Sensitivity analysis of effective parameters on water curtain performance for crude oil storage in Iranian URC using the 2k factorial design and numerical modeling

Underground storage of hydrocarbons in unlined rock caverns (URC) has advantages over above-ground storage in terms of safety, environmental protection and economy. However seepage of products can cause many environmental and economical problems. Water curtain system is used as a part of hydrodynamic method to control seepage. Water curtains system is composed of a network of underground galleries and horizontal boreholes drilled from these galleries to establish groundwater pressure artificially. Iranian crude oil unlined storage caverns are to be excavated in Asmari limestone formation. This study aimed to clarify the effects of effective parameters on water curtains performance in the establishment of water pressure. To aim this purpose 2^k factorial statistical experimental design and numerical modeling using FLAC3D has been employed to evaluate the performance of artificial water curtain systems under various conditions include equivalent permeability and effective porosity of Asmari limestone, borehole pressure, borehole spacing and elevation, groundwater level and operation time of boreholes before the storage operation. The results showed that borehole pressure, permeability, borehole elevation and porosity have most significant effect in order of magnitude respectively. Regression model for 2^k factorial design was presented as well.     

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。     

某地下水封洞库水幕多孔联合试验参数分析

能源储备体系不仅是保障国家社会经济安全,应对突发事件的必要手段,更可以有效控制能源产品的价格,稳定供求关系。水幕系统水力效率试验中,多孔联合试验对水幕孔孔间水力传导效率进行直接判断,通过3个阶段的试验,得到水幕孔压力、流量等重要水力参数。在大量工程试验的基础上筛选出标准曲线,对水幕孔压力曲线进行定性评价。但由于此方法主观性强,识别上存在一定困难,因此难以推广成为评价标准。在洞库封存原理和水平水幕孔工作原理的前提下,将水平孔视为等强度的线汇,不考虑水平井井管中的流动对地下水渗流场的反作用,假设水幕层岩体为均值各项同性,通过对水幕孔周围裂隙水流态识别,结合Åberg关于洞室储存的水力梯度理论,推导出阈值求解路线。根据已知条件求解运营期的水幕系统临界效率值,通过线性函数拟合求解试验阶段的阈值,为定性评价水幕系统效率、优化系统结构提供了可靠的数据支持。数据分析的工程中,总结了一套适用于阈值法评价水幕系统的补孔原则。     

Experimental study of water curtain performance for gas storage in an underground cavern

An artificial water curtain system is composed of a network of underground galleries and horizontal boreholes drilled from these galleries.Pre-grouting measures are introduced to keep the bedrock saturated all the time.This system is deployed over an artificial or natural underground cavern used for the storage of gas（or some other fluids） to prevent the gas from escaping through leakage paths in the rock mass.An experimental physical modeling system has been constructed to evaluate the performance of artificial water curtain systems under various conditions.These conditions include different spacings of caverns and cavern radii located below the natural groundwater level.The principles of the experiment,devices,design of the physical model,calculation of gas leakage,and evaluation of the critical gas pressure are presented in this paper.Experimental result shows that gas leakage is strongly affected by the spacing of water curtain boreholes,the critical gas pressure,and the number and proximity of storage caverns.The hydraulic connection between boreholes is observed to vary with depth or location,which suggests that the distribution of water-conducting joint sets along the boreholes is also variable.When designing the drainage system for a cavern,drainage holes should be orientated to maximize the frequency at which they encounter major joint sets and permeable intervals studying in order to maintain the seal on the cavern through water pressure.Our experimental results provide a significant contribution to the theoretical controls on water curtains,and they can be used to guide the design and construction of practical storage caverns.     

大连地下石油储备库初始渗流场数值反演

 初始渗流场分析是水封式地下石油储备库设计中的重要内容和先决条件,现场压水试验只能提供较准确的各向同性渗透系数,而不能反映各向异性的渗透特征。结合大连地下石油储备库工程,提出一种基于随机节理网络模拟技术反演岩体各向异性渗透特征的方法。首先,采用三维离散元程序3DEC内置的Fish语言,直接生成不同尺寸的三维节理网络模型,通过推导的判别式来统计模型中各组节理的个数及产状信息。其次,利用裂隙介质的渗透张量理论计算不同尺寸的岩体渗透张量,进而确定节理岩体的表征体元(REV)。根据现场压水试验实测资料,修正节理岩体的渗透张量,再利用Matlab软件计算渗透主值及渗透特征向量。最后,考虑渗透系数的空间正交各向异性,采用FLAC3D的Fl_anisotropic的渗流模型反演库区的初始渗流场,为水封式地下石油储备库水幕设计及稳定性分析提供较合理的初始渗流场条件。     

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。     

水封式LPG地下储库渗流场三维分析

介绍了水封式LPG地下储存的气密条件。对汕头LPG地下储库的丙烷储库做了渗流场三维分析 ,分析水幕作用及其对储洞周围渗流场的影响 ,论证了水封式LPG储库的有效性。对我国水封式地下LPG储库的设计、施工和理论的发展提供了依据     

