塔河侧钻水平井硬脆性泥页岩井壁失稳研究及对策

考虑到避水与垂深的限制,将塔河侧钻水平井的造斜点设置在石炭系巴楚组或桑塔木组。此外,造
斜段在泥岩段钻进井段较长,钻井液的浸泡作用使井壁极易掉块坍塌,卡钻等复杂情况经常发生。通过黏土矿物、
理化特性、ＣＴ扫描等手段分析了易失稳泥岩的组构特征,易失稳地层属硬脆性泥岩,微裂隙发育。高温高压浸泡
岩心,进行ＣＴ扫描观察微裂隙扩展,并测试其抗压强度评价钻井液的抑制封堵性。采用多元协同的钻井液防塌机
理,兼顾物理化学封堵、抑制泥页岩表面水化、井壁固结以及合理的钻井液密度,开发了可以有效应对硬脆性泥页
岩剥落掉块的强抑制强封堵钻井液。经过ＴＫ２２７ＣＨ井的现场试验,取得良好的应用效果,垮塌掉块明显减少,井
径规则,保证了侧钻水平井在复杂泥岩段的安全施工。     

高庙子气田井壁稳定性研究及钻井技术对策

通过运用伊顿法建立了地层孔隙压力剖面,采用库仑-摩尔强度准则建立了地层坍塌压力剖面,根
据岩石最大拉应力理论建立地层破裂压力剖面。综合应力、掉块形态、裂缝发育、井斜等多因素分析,高庙地区地
层裂缝发育,钻井液密度过小引发力学原因垮塌,密度过高滤液易进入地层造成缝隙中地层压力的增大并降低地
层强度,从而增大坍塌压力加剧井壁失稳;同时井斜角在３０°～４０°之间的定向井坍塌压力最高,斜井段掉块最严
重,是造成地区地层失稳的主要原因。通过设计合理钻井液密度、优化钻井液性能、增加其封堵性和润滑性,基本
解决了钻井过程地层掉块,有效减少工程复杂情况,实现气田高效开发。     

高庙103D典型定向井复杂处理技术探索

川西高庙区块岩性疏松,成岩作用差,胶结差,泥岩发育,易发生井壁垮塌等复杂情况。钻井液密度偏低可能造成井壁的不稳定,发生垮塌。沙溪庙组砂岩的渗透性较好,钻井中遇到泥岩较发育就易水化膨胀掉块,造成井壁失稳。高庙103D井钻进至沙溪庙组,前期出现掉块,钻井液密度由1.74g/cm3经5次上提至2.13g/cm3,上提钻井液密度滞后,失去了维持泥岩稳定的最佳时机,最终钻井液密度上提至2.13g/cm3无法恢复井下稳定,导致填井侧钻。侧钻后,井下再次出现复杂状况一直持续到完钻,给施工造成无法挽回的损失。通过详细分析高庙103D井前后复杂的基本情况,并分析出现复杂的原因以及处理过程,最后提出施工的经验教训和建议。     

英买力地区古近系地层钻井液技术

英买力地区古近系地层在钻井中频繁出现卡钻、掉块、坍塌、井漏等井下故障,严重影响了钻井速度。为了弄清英买力地区古近系地层的井壁失稳机理,为钻井液选型和性能优化提供理论依据,对该地区黏土矿物组成及理化性能进行了系统分析。结合该地区盐膏层钻井液技术研究,对 KCl-聚磺欠饱和盐水钻井液体系性能进行了优化,提出了该钻井液体系在维护井壁稳定方面的技术要求。YM2-6 井现场应用结果表明,KCl-聚磺欠饱和盐水钻井液体系能够满足古近系膏泥岩段井壁稳定的要求,减小了发生井下故障的风险;黏土矿物的膨胀并不是导致膏泥岩段井壁失稳的主要原因。通过研究该地区古近系地层的井壁失稳机理,减小了井壁失稳的风险,为古近系地层的顺利钻进提供了理论支持。      

G构造深部地层井壁稳定研究

在东海西湖凹陷G构造勘探开发作业过程中,花港组以下深部地层多次发生由井壁失稳引发的起下钻遇阻、井壁掉块等井下复杂情况。该文选取伊顿法计算了地层孔隙压力纵向剖面,发现异常压力主要集中在花港组以下深部地层。并根据莫尔库伦准则进行井壁稳定钻后分析,该构造地区井壁失稳的主要原因是钻井液密度低于地层坍塌压力导致的力学失稳,以及由钻井液泥浆性能引起的泥岩水化。为确保后续钻井作业安全,建议在G构造相关区块开展钻前压力预测研究,并优选油基钻井液以避免泥岩水化。     

