Design and operation problems related to water curtain system for underground water-sealed oil storage caverns

The underground water-sealed storage technique is critically important and generally accepted for the national energy strategy in China.Although several small underground water-sealed oil storage caverns have been built in China since the 1970 s,there is still a lack of experience for large-volume underground storage in complicated geological conditions.The current design concept of water curtain system and the technical instruction for system operation have limitations in maintaining the stability of surrounding rock mass during the construction of the main storage caverns,as well as the long-term stability.Although several large-scale underground oil storage projects are under construction at present in China,the design concepts and construction methods,especially for the water curtain system,are mainly based on the ideal porosity medium flow theory and the experiences gained from the similar projects overseas.The storage projects currently constructed in China have the specific features such as huge scale,large depth,multiple-level arrangement,high seepage pressure,complicated geological conditions,and high in situ stresses,which are the challenging issues for the stability of the storage caverns.Based on years' experiences obtained from the first large-scale(millions of cubic meters) underground water-sealed oil storage project in China,some design and operation problems related to water curtain system during project construction are discussed.The drawbacks and merits of the water curtain system are also presented.As an example,the conventional concept of "filling joints with water" is widely used in many cases,as a basic concept for the design of the water curtain system,but it is immature.In this paper,the advantages and disadvantages of the conventional concept are pointed out,with respect to the long-term stability as well as the safety of construction of storage caverns.Finally,new concepts and principles for design and construction of the underground water-sealed oil storage caverns are proposed.     

惠州地下水封油库三维非恒定渗流场研究

水封地下油库渗流场的分布是油库区地下水管理和油库运行方案的基本依据之一。为了解惠州水封地下油库区地下水在施工期和运行期的变化情况,应用三维非恒定流数值方法对复杂水文条件下的洞库区渗流场进行模拟,分析了不同初始地下水位条件对洞库区围岩渗流场的影响,探讨了施工期水幕系统不注水条件对油库运行的影响。研究表明:储油主洞开挖期间,水幕系统不注水将导致洞库围岩出现大范围的非饱和区,从而影响洞库多品种油品的储存。运行期水幕注水时的水封效果良好,洞库区围岩在进行灌浆处理后的涌水量较小。     

海岛地下水封洞库围岩稳定性及水封可靠性研究

为提高我国的石油储备量及海岛资源利用率,在海岛环境建造地下水封油库成为了一种新的思路。海岛环境相比于内陆具有更好的水力条件,且可作为港口,便于油品运输。以某海岛地下水封油库为依托,基于流固耦合理论,采用有限元数值模拟方法对海岛环境建造地下水封洞库的围岩稳定性和水封可靠性进行研究。结果表明:在海岛环境建造地下水封洞库围岩的应力和位移均较小,可以满足围岩稳定性要求;在不设置水幕系统情况下,开挖地下洞库会在洞库上方形成明显的降落漏斗,部分洞库顶部甚至发生疏干现象,无法满足水封可靠性要求;在设置水幕系统后,地下洞库上方可形成较大厚度的地下水覆盖层,可以满足水封可靠性要求。该成果对在海岛环境下建造地下水封洞库的研究具有借鉴意义。     

大型地下石油洞库自然水封性应力-渗流耦合分析

根据地质条件,地下水封石油洞库可以选择自然水封或人工水封方式。以中国首个大型地下水封石油洞库为背景,开展了岩石三轴压缩试验和现场水文试验,获得了洞库围岩变形特征和渗透特性,采用应力-渗流耦合理论,分析了该地下石油洞库的自然水封性与稳定性。岩石三轴实验表明,岩体受剪作用下体积变化情况与剪胀性密不可分。现场水文试验表明,洞库渗透系数存在一定的不确定性。通过数值分析得出如下结论：自然水封条件下,洞库水位将不满足水封要求;地下水封洞库实现水封条件的水头受水力梯度和岩体渗透性影响;洞库施工期涌水量与渗透系数存在着分形关系;施工期各洞室拱顶沉降为19～32 mm,水平收敛为16～35 mm。研究成果为中国首个大型地下水封石油洞库工程建设提供了科学依据。     

