Analysis of the behavior of large underground oil storage caverns in salt rock

The storage of petroleum products above ground surface has many constraints and limitations. A viable alternative is to excavate large underground spaces in rock to provide a safer way for oil storage. Soft rock formations such as salt domes provide suitable conditions from environmental and operational aspects. The potential for high volume storage and low permeability are among advantages of oil storage in caverns excavated in salt rocks. The complicated shape of oil storage caverns, complex behavior of salt rock, and boundary conditions associated with large underground openings are major challenges in the design of salt caverns excavated for oil storage purposes. In this study, the deformation mechanism and stability of salt caverns were investigated. A comprehensive 3D numerical study was carried out to investigate the effects of cavern size and depth, salt rock deformation modulus, and ground in‐situ stress regime on the behavior of large salt caverns. The stress field and deformation mechanisms were studied numerically aiming at shedding lights into the design aspects of salt caverns for oil storage. The analysis results show that the cavern safety factor is reduced as a function of cavern depth and storage volume. Also, with decrease in k (ratio of horizontal to vertical in‐situ stress), the stability of salt caverns will increase; however, with increase in salt rock young modulus, the sensitivity of cavern stability to k ratio is reduced. Copyright © 2016 John Wiley & Sons, Ltd.     

压气储能浅埋地下储气库性能试验研究

利用地下岩穴进行压缩空气储能是大规模能源存储的可行方式之一。压缩空气地下储存库建设的核心任务是保证储气库的密封性和洞室结构安全性。为了验证浅埋地下储气库的可行性,在湖南平江抽水蓄能电站勘探平硐的花岗岩地层内建造了国内第1个硬岩浅埋衬砌地下储气室,并进行了10次完整的压缩空气充放气循环试验。试验结果表明：储气室内压缩空气温度场呈现出显著不均匀分布的特性,温控系统可以有效地控制储气室的温度变化过程。长时高压储气条件下,试验库的漏气率约为充气率的3.2%,试验库密封性能良好。在8.7 MPa的内压作用下围岩的最大变形量只有0.35 mm左右,高内压引起的变形影响区在10 m范围内,围岩变形安全性良好。试验成果有助于全面深入地认识高压地下储气库的工作性能,并为压气储能地下储气库的设计提供有益参考。     

层状盐岩中储备库油气渗漏风险的故障树分析

油气渗漏是盐岩地下储备库事故的重要类型之一,具有突发性强、损失难以估计的特点。针对国内层状盐岩中储备库运营过程中的油气渗漏风险进行分析,揭示了油气渗漏事故的发生机制并建立了相应的故障树模型。通过对该模型的分析,找出了事故发生的各基本致因事件和故障模式,并得出适用于典型层状盐岩储备库油气渗漏事故的发生概率公式。分析结果表明,国内层状盐岩中储备库发生油气渗漏事故的可能故障模式有28种,且发生条件易于满足而难于防范,因此事故发生的可能性较大;按照各基本事件结构重要度的计算结果,盐岩强度低、盐岩蠕变过量、附近有断层、地震、造腔参数控制不当、非均匀地应力、人为操作失误等是层状盐岩中储备库油气渗漏事故的主要致因事件,并据此提出有效措施防止事故发生;通过专家调查法和故障树法的综合分析得出,金坛盐矿5口老腔储库在近10年的运营期内发生油气渗漏事故的概率为0.703%,属于偶发性事故。     

Analyses of gas storage capacity in unlined rock caverns

Summary Groundwater control is a means of ensuring that no gas leakage occurs from unlined rock storage caverns. To achieve a better understanding of the principles of gas containment under groundwater and how to obtain maximum gas storage capacity, analyses of groundwater conditions surrounding storage caverns and the effects of different factors on gas storage capacity have been performed and are reported in this paper. The analysis results indicate that the critical gas pressure of a storage facility is considerably less than the natural hydrostatic pressure around the caverns and somewhat less than the water curtain pressure. High gas storage capacity can be obtained by optimizing the design of cavern configuration, water curtain layout, cavern depth, etc. The principles of such optimization are outlined in this paper.     