冀东NP280 Es31井壁稳定钻井液技术

针对冀东油田南堡280区块多口井钻遇至沙三₁亚段(Es₃¹)时发生井壁失稳,研究表明区块内泥岩遇水易产生水化作用,其漏失段间裂缝发育,裂缝多为中高角度裂缝,原裂缝宽度(0.1～100μm)受压力等诱导因素后变大导致成为致漏性裂缝漏失频繁,同时也会诱发大规模的掉块从井壁上剥落进而导致了井下的坍塌卡钻等井下复杂问题。对南堡280区块破碎地层进行井壁稳定机理、评价方法的相关研究,以原三开抗高温抑制钻井液为基础,进行室内优化实验,构建了适合诱导性裂缝地层的强封堵性井壁稳定钻井液,现场应用表明该钻井液体系可有效防止Es₃¹地层的坍塌失稳问题,具有重大的推广应用意义。     

定向井坍塌压力上限对钻井安全密度窗口的影响

一般钻井安全密度窗口通过计算坍塌压力与破裂压力确定,钻井液密度过低会引起井壁坍塌。实际钻井情况反映,钻井液密度超过坍塌压力上限也会造成井壁坍塌。结合井壁成像测井,分析了高密度钻井液下的井周应力状态,建立了σ_z'＞σ_r'＞σ_θ'模式的坍塌压力上限计算模型,推导得出了直井的解析表达式与定向井的数值计算方法。结果显示:不论直井或定向井,对于强度低于某一临界值的地层,以传统的破裂压力作为安全密度窗口的上限将会低估井壁失稳风险;地层强度临界值的大小取决于主地应力、孔隙压力、有效应力系数。对定向井而言,坍塌压力上限随井斜角和方位角变化的敏感性较高,沿水平最小地应力方向钻进的井眼坍塌压力上限较高;随井斜角增大,坍塌压力上限与破裂压力值逐渐趋于接近。研究结果可防范高密度钻井液引起的井壁损伤和井塌现象。     

流-固-化-热耦合的陆相页岩井壁稳定力学模型及应用

由于钻井液浸泡,陆相页岩中的黏土矿物发生水化膨胀,页岩力学强度会发生弱化,诱发井壁坍塌现象。为探讨陆相页岩井壁稳定机理,假设井壁页岩为多孔弹性介质,考虑页岩基质和层理随着钻井液浸泡时间的水化过程,构建了流-固-化-热耦合的井壁应力场模型,再结合剪切破坏准则,形成了陆相页岩井壁坍塌压力评价模型。以泌阳凹陷陆相页岩油藏A水平井基础参数为例进行计算,揭示了A井井壁失稳原因,并优选了钻井液密度。结果表明：水平井若沿着最小水平主地应力方向布置,则井壁坍塌风险最小;在井斜角为45～70º的造斜段内,可采用水基钻井液,但其密度应高于1.35g/cm³,在井斜角为70～90º的高造斜段内,应采用油基钻井液;研究结果与A井钻井情况吻合。该研究结果可应用于指导陆相页岩井壁坍塌压力预测和钻井设计。     

硬脆性地层井眼失稳剪切破坏程度定量预测

钻井过程中,硬脆性地层的井壁失稳的主要形式为剪切破坏（坍塌或掉块）。由传统的井壁失稳力学模型设计出的钻井液密度值偏高,不利于提高钻井速度和降低钻井成本。然而,实钻过程中井眼往往存在一定的井径扩大现象,并产生一定程度的坍塌掉块而不会发生井壁失稳和井筒复杂事故。为此,有必要建立硬脆性地层
井壁失稳程度的定量预测模型。根据硬脆性地层井壁破碎前仅出现弹性变形的特征,基于线弹性理论!推导出直井的井壁围岩应力模型!建立了井壁失稳（剪切破坏）程度与地应力、孔隙压力、岩石力学参数、井筒液柱压力之间的定量关系,并对主要影响因素进行了敏感性分析。对比实例井的实测数据,该模型计算结果与实钻情况一致,具有很好指导意义。     

雪古2井钻井液技术

雪古2井位于胜利油田沾化东区块,目的层为第三系地层。该井东营组以上地层胶结松散,易水化分散引起井壁坍塌;沙河街组以下地层以泥岩,砂岩、泥页岩、薄煤层为主,地层裂缝发育,易水化膨胀引起坍塌掉块,导致井壁失稳。使用氯化钾聚合醇(KCl-AQUAL)钻井液,井壁稳定,井下正常,较好地解决了这一技术难题。     

