Dynamic simulation research on injection and withdrawal performance of underground salt cavern natural gas storage

Owing to perfect impermeability,dynamics stability,flexible and efficient operation mode and strong adjustment,underground salt cavern natural gas storage is especially adapted to be used for short-term dispatch.Based on characteristics of gas flow and heat transfer,dynamic mathematic models were built to simulate the injection and withdrawal performance of underground salt cavern gas storage.Temperature and pressure variations of natural gas in gas storage were simulated on the basis of building models during withdrawal operation,and factors affecting on the operation of gas storage were also analyzed.Therefore,these models can provide theore-tic foundation and technology support for the design,building and operation of salt cavern gas storage.

Determination of the maximum allowable gas pressure for an underground gas storage salt cavern——A case study of Jintan,China

Increasing the allowable gas pressure of underground gas storage(UGS) is one of the most effective methods to increase its working gas capacity. In this context, hydraulic fracturing tests are implemented on the target formation for the UGS construction of Jintan salt caverns, China, in order to obtain the minimum principal in situ stress and the fracture breakdown pressure. Based on the test results, the maximum allowable gas pressure of the Jintan UGS salt cavern is calibrated. To determine the maximum allowable gas pressure, KING-1 and KING-2 caverns are used as examples. A three-dimensional(3D)geomechanical model is established based on the sonar data of the two caverns with respect to the features of the target formation. New criteria for evaluating gas penetration failure and gas seepage are proposed. Results show that the maximum allowable gas pressure of the Jintan UGS salt cavern can be increased from 17 MPa to 18 MPa(i.e. a gradient of about 18 k Pa/m at the casing shoe depth). Based on numerical results, a field test with increasing maximum gas pressure to 18 MPa has been carried out in KING-1 cavern. Microseismic monitoring has been conducted during the test to evaluate the safety of the rock mass around the cavern. Field monitoring data show that KING-1 cavern is safe globally when the maximum gas pressure is increased from 17 MPa to 18 MPa. This shows that the geomechanical model and criteria proposed in this context for evaluating the maximum allowable gas pressure are reliable.

Theoretical research on gas seepage in the formations surrounding bedded gas storage salt cavern

When constructing salt cavern gas or petroleum storage in lacustrine sedimentary salt formations rich in mudstone interlayers, the influence of the sealing performance of interlayers and salt-mud interface on the storage tightness should be considered adequately. In order to reveal the gas seepage in deep formations surrounding bedded salt cavern underground storage, a leakage analysis model was established based on the characteristics of a low dip angle and the interbedded structure of bedded rock salt. The gas seepage governing equations for one-dimensional and plane radial flow were derived and solved. A gas seepage simulation experiment was conducted to demonstrate the accuracy and reliability of the theoretical calculation results. The error of the seepage range was approximately 6.70%, which is acceptable. The analysis and calculation results indicate that the motion equation of gas in deep formations satisfies a non-Darcy's law with a threshold pressure gradient and slippage effect. The sufficient condition for the gas flow to stop is that the pressure gradient is equal to the threshold pressure gradient.The relationship between the leakage range and operating time is a positive power function, that is, the leakage range gradually increases with time and eventually stabilizes. As the seepage range increases, the seepage pressure decreases sharply during the early stage, and then decreases gradually until the flow stops.Combining the research results with engineering applications, three quantitative evaluation indexes named the maximum admissible leakage range, leakage volume and leakage rate are proposed for the tightness evaluation of gas storage salt cavern during their operating stage. These indexes can be used directly in actual engineering applications and can be compared with the key design parameters stipulated in the relevant specifications. This work is expected to provide theoretical and technical support for the gas loss and tightness evaluation of gas storage salt caverns.

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.

Dynamic subsidence prediction of ground surface above salt cavern gas storage considering the creep of rock salt

A new model is proposed to predict the dynamic subsidence of ground surface above salt cavern gas storage during the leaching and storage, which takes into account the creep of rock salt. In the model, the extended form of Gaussian curve is adopted to figure out the shape of subsidence areas. The corresponding theoretical formulas are derived. In addition, parameters are studied to investigate the surface subsidence as a function of the salt ejection rate, internal pressure, buried depth, diameter, height, running time, etc. Through an example, the subsidence of the salt cavern gas storage located at Jiangsu of China obtained by the new model was compared with those by Peter A F formula, Schober & Sroka formula and FLAC3D through simulation. The results showed the proposed model is precise and correct, and can meet the actual engineering demands. The surface subsidence is equidirectional with the increase of salt ejection rate, depth, diameter, height, and running time, but reverse to the increase of internal pressure. The depth, diameter, running time and internal pressure have great effects on the subsidence, whereas the salt ejection rate and height have little influences on it.

