Maintaining the stability of deviated and horizontal wells: Effects of mechanical,chemical and thermal phenomena on well designs

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.     

PPTS-1压力传递型泥页岩渗透性测试系统

井壁失稳一直是困扰油气勘探开发的难题,而泥页岩渗透性是评价泥页岩井壁稳定性的重要指标之一。介绍了一套基于LabVIEW软件平台的PPTS-1压力传递实验系统平台,采用岩心分析法和压力传递测试技术精确测试泥页岩的渗透率。实验结果表明,该实验平台操作简单,性能稳定,测试精度高,为井壁稳定性深入研究提供了支撑。      

云南盐津页岩气调查盐津1-2井施工技术

页岩气是指开采自富烃页岩层的非常规天然气资源,资源储量的调查评价主要依托钻探技术。页岩具有较强的水敏性,在页岩气勘察钻进施工中,井内易发生坍塌、剥落造成超径或缩径等井壁失稳现象。盐津1-2井完井井深1554.06 m,是目前云南省页岩气资源勘察施工中最深的一口井。针对页岩气井钻井技术要求,从钻井设备、井身结构、钻进参数、钻具组合、钻井液、井斜控制、事故预防等方面进行选择、设计、优化,成功地完成了盐津1-2井的钻井施工。总结了该井施工中的经验和存在的问题,可为以后同类工程施工提供参考。     

中国页岩气开发的实质性突破

页岩气是指吸附在页岩中的天然气或自生自储在页岩纳米孔隙中连续聚集的天然气。新世纪以来,美国发生的页岩气革命影响了世界油气资源格局; 中国的非常规油气储存量非常可观,是世界上具有页岩气可采储量最大的国家; 但页岩气地质条件、水平钻井、分段压裂等技术储备和页岩气管理经验等还面临很大挑战。近年来,中国大力推进页岩气的开发利用,中石化、中石油和延长油田三家公司在示范区块开发的成功,以及短时间内在勘探开发方面取得的技术突破,标志着中国页岩气的开发已取得了实质性突破。但中国今后是否采取页岩气开发对多元资本开放的模式,还需要进一步研讨。     

桂北地区罗地1井钻探施工实践

页岩具有较强的水敏性,在页岩气勘查钻进施工中,井内易发生坍塌、剥落造成超径或缩径等井壁失稳现象。罗地1井采用金刚石绳索取心工艺进行钻进,完井井深1501.06 m,岩心采取率、井斜等各项指标均符合地质设计要求。本文主要从罗地1井的钻井设备、井身结构、施工难点等方面进行总结,可为今后页岩气调查井的施工提供参考。     

中牟页岩气区块泥页岩井壁稳定影响因素分析及技术对策

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。     

Modeling fracturing-fluid flowback behavior in hydraulically fractured shale gas under chemical potential dominated conditions

Shale with high clay content has caused instability from hydration during the hydraulic fracturing process. Macro-level migration phenomenon of water molecules is induced by the chemical potential difference between low-salinity fracturing fluid and high-salinity formation brine. This study aims to establish the equation for the chemical potential difference between fracturing fluid and formation brine by theoretical deduction in order to investigate the effect of the aforementioned phenomenon on fracturing flowback. Accordingly, a mathematical model was established for the gas–water two-phase flow which driven by the chemical potential difference. Viscous force, capillarity and chemiosmosis were considered as the driving forces. A numerical simulation of fracturing fluid flowback with or without considering of the effect of chemiosmosis was performed. A simulation analysis of the water saturation and salinity profiles was also conducted. Results show that capillarity and chemiosmosis hinder fracturing fluid flowback in different degrees. As the condition worsens, they inhibit more than 80% of water to flow back out of the formation, forming a permanent water lock. This study contributes to improvement of the theory on shale gas–water two-phase flow, establishment of a flowback model that suitable for shale gas wells, and accurate evaluation of the fracturing treatment.     

