汶川地震断裂带科学钻探孔壁稳定时效特性研究

发布时间：2018-08-31 20:10

【摘要】：针对断裂带地层钻探孔壁失稳问题,采用理论与实验研究相结合的方法,以汶川地震断裂带地层为例,对孔壁失稳的时效性问题进行较系统的研究。首先,详细分析了汶川地震断裂带地层钻探项目概况、地层特性以及原地应力分布特征和煤系泥页岩的影响。接着,通过微观试验得到了断裂带地层岩样的物质组成和微观结构,通过室内实验得到了断裂带地层岩样的水化应力及围岩抗压强度随水化时间的变化过程。然后,基于断裂带地层岩样的研究成果,展开了断裂带地层孔壁稳定时效数学模型的建立与分析,对断裂带地层钻探孔壁稳定时效特性进行了较深入研究。主要成果体现在如下几方面:(1)通过现场资料收集及差应变分析法,获得了岩样所在地层的地应力,并由此推导出地应力随深度变化的公式:σH=0.098×H-2.92(R2=0.605),该公式对地应力的计算具有一定的参考价值;(2)对岩样进行了一系列室内实验,其中,对断裂带地层岩样进行了X射线衍射实验和红外扫描实验,分析出了断裂带地层岩样主要矿物成分为伊利石、石英以及绿泥石等,其中的粘土矿物以降解的形式存在,易吸水膨胀造成孔壁失稳;通过扫描电镜实验观察分析,得到了岩样微观结构:片状结构且存在大量微小缝隙及孔喉,是孔壁失稳的内在结构因素。(3)根据应变实验绘制出了水化应力随水化时间的变化曲线,得到了在不同溶液中的最大水化应力及最长水化应力时间;并通过FLAC3D软件模拟钻孔水化过程,经计算分析发现:在浆液浸泡下,岩石力学强度的大幅变化基本在15h内完成。15h后,曲线平滑,降低趋势缓慢。(4)根据强度试验,获得了不同水化时间及不同浆液类型条件下的岩样抗压、抗剪强度。试验发现,随着水化时间的延长,岩石抗压强度、弹性模量都相继降低,岩石抗压强度受浸泡时间影响尤为明显;不同浆液类型浸泡后岩样抗压强度差别较大:清水浸泡后的岩样抗压强度大幅降低,2#、3#钻井液浸泡的岩心的抗压强度降低幅度最小,抗压强度仍可达36MPa;(5)通过膨胀实验,得到了水化应变随水化时间的变化关系,直观地了解到岩样在不同溶液中的膨胀量及最终破坏形态,在清水中膨胀量最大,在配制的钻井液中膨胀量得到了不同程度的抑制;(6)在以上一系列试验的基础上,为更加清楚形象地观察分析失稳过程中孔壁形态的变化以及相应应力的分布、变化规律,本项目分析了原地应力、钻井液液柱压力、孔隙压力以及水化应力所引起的应力共同作用于孔壁围岩上,得到了断裂带地层深部取心钻探孔壁围岩应力分布状态方程,并选定Mohr-Coulomb准则作为断裂带地层孔壁围岩失稳的判别准则。(7)利用COMSOL Multiphysics平台,采用岩土力学模块、多孔弹性模块以及自定义方程模块,对断裂带地层取心钻探孔壁稳定时效数学模型进行求解。得到了断裂带地层孔壁围岩上轴向应力及径向应力分布变化规律,及不同时刻孔壁围岩压力分布。(8)以WFSD-1孔水敏强蠕变破碎地层的钻进施工为例,研制出了具有高密度、低失水、低渗透、强润滑等特点的改性磺化钻井液体系,该体糸基本配方为:4%膨润十0.2%纯碱+0.5%高黏羧甲基纤维素钠(HV-CMC)+2%降失水剂(S-1)+5%成膜剂(X-1)+3%磺化沥青(SAS)+1%无铬磺化褐煤(SMC)+重晶石粉。该体系顺利解决了断裂带孔壁稳定的时效问题。
[Abstract]:Aiming at the problem of borehole wall instability in fault zone strata, this paper takes Wenchuan earthquake fault zone strata as an example to systematically study the time-effect of borehole wall instability. Firstly, the general situation of drilling project, stratum characteristics and in-situ stress distribution characteristics in Wenchuan earthquake fault zone strata are analyzed in detail. Secondly, the material composition and microstructure of rock samples in fault zone are obtained by microscopic test, and the variation of hydration stress and compressive strength of surrounding rock with hydration time are obtained by laboratory test. Based on the establishment and analysis of the mathematical model of formation borehole wall stability aging, the characteristics of drilling borehole wall stability aging in fault zone are studied in depth. The main achievements are as follows: (1) Through field data collection and differential strain analysis, the ground stress of the stratum where the rock sample is located is obtained, and the variation of ground stress with depth is deduced. Formula: _H = 0.098 *H-2.92 (R2 = 0.605), the formula has a certain reference value for the calculation of in-situ stress; (2) A series of laboratory experiments were carried out on rock samples, in which X-ray diffraction and infrared scanning experiments were carried out on rock samples in the fault zone, and the main mineral components of rock samples in the fault zone were analyzed as illite, quartz and chlorite. Stone and other clay minerals exist in the form of degradation, which is easy to destabilize the pore wall due to water swelling. Through scanning electron microscopy observation and analysis, the microstructure of the rock sample is obtained: sheet structure with a large number of micro-cracks and pore throats is the internal