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.

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.

Simulation of pore space production law and capacity expansion mechanism of underground gas storage

One-dimensional gas injection storage building and one-cycle injection-production modeling experiment,and two-dimensional flat core storage building and multi-cycle injection-production modeling experiment were carried out using one-dimensional long core and large two-dimensional flat physical models to find out the effects of reservoir physical properties and injection-production balance time on reservoir pore utilization efficiency,effective reservoir capacity formation and capacity-reaching cycle.The results show that reservoir physical properties and formation water saturation are the main factors affecting the construction and operation of gas-reservoir type underground gas storage.During the construction and operation of gas-reservoir type gas storage,the reservoir space can be divided into three types of working zones:high efficiency,low efficiency and ineffective ones.The higher the reservoir permeability,the higher the pore utilization efficiency is,the smaller the ineffective working zone is,or there is no ineffective working zone;the smaller the loss of injected gas is,and the higher the utilization rate of pores is.The better the reservoir physical properties,the larger the reservoir space and the larger the final gas storage capacity is.The higher the water saturation of the reservoir,the more the gas loss during gas storage capacity building and operation is.Optimizing injection-production regime to discharge water and reduce water saturation is an effective way to reduce gas loss in gas storage.In the process of multiple cycles of injection and production,there is a reasonable injection-production balance time,further extending the injection-production balance period after reaching the reasonable time has little contribution to the expansion of gas storage capacity.

Survey on Storage of Water for Domestic Use in Underground Reinforced Concrete Tanks: The Case of Brazzaville (Republic of Congo)

The problem of water supply from the public distribution network still poses very serious problems in many cities in developing countries. Intermittent water supply pushes some households to build underground reinforced concrete tanks for water storage to cope with unwanted water breaks. This study that relies on the results of a survey of households in some areas of the city of Brazzaville (Republic of Congo) aims to verify the importance that users attach to the quality of the works constructed. Indeed, the reliability of the tanks resulting in their impermeability to the external environment has a direct impact on the quality of stored water and therefore the use that is made of water daily. Five areas were selected because of their soil moisture. By 256 tanks identified, 143 are made of reinforced concrete and 113 in masonry. The coating materials used to seal the walls are preferably the earthenware tiles (64% of tanks), then the Sika cement (31%). Food painting (5%) is only rarely used. However, 66% of households are not assured of the potability of the water stored. A significant number of households (46%) think that the stored water could be contaminated with noxious substances seeping from the outside through the walls of the tanks. The issue of sealing of underground water tanks, especially in areas where the water table is shallow, seems concerned users.

“Extreme utilization” theory and practice in gas storages with complex geological conditions

Based on more than 20-year operation of gas storages with complex geological conditions and a series of research findings, the pressure-bearing dynamics mechanism of geological body is revealed. With the discovery of gas-water flowing law of multi-cycle relative permeability hysteresis and differential utilization in zones, the extreme utilization theory targeting at the maximum amount of stored gas, maximum injection-production capacity and maximum efficiency in space utilization is proposed to support the three-in-one evaluation method of the maximum pressure-bearing capacity of geological body, maximum well production capacity and maximum peak shaving capacity of storage space. This study realizes the full potential of gas storage(storage capacity) at maximum pressure, maximum formation-wellbore coordinate production, optimum well spacing density match with finite-time unsteady flow, and peaking shaving capacity at minimum pressure, achieving perfect balance between security and capacity. Operation in gas storages, such as Hutubi in Xinjiang, Xiangguosi in Xinan, and Shuang6 in Liaohe, proves that extreme utilization theory has promoted high quality development of gas storages in China.

International experience of carbon neutrality and prospects of key technologies:Lessons for China

Carbon neutrality(or climate neutrality)has been a global consensus,and international experience exchange is essential.Given the differences in the degree of social development,resource endowment and technological level,each country should build a carbon-neutral plan based on its national conditions.Compared with other major developed countries(e.g.,Germany,the United States and Japan),China's carbon neutrality has much bigger challenges,including a heavy and time-pressured carbon reduction task and the current energy structure that is over-dependent on fossil fuels.Here we provide a comprehensive review of the status and prospects of the key technologies for low-carbon,near-zero carbon,and negative carbon emissions.Technological innovations associated with coal,oil-gas and hydrogen industries and their future potential in reducing carbon emissions are particularly explained and assessed.Based on integrated analysis of international experience from the world's major developed countries,in-depth knowledge of the current and future technologies,and China's energy and ecological resources potential,five lessons for the implementation of China's carbon neutrality are proposed:(1)transformation of energy production pattern from a coal-dominated pattern to a diversified renewable energy pattern;(2)renewable power-to-X and large-scale underground energy storage;(3)integration of green hydrogen production,storage,transport and utilization;(4)construction of clean energy systems based on smart sector coupling(ENSYSCO);(5)improvement of ecosystem carbon sinks both in nationwide forest land and potential desert in Northwest China.This paper provides an international perspective for a better understanding of the challenges and opportunities of carbon neutrality in China,and can serve as a theoretical foundation for medium-long term carbon neutral policy formulation.

