Comparative analysis of thermodynamic and mechanical responses between underground hydrogen storage and compressed air energy storage in lined rock caverns

Underground hydrogen storage(UHS)and compressed air energy storage(CAES)are two viable largescale energy storage technologies for mitigating the intermittency of wind and solar power.Therefore,it is meaningful to compare the properties of hydrogen and air with typical thermodynamic storage processes.This study employs a multi-physical coupling model to compare the operations of CAES and UHS,integrating gas thermodynamics within caverns,thermal conduction,and mechanical deformation around rock caverns.Gas thermodynamic responses are validated using additional simulations and the field test data.Temperature and pressure variations of air and hydrogen within rock caverns exhibit similarities under both adiabatic and diabatic simulation modes.Hydrogen reaches higher temperature and pressure following gas charging stage compared to air,and the ideal gas assumption may lead to overestimation of gas temperature and pressure.Unlike steel lining of CAES,the sealing layer(fibre-reinforced plastic FRP)in UHS is prone to deformation but can effectively mitigates stress in the sealing layer.In CAES,the first principal stress on the surface of the sealing layer and concrete lining is tensile stress,whereas UHS exhibits compressive stress in the same areas.Our present research can provide references for the selection of energy storage methods.

Key issues in water sealing performance of underground oil storage caverns: Advances and perspectives

Water sealing performance is important for underground water-sealed oil storage(UWSOS).The key issues concerning water sealing performance mainly include the permeability of fractured rock mass(FRM),water-sealed safety(WSS),water curtain performance,and prediction and control of water inflow.This paper reviews the progress of above four key issues on water sealing performances.First,the permeability of an FRM is the basis of water sealing performance,and several commonly used permeability test methods and spatial variation characteristics of permeability are outlined.Second,the current water sealing criteria are compared,and the evaluation methods of WSS are summarized.Third,the design parameters and efficiency evaluation of water curtain systems(WCSs)are introduced.The water inflow of oil storage caverns(OSCs)can reflect the water sealing effect,and the prediction methods and control measures of water inflow are also summarized.Finally,the advantages and disadvantages of the current research are discussed,and the potential research directions are pointed out,such as optimization of water sealing criteria and FRM model,quantitative evaluation of WCS efficiency,accurate prediction of water inflow,and improvement of grouting technology.

Two-and three-dimensional stability analysis of underground storage caverns in soft rock(Cappadocia, Turkey) by finite element method

Engineering design in soft rocks and its stability analysis exerts many challenges to rock engineers. Many engineering works in Turkey’s Cappadocia region must face and tackle the existing sites covered by the soft rocks. This study is aimed to examine the stability condition of a typical underground storage cavern(USC) excavated in a soft rock in this region. For this purpose, two-and threedimensional stability analyses of the USCs were performed using the finite element method(FEM).Because of the inherent difficulty in characterizing soft/weak rock masses in the region using traditional classification systems, the stability of a typical USC was evaluated by representing the rock mass condition with two distinct scenarios in FEM analysis.While these structures were unstable according to the 2D analysis conducted in RS2 software in the worstcase scenario, they were stable in the 3D analysis using RS3 software in both scenarios. Besides,feasible cover depths were examined to assess their possible effects on the factor of safety and deformation measurements. It was found that 15 m seems to be an optimal depth for excavating a typical USC in the soft rocks exposed in the region. The 3D FEM results provide valuable information to optimize the future planning and preliminary design of USCs.

Design and operation problems related to water curtain system forunderground 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 1970s, 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.

Rock engineering problems related to underground hydrocarbon storage

Oil and gas can be stored underground by a variety of means,such as in depleted oil and gas fields,in aquifers,in rock salt caverns,in unlined mined rock caverns,in lined shallow caverns and abandoned mines.Different types of underground storages require different geological and hydrogeological conditions and are associated with different rock engineering problems.However,the common issue is to ensure the gas-and oil-tightness of storage caverns.In other words,the stored oil and gas must not escape from the storage caverns.This may be realized by different means according to the types of storages and the sites geological conditions.There are basically two approaches of gas leakage control,i.e.permeability control and hydrodynamic containment.The latter involves the use of a water curtain system in many cases,which creates an artificial hydraulic boundary condition and helps to establish the required groundwater condition when needed.In addition to the common problems,the underground storage of liquefied petroleum gas(LPG) requires special attentions to the opening of rock joints,which result from the tensile thermal stress induced by the low storage temperature.Great care must be taken in choosing abandoned mines for oil and gas-storage since it is quite rare that the natural site conditions can meet the usual requirements,in particular for the gas tightness.The paper provides a general description of the gas leakage control for underground oil and gas storage projects,and addresses various rock engineering problems associated with selected types of storages in detail.