盐岩CO2处置相关研究进展

现代工业生产排放了大量的CO2,为了缓解CO2造成的温室效应,对CO2进行捕获并进行地下处置是减少CO2排放量的一个有效可行的措施。在各种地下处置方法和介质中,利用盐岩溶腔进行CO2地下处置具有单个溶腔处置量大、注入速度快等优点。简要介绍了盐岩CO2地下处置存在的主要岩石力学问题,即溶腔内存在长期增压的过程。综述了影响溶腔内压的主要因素及其相互耦合作用的研究进展。这些因素包括：盐岩的蠕变性、CO2的高压缩性、盐岩在高应力下的渗透性、CO2沿管鞋的渗漏等。由于我国CO2排放的持续增加,结合我国层状盐岩的地质条件和力学特性,对各种因素的耦合作用的理论研究是今后的一个重要研究方向。     

内衬式高压储气库群布局参数优化及稳定性分析

内衬式岩洞高压储气库兼具抽取率高、循环能力强,且能承受更高的内压力等优点,克服了传统压缩空气储能系统的诸多缺陷,是一种应用前景广阔的储能方式。论文以洞室埋深、内径和间距等3个最主要的储气库布局参数为影响因素,采用ABAQUS有限元软件基于正交试验设计模拟工况,以关键点的位移和塑性区面积作为评价指标,通过单因素试验研究了洞室间距、埋深及内径对围岩变形和稳定性的影响规律,提出了洞室群优化布局建议。研究表明:洞室埋深是影响储气库围岩变形和塑性区面积的最显著因素,其次为洞距和洞径;随着埋深的增大洞室围岩塑性区的发育区域得到有效的抑制,且塑性区主要分布于洞室顶部;增大洞距可有效削弱高内压对围岩的启裂效应;衬砌的最大拉应力主要分布在结构的顶部和底部,增大埋深或减小高径比都有助于提高衬砌的稳定性;综合分析表明储气库群的最优布局方案为埋深400 m、内径42 m、间距60 m。研究成果为内衬式高压储气库群的优化布局和稳定性评价提供了参考依据。     

盐穴储气库破坏后地表沉陷规律数值模拟研究

地下盐穴储气库在天然气调峰和保障供气安全上具有不可替代的作用。地下盐穴储气库达到设计年限后,将报废而逐步垮塌,必然引起严重的地表沉陷。因此,对盐穴储气库破坏后地表沉陷规律进行研究具有十分重要的意义。考虑到目前的数值分析软件进行地表沉陷分析的不足,开发了用于盐穴储气库破坏后地表沉陷数值模拟的有限元专用软件-2D-Sink,该软件具有处理破碎岩块的能力。应用2D-Sink对盐穴储气库破坏后引起的地表沉陷规律进行了系统的研究,共建立了6种模型进行数值模拟,分别研究了地表沉陷层理效应、地表沉陷的岩层倾斜效应、地表沉陷的断层效应和多盐穴地表沉陷规律。对多溶腔地表变形曲线与单溶腔叠加的地表变形曲线进行比较,验证了地表沉陷叠加原理的正确性。研究成果为盐穴储气库报废后地表沉陷灾害控制提供了理论基础。     

Use of solution-mined caverns in salt for oil and gas storage and toxic waste disposal in Germany

The need for storage caverns for oil and gas, and repositories for toxic chemical waste is increasing world-wide. Rock salt formations are particularly suitable for the construction of cavities for such purposes. Owing to its favourable geomechanical properties, rock salt remains stable over long periods of time without support, and it can be shown that the geological barrier of the host rock remains intact for a remarkably long time.

Safety analysis must be made for each proposed site based on site-specific data. The methods of doing this are well known and related technical recommendations exist in Germany. These recommendations apply to the planning, construction, operation and post-operational management of salt caverns used for the underground disposal of hazardous wastes. In particular, geotechnical site-specific safety verification, as required by the government's technical regulations on wastes (TA-Abfall) under the section “Underground Disposal”, is required. This safety verification must cover the entire system comprising the waste, the cavern and the surrounding rocks. For this purpose geomechanical models have to be developed. The steps which must be taken when carrying out geological engineering site explorations and when determining geotechnical parameters are discussed. In addition, recommendations are made for the design and construction of underground repositories.

For liquid-filled caverns, long-term sealing from the biosphere is of particular interest. In this instance it must be shown that the natural increase in pressure in the closed cavity due to long-term convergence does not exceed the fracture pressure. A special filled test (scale 1:1) has been performed to study this.     

变形稳定理论在盐岩储气库优化设计中的应用

为解决盐岩储气库洞室形状以及库群布置的优化设计问题,将变形加固理论发展和完善为变形稳定理论,把塑性余能与强度折减系数的K-ΔE关系曲线作为储气库群的整体稳定性判据。在变形稳定理论的基础上,对不同形状和布置方式的洞室的整体稳定性进行定量评价,优化分析了洞室形状以及库群的布置方式,进而获得最具安全稳定性的洞室形状和布置方式。研究结果表明,变形稳定理论为盐岩储气库洞室形状和洞群布置方式的优化设计提供了一套实用有效的分析理论和方法。     

