the layered strata horizontal well casing collapse main control factors of indoor experiment mechanics test method,using the dragon stream set underground core direct shear and triaxial experiment.Based on experimental data,by considering the underground stress anisotropy and shale rock mass mechanics in the environment space bedding plane mechanical properties,and considering the seepage characteristics of the layered formation anisotropy,established the shale strength anisotropy well circumferential stress distribution model,calculated the layered strata formation caving pressure,combined with the actual drilling situation,analyzed the different bedding conditions on the sidewall rock collapse instability and borehole wall caving influence law.The main research work is:(1)We conducted laboratory experiments on rock mechanics.The experimental results showed that,the shale rock in Jiaoshiba area contains a large number of horizontal bedding fractures which display lower mechanical strength properties,and the shear strength of rocks along the bedding planes is much weaker than that perpendicular to bedding planes.The shale rocks have a strong anisotropy of mechanical parameters,and the variation of mechanical parameters is closely related with coring direction in shale rocks.The rock strength attains the highest value while the angle between coring direction and normal direction of bedding planes equal to 0°or 90°,the rock mechanical strengths reduce firstly and increase in the range of 30°to 90°,and the mechanical strength is lowest while the angle meets 60°.This paper successfully explain the main controlling factors for the wellbore instability of shale reservoirs drilled with horizontal well in Jiaoshiba area.(2)Studied the layered anisotropic seepage characteristics of strata,and reveal the bedding occurrence of horizontal Wells weeks the influence law of the seepage stress,without considering seepage are analyzed comprehensively,considering seepage isotropic seepage anisotropy,weeks seepage stress distribution law.(3)Layered stratigraphic principle is studied occurrence and relation between the Angle of principal stress,and the horizontal Wells weeks and transverse isotropic conditions is studied,and the elastic parameters,bedding,the influence law of occurrence of circumferential stress in the horizontal well,considering the maximum main stress is established and the intermediate principal stress of the horizontal well collapse pressure calculation model.The results show that the collapse pressure of the model is decreased with the increase of the well slope,and the calculation results are more consistent with the actual situation.(4)At the same time,the stability of borehole wall with anisotropic seepage is studied under the condition of both homogeneous and stratified strata.Based on the calculation model of the wall collapse pressure based on the mohr-coulomb criterion and the weak surface criterion,the distribution law of the collapse pressure of the borehole wall under different weak surface characteristics is analyzed.(5)Based on anisotropic formation caving pressure calculation model,further analysis when the instability of borehole wall collapsed,the direction of the borehole wall instability under the conditions of different bedding and borehole wall caving characteristics of borehole wall instability is calculated under the different conditions of hole enlargement ratio distribution,wall caving stratified layers model and predict the layered strata borehole wall caving characteristics.The research results of this paper lay a foundation for the structure of horizontal drilling well structure and optimization design of engineering parameters,and have high field application value.更多还原