基于可靠度理论的斜井井壁失稳风险评价方法

由于地质环境的隐蔽性和复杂性,地质力学参数和岩石力学参数具有很大的不确定性,井壁稳定分析中忽略不确定的影响可能导致钻井液密度设计不合理,进而直接影响钻井井壁稳定。国内外学者对确定参数条件下的井壁稳定开展了深入的研究,但对不确定参数条件下井壁稳定影响的研究并不深入,尤其是对于任意斜井失稳风险的评价。为此,在井壁稳定孔弹性力学模型和崩落宽度模型基础上,建立了基于可靠度理论的井壁失稳风险评估方法,采用Monte-Carlo随机方法模拟了四川盆地CW气田直井、斜井和水平井的井壁失稳风险,并系统分析了参数均值和方差对井壁失稳的影响规律。研究结果表明：①随着井斜角增加,井壁坍塌当量密度显著增加,井壁破裂当量密度显著降低,不同井型失稳风险与常规井壁稳定规律基本一致。②考虑参数不确定影响后,坍塌当量密度增加、破裂当量密度降低,安全密度窗口逐渐变窄,说明参数不确定影响不可忽略。③崩落宽度对井壁坍塌影响显著,崩落宽度越大则井壁坍塌可靠度越高,在不发生井壁失稳事故的前提下,允许适当的井壁崩落有助于提高成功钻井概率。④4参数均值和变异系数敏感性分析结果表明,影响井壁稳定最为显著的因素为地应力,其次为孔隙压力和岩石强度;随着变异系数的增加,坍塌当量密度逐渐增加、破裂当量密度逐渐降低,安全密度窗口逐渐变窄,井壁失稳的风险越高。     

A study on wellbore stability in fractured rock masses with impact of mud infiltration

Maintaining a stable borehole is one of the major tasks encountered in the oil and gas industry due to the fact that wellbore instability-related problems will result in additional high drilling costs and have a severe impact on drilling schedule. Wellbore stability analysis has therefore been included at the well planning stage of many operating companies. However, majority of such wellbore stability analyses are based on continuum mechanics. Factors contributing to wellbore instability, such as trajectory of the wellbore, orientation and magnitude of the in situ stress field, rock properties, in situ and induced pore pressures and mud pressure, are normally considered in the analyses. In addition to failure in intact rock, wellbore instability can also be initiated along natural discontinuities, such as bedding planes and fractures, in rock masses. Furthermore, the rock masses will become more prone to wellbore instability along fractures penetrated by mud filtrate due to reduction in the fracture friction angle and loosening of blocks. In this paper, coupled numerical analyses are presented to investigate the influence of fractures in rock masses, in particular mud infiltration into the fractures, on wellbore stability under both isotropic and anisotropic stress states. Two regular fracture geometries are considered in the analyses. A simplified approach is developed to take into account the friction angle reduction of the fractures that occurs when infiltrated with mud. The results show that the presence of natural fractures and friction angle reduction of fractures due to mud infiltration significantly affect wellbore stability during drilling.     

Wellbore Instability and Countermeasures in Offshore Bedding Shale Formations

Abstract

The properties of bedding shales are different from that of normal formations. Strength anisotropy is their outstanding feature. Experimental study and theoretical analysis show that this kind of anisotropy of bedding shales is the main reason of wellbore instability. W-2nd section shales in WZ12-1N oilfield are in typical bedding formation, and there were some problems such as severe borehole collapse and pipe sticking in drilling. Bedding shale formation was assumed to be a transversely isotropic material, and a collapse pressure calculating method was established. The calculation result of directional drilling collapse pressure in W-2nd bedding shales shows that if hole deviation exceeds a certain critical value, collapse pressure will increase sharply. This result was used in mud density design and well trajectory optimization, which solved the wellbore instability problems of the W-2nd formation. This research method has reference value to solve problems of wellbore instability and improve drilling efficiency in other similar regions.     

渗透性砂岩地层漏失压力预测模型

为了预测渗透性砂岩地层的漏失压力,提高钻井的安全性。根据塑性流体的本构方程和毛细管渗流理论,分析了钻井液（宾汉流体）在井壁泥饼带、地层侵入带和原地层孔隙中的流动特性,分别建立了井壁有无泥饼2种情况下的渗漏压力计算模型。利用建立的数学模型,对崖城13-1-A15井压力衰竭储层段的漏失压力进行了预测,结果表明:井壁上未形成泥饼时,漏失压力当量密度为0.613 kg/L;井壁上形成厚度1 mm、渗透率小于4×10-5 D的泥饼时,漏失压力当量密度可提高到1.21 kg/L以上。崖城13-1-A15井钻井施工中,采用密度1.10 kg/L的抗高温Versaclean油基钻井液,没有发生井漏。建立的渗透性砂岩地层漏失压力预测模型,可为渗透性砂岩地层安全钻井提供参考。      