基于两相流的水封油库油气泄漏运移规律及控制措施

地下水封油库运行的关键是保持一定的水封厚度,为确定合适的水封厚度,基于气液两相流理论,采用有限元数值模拟方法,以我国某石油储备地下水封洞库为依托,模拟了地下水封石油洞库储油运行期油气的泄漏运移演变过程。结果表明:施工期不设置水幕系统情况下,洞室顶部出现了大面积的疏干区,造成后期无法储油;设置水幕系统情况下,洞库上方能够维持一定水封厚度,洞库周围岩层油气泄漏范围和泄漏量均与储油运行时间呈正幂函数关系;水封厚度越大油气泄漏范围和泄漏量越小,但过大的水封厚度会大大增加工程成本,所对应的案例在水封厚度为30 m时对油气泄漏控制最为经济合理,《地下水封石洞油库设计标准》推荐的水封厚度合理且有一定安全裕度。研究成果可为水封油库工程的设计及油气泄漏控制提供一定理论参考。

基于地下水化学特征的水封油库水幕系统有效性评价

水幕系统有效性是地下水封油库安全稳定运行的重要基础条件,然而目前评价水幕系统有效性的方法并不高效便捷。以我国首个大型地下水封油库工程为背景,采集油库运行期现场水样和岩样进行水质检测分析和电镜扫描试验,获取库址区地下水水化学类型和岩石的矿物成分组成特征。采用数理统计方法,基于地下水水化学特征获得了不同部位地下水之间的水力联系,开展水幕系统有效性评价。研究表明:油库运行初期库址区地下水主要为HCO^(3)—Na•Ca型水,围岩中的钾长石、钠长石和钙长石发生水化学反应,地下水中的K^(+)、Na^(+)、Ca^(2+)和HCO_(3)^(-)浓度总体呈上升趋势,pH值总体呈下降趋势;Cl^(-)浓度低于造成钢筋腐蚀的浓度,地下水对洞库支护系统无明显腐蚀作用;洞库周边监测孔地下水与水幕供水的水化学特征相似,说明水幕系统与油库围岩之间存在较好的水力联系,形成良好的水封效果。该研究可为判断地下水封油库运行情况提供重要依据,并为评价水幕系统有效性提供了一种科学方法。

地下水封储油洞库惰性气体注入系统分析

首先对地下水封储油洞库惰性气体注入的重要性进行了说明。然后对氮气的生产工艺原理进行了介绍,并通过工程设计实例对比分析了3种惰性气体注入系统的优缺点、投资额,对水封洞库氮气置换对建设工期的影响进行了分析,最后分析说明了地下水封洞库惰性气体注入系统分析结论及设计建议,为后续项目设计及生产运营提供了决策依据。

青海某抽水蓄能电站地下厂房洞室群围岩稳定性及支护效果研究

青海某抽水蓄能电站地下厂房属典型深埋大型地下厂房洞室群,具有埋深大、跨度大、边墙高的特点,且受厂区内小断层发育等地质条件限制,其围岩稳定性问题复杂且重要。通过现场实测结合数值模拟计算的方法,对地下厂房洞室群围岩稳定性及支护效果进行了研究。研究表明,地下洞室以降低围岩受开挖扰动的程度和维持围压水平的方式进行支护,支护后围岩塑性区深度、变形均改善,支护结构受力情况较好,说明洞室间距合理,围岩整体稳定,具备成洞条件。本研究对类似地下洞室群的设计和施工具有参考意义。

A study of water curtain parameters of underground oil storage caverns using time series monitoring and numerical simulation

Water curtain systems(WCSs)are key components for the operation of underground oil storage caverns(UOSCs)and their optimization and design are important areas of research.Based on the time series monitoring of the first large-scale underground water-sealed storage cavern project in China,and on finite element analysis,this study explores the optimum design criteria for WCSs in water-sealed oil caverns.It shows that the optimal hole spacing of the WCS for this underground storage cavern is 10 m in order to ensure seal effectiveness.When the WCS is designed with a 10-m horizontal hole spacing and a water curtain pressure(WCP)of 80 kPa,a water curtain hole(WCH)has an influence radius of approximately 25 m.The smaller the vertical distance is between a WCH and the main cavern,the greater the water inflow into the main cavern.The vertical hydraulic gradient criterion can be satisfied when this distance is 25 m.It shows that the optimal WCP is 70 kPa,which meets sealing requirements.

