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《Geomechanics and Geoengineering》2013,8(3):167-178
Wellbore instability, particularly in shale formations, is regarded as a major challenge in drilling operations. Many factors, such as rock properties, in-situ stresses, chemical interactions between shale and drilling fluids, and thermal effects, should be considered in well trajectory designs and drilling fluid formulations in order to mitigate wellbore instability-related problems. A comprehensive study of wellbore stability in shale formations that takes into account the three-dimensional earth stresses around the wellbore as well as chemical and thermal effects is presented in this work. The effects of borehole configuration (e.g. inclination and azimuth), rock properties (e.g. strength, Young's modulus, membrane efficiency and permeability), temperature and drilling fluid properties (e.g. mud density and chemical concentrations) on wellbore stability in shale formations have been investigated. Results from this study indicate that for low-permeability shales, chemical interactions between the shale and water-based fluids play an important role. Not only is the activity of the water important but the diffusion of ions is also a significant factor for saline fluids. The cooling of drilling fluids is found to be beneficial in preventing compressive failure. However, decreasing the mud temperature can be detrimental since it reduces the fracturing pressure of the formation, which can result in lost-circulation problems. The magnitude of thermal effects depends on shale properties, earth stresses and wellbore orientation and deviation. Conditions are identified when chemical and thermal effects play a significant role in determining the mud-weight window when designing drilling programmes for horizontal and deviated wells. The results presented in this paper will help in reducing the risks associated with wellbore instability and thereby lowering the overall non-productive times and drilling costs. 相似文献
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科学钻探深井结晶岩处在高地应力、高地层压力和高地温的“三高”环境中,自身的结构特征和物化特性会发生根本性变化,因温度变化引起的应力变化极易导致井壁失稳。本文依据温压耦合影响下坍塌压力和破裂压力计算模式,确定不同井壁温度下的安全钻井液密度窗口,通过FLAC3D开展温压耦合影响下井壁稳定数值模拟,分析在不同钻井液密度下井眼打开后不同时间的井壁周边温度和井壁稳定变化情况。结果表明：地层弹性参数对地层破裂压力的影响较大,对于花岗岩此类弹性模量较大的结晶岩,温度变化对破裂压力影响更大;井壁处附加应力受温度变化的影响程度：附加周向应力>附加径向应力>附加垂向应力;在最小主应力方向的井壁周边地层等效应力与钻井液密度呈正比关系,在最大主应力方向呈反比关系。 相似文献
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针对钻井工程常遇的层理性地层,以应力张量坐标转换关系和井孔应力集中方程为基础,引入弱面剪切滑动和岩体Mogi-Coulomb双强度准则,建立了分析层理性地层井壁稳定性的模型。对含层理弱面的典型油气储层中钻井的合理钻井液密度和安全钻井方向进行研究,结果表明：层理面的存在加剧了井壁围岩的破坏,且改变了围岩破坏的位置;水平井坍塌压力随着钻井方向变化而连续性变化,其在特定钻井方向取得最小坍塌压力;斜井取得最小坍塌压力的方位与层理面在空间中并不垂直,空间中关于主平面对称的斜井破裂压力相同;既可获得较大钻井液安全压力窗口又可取得较小坍塌压力的方向为优选钻井方向,在钻井液压力窗口变化大的倾向上钻井需严格控制钻井轨迹曲线。 相似文献
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Jun-Liang Yuan Jin-Gen Deng Qiang Tan Bao-Hua Yu Xiao-Chun Jin 《Rock Mechanics and Rock Engineering》2013,46(5):1157-1164