我国页岩气资源及影响因素

在世界面临能源短缺的背景下,页岩气作为油气勘探的一个新领域,越来越得到世界各国的重视。我国页岩气资源丰富,许多盆地或地区具有页岩气大规模成藏的地质条件,对页岩气的研究显得尤为重要。该文介绍了我国页岩气资源储量、分布及开采面临的问题,概述了页岩气地质特征。在此基础上探讨了我国页岩气的影响因素,认为我国页岩气主要受有机碳含量、成熟度、裂缝的发育程度、地层压力的控制;页岩气与煤层气同属于非常规天然气,其赋存形态、成因类型、富集规律具有很多相似之处,因此可将页岩气与煤层气进行对比研究。     

涠西南地区岩石特性及钻井液技术研究

北部湾盆地涠西南油田群是南海西部重要的原油产区，同时油田群紧邻众多国家级自然保护区，属于环境敏感区域。针对北部湾盆地涠西南地区环保要求，以及涠洲组和流沙港组钻井过程经常出现井壁失稳导致的憋卡、起下钻阻卡等问题，开展了涠西南地区地层泥页岩特性及环保钻井液技术研究。通过地层岩石黏土矿物分析、孔喉结构分析以及理化性能评价，明确了涠西南地区泥页岩井壁失稳的机理；提出以类油基的水溶性复合基基液为核心，构建了一套具有油基钻井液工程特性和水基钻井液环保特性的新型环保防塌钻井液技术，并进行了相关的现场应用。现场应用显示：应用井与邻井相比，12-1/4″井段阻卡划眼时间减少，井径扩大率大幅度降低，并且在128 h的长时间浸泡过程中没有复杂情况产生，有效地解决了涠洲组、流沙港组易失稳地层的井壁稳定问题；同时，钻井液环保性能达到一级海域环保要求，可以替代目前应用的油基钻井液体系，解决了海上使用油基钻井液存在配制成本高、含油钻屑需全回收及环境危害隐患大等技术难题。该研究对于涠西南油田环保、井壁失稳和钻井液技术发展具有较高的理论价值和借鉴意义。     

Study of mechanical properties of Vindhayan shaly rocks at elevated temperature

Shale is an important rock due to its suitability for different engineering and scientific applications. Elevated temperature may cause major deformation or damage in shale rock and it may be of irreversible in nature. Such damage have adverse effect on the physicomechnical properties of shale rock. The uniaxial compressive strength and tensile strength of two shales (upper Vindhyan basin, India) have been estimated at elevated temperature using point load strength index method. The rock samples have been analyzed at various temperatures starting from room temperature to 900 °C. The effect of elevated temperature on the physicomechanical properties and their influence on the uniaxial compressive strength has been studied in detail. Damage induced, in both shale have been estimated using compressional wave velocity. The analysis of the experimental result shows that the uniaxial compressive strength decreases from 63.45 to 18.45 MPa and 60.94 to 22.22 MPa, for Jhiri and Ganurgarh shale respectively. Tensile strength of shales have been also estimated. The value of tensile strength decreases from 3.65 to 1.05 MPa and 3.46 to 1.26 MPa respectively for Jhiri and Ganurgarh shale. Multivariate regression analysis has been carried out to obtain the correlation between physicomechanical properties and uniaxial compressive strength of Jhiri and Ganurgarh shale.     

Borehole Stability Analysis of Horizontal Drilling in Shale Gas Reservoirs

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.     