Stability analysis of the pillars between bedded salt cavern gas storages by cusp catastrophe model

The failure of pillars between bedded salt cavern gas storages can be seen as processes that the deformations of pillars convert from continuous gradual change system to catastrophe state,which are typical nonlinear catastrophe problems.In the paper,the cusp catastrophe model is proposed to obtain the stability factors of pillars.It can overcome the shortages of traditional strength reduction finite element method(SR FEM) and greatly improve the accuracy of stability factors obtained by numerical simulations.The influences of cavern depth,gas pressure,pillar width,and time on the stability factors are studied.Y-1 and Y-2 salt cavern gas storages,located at Jiangsu province of China,were simulated as examples.The stability factors of pillars between Y-1 and Y-2 were evaluated,and the running parameters were recommended to ensure the pillars stability.The results showed that the cusp catastrophe model has high practicability and can precisely predict the stability factors.The stability factors are equidirectional with the increase of gas pressure and pillar width,but reverse to the increase of cavern depth and time.The stability factors of pillars between Y-1 and Y-2 are small for narrow widths,which are influenced greatly by gas pressure,time,pressure difference,and gas production rate.In order to ensure the safety of pillars,the lowest gas pressure,safe running time,max.pressure difference and max.gas production rate of Y-1 and Y-2 were recommended as 7 MPa,5 years,3 MPa,and 0.50 MPa/d,respectively.

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.

碳封存与压缩气体地质储能现状、挑战与展望

碳封存与地质储能对于减缓全球变暖、实现我国“双碳”目标都是不可缺少的重要技术。文章首先介绍了碳封存与地质储能的含义,明确两者的储库选择具有共性,含水层、枯竭油气层、盐穴都可作为储层,但碳封存要求长期储存,而地质储能则需多次循环储存和释放,选址评价时需充分考虑。碳捕集与封存(CCS)项目在全球快速增长,正在向网络化和集群化发展,我国CCS项目目前以CO_(2)驱油为主,直接封存项目较少,但未来直接封存项目将成为主流,也在积极向集群式发展。我国碳封存地质条件良好,油气层封存潜力估计比较准确,咸水层封存潜力还存在较大不确定性。目前地质储能项目以盐穴压缩空气储能为主,德、美及我国共有5座压缩空气盐穴储能电站投产运行。我国盐穴资源丰富,但地质条件复杂,适宜的建库地点集中在东部地区,已有多个项目在建。相比盐穴,孔隙地层如含水层和枯竭油气层分布更广,具备储能潜力,但需解决多相流和化学反应等技术问题。现有场地选址、潜力评价、效率优化和监测预警技术与大规模实际工程应用要求仍存在显著差距。目前传统的水文地质勘查方法与技术已不能满足碳封存与地质储能的选址要求,另外也缺乏高效的CO_(2)地质封存的地质环境背景监测与风险控制技术及针对储层及盖层压力和地应力变化的低成本、精准连续监测技术。在碳封存与地质储能工程应用中,一些关键设备组件(如监测、动力等)也比较缺乏自主知识产权的针对性设计与优化。我国储层模拟软件在超大规模实际场地复杂储层的高效模拟方面亟待突破。未来应在碳封存及地质储能资源调查与场地选址关键技术、碳封存与地质储能工程化装备方面加大研发力度,并针对咸水层、枯竭油气藏等主要储库资源开展多类型工程示范研究,建设多类型碳封存及压缩空气储能工程示范基地。