地下水封石油洞库施工期监控量测与稳定性分析

现场监控量测是确保大型地下工程建造和运营安全的重要手段。地下水封石油洞库在中国刚刚起步,不但缺少监测方案设计原则、实施方法等方面的规范标准,还缺少对相关监测数据分析方面的研究。以国内首个正在实施的大型地下水封石油洞库建设项目为依托,首先介绍了适用于大型地下水封石油洞库的监测原则与实施方法,该原则和方法充分考虑工程特征、地质情况和经济适用性;其次介绍了洞库监测结果:洞室大部分监测断面的洞周围岩收敛变形、拱顶沉降、内部位移和围岩松动圈分别处于4~8 mm、3~6 mm、4~8 mm和0.9~1.8 m区间范围内,锚杆应力和接触应力值大部分控制在50 MPa和0.5 MPa以内;而后分析了监测数据:1黄岛地下水封石油洞库围岩变形和支护受力较小、岩体稳定性良好、设计支护方案合理;2综合全面的监控量测结果可准确地反映地下水封石油洞库稳定性特征;3监测数据显示地下水封石油洞库稳定性表现出显著的时空演化特征。该研究可为中国地下水封石油洞库监测技术和稳定性评价研究提供重要依据。     

废弃盐穴地下储气库稳定性研究

国际上公认盐岩体是地下能源（石油、天然气）储存最理想的介质，作为储气库的盐岩溶腔，一般都是根据设计要求通过水溶开采形成。目前，国内外鲜见利用地下废弃盐岩溶腔作为天然气储气库的先例。通过对ABAQUS有限元的二次开发，对某废弃盐岩溶腔的储气库围岩和岩柱的蠕变变形规律及腔顶蠕变损伤区的范围进行数值模拟，并对废弃溶腔作为储气库时的工作压力和储库套管鞋高度设计作了有益的探讨，这对指导工程实践具有一定的指导意义。     

Construction and utilization of rock caverns in Singapore Part A: The Bukit Timah granite bedrock resource

The Bukit Timah granite underlaying central and northern Singapore has been studied for the feasibility of hosting large unsupported rock caverns. Detailed geological investigation, comprising mapping, seismic refraction and electrical resistivity surveys, deep vertical and inclined drilling, conventional and geophysical borehole logging and in-situ hydraulic testing (at a selected location), as well as laboratory testing, have been performed. The results indicate that the granite is of extremely good quality and suitable for the construction of large unsupported caverns. Therefore, the Bukit Timah granite should be considered as a valuable resource for cavern and underground space development in Singapore.     

Proposed future underground projects in sweden

The author describes a number of underground projects proposed by Swedish architects, engineers and planners. These include an underground wind tunnel built in rock, an underground museum, underground gas storage facility, an underwater traffic tunnel for Stockholm, and a large conference center under Stockholm, an underground concert hall in Jönköping, underground grain storage and oil storage facilities in rock caverns, and an underground pipeline to bring fuel to Stockholm airport, underground peak power-stations, and an underground waste treatment facility.     

基于离散介质流固耦合理论的地下石油洞库水封性和稳定性评价

 以我国首个大型地下水封石油洞库工程为背景,基于离散介质流固耦合理论,开展地下石油洞库水封性和稳定性评价。通过室内岩石三轴试验和结构面剪切–渗流耦合试验,获得岩石的弹性模量、泊松比和结构面的剪切模量、水力开度等参数。根据施工巷道开挖过程中围岩变形和水位变化情况,对围岩参数进行反分析,获得较为可靠的洞库围岩参数。综合上述成果,分析地下石油洞库的水封性和稳定性特征。研究发现,在水幕压力为50 kPa条件下,该地下水封石油洞库稳定水位位于主洞室上方约60 m,且大于洞内储存介质的压力,满足洞库水封条件;洞库各主洞室位移为9～30 mm,达到洞室稳定相关控制标准;分析8#和9#主洞室边墙附近的水平应力、竖向应力、法向应力和切向应力的变化,并将其划分为3个区域,即松动区、扰动区和未扰动区,其中洞室松动区范围约为6 m。研究为大型地下石油洞库水封性和稳定性评价提供理论依据。     