Serious wellbore instability occurs frequently during horizontal drilling in shale gas reservoirs. The conventional forecast model of in situ stresses is not suitable for wellbore stability analysis in laminated shale gas formations because of the inhomogeneous mechanical properties of shale. In this study, a new prediction method is developed to calculate the in situ stresses in shale formations. The pore pressure near the borehole is heterogeneous along both the radial and tangential directions due to the inhomogeneity in the mechanical properties and permeability. Therefore, the stress state around the wellbore will vary with time after the formation is drained. Besides, based on the experimental results, a failure criterion is verified and applied to determine the strength of Silurian shale in the Sichuan Basin, including the long-term strength of gas shale. Based on this work, horizontal well borehole stability is analyzed by the new in situ stress prediction model. Finally, the results show that the collapse pressure will be underestimated if the conventional model is used in shale gas reservoirs improperly. The collapse pressure of a horizontal well is maximum at dip angle of 45°. The critical mud weight should be increased constantly to prevent borehole collapse if the borehole is exposed for some time. 相似文献
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井壁失稳是钻井过程中常常遇见的难题之一,尤其在钻遇泥页岩井段。针对河南中牟页岩气区块在山西组-太原组泥页岩钻进过程中发生井壁坍塌掉块、卡钻、井径扩大率大等复杂情况,利用MY1井钻井岩心从泥页岩类型划分、孔渗特征、微观结构、岩石力学以及地应力等方面开展井壁稳定性影响因素实验分析。通过分析可知,中牟区块泥页岩属硬脆性泥页岩,造成井壁失稳的主要因素为地层非均质性强,岩石脆性程度较高,微裂缝发育,易导致井壁机械剥落、坍塌掉块。通过合理控制钻井液密度、优化井身结构及钻井参数、研发低自由水强封堵钻井液提高井壁稳定性,在区块钻井实践中取得了较好的应用效果,基本解决了井壁失稳难题。 相似文献
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横观各向同性水敏性地层斜井眼坍塌压力确定 总被引：1，自引：0，他引：1
在以泥页岩为目标储层的非常规油气藏水平井开发中, 钻遇井壁的稳定性问题突出, 一方面是由于在设计钻井液密度时简单采用各向同性介质模型和Mohr-Coulomb强度准则, 另一方面则是由于选用的钻井液性能欠佳, 难以保证建井全过程的井壁稳定。为此, 将地层视为横观各向同性介质, 采用Mogi-Coulomb强度准则判别岩石基体和层理面的稳定性, 同时考虑泥页岩水化作用对岩石力学强度参数的影响, 建立了水敏性地层井壁稳定分析模型, 分析了坍塌压力随井斜、方位、钻井液性能、钻井时间等因素的变化规律。研究结果表明:对于具有显著层理面结构的泥页岩地层, 采用横观各向同性模型比各向同性介质模型更能描述强度的各向异性;采用Mogi-Coulomb准则比Mohr-Coulomb强度准则得到的坍塌压力值与实际吻合程度更高, 在保证井壁稳定的前提下有利于降低钻井液密度, 实现钻井提速;提高钻井液封堵能力、减小泥页岩吸水扩散能力, 有利于延长坍塌周期。利用东濮、威远、焦石坝等工区多口页岩气水平井的实钻资料对本文方法进行了验证, 证实本文方法确定的钻井液密度窗口下值更能满足安全钻井需求。 相似文献
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基于三维快速拉格朗日有限差分法多孔介质流固耦合理论及弹塑性极限平衡理论,根据羌塘盆地天然气水合物钻探试验井工程QK-2井实钻资料,分析在渗流条件下井壁失稳机理,并对失稳段井壁稳定性进行了数值模拟分析,研究在不同钻井液密度下井径周围围岩应力分布和井眼坍塌或拉裂变形规律,为羌塘盆地天然气水合物钻探试验井工程确定地层不坍塌（不缩径）、不压漏的钻井液安全密度窗口,以便为钻井井身结构设计及合理钻井液密度的确定提供依据。 相似文献
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为了维护极地深部冰层取心钻探工作中钻孔的稳定,避免孔内事故的发生,冰层孔壁的水压致裂问题是亟待解决的重要科学问题之一。本文在深入分析国内外冰层钻探资料的基础上,结合冰盖动力学相关理论,计算得出了钻孔所在区域冰层的密度、温度及内部应力随深度的变化规律。在此基础上,结合油气资源勘探水力压裂技术与冰层钻进钻井液等相关理论,建立了合理的孔壁压差计算方法,深入探讨了适用于深部冰层钻探孔壁水压致裂机理。研制了冰层钻孔水压致裂模拟实验装置,可分析研究不同围压条件下冰样的脆性变形机理。结合我国Dome A深冰心钻探工程实际,提出钻孔可能发生水压致裂的深度区域及孔壁所需的起始裂纹长度判定,以期为后续的安全高效冰层钻进提供重要的理论依据。 相似文献
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地热井钻井作业时,井深越大,井眼温度越高,给钻探施工造成的难度越大,因此有必要研究井内循环温度分布。通过分析钻井液循环时热量传导过程,利用井筒温度控制方程,结合雄安新区地热井工程实例中的各项参数,使用全隐式有限差分法求解方程,求解井内钻井液循环时各部分的温度分布。且通过方程模拟研究了钻井液的密度、粘度、排量等工程参数对井壁温度分布的影响,结果表明：钻井液密度、粘度、排量越大,井壁温度越低,井底附近的井壁温度降低幅度越大,其中钻井液的排量改变对井壁温度分布的影响最大。模拟研究结果对于现场施工设计有一定的参考价值。 相似文献