多夹层盐矿水采沉渣空隙特征与储气能力评价

在低品位、多夹层盐矿地层中建设地下储库,利用水采溶腔（盐穴）底部不溶物沉渣空隙储气有望较大幅度扩大储气库库容,但需要开展沉渣空隙储气可行性和适用性评估。首先,采用不溶物沉渣制备大尺寸CT扫描试样,构建了沉渣空隙三维重构模型,定性分析了沉渣空隙尺寸和空隙连通性,发现沉渣空隙尺寸大且连通性好;其次,采用自主研制的盐矿水采沉渣储气试验装置,利用不溶物小颗粒和夹层垮塌大尺寸块体混合堆积样品进行注气排卤试验,测定注气排卤前后沉渣空隙率,分析了沉渣空隙率变化的原因;最后,建立沉渣空隙体积预测模型,提出了盐腔采动空间和沉渣可排卤水体积的计算公式。通过考虑盐层不溶物小颗粒连续堆积,又考虑夹层垮塌大尺寸块体无序堆积,计算了沉渣堆积体积及可排卤储气体积,计算结果与现场采卤数据吻合较好。该研究可为评价低品位、多夹层盐矿沉渣空隙储气能力提供参考。     

基于裂隙渗流效应的水封油库涌水量预测分析

准确预测洞室涌水量和库区渗流场的空间分布特征是确保地下水封油库施工期安全性和运行期经济性的基础性工作之一。为真实地反映地下水封油库围岩随机分布裂隙的渗流效应对涌水量预测和渗流场空间分布特性的影响,提出了一种基于嵌入裂隙单元模型（EFE模型）的裂隙岩体渗流分析方法,并采用该方法对湛江水封油库的三维渗流场进行了计算分析,通过对比工程实测资料,验证了所提出方法的可靠性,进而预测了实例工程在运行期的涌水量。计算结果表明,EFE模型能够较好地模拟裂隙对洞室岩体局部渗流场的影响,反映库区渗流场及洞室涌水量空间分布不均匀的特性。研究成果可为水封洞库渗控措施的精准设计以及运行期污水处理设施配套设计工作提供参考。     

金坛盐矿老腔储气库长期稳定性分析数值模拟

盐穴储气库作为油气储气库的主要类型之一,已经在发达国家普遍采用。随着“西气东输”工程的进行以及天然气工业的不断发展,我国将会有更多的盐穴地下储气库建成并投入运行,因此怎样科学合理地分析盐穴储气库的稳定性已显得越来越重要。利用国际上著名的有限差分软件FLAC3D,对金坛盐矿某区老腔1号井、2号井建库完成后的腔体稳定性以及腔体蠕变规律进行了数值模拟,模拟结果表明,储气库在运行期间,流变会引起溶腔体积的减少,溶腔内压对储库的体积减少有直接的作用。并且利用该软件确定了储气库的运行压力在6 MPa～14.5 MPa之间,溶腔的体积缩小率在22 %以内,为储气库的修建及管理提供了指导依据。     

变权和相对差异函数在盐穴储气库腔体稳定性评价中的应用

盐岩地下储气库腔体以钻井水溶方式开采,溶腔形态可见性差、形态发展可控性难度高,针对畸形溶腔进行科学的稳定性评价是保证其安全运营的重要手段。将变权和相对差异函数理论引入到盐岩溶腔的安全评价中,建立适用于盐穴储气库畸形单腔的稳定性评价模型,首次以溶腔声纳测腔数据为基础,建立三维真实仿真模型并进行数值模拟,将数值模拟结果作为评价指标的评分依据,最后应用该方法对金坛储气库某腔体进行稳定性评价,并针对评价结果提出安全改善措施。研究结果表明,用变权方法对评价指标权重进行处理后得到的结果更加合理,通过将该方法与其他安全评价方法计算结果进行对比,证明了该模型在盐岩储气库畸形溶腔的稳定性评价中具有较好的适用性。     

盐穴储气库造腔工艺技术研究

盐穴储气库以其独特的优势在世界范围的石油工业领域中受到越来越多的重视。以一定的形状在盐层内建造一个地下储气溶腔,是一项复杂的系统工程。结合我国在盐层建设储气库的特点,围绕造腔设计的腔体目标和实施工艺,对盐穴储气库造腔工艺技术进行了全面的论述。通过对储气库腔体形成过程的分析,从造腔工艺、腔体控制与检测方法等方面,提出了造腔井型、水循环方式、溶腔步骤、两口距调节方式、形状控制方法、顶板保护工艺、密封检测、腔体稳定性等多项技术,同时推荐了造腔管柱组合方式、注水流量确定方法和保持腔体稳定的措施,对盐穴储气库造腔设计和施工有一定的指导意义。     