地下水封石油洞库水封准则研究

水封准则是地下水封石油洞库设计与运行管理的基础。为获取工程应用更加简便实用的地下水封石油洞库水封准则,基于裂隙水流动阻力效应的研究,建立了气压推动裂隙水迁移的油汽逃逸模型;根据裂隙水迁移启动的临界条件,推导了铅直裂隙和倾斜裂隙中裂隙水满足油汽封存的临界水封厚度计算公式,讨论了临界水封厚度条件下洞库的原油水封效果。利用气液两相流数值分析成果和工程实际监测成果,论证了提出基于临界水封厚度的地下水封石油洞库水封准则的正确性。     

地下水封石油洞库渗水量预测与统计

渗水量规模与空间分布特征是地下水封石油洞库建设中的关键问题。以中国首个大型地下水封石油洞库项目为背景,采用经验公式、有限元法计算和现场实测等方法研究了该洞库渗水量规模和空间分布特征。在大量现场岩体渗透性试验基础上,获得了可靠的岩体渗透系数,采用经验公式和数值计算等方法对洞库渗水量规模和空间分布特征进行了预测。根据现场揭露的渗水形态,统计了洞库渗水量规模,获得了渗水量空间分布特征,调查了渗水部位地质特征,据此提出了渗水量控制标准和有针对性的工程注浆防渗对策。通过对比预测与统计结果,讨论了渗水量规模预测方法适用性和渗水量空间分布特征离散性等问题。研究成果为提高中国地下水封石油洞库建设水平提供了理论支持,并为复杂条件下地下工程渗流特性研究提供了工程实例。     

地下石油洞库水幕设计原则与连通性判断方法研究

 地下水封石油洞库建设技术在我国刚刚起步,其水幕系统设计理念和方法还不成熟。结合我国首个大型地下水封石油洞库工程,研究水幕系统设计原则与连通性判断方法,分析水文地质条件对水封方式选用、水幕系统布置和水幕连通性测试的影响,并根据现场试验结果,研究水幕连通性判断方法,提出改进的连通性测试方法。通过研究发现,地下水封石油洞库水封方式的选择需充分考虑库区水文地质情况,而垂直水力梯度是判断洞库水封性的重要参数;人工水封方式中水幕孔应尽量垂直于结构面走向布置;水幕连通性判断可综合单孔注水试验与分区有效性试验结果进行,并考虑库区渗流场分布与变化规律对试验结果的影响;改进的水幕连通性测试方法适用于不同水文地质条件下水幕孔连通性测试。该研究成果可为地下水封石油洞库水幕设计提供重要依据,并为岩体渗流特性研究提供不可多得的工程实例。     

Stability analysis of underground oil storage caverns by an integrated numerical and microseismic monitoring approach

Underground storage in unlined caverns is of great significance for storing energy resources. Construction of underground storage caverns is an extremely complex process, involving extensive multi-bench excavation and strong unloading. Excavation-induced damage of surrounding rock masses may lead to instability of underground storage caverns. The aim of this paper is to put forward a method by integrating numerical simulation and microseismic monitoring for evaluation of cavern stability. A novel numerical method called Continuous–Discontinuous Element Method (CDEM) is applied to simulate micro-cracks under excavation-induced unloading conditions. Meanwhile, a microseismic (MS) monitoring system is employed to monitor real-time MS events during construction of storage caverns. Numerical results are validated using the monitoring data from the MS monitoring system. The integrated method is proved to be successful in capturing micro-cracks in underground storage caverns. Local instability, potential unstable zones and micro-crack evolution are analyzed, and cracking mechanisms are also discussed.     