Status and Prospect of CTL and SNG Industry

Since the beginning of this century, revolutionary progress has been made in the understanding of resources and in the mining technologies of the oil and gas industry. Advances in petroleum engineering technology represented by horizontal wells and large-scale fracturing have promoted the scale development of low-grade and unconventional oil and gas resources. After the rapid growth of natural gas production in China for more than 10 consecutive years, the replacement of conventional natural gas resources has been weak and unconventional natural gas has become the major force for increasing production. Coal based SNG(synthetic natural gas) has also become a major competitor in the domestic market. The development of CTL(coal-toliquids) and SNG industries has brought coal resources into the oil and gas product market, expanding the concept of traditional oil and gas resources. The continuous improvement of petroleum engineering technology has promoted the development of deep underground coal gasification technology, which has given economic value to the huge amount of deep coal resources that are unable to be exploited by underground mining, and provides a tremendous resource guarantee for the sustainable development of the traditional oil and gas industry. A preliminary calculation shows that deep underground coal gasification has a competitive advantage in cost compared with high-cost, low-grade, unconventional gas and coal-based natural gas. Deep underground coal gasification is a typical cross-disciplinary and cross-sectoral sophisticated technology. Domestic oil and gas enterprises have dominant advantages in the engineering technology of this field. Further technical integration innovation and multi-industry joint research are needed to eventually realize the commercial application of this deep underground coal gasification technology.

某地下储油洞库围岩块体稳定评价与支护分析

当前,我国石油储库建设处于非常重要的发展期,地下储油洞库的围岩稳定性分析评价是影响储库设计的重要内容。因洞库区域岩体内各种地质缺陷的存在、岩体结构特征的复杂性和探测手段的局限性,以及当前裂隙岩体稳定分析技术的发展水平局限性,致使洞库围岩稳定分析的难度很大,成果的可靠性仍然不足。地下储油库通常浅埋于硬岩中,洞室围岩失稳往往表现为结构面切割形成的块体失稳,采用块体理论可以对结构面不同组合形成的可动块体及关键块体进行识别,并对这些块体进行稳定性评价和支护分析。本文以某地下储油洞库为例,首先分析洞库区域结构面发育特征,并采用全空间赤平投影分析不同结构面组合形成的可动块体。在此基础上识别关键块体,并根据其形态特征进一步确定支护块体,最后根据多种支护块体所需的支护力计算结果,给出了如何确定洞室围岩支护设计参数的分析方法。

水封石油洞库污染物运移规律研究

水封石油洞库储油可能造成地下水污染。明晰石油污染物在裂隙岩体中的运移规律是库区地下水污染防控的前提。为揭示石油污染物在洞周围岩地下水中的运移规律,基于裂隙-孔隙双重介质模型,采用数值模拟方法研究了石油中的特征污染物——苯的运移扩散过程,并分析了裂隙倾角、裂隙开度、基质渗透率和纵向弥散度对苯运移规律的影响。研究表明:储库正常运行50 a后,苯的迁移被限制在较小的范围内,不会到达水幕系统,也不会进入到地面表层下的水体中。在长期运行条件下,相邻洞周围岩中的污染晕可相互连通,并将引起相邻洞罐中油品污染物之间的交叉污染。苯的竖向污染距离对纵向弥散度和裂隙倾角大小敏感性强,而对裂隙开度和基质渗透率的敏感性较弱。洞室间岩柱中轴线上苯的最大浓度对裂隙倾角最为敏感,且随裂隙倾角和基质渗透率的增大而减小,随纵向弥散度和裂隙开度的增加而增大。

扩建洞库施工巷道开挖对相邻运营洞库影响分析

对已建运营地下水封洞库进行扩建是增大石油安全储备的重要方式。但在扩建洞库开挖爆破过程中,不可避免地会对相邻已建洞库的运营安全产生影响。然而,需要注意的是,开展洞库扩建施工时,必须科学制订开挖爆破方案,并进行合理爆破振动监测和控制,以减少对相邻已建洞库运营安全造成的影响。为了全面评估这种影响,选择了国内首个大型地下水封洞库扩建项目作为研究依托,并通过对扩建洞库施工巷道开挖爆破过程中已建运营洞库渗透压力、围岩内部位移、地下水位、水幕系统水位和主洞室涌水量等数据的分析和总结,对扩建洞库施工巷道开挖爆破对相邻已建洞库的运营安全影响进行了评价。研究结果显示,在进行现场10次爆破试验时,通过合理设置爆破振动监测参数,爆破对已建洞库围岩的稳定性和水封安全性无直接影响。