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.

Evaluation method of underground water storage space and thermal reservoir model in abandoned mine

A large number of mines are closed or abandoned every year in China.Geothermal utilization is one of the important ways to efficiently reuse underground resources in abandoned mines.How to calculate the volume and distribution of underground water storage space is the key to accurately evaluate the sustainable geothermal production in abandoned mines.In this paper,according to the multi-scale characteristics of the underground space in abandoned mine,the flow and heat transfer equations in the multi-scale space are sorted out systematically,and the calculation methods of different secondary space volumes are derived in detail.Taking Jiahe abandoned mine as the background,the volume and distribution of underground secondary space are calculated,and three heat storage evaluation models considering different water storage spaces are established by using COMSOL.The simulation results show that there are great differences among different models,and the results of the equivalent porous media model considering the multi-scale space are most consistent with the reality.Sensitivity analyses of key parameters model results indicated that the heat production is closely related to not only the recharge flow rate but also the recharge temperature and operating time.Furthermore,the energy saving and emission reduction benefits of geothermal utilization in abandoned mines are calculated,the results show that geothermal utilization of abandoned mines can effectively reduce energy consumption and CO_(2)emissions,and it has great economic benefits.

二氧化碳-水-岩作用机理及微观模拟方法研究进展

系统综述CO_(2)-水-岩复杂作用机理、多孔介质反应输运(溶解、沉淀及沉淀运移)微观模拟、CO_(2)-水-岩系统微观模拟3个方面的研究进展,指出目前研究存在的主要问题并提出了关于未来研究方向的建议。CO_(2)注入储集层后,不仅存在常规渗流体系的流动和传质作用,还会产生溶解、沉淀及沉淀运移等特殊物理化学现象,其耦合作用导致多孔介质的孔渗参数变化规律复杂。孔隙尺度的微观渗流模拟,可以得到孔喉三维空间内的详细信息,且能显性观察到多孔介质流-固界面随反应的变化。目前研究主要在复杂作用机理解耦合、多矿物差异性反应表征、沉淀生成机理及表征(晶体成核和矿物脱落)、沉淀-流体相互作用模拟方法、多物理化学过程耦合渗流机制等方面存在局限。未来研究中,需要创新实验方法对“溶解—沉淀—沉淀运移”解耦合,提高矿物地球化学反应相关参数实验测试的准确度,在不同沉淀机理可靠表征的基础上,建立沉淀-流体相互作用模拟方法,并有机耦合各个物理化学过程,最终实现对CO_(2)-水-岩系统中“溶解—沉淀—沉淀运移”的耦合渗流模拟。

水侵气藏型储气库全周期高效建设微观模拟实验

借助微观可视化模型与微流控技术,开展了水侵气藏型储气库初期建库阶段注气驱水及循环储采阶段采气底水上侵、储气排驱水体的模拟实验,分析气液界面稳定机制、气液渗流与赋存规律,探索储气库全周期高效运行的优化调控方式。研究表明:储气库初期建库阶段应调控注气速度,充分发挥重力作用保证气液界面宏观稳定运移,大幅度提高气体的波及能力,为储气库后续循环储采阶段提供更大的储气孔隙空间。储气库循环储采阶段,恒定的储采气速度导致孔隙空间利用率低,逐渐提高储采气速度,从“小吞小吐”逐渐过渡到“大吞大吐”,可以持续打破孔喉内流体的平衡受力状态,扩大储气孔隙空间与流动通道,有利于储气库扩容增效和调峰保供。