A new Cosserat-like constitutive model for bedded salt rocks

Salt rocks are commonly used as geologic host rocks for storage of gas and crude oil, and are being considered for the disposal of radioactive waste. Different from the salt rock domes in many countries, the salt rock formations in China are usually laminar with many alternating layers, i.e. rock salt, anhydrite, and/or mudstone. Considering the unique stratigraphic characteristics of these salt rocks, a new Cosserat-like medium constitutive model is proposed in order to facilitate efficient modeling of the mechanical behavior of these formations. In this model, a new representative volume element, containing two different layers, is employed to simulate the compatibility of the meso-displacement between two different layers and also the bending effect. A new method for the deformation and failure analysis of bedded salt rocks is derived therefrom. Having the macro-average stresses, the conventional stresses in the different layers can be obtained in sequence. The conventional stresses can then be utilized in a routine way for the strength and failure analysis. For the initial numerical modeling, the new Cosserat-like medium is reduced to a transversely isotropic one. The simplified constitutive model for layered media is then implemented into FLAC3D codes. A test sample validates that the results by using the numerical model are in good agreement with that by using the built-in model, and the mesh size for the new model is reduced greatly. Finally, an application for the stability of oil storage caverns in deep thinly bedded salt rocks is carried out. The effects on convergence of storage caverns and on the failure of surrounding rock due to the presence of the mudstone interlayers (hard phase) are discussed in detail. Copyright © 2009 John Wiley & Sons, Ltd.     

盐岩储气库最佳采气速率数值模拟研究

由于已采盐矿存在着大量的采卤溶腔群,对采卤溶腔群进行改造作为天然气储存库使用,能有效缩短储气库的建设周期,并消除采卤溶腔对环境带来的不利影响。基于盐矿地质资料、盐岩的力学试验及本构关系分析,对作为西气东输储气库使用4口采卤溶腔群进行了研究,通过三维数值模拟方法研究了该溶腔群在不同采气速率下盐腔周的应力状态和体积变形规律,并通过分析,对该溶腔群的最佳采气速率得出了有益的结论。     

Deformation behaviour of a large underground cavern

Summary The Imaichi underground power station, with a cross sectional area of 1420 m², which is now under construction by Tokyo Electric Power Co., Inc., is one of the largest underground caverns in the world. Due to the considerable depth of the over-burden of 400 m, the horseshoe-shaped section was adopted for the first time in Japan to minimize excesive stress concentration on the surrounding bedrock and keep loosened zones to a minimum.The bedrock consists of sandstone, slate, siliceous sandstone and breccia. The rock is generally hard and compact, with few fractured zones which may have an adverse influence on the excavation of the cavern.The supporting system of the cavern consists of prestressed rock anchors, rock bolts and shotcrete.Approximately 800 instruments, mainly multiple stage extensometers, were used to monitor behaviour of the surrounding rock during excavation of the cavern. With the exception of some cracks which occurred in a portion of the shotcrete when about half the height of the cavern had been excavated, excavation work was completed without any major trouble. In spite of the symmetrical shape of the cavern, the deformation behaviour of the surrounding rock during excavation was remarkedly asymmetric. The reason for this was concluded to be the peculiar deformation behaviour exhibited by Breccia during stress relief, as shown by in-situ rock tests, etc., and analysis of deformation data after completion of the excavation work.     

水平薄层岩体中大跨度地下洞室工程地质研究

山西西龙池抽水蓄能电站地下厂房围岩为水平薄层岩层,工程竣工发电已多年,施工及运行期安全,但工程开工前,还没有在水平薄层岩体中开挖大跨度高边墙地下洞室的成功范例,鉴于此,以山西西龙池抽水蓄能电站工程为依托,从工程地质角度,对水平薄层围岩岩性特征、岩体结构特征、岩体力学特性、大跨度高边墙地下洞室围岩分类、围岩变形特征等方面进行了研究,依据研究成果,对洞室开挖支护施工、围岩变形监测等进行了分析,依据围岩变形监测成果对围岩力学参数进行了反演,验证了前期勘察成果,取得了在水平薄层状地质环境中开挖大型地下洞室的宝贵经验,进而为在水平薄层状地质体中修建大跨度、高边墙地下洞室提供了更多的技术支持,对此类不良地质条件下大型地下洞室群建设具有重要的指导意义。     

岩盐中不溶物含量对储气库腔体有效空间大小的影响

主要研究了岩盐不溶物含量对岩盐储气库水溶建腔有效空间大小的影响。根据水溶建腔机理,建立岩盐储气库水溶建腔数学模型,通过岩盐溶腔数学模型,分别对岩盐中不溶物含量不同的地层条件下,岩盐储气库水溶建腔进行动态模拟数值计算,综合分析岩盐中不溶物含量对岩盐储气库水溶建腔的影响规律。