Discrete element analysis of hydro-mechanical behavior of a pilot underground crude oil storage facility in granite in China

The hydro-mechanical behavior of a pilot underground crude oil storage facility in granite in China is analyzed using Discrete Element Method (DEM). Characterization of hydro-mechanical coupling behavior of rock mass was performed using geological investigation, laboratory test, field monitoring and case study. Geological investigations were performed to obtain the geometrical properties of joints. Direct shear tests were performed to obtain the mechanical behavior of joints. A case study was performed to obtain the hydro-mechanical parameters of rock mass around the facility. Discrete element method was employed to assess the hydro-mechanical behavior of the facility. The groundwater pressure distribution and flow rate of the facility under different water curtain pressures were obtained. The groundwater inflow, deformation and stability of the caverns were obtained through the numerical simulations. It was found that the water seal property could not maintain if there is no water curtain system for the facility. The groundwater flow rate increases with the water curtain pressure. Both groundwater flow rate and crown settlement from this study are comparable to those from field measurements. However, the simulated flow rate and crown settlement are less than those predicted using empirical equations, due to the interaction between neighboring caverns and the effect of groundwater table dropdown.     

Effects of anisotropic permeability of fractured rock masses on underground oil storage caverns

An isotropic assumption is often applied to analyze permeability tests of in situ fractured rock mass, and the homogeneous hydraulic conductivities are then used directly in the seepage analysis. However, the hydraulic conductivities are normally anisotropic in fractured rock masses and the effects of the anisotropic permeability should be taken into account in rock engineering analysis, especially for seepage analysis of underground oil storage caverns. In this study, an underground oil storage cavern project is analyzed and the Oda’s method is used to determine the anisotropy in permeability, where the anisotropy in permeability is determined using the fracture orientation and the in situ stress information from the field survey. The horizontal hydraulic conductivities are obtained based on the geometric average hydraulic conductivities from the injection tests of six boreholes. A typical cavern unit is numerical modeled using code FLAC. The effects of anisotropic permeability on water pressure, water quantities and critical gas pressure are studied carefully. The results indicate that most calculated results based on in situ hydraulic tests with isotropic permeability assumption can be used safely in the underground oil storage cavern project.     

An appraisal of the test grouting data for the Tehri Dam,India

Test grouting has been carried out in the three different rock units (phyllites grade I, II & III) exposed around Tehri Dam Project to evaluate the groutability of these rocks and to evolve optimum spacing of grout holes to be adopted for the grout, curtain. Since it has been observed that permeability of the rock mass is essentially secondary and is mainly joint and fissure controlled, the structural discontinuities observed in the rock types have been analysed for finding out the direction of grout holes that can intersect the maximum numbers of discontinuities and hence seal the rock mass properly. The grouting has been carried out through grou holes and its effectiveness has been observed through inspection holes drilled in between and depending upon the effectiveness, secondary and tertiary holes were drilled in between to reduce the spacing of holes from inspection holes. Finally, when the permeability values of inspection holes were reduced to 1 lugeon or less after grouting through tertiary holes, it has been considered to have achieved optimum grouting efficiency. The effective grout travel distance in the phyllites has been proved to be 0.75 m. It has been inferred that adoption of high grout pressures while emplacing the grout curtain might change the spacing to around 1.5 m apart.     

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.     

地下水封式液化石油气储藏洞库修建技术

结合汕头地下水封式LPG储库的修建,研究储气库的水压密封原理及LPG洞储的气密条件,并通过渗流场的三维数值模拟,得出储气库周围的压力水头及水力梯度的分布规律,验证气密性条件和设置人工水幕的必要性。由于洞库是裸洞储气,且埋深大、跨度大,因此进行了洞室稳定性的三维数值分析,同时优化施工方案,确保施工及运营过程洞室的稳定性。介绍注浆和水幕钻孔技术,这是地下水封式LPG储库修建的两项关键技术,良好的注浆效果可以减少开挖期间的渗漏水、有利于保持必要的水位线、有利于封闭裂隙而减少气体逃逸,水幕钻孔是运营期间水幕保持良好工作状态的保证。汕头地下水封式LPG储库的修建技术对今后我国地下水封式储气库的设计、施工都有一定的参考价值。     

广州地铁燕塘站基坑降水的三维渗流场有限元分析

基坑降水是地铁深基坑工程施工设计所关注的重点问题,尤其要关注基坑降水后的三维渗流场分布、降水效果和渗透稳定等。本文采用了潜水承压水稳定渗流场理论和改进的截止负压法对广州地铁燕塘站深基坑降水后的三维渗流场进行了有限元分析。研究了布置不同抽水井和帷幕灌浆等多个工况的渗流场分析和基坑涌水量。研究结果表明,采用抽水井和对承压含水层进行灌浆帷幕的设计方案,深基坑降水后的渗流场和地基的渗透比降满足设计要求。     