干旱地区河槽暗蓄雨洪资源化利用模拟

目的 研究利用雨洪资源解决干旱地区用水短缺问题,提出利用河槽暗蓄收集雨洪最佳工程方案,为该类工程的设计提供参考。方法 应用Visual Modflow软件模拟研究辽西喀左地区内第二牤牛河流域中不同调蓄方案和拦蓄入渗方案对河槽暗蓄雨洪资源化的影响。结果 通过不同调蓄方案的对比,采用可调控悬挂截渗坝代替现有截渗坝时,雨洪资源利用率可提高至20.3%;通过不同拦蓄入渗方案的对比,“不清河床+坑塘+拦水堰”方案的雨洪资源入渗量为天然条件下雨洪资源入渗量100倍以上。结论 河槽暗蓄雨洪资源化工程最佳的拦蓄入渗和调蓄组合方案为在“不清河床+坑塘+拦水堰”的情况下采用可调控悬挂截渗坝,可显著提高雨洪资源利用率。

深圳沙河水质净化厂及3#调蓄池工艺设计要点及特点

沙河水质净化厂设计规模为旱季10万m^(3)/d,雨季额外处理10万m^(3)/d初期雨水,3#调蓄池设计规模为15.3万m^(3)。污水及初期雨水处理采用预处理+多段厌氧-好氧(AO)+二沉池+磁混凝高效沉淀池+精密过滤+紫外消毒的工艺,出水水质执行深圳市地方标准《水质净化厂出水水质规范》(DB 4403/T 64—2020)B级标准,其中总氮(TN)≤8 mg/L。污泥处理采用离心浓缩+低温热干化工艺,处理后含水率≤40%。作为国内首个将水质净化厂与初期雨水调蓄池深度融合的全地下式水污染治理综合体,项目采用多段AO耦合“3W法”(Wet-Weather-Wastewater法),并以此为核心提出了一种实现大规模污水及初期雨水高标准协同处理的系统解决方案,且无需大幅度增加污水处理设施体量、投资和运行成本。

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。

储气库救援井磨料水射流管外开窗试验研究

针对井筒不完整和存在落鱼的废弃事故老井出现井下封堵困难和气窜问题,如何实现有效封堵已成为老井改造储气库的关键。为此开展了储气库救援井磨料水射流钻杆成孔试验。试验结果表明:随着喷射距离的增大,单位时间内钻杆成孔深度显著减小;随着喷射压力的增大,钻杆成孔所需的时间缩短;钻杆成孔所需的最佳磨料质量分数为6%~8%,磨料粒径分布在40~60目范围内,可实现较好的破坏效果。通过正交试验分析认为,钻杆成孔的极限喷距随着喷射压力的增大而增大,随着喷射距离增大而减小;为缩短作业时间,应调整参数为高喷射压力(>25 MPa)和短喷射距离(<20 cm)。所得结论可为现场作业提供技术借鉴。

煤矿区固废矿化固定封存CO_(2)与减污降碳协同处置利用的研究进展

“双碳”战略目标对煤炭行业转型升级和绿色低碳发展提出了新要求。以煤为主的能源结构和煤炭高强度开发带来矿区固废占用土地空间、破坏生态环境和排放温室气体,已成为制约煤炭行业绿色低碳发展的突出问题之一。基于“利废固碳、从哪里来到哪里去”的理念,探寻煤矿区固废无害化、减量化、资源化、低碳化的处置新路径,创新发展矿区固废处置、采空区地下空间充分利用、CO_(2)捕集利用与封存(CCUS)相融合的关键技术,是“双碳”目标下我国矿区绿色低碳发展的紧迫需求。研究工作表明:煤矸石、粉煤灰、炉底渣和煤气化渣等矿区固废在矿山地下空间充填开采与沉陷治理、煤矿防灭火、建筑用材及农业等领域的资源化利用路径与处置技术已取得重要进展,为矿区固废固定封存CO_(2)研究提供了基础和启示,但矿区固废固定封存CO_(2)的工程化技术研究亟待加强;矿区固废矿化固定与封存CO_(2)潜力大、具有工程可行性,正在形成矿区固废处置-煤基CCUS-采空区充填新的技术体系;矿区固废与CO_(2)基气-液-固三相介质矿化强化、高效吸收与矿化固碳调控技术、地下空间矿化固碳充填与CO_(2)密闭封存、采空区充填固定封存CO_(2)潜力评价与碳去除量核算、采空区充填固定封存CO_(2)环境与安全性评价等将构成固废处置-煤基CCUS-采空区充填技术体系的核心内涵;矿区固废处置–煤基CCUS–采空区充填技术是未来实现“煤炭生产加工-矿区固废处置-高效矿化固碳与CO_(2)封存-地下空间充填与利用-矿区地面沉陷防治与生态修复”的无废矿山循环经济模式的关键,矿区固废+CO_(2)基地下充填与封闭功能材料研发是重要突破口。矿区固废处置、煤基CCUS、采空区充填与地下空间利用、矿区生态修复保护等融合技术研发应用为绿色低碳型矿山建设提供了新的发展思路。