页岩I型断裂韧性的分形计算方法与应用

水平井分段体积压裂是页岩气商业规模开发的重要工艺措施,如何评价页岩储层可压性是该工艺成功的关键。页岩断裂韧性是可压性评价的重要支撑参数,从I型断裂裂纹（裂缝）微观形态入手,结合断裂力学理论和分形理论,建立了页岩I型断裂韧性分形计算方法;借助晶体劈裂功法计算页岩表面能,采用密度、声波时差2种参数获取计算结果,对比分析新的分形方法计算数据、传统方法预测数据与试验测试数据,新的分形方法计算平均误差为3.63%,传统预测方法平均误差为 %,验证了方法的准确性;参考实例水平井测井解释数据,计算了水平段I型断裂韧性指数的全井筒连续性剖面,结合可压性级别与较大储层改造体积概率关系,优选可压性级别为III级及II级改造。建立的页岩I型断裂韧性分形计算方法对定量评价页岩储层可压性具有重要意义。     

深部硬脆性泥页岩含水率与强度分布规律研究

泥页岩井壁稳定问题是钻井工程中经常遇到的一个十分复杂且带有世界性的难题。所取岩芯为准噶尔盆地沙窝地区块垮塌严重的深部泥页岩,通过室内试验测定泥页岩不同含水率条件下强度参数（内聚力、内摩擦角、弹性模量、泊松比）值,对试验数据进行回归分析,得出泥页岩含水率与其强度参数的分布规律;并根据渗流力学原理对泥页岩含水率的分布规律做了理论推导。研究结果为计算水化后泥页岩井壁围岩的应力及评价井眼稳定性提供了试验依据和理论基础。     

页岩气钻探冲洗液体系的研究与应用

中国页岩气资源开发潜力巨大,近年来页岩气勘探开发力度不断加大,对钻探工艺和技术的要求不断提高。页岩气地层岩性主要为泥岩、砂岩、页岩、碳质板岩、灰岩,该类地层胶结性差、破碎、井壁强度低,钻进中易出现孔壁失稳,发生坍塌、卡钻、埋钻等孔内事故,需要研制具有强抑制性、低成本、绿色环保的冲洗液体系来保证施工安全。本文通过对页岩气井壁稳定机理的探究,优选出一种适用于页岩地层双聚防塌和成膜防塌低固相冲洗液体系,该体系由抑制剂、防塌剂、降失水剂、润滑剂、封堵剂、流型调节剂等处理剂组成,具有良好的抑制性和胶结性。现场应用取得了良好的效果,保证了项目的顺利施工。     

陵页岩气井新工具的应用与经济评价

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。     

Discovery and Analysis of Shale Gas in a Carboniferous Reservoir and its Enrichment Characteristics in the Northern Nanpanjiang Depression,Guizhou Province,China

Shale gas resources are considered to be extremely abundant in southern China, which has dedicated considerable attention to shale gas exploration in recent years. Exploration of shale gas has considerably progressed and several breakthroughs have been made in China. However, shale gas explorations are still scarce. Summary and detailed analysis studies on black shale reservoirs are still to be performed for many areas. This lack of information slows the progress of shale gas explorations and results in low quantities of stored black shale. The Carboniferous Dawuba Formation, which is widely distributed and considerably thick, is one of the black shale formations targeted for shale gas exploration in southern China in the recent years. The acquisition and analysis of total organic carbon, vitrinite reflectance,types of organic matter, mineral composition, porosity, and permeability are basic but important processes. In addition, we analyzed the microscopic pores present in the shale. This study also showesd the good gas content of the Dawuba Formation, as well as the geological factors affecting its gas content and other characteristics. To understand the prospect of exploration, we compared this with other shale reservoirs which have been already successfully explored for gas. Our comparison showesd that those shale reservoirs have similar but not identical geological characteristics.     

松辽盆地北部页岩油水力压裂微地震监测技术及应用

松辽盆地页岩油储量丰富,是重要的油气资源接替领域.页岩油是一种重要的非常规油气类型,但是其形成和埋藏的地质条件复杂,储层物性差.页岩油的勘探、开发都需要进行水力压裂,微地震监测是压裂效果需要评价的重要技术.根据松页油1HF井的地表、地下的地震地质条件和水平段展布特征,设计较为规则的矩形观测系统实施地面微地震监测,保证全方位均匀地覆盖目标区.通过保证检波器和地表良好耦合的系列措施,对埋深2 000 m以下的页岩油目标,采集到肉眼可识别的压裂微地震信号,采用层析成像技术进行压裂破裂范围计算和微地震事件反演定位.成像结果表明,各段压裂后造缝效果较为明显,有效沟通了储层与井眼的流体通道.微地震监测的实践初步证明,合理的压裂参数设计和工程施工,可获得页岩油压裂的良好效果,形成的微地震监测技术是评价压裂效果的重要而有效的手段,为页岩油的勘探开发提供技术支撑.     