Application of heat transfer analysis for frozen food storage caverns

Supply of high quality preserved food products has always been very important. Storage of food in underground caverns is superior over food storage tanks constructed at surface from an energy conservation point of view. There are a lot of underground openings excavated in tuff used for the storage of fruits and vegetables at the Cappadocia Region of Turkey. However, there has not been any attempt to use these underground openings for deep frozen food storage and related heat transfer details. The main purpose of this work was to investigate underground food storage openings in the Cappadocia Region and their potential use for frozen food storage. Details of heat transfer around openings for various geometrics in three-dimensional have been modelled by using a finite element software package called MARC. For the sake of comparison, heat transfer details around a similar opening excavated in granite were also determined. A comparison of underground caverns excavated in tuff and granite with a surface deep freeze storage tank was also made by both taking construction and operational costs into account. Construction of an underground deep freeze storage cavern excavated in tuff would cost one half of a same size surface tank whereas, energy loss due to heat transfer is three times lower in the favour of underground storage cavern opened in tuff.     

Norwegian oil and gas storage in rock caverns-Technology based on experience from hydropower development

Underground storage in rock caverns is widely used in Norway for many different petroleum products,such as crude oil,fuel,propane and butane.Basically,the caverns for such storages are unlined,i.e.containment is ensured without using any steel lining or membrane.The main basis for the storage technology originates from the extensive hydropower development in Norway.As part of this activity,about 4500 km of tunnels and shafts have been excavated,and around 200 large powerhouse caverns have been constructed.The hydropower tunnels are mainly unlined,with hydrostatic water pressure on unlined rock of up to 1000 m.Some of the projects also include air cushion chambers with volumes of up to 1×10⁵m³and air pressure up to 7.7 MPa.Many lessons which are valuable also for underground oil and gas storage have been learnt from these projects.For a storage project to become successful,systematic,well planned design and ground investigation procedures are crucial.The main steps of the design procedure are first to define the optimum location of the project,and then to optimize orientation,shape/geometry and dimensions of caverns and tunnels.As part of the procedure,ground investigations have to be carried out at several steps integrated with the progress of design.The investigation and design procedures,and the great significance of these for the project to become successful will be discussed.Case examples of oil and gas storage in unlined rock caverns are given,illustrating the relevancy of experience from high-pressure hydropower projects for planning and design of unlined caverns for oil and gas storage.     

Planning and utilisation of rock caverns and tunnels in Norway

This paper describes the extensive use of rock caverns and tunnels in Norway. Caverns are used for a variety of storage purposes such as storing of food, drinking water, oil and other liquid hydrocarbons, pressurised gas and air and industrial waste. Caverns are also used for industrial and municipal installations such as hydropower caverns and water and sewage treatment plants. A third main category of use in Norway involves dual purpose caverns used as civil defence shelters in war time and for entertainment and recreation (e.g. sports halls and swimming pools) in peace time. The intent of this paper is to discuss why these various underground space applications developed, to show the typical layout considerations for the different types of application and to introduce reference examples from the Norwegian experience.     

Hydrocarbon storage in unlined rock caverns: Norway's use and experience

In Norway, approximately 10 large unlined cavern storage plants for crude and refined oil products currently are in operation, and two are under construction. A large number of small underground storage plants for refined oil products, consisting of steel tanks in rock caverns, also are in operation. The caverns are constructed in mostly good quality rock of the Precambrian or Cambro-Silurian age, and few stability problems have occured. Cavern spans up to 22 m and heights up to 40 m have been used. Bolting and shotcrete are partly used to increase rock mass stability. Norwegian experience indicates that for installations larger than roughly 50,000 m³, unlined rock caverns would be the most cost advantageous alternative. Other advantages are better environmental protection, better security with regard to fire and explosion hazard and sabotage, and lesser land requirements.     

Latest technology of underground rock cavern excavation in Japan

Four major projects with large-scale rock underground caverns are discussed in this report; two hydropower stations, one underground oil storage facility and one underground museum in Japan. The technology applied to the construction of these caverns have some unique characteristics and can be applied to various other underground uses for different purposes and applied to larger-scale underground rock caverns with different geological and in situ stress conditions. Generally, construction of an underground cavern is comprised of five major activities: geological investigation; cavern stability analysis; initial rock support design; excavation works; and redesign of rock support according to the observational construction method. Weighted factors allocated among these factors should be established based on the rock properties and the purpose of the underground cavern use, which would define the major characteristics of the construction project. This report discusses some of major characteristics of these projects in Japan.