各向异性地层定向井井壁坍塌压力计算方法

层理性地层的力学性质和强度特征具有各向异性,受层理弱面的影响,钻井过程中容易发生井壁失稳的问题。各向异性地层中的井壁坍塌压力分析方法与普通完整性地层不同,强度准则应选用弱面破坏准则,并且层理面的存在也对井眼周围应力分布产生影响。对于各向异性地层中定向井钻进时井壁稳定的分析,需采用有限元等方法进行数值求解。某油田层理性泥页岩地层中不同井斜角和方位角条件下井壁坍塌压力的计算结果表明：定向井钻井中存在最佳钻入角,解决这类地层的井壁失稳问题主要应从控制井斜角和钻井方位入手,避免在井壁坍塌压力较高的井斜和方位范围内钻进定向井。     

The Permeability Property and Borehole Stability in Bedding Shale

Wellbore collapse is one of the often encountered problems when drilling through shale formations. The instability mechanism and effect factors should be made sure to adopt suitable countermeasures. The bedding shale's permeability was measured by experiment, and with this foundation, the effects of drilling fluid seepage on formation strength and wellbore stability were discussed. Results showed that laminar shale's permeability is anisotropic and random. The permeability is extremely low in the direction perpendicular to the bedding plane, and it is very high parallel to the bedding plane when there are interlayer microcracks. The drilling fluid permeating along the bedding plane leads to great decrease on cohesion and internal friction angle, and then decreases the shale formation's strength, finally leading to borehole shrinkage, pipe sticking, and borehole collapse. Increasing mud weight only is good for borehole stability in short term. However, it intensifies seepage finally and can't control borehole shrinkage. In proper mud density, increasing the mud sealing capacity to control the seepage speed is an effective means to prevent borehole instability.     

逆冲构造带精细地应力和井壁稳定性研究及应用

逆冲构造区的构造应力强,层理、裂隙发育,井壁失稳是一个一直困扰着这一地区钻井工程的难题。认识此类构造地应力分布规律是井壁应力状态分析以及井壁稳定性研究的基础。提出了一套逆冲构造带精细地应力场研究方法,该方法以地应力测量为基础,采用基于有限元法及数学优化理论的有限元约束优化反演法对逆冲构造带三维地应力场进行模拟,并利用现场地漏实验等资料进行验证。通过泥页岩水化实验,分析了泥页岩水化特性以及岩石力学性质与含水量的关系,在此基础上,建立了分析水敏性泥页岩井壁围岩应力状态的基本模型,并结合岩石强度准则,编制了井壁稳定分析程序,用于分析坍塌压力、破裂压力、安全钻井液密度窗口以及泥页岩坍塌周期等。这一研究成果对于认识逆冲推覆带泥页岩井壁失稳内在机理以及相关对策的制定具有指导意义。     

Numerical Wellbore Stability Analysis Using Discrete Element Models

Wellbore instability, which is considered as failure of borehole wall, is a complex and time-consuming analysis. Numerous factors such as well path, rock mechanical properties, in situ stress regimes, pore pressure, mud weight, bedding planes, and fractures play a role in borehole instability. Many wellbore stability analyses methods consider only a few of mentioned parameters and majority of them are based on continuum mechanics. However, most of the methods presented for wellbore stability analyses do not consider the impact of fractures. In the present work discrete element models (DEM) are used for numerical wellbore stability analysis of horizontal wells, while the presence of fractures is considered. In this study the effect of mud cyclic loading, hole length, stress regimes, and fluid pressures in fracture plane are examined. The results of analyses showed that direction of minimum horizontal stress is the optimum drilling direction. To evaluate the effects of mud cyclic loadings and open hole lengths, two other models are also considered. These models reveal that mud cyclic loading reduces the stability of borehole. Moreover, it was concluded that mud weight must be increased as open hole length increases and it should not exceed the upper mud weight limit.     

力化耦合作用下的层理性页岩气水平井井壁失稳研究

针对现有页岩气水平井井壁稳定力化耦合分析大都仅考虑水化作用对岩石强度的影响,鲜有考虑水化应力应变影响的情况,以弹性力学和岩石力学等理论为基础,同时考虑水化作用对岩石力学参数的弱化效应和附加水化应力,建立了力化耦合作用下层理性页岩气水平井井壁坍塌压力预测模型,研究了层理性页岩气水平井井壁失稳机理,分析了影响井壁稳定的因素及影响规律。研究结果表明:存在层理面时,会使坍塌压力大幅升高;沿层理面方位钻进,井壁稳定性最好;当水化时间一定时,坍塌压力随距井壁径向距离增加而降低,水化时间越长,近井壁处易坍塌区域越大;考虑水化应力影响后坍塌压力会大幅升高,在设计钻井液密度时,不能忽略水化应力的影响。研究成果丰富了页岩气水平井井壁失稳理论,对层理性页岩气水平井钻井设计具有指导作用。