吐哈盆地二叠系暗色泥页岩矿物组合特征及其地质意义

吐哈盆地是我国重要的含油气盆地之一,对于常规油气前人做了大量工作。然而对非常规页岩气的研究才刚刚起步。页岩气以吸附或游离的形式存在于泥页岩及其夹层中,而泥页岩的矿物组分研究为页岩气的吸附储存以及泥页岩的裂缝评价、渗流运移、压裂造缝等的研究提供了必要的基础。本文在野外露头及钻井岩心观察的基础上,通过显微薄片分析和 X-衍射分析,结合有机地化及镜质体反射率测试结果,对吐哈盆地周边二叠系8个剖面及两口取心井的暗色泥页岩样品进行了系统分析,结果表明：1）吐哈盆地二叠系暗色泥页岩分布广、厚度大、有机质丰度高;暗色泥页岩主要形成于微蒸发、微咸水的浅湖—半深湖—深湖环境,主要由粘土矿物和石英组成,粘土矿物主要为伊 /蒙混层、绿泥石和高岭石组合;2）暗色泥页岩矿物组合分布具有一定规律性,反映了盆内“多凸多凹,凸凹相间”的特点;粘土矿物组合反映了中二叠世晚期干旱—潮湿频繁交替的气候条件,且风化程度中等;3）暗色泥页岩总体处于中 ?晚成岩作用阶段,成熟度高,达到了成熟—高成熟阶段,有利于页岩气藏的形成;4）脆性矿物含量大于40%,有利于页岩气的压裂开发。     

煤层气钻井井壁失稳机理及防塌钻井液技术

针对沁水盆地煤层气钻井中存在的井壁稳定技术难题,采用X射线衍射、扫描电镜、泥页岩膨胀实验、页岩分散实验测试了泥页岩和煤岩体的组构及理化性能,分析了井壁失稳机理。依据"多元协同"防塌原理,研选出了高效包被抑制剂、封堵防塌剂和活度平衡剂,构建了泥页岩地层防塌钻井液体系QSFT和煤层钻开液QSMZ。评价结果表明,QSFT体系的粘度、切力适中,滤失量低、泥饼薄,对200 μm裂缝的封堵承压能力达3.0 MPa;QSFT和QSMZ具有较强的抑制水化能力,并能显著增加岩样单向抗压强度,对煤岩体岩心湿测渗透率的损害均低于30%,干测渗透率恢复值达到95%以上,可作为沁水盆地煤层气井的钻井液和储层钻开液。      

http://www.sciencedirect.com/science/article/pii/S1674987111000892

Shale with high quartz,feldspar and carbonate,will have low Poisson’s ratio,high Young’s modulus and high brittleness.As a result,the shale is conducive to produce natural and induced fractures under external forces.In general,there is a good correlation between fracture development in shale and the volume of brittle minerals present.Shale with high TOC or abnormally high pressure has well-developed fractures.Shale fracture development also shows a positive correlation with total gas accumulation and free gas volume,i.e.,the better shale fractures are developed,the greater the gas accumulation and therefore the higher the gas production.Fractures provide migration conduits and accumulation spaces for natural gas and formation water,which are favorable for the volumetric increase of free natural gas.Wider fractures in shale result in gas loss.In North America,there is a high success ratio of shale gas exploration and high gas production from high-angle fracture zones in shale.Good natural gas shows or low yield producers in the Lower Paleozoic marine organic matter-rich rocks in the Sichuan Basin are closely related to the degree of fracture development in brittle shales.