【作者】 杨敬源；

【导师】 唐立强；

【作者基本信息】 哈尔滨工程大学 ， 固体力学， 2009， 博士

【摘要】 井壁失稳问题是石油钻井过程中普遍存在并一直困扰石油工业界的一个重大问题。钻井过程中井壁失稳易造成井壁垮塌、缩径、漏失、卡钻及储层污染等井下复杂情况和事故,严重制约了油气田勘探开发的发展。在油气勘探开发中钻井费用占了勘探开发总费用的50%-80%,研究和应用具有先进、适用性的钻井技术是降低钻井成本的关键。钻井过程是地下工程,涉及到复杂的地质结构,因而井壁失稳问题是国内外石油钻井界十分关注和亟待解决的难题之一。论文从力学的角度,应用地质力学、弹塑性力学、有限变形弹塑性理论、断裂力学和损伤力学理论对井壁稳定机理进行研究。1、岩石材料的强度(破坏)准则在钻井工程中发挥着基础作用,对于硬脆岩石它为岩石材料的破坏提供判定标准,而对于塑性变形岩石,它是进一步建立岩石弹塑性本构关系重要的基础。论文对岩石材料的强度(破坏)准则进行了评述。在材料为均匀各向同性时,考虑到岩石材料从弹性到非线性变形过程的连续性,认为采用双参数强度准则,不但给处理问题带来方便,同时也具有物理意义上的合理性。2、当井眼完钻后,在井眼周围引起应力重新分布,形成井壁周围的应力集中。在外载荷作用下,井壁内部区域介质由于弹性而进入塑性变形阶段。将地层岩石视为多孔弹塑性介质,建立了考虑孔隙压力和渗流作用的影响以及岩石拉、压屈服强度不等的SD效应的井壁稳定问题的理论分析模型。采用自相似假设,对井壁周围岩石进行了弹塑性力学分析,给出了井壁周围的应力和位移分布。3、在岩盐层和塑性泥岩层中的井眼缩径问题的研究是钻井工程关注问题之一。从变形量级的分析和现场观测的结果可以发现,采用小变形理论分析井眼的缩径具有明显的缺陷。应用有限变形次弹--塑性理论,建立了井眼的缩径模型,分析井眼附近力学量随外载荷和本构参数的变化规律,力图为岩石材料本构参数的实验测定和调节钻井液密度防止井眼失稳提供理论参考依据。4、针对井壁附近的软岩在有限变形过程中产生的井眼挤毁问题,采用有限变形弹性理论研究井眼从圆形变形到椭圆形的变化过程,探讨了井眼挤毁的力学机理。5、通常在岩层中存在大量的随机分布的缺陷(孔洞、微裂纹等),岩石的微结构对井眼的稳定性有根本性的影响作用。在钻井工程中,人们把泥岩层作为含微裂纹的准脆性材料加以研究。论文采用细观力学和断裂力学相结合的方法,对井壁稳定性的问题中的井壁坍塌和地层破坏进行了定量的分析,确定了钻井液密度的范围。井壁失稳问题是一个复杂和需要进一步开展研究的问题,随着能源需求的加大和石油工业的不断发展,解决井壁失稳的问题就更加迫切,本文研究所得到的理论结果将为防止井壁失稳提供参考依据。更多还原

【Abstract】 It is a big problem in petroleum industry for the wellbore to lose stability in the process of drilling. It exists everywhere and troubles the petroleum industry. Many complex situations and accidents, such as borehole wall caving, shrinkage, leakage, stickiness and reservoir pollution, are caused by the instability of wellbore in the process of drilling, seriously constraining the exploration and development of oil and gas field. Drilling costs are accounted for 50% to 80% of the total costs of exploration and development in the exploration and development of oil and gas. It is the key of reducing drilling costs to investigate and apply more advanced and applicable drilling technology.Since drilling process is an underground engineering and correlative with complicated geologic structures, it becomes worldwide and more sophisticated for the wellbore to lose stability, and receives the attention of petroleum drilling industry at home and abroad. In this thesis, the mechanism of wellbore stability is investigated from the perspective of mechanics, in geological mechanics, elastic-plastic mechanics, finite deformation elastic-plastic theory, fracture mechanics and damage mechanics.1. The strength (damage) criterion of rock material plays a fundamental role in drilling engineering. The strength criterion provides criteria for the damage of rock material in the case of hard and brittle rock, and is the important basis for further establishing the elastic-plastic constitutive relation of rock material in the case of plastic deformation rock. The strength criteria of rock material are reviewed in this thesis. When the material is homogeneous and isotropic, taking into account the continuity of the process for rock material to deform from elasticity to nonlinearity, it is believed that double parameter strength criterion used can bring the convenience of solving problems, and is reasonable in physical significance as well.2. When the wellbore is drilled, stresses around the wellbore are redistributed, stress concentration is formed around the wellbore. Under the application of external loads, wellbore internal region media enters the stage of plastic deformation because of the elasticity. Formation rock being thought as multi-aperture elastic-plastic medium, the theoretical analysis model of wellbore stability problem is established, considering the affect of pore pressure and seepage application, and the SD effect caused by different tension and compression yield strength of rocks. Self-similar assumption is used, elastic-plastic mechanics analysis is done for the rock around wellbores, and the distributions of stress and displacement are obtained.3. The investigation on the borehole shrinkage problem in rock salt and plastic mudstone formation is one of the problems widely concerned in drilling engineering. From the analysis of deformation order of magnitude and the results observed on site, it is found that the defect is obvious to analyze borehole shrinkage in small deformation theory. Finite deformation minor elastic-plastic theory being used, borehole shrinkage model is established, in order to provide theory reference for experimental determination of rock material, adjustment of drilling fluid density, prevention of wellbore instability.4. Aim at the borehole crush problem of the soft rock around borehole wall, which is produced in the process of finite deformation, the change process of borehole changing from circle shape to ellipse shape is investigated in finite deformation elastic theory, and the mechanics mechanism of borehole crush is discussed.5. There usually are a large number of random-distributed defects (cavities, micro-cracks, etc.) in rock formation. These micro-structures of rocks have fundamental influence on borehole stability. In drilling engineering, mudstone formations are investigated considering as quasi-brittle materials containing micro-cracks. The method of combining microscopic mechanics with fracture mechanics being used in the thesis, the borehole wall collapse and formation damage of borehole wall stability problems are analyzed quantitatively, the range of drilling fluid density is determined.The instability of wellbore is a complex problem which needs further investigation. With the more need of energy and the development of petroleum industry, it is urgent to solve the problem. The theory in present thesis provides references to avoid wellbore instability.更多还原