裂隙岩体基渗流分析

裂隙岩体坝基渗流分析成果是进行大坝工程设计的重要依据之一。采用非连续介质的裂隙网络渗流原理对裂隙岩体坝基进行渗流分析 ,计算工况包括设置灌浆帷幕和排水孔与否及其组合共四种情况。由计算结果可以看出 ,坝基总渗流量主要由灌浆帷幕的质量和帷幕区的渗透系数决定 ,坝基排水孔在排出渗水和降低渗透压力方面起到极其重要的作用。     

地下水封石油储备库初始渗流场数值反演分析

渗流场分析是地下水封石油储备库设计的重要内容,而合理可靠的渗透系数是准确分析裂隙岩体渗流场的前提。以黄岛地下水封石油储备库工程为背景,对库区初始渗流场进行反演分析。首先,采用离散元3DEC软件直接生成尺寸分别为5 m×5 m,10 m×10 m,15 m×15 m,20 m×20 m,25 m×25 m,30 m×30 m的三维节理离散网络模型,并给出判别模型与节理相交的条件;基于裂隙介质的渗透张量理论,利用 MATLAB计算不同尺寸的裂隙岩体渗透张量,并确定了库区裂隙岩体表征体单元(REV)的大小,并结合库区现场试验实测数据,对节理裂隙岩体的渗透张量进行校核;最后,采用COMSOL Multiphysics软件,在裂隙岩体渗透系数各向异性条件下,反演库区的初始渗流场。研究成果为地下水封石油储备库水封性评价及稳定性分析提供较合理的初始渗流场条件。     

隧道开挖过程中复杂裂隙围岩的固流耦合分析

隧道通过裂隙岩体的含水区段时,人为扰动了裂隙岩体、地下水等构成的复杂地质系统,是造成各种涌水、突水、突泥事故的重要原因。为了研究复杂地质条件下隧道开挖过程中岩体变形、流体运移相互作用过程,探讨其对隧道涌、突水的影响,在上述复杂过程进行理论分析的基础上,根据深埋隧道围岩裂隙发育规模与工程尺度的关系,建立可以同时考虑不同级别裂隙网络的复杂裂隙岩体水力学模型,采用有限元法对复杂裂隙岩体中开挖隧道的固流耦合过程进行了数值模拟,模拟结果体现了主干裂隙在渗流中的强导水作用和网络状裂隙的贮水功能与渗流滞后效应,开挖过程中复杂裂隙岩体渗流场与应力场的耦合作用显著的增加了隧道围岩屈服区。     

Design and construction aspects of unlined oil storage caverns in rock

An underground oil storage facility comprising six storage caverns is under construction in southern Korea. Each of the horseshoe-shaped caverns is 18 m wide, 30 m high, and 400–600 m long. The artificial water curtain system used consisted of water curtain tunnels and horizontal boreholes drilled from these tunnels, and pre-grouting measures have been introduced to keep the bedrock saturated all the time in order prevent oil from migrating through rock mass. The results of site investigation show that the bedrock at the site was very competent and impermeable and, hence, a suitable medium for the storage of oil. This conclusion was confirmed later by the results of design analysis, the revised instrumentation program, and hydraulic tests performed during construction. In general, design concepts for the excavation and support and water curtain system have been verified to be reasonably good in terms of the technical soundness and economy. The results of the revised instrumentation program indicate that the three-dimensional excavation behaviour is complex and should be studied in more detail.     

广州地铁越秀公园站注浆截水帷幕施工技术

介绍广州地铁越秀公园站基坑开挖中采用的人工挖孔桩桩外垂直注浆截水帷幕和基底水平注浆帷幕施工技术。     

复杂边界条件下的岩体网络渗流分析

初步建立了适用于岩体网络渗流分析的防渗帷幕和排水孔幕模拟方法,提出复杂边界条件下渗流分析的边界预调整法,并通过算例表明所提方法是合理有效的。     

裂隙岩质边坡渗流与非连续变形耦合过程分析

 裂隙岩体中的渗流–应力耦合作用是岩质边坡失稳的重要因素之一。离散裂隙网络(DFN)模型用于研究裂隙岩体渗流,具有概念简单、效率高、适用性强的优点,是研究裂隙岩体渗流问题最为有效的手段之一。非连续变形分析(DDA)方法是专门针对裂隙岩体的非连续特性提出的一种变形场求解方法,能够更加真实地刻画工程岩体。将DFN模拟和DDA方法结合起来,提出基于DDA-DFN的渗流–应力耦合模型,给出考虑裂隙渗流情况下岩体块体系统的瞬时平衡方程,用于研究裂隙岩体变形对渗流的影响和渗流–应力耦合作用下裂隙岩体的变形破坏特征。利用该耦合模型,对一大型水利水电工程边坡稳定性进行分析。结果表明,水库蓄水后,地下水大幅度抬升,渗流–应力耦合作用加剧,导致边坡裂隙岩体中的关键部位发生大变形甚至破坏,进而触发边坡的进一步失稳。实例分析验证了这种方法用于边坡稳定性分析的有效性。