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贵州地热井钻遇地层以灰岩和白云岩为主,夹杂泥岩、砂岩及煤层等不稳定地层,为满足井壁稳定及配合螺杆钻进工艺的需求,确定采用强抑制聚合物钻井液体系。通过正交试验确定了室内配方,并对配方的综合性能进行了室内测评。FT-1与QS-2协同作用可有效改善泥皮质量,白油润滑剂在1%加量时即可将润滑系数降低至0.2以下。其综合性能测试结果表明：该钻井液体系具有良好的流变性,抑制性强且润滑性良好。相比于无固相聚合物钻井液,井眼清洁能力明显增强,机械钻速提高了129%,漏失风险有所下降,取得了良好的实钻效果。 相似文献
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龙门山地震断裂带地应力分布及其对井壁稳定的
影响———以WFSD-2 井为例 总被引：2，自引：0，他引：2
[摘 要]龙门山地震断裂带是我国最为强烈的地震带之一,地层破碎、地应力异常,钻孔缩径造成孔内事故频发,井壁稳定问题十分突出。本文介绍了汶川地震断裂带科学钻探施工中所发生的孔内事故情况,并通过对地层应力数据的统计分析,得出龙门山地震断裂带最大水平应力和最小水平应力随深度变化的回归曲线,最大水平应力梯度为4. 52MPa/100 m,最小水平应力梯度为2. 51 MPa/100 m。以WFSD-2 井为例,分析了龙门山地震断裂带地层应力、尤其是断层泥应力对井壁稳定的影响;针对膨胀性地层,介绍了一种通过泥浆密度微调现场测定地层坍塌压力和破裂压力的简易方法。 相似文献
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Weifeng Ge Mian Chen Yan Jin Fuxiang Zhang Yunhu Lu Pei Yang Jihui Ding Hao Zeng 《Rock Mechanics and Rock Engineering》2011,44(6):711-723
To alleviate the problems of casing collapse induced by the coupling effect of salt creep movement, as it relates to the curved
sections of horizontal wells, an experimental approach was taken to determine the creep (visco-elastic) property of the salt-gypsum
formation, using finite-difference software to establish a creep model with curved casing, wellbore and salt formation. With
this model, the effects of borehole curvature, drilling direction and casing thickness on external pressure on casing were
analyzed, and casing deformation in the non-uniform in situ stress field was simulated. For horizontal wells drilled through
salt-gypsum formations, this analysis led to the following conclusions: (1) the casing tends to be much safer when drilling
is undertaken along the direction of the minimum horizontal stress; (2) casing deformation occurs and stress increases as
the borehole curvature increases; (3) for the same curvature and drilling direction, thicker casings are safer; (4) as the
creep time increases, the external pressure on the casing rapidly increases until it reaches its maximum value, whereupon
it stays at that value; (5) under the effect of non-uniform in situ stress, a larger non-uniform coefficient would result
in greater external pressure on the casing. This model has been successfully applied to analyze the external pressure on curved
casings in a build-up section for horizontal wells drilled through salt-gypsum formations in an oilfield in Northwest China.
The model has helped to improve the casing design and reduce drilling downtime with greater wellbore stability in salt-gypsum
formations. 相似文献
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涪陵地区页岩层蕴含着丰富的天然气资源,具有较大的开采前景。区块主要目的层为上奥陶统五峰组-下志留统龙马溪组下部页岩气层。上部泥页岩地层井壁稳定性差,地层承压能力低,溶洞发育、易坍塌、易漏失;海相沉积地层流体分布复杂,部分地层岩性变化大,可钻性差,机械钻速较低;采用丛式布井,水平井井眼轨迹复杂,靶前位移大,大井眼定向扭方位困难、托压严重。现场试验使用了旋转导向、扭力冲击器、旋冲马达、水力振荡器等新技术、新工具,大幅度提高机械钻速,缩短钻井周期,取得一定的经济效益。阐述了几种新技术和新工具的工作原理、现场应用情况,并对其经济效果进行了评价。 相似文献
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