微地震监测在油气藏型储气库地质体完整性评价中的应用

油气藏型储气库是利用枯竭油气藏改建而成的地下储气空间,是最主要储气库类型。与国外油气藏型储气库相比,中国储气库地质体大多为复杂断块,具有埋藏深、储层渗透性差、非均质性强等特点。中国独特的复杂地质条件给储气库地质体安全运行带来巨大挑战,微地震监测技术可实时监测地层岩石破裂情况,是储气库地质体活动最直接的监测手段。为此,从微地震监测原理及储气库地质体完整性定义出发,针对储气库微地震监测数据特点对数据处理方法进行研究,并以新疆呼图壁储气库为例,开展微地震监测数据处理、解释,对呼图壁储气库地质体完整性进行评价。结果表明:①微地震监测技术在保障储气库地质体安全中具有重要作用,可实时监测断层、盖层、底层等岩石破裂活动;②在研究期内呼图壁储气库地质体较稳定,储层深度附近并未发生微地震事件明显聚集、大震级微地震事件等现象,但仍需长期监测;③可实现三维立体微地震监测,相比于常规方法,其监测范围更广、监测信息更丰富。

五岳抽水蓄能电站地下厂房初始地应力反演及围岩稳定性分析

河南五岳抽水蓄能电站地下厂房洞室群结构复杂,主厂房最大跨度26.0 m,高55.1 m,为大型地下洞室。岩体结构面发育,强度低,断层f1贯穿三大厂房,安全问题突出,需分析其开挖后围岩的稳定性。为此,使用FLAC3D程序建立地质模型,采用BSA-BP神经网络反演计算了该区的初始地应力场,而后进行地下厂房开挖的模拟计算,分析了围岩应力场、位移场及塑性区发育分布规律,结果表明地下厂房洞室群围岩基本稳定,但在断层发育部位及母线洞两端存在局部变形破坏的可能。研究成果可为该工程设计、施工提供指导,也可为同类工程提供参考。

中国深部地下空间储能的理论和技术挑战

深层地下储能是利用深层地下空间进行大规模储能,是提供稳定的清洁能源供应、实现石油战略储备、促进天然气调峰的重要途径。岩盐地层是大规模储能的理想地质介质,而中国盐岩资源丰富,储能空间严重短缺。与其他国家的盐丘相比,中国的盐类岩层为典型的湖相层状盐岩,具有层薄、杂质含量高、夹层多的特点。盐类储层大规模储能的发展面临着科学和技术上的挑战,包括:①考虑多场多相耦合的影响,建立储能洞室周围岩体的多尺度递进破坏和表征方法;②了解大型地下深层蓄能洞室渗漏演化规律;③了解大型地下深层储能洞室的长期性能演化;④开发深层地下盐穴储能智能施工技术;⑤保证深层地下蓄能空间的长期功能。解决这些关键科技问题的关键在于为中国大规模地下深层储能的发展奠定理论和技术基础。

地下水封石洞油库对地下水的影响数值模拟分析

根据钻孔提水试验数据求出影响半径和渗透系数,按照地下水动力学方法求出了洞库涌水量,采用三维地下水数值模拟模型MODFLOW对山东某地地下水封石洞油库涌水对地下水位的下降影响规律和地下水漏斗进行了数值模拟和预测,分析石洞油库涌水对区域地下水的影响。分析结果表明:洞库涌水量较小,在施工3 a期间涌水主要来自岩石的弹性释水,对地下水位基本无影响;不考虑储油的情况下,模拟洞库运行50 a,地下水位在垂向随时间线性下降,平面上影响范围不大。

盐穴地下储油库热质交换及蠕变

为了确保盐穴储油库的密闭性和安全性,建立了油、卤水和围岩的热交换模型以及由于温度变化而引起的溶腔压力变化模型,同时建立了岩盐蠕变和渗透模型.通过TDMA算法对模型进行了求解,结果表明,油在7a的放置过程中,温度升高了8.635℃,压力升高了8.97MPa,即温度升高1℃压力约升高1MPa.另外,盐穴的蠕变量随着放置时间的增加而减小.岩盐的渗透率很小,油的渗透量可以忽略.温度变化对溶腔压力有重要的影响,油和卤水的热膨胀系数与可压缩系数的比值决定了温度变化对压力的影响程度.在实际注油时,要准确测量油和卤水的可压缩系数和热膨胀系数,以便对溶腔内液体的温度和压力做出正确的预测和判断.