structural factor of pore wall instability. (3) According to strain experiment, the hydration stress with hydration time is drawn. The maximum hydration stress and the longest hydration stress time in different solutions are obtained. The hydration process of boreholes is simulated by FLAC3D software. The results show that the great change of rock mechanical strength is basically completed within 15 hours after the slurry immersion. After 15 hours, the curve is smooth and the decrease trend is slow. (4) According to the strength test, the result is obtained. The compressive strength and shear strength of rock samples under different hydration time and different grout types are obtained. The results show that the compressive strength and modulus of elasticity of rock decrease successively with the extension of hydration time, and the compressive strength of rock is especially affected by soaking time. The compressive strength of the core immersed in 2#, 3# drilling fluid decreases greatly, the compressive strength of the core immersed in 2#, 3# drilling fluid decreases minimally, and the compressive strength can still reach 36 MPa. (5) The relationship between hydration strain and hydration time is obtained by swelling test, and the swelling amount and ultimate failure form of the rock sample in different solutions are intuitively understood. Expansion of drilling fluid is restrained to some extent; (6) Based on the previous series of tests, in order to observe and analyze the change of hole wall morphology and the distribution and variation of corresponding stress in the process of instability more clearly and vividly, the in-situ stress, drilling fluid column pressure, pore pressure and hydration stress are analyzed in this project. The stress caused by the force acts on the surrounding rock of the hole wall together, and the stress distribution equation of the surrounding rock of the deep core drilling hole wall in the fault zone is obtained, and the Mohr-Coulomb criterion is selected as the criterion for judging the instability of the surrounding rock of the hole wall in the fault zone. (7) Using COMSOL Multiphysics platform, geomechanics module, porous elastic module and so on are adopted. A self-defined equation module is used to solve the mathematic model of borehole wall stability and aging in coring drilling in fault zone. The variation law of axial stress and radial stress distribution in the surrounding rock of borehole wall in fault zone is obtained, and the pressure distribution of borehole wall at different time is also obtained. (8) Taking the drilling operation in WFSD-1 water-sensitive creep fractured formation as an example, a drilling tool is developed. A modified sulfonated drilling fluid system with high density, low water loss, low permeability and strong lubrication is developed. The basic formula of the system is: 4% bentonite 10.2% soda + 0.5% high viscosity sodium carboxymethyl cellulose (HV-CMC) + 2% dehydrating agent (S-1) + 5% film forming agent (X-1) + 3% sulfonated asphalt (SAS) + 1% chromium-free sulfonated lignite (SMC) + barite powder. The aging problem of hole wall stability.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P634

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