CO_(2)与绿氢合成甲醇的过程模拟及储能性能分析

文章模拟了CO_(2)与绿氢合成甲醇的过程,提出了CO_(2)储能密度指标,研究了多个参数对甲醇储能性能的影响。研究结果表明:系统能效和甲醇能量产率随着电解水效率、单程CO_(2)转化率、电解水压力和CO_(2)初始压力的升高而升高,随着甲醇合成压力的升高而降低;CO_(2)储能密度随以上参数的变化趋势与系统能效和甲醇能量产率相反;电解水效率和单程CO_(2)转化率是敏感关键的参数;在最优组合工况下,基于甲醇高位和低位热值的系统能效分别为68.0%和59.6%,CO_(2)储能密度为6.07 k W·h/kg,能量产率为0.108 kg/(k W·h),表明以CO_(2)为原料的电制甲醇的系统能效不够理想,但储能密度优势显著。

地下水封石油洞库竖直水幕设计参数及其影响分析

滨海地区地下水封石油洞库工程中,需要增设竖直水幕系统,以满足其水封性和控制海水入侵。为研究竖直水幕系统的设计方法与参数,以滨海地区某地下水封石油洞库为例,通过有限元数值模拟方法获得了竖直水幕孔距主洞室距离d、竖直水幕孔间距b、竖直水幕孔长度l和竖直水幕孔注水压力p_(i)4个参数对洞库周围地下水渗流场、水封性、涌水量以及海水分布范围的影响规律,并与现有结果进行了对比验证。研究表明:竖直水幕孔距主洞室距离主要影响竖直水幕孔的埋深范围,长度的影响范围取决于超出主洞室的变化位置,间距和注水压力影响整个深度范围;4个参数对水封性和抑制海水入侵的影响程度顺序分别为:b<l<d<p_(i),d<b<l<p_(i);研究中共7个工况存在海水入侵洞室的风险,需进一步增强淡水补给。研究结论可为滨海地区地下水封石油洞库的竖直水幕设计参数提供一定理论依据。

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。

MICP技术在地下水封油库渗控注浆中的应用潜力

地下水封油库在建设及运营过程中洞室涌水量大小是影响洞库水封安全和运营成本的重要因素。目前地下水封油库工程建设中采用传统的注浆方式难以将围岩渗透性降低到设计要求,因此洞室涌水量得不到很好的控制。微生物诱导碳酸钙沉淀(MICP)技术具有注浆黏度低、环境适应性强、生成矿化物质稳定等显著优点,引起了学术界与工程界广泛的兴趣和研究。本文首先分析了地下水封油库涌水量控制中存在的相关问题,然后阐述了MICP技术对裂隙渗流控制的机理、影响因素以及对裂隙渗透性的影响效果,最后探讨了MICP技术在地下水封油库中应用的关键问题。通过分析表明,MICP作为地下水封油库渗流控制的一种辅助注浆方式,可以较为准确地控制围岩渗透性变化,达到对洞室涌水量有效控制的目的。

黄河流域抽水蓄能开发研究与思考

抽水蓄能作为新能源大范围开发的稳定器与助推剂,是促进黄河流域节水减排的关键,其大规模发展势在必行,但黄河流域水资源短缺,如何在碳排放与水资源双重约束下,实现能源结构绿色低碳转型,对黄河流域生态保护与高质量发展具有重要意义。依据《抽水蓄能中长期发展规划(2021—2035年)》,系统梳理了黄河流域八省(区)(不包括四川)抽水蓄能已建、在建及拟开发项目规模,初步估算了抽水蓄能大规模开发对地表水资源指标的占用情况,从调节库容占用和综合利用效益发挥两个方面分析了抽水蓄能运行对既有水利工程的影响。结果表明:黄河流域已建、在建、规划、储备抽水蓄能站点共计100座,总装机规模126050 MW,累计耗水约2.521亿m^(3);依托已建水利工程加装可逆式机组对梯级水电功能进行再造时,应充分评估对原有水利枢纽综合利用任务与工程安全的影响。