地下储氢技术现状及在中国加快发展的可行性

随着能源转型升级需求的日益迫切,氢能以其零污染、零碳排、无次生污染的优势,将成为中国能源体系的重要组成部分,也是中国石化新能源业务的主要主攻方向。目前,中国主要采用高压气态储氢、低温液态储氢和固态合金储氢等地面储氢方式,其储氢成本高,储氢效率低。与地面储氢相比,地下储氢以其规模大、成本低、更高的安全性,展现出更为广阔的发展潜力和应用前景。在国际上,混合储氢技术已在法国、德国等国家实现了一定规模的应用;纯氢气地下存储技术在美国取得较好的应用效果,但在中国这一领域的应用和研究近乎空白,尚处于起步阶段。针对氢气强流动性、高泄漏风险及强腐蚀性的特点,通过研究明确地下储氢面临的技术挑战,包括对圈闭密封性、地层条件、完井材料、地面工艺等方面。从枯竭油气藏资源、盐岩资源、储气库建设与运行管理技术等方面出发,分析中国开展地下储氢技术的可行性。中国西部和中东部拥有多个大型油气藏,枯竭油气藏资源丰富,具备开展地下混合氢储试验和氢储能的条件;盐岩分布广泛,用盐穴储存纯氢或氢储能切实可行;中国在气藏型储气库和盐穴型储气库建设与运行管理技术方面已积累了丰富经验和技术储备。综合分析认为中国具备了开展地下储氢的条件和技术。

中国天然气战略储备的需求和对策

通过对世界上部分国家和地区天然气战略储备发展状况及天然气储备经验的分析,得出:①天然气地下储备优于地表储备;②直接将天然气储存于地下的成本低于以液化天然气形式的储备;③枯竭油气藏地下储气最优,含水层地下储气次之。我国2020年前天然气战略储备的需求将达到250×108m3的工作气量,面对如此巨大需求,选择合适的库址和库型是非常重要的,结合我国油气资源远离天然气消费大城市和主要富集在非均质性较强的陆相地层中的特点,提出我国未来天然气地下战略储备应以海相含水层作为主要储集空间、并考虑其它多种库型的对策,并就不同投资主体在不同类型地下储气库建设中应发挥的作用提出了建议。

盐穴储油(气)库水溶造腔管柱动力特性初探

针对盐穴储气库单井水溶造腔过程中管柱动力特性开展了初步探讨,认为造腔工程中,管柱在受限空间的自激振动和动力失稳是导致管柱发生严重弯曲或者破损的主要原因。初步分析了无空间约束条件下内外管柱的振动特性,得到了理想条件下管柱临界流速的计算式。计算表明,无约束条件下造腔管柱一般会由于液-固耦联振动而发生动力失稳,而且造腔内管一般会先于造腔外管发生失稳破坏。鉴于问题的重要性和复杂性,还对造腔管柱临界流速全面计算力学模型应考虑的诸因素进行了探讨,初步分析了管道轴力、液体压力、造腔循环方式、管道水平支撑,以及轴向水击和管道横向振动耦合的影响,为进一步结合工程实际开展空间约束条件下造腔管柱动力特性全面分析提出了建议。

盐岩地下油气储库运营期风险的故障树分析

盐岩以其良好的蠕变特性、低渗透性和损伤自我恢复性而被广泛用于地下油气能源储备,虽然目前国内外对盐岩力学特性的研究成果较多,但关于盐岩地下油气储库风险分析的研究报道却尚不多见。为了探讨盐岩地下油气储库运营期的风险机制,以江苏金坛盐岩地下油气储库为示范工程,对储库运营期的风险因子进行了辨识。应用故障树分析方法对储库运营期事故进行研究,建立了储库运营期腔体失效、地表沉陷、油气渗漏的故障树模型。通过对运营期故障树最小割集和结构重要度的分析,将储库运营期的风险因子按其影响程度进行了排序,并对故障树分析方法进行了评价,所得结论为进一步开展储库风险评估与控制提供了指导意见。

基于事故统计分析的盐岩地下油/气储库风险评价

基于国外盐岩地下油气储备库曾发生过的重大事故的统计资料,采用风险矩阵法对盐岩储备库在建设和运营过程中的存在的重大风险进行了评价,分析了储备库重大事故的发生概率、风险等级、事故类型以及引发事故的主要原因,为我国盐岩储备库在建设和运营中的风险管理提供理论依据。研究结果表明,单个盐穴在建设和运营过程中发生重大事故的统计概率为1.51%,风险等级介于三级和四级之间,属于基本可接受的风险,但必须制定防范、监控措施;事故类型可分为油气渗漏、腔体失效和地表沉陷,其中油气渗漏事故的风险等级为三级,属于可接受风险,其他类型的事故风险等级均为二级,属于可容许风险;引发事故的原因主要是套管破损、蠕变过量和人为失误,其次还有地面装置损坏和盖层失效。

盐岩夹层蠕变特性实验研究与理论分析

通过对湖北应城盐岩夹层160 d的单轴压缩蠕变试验研究,可知湖北应城盐岩夹层具有良好的蠕变特性,盐岩夹层蠕变来自两部分,一部分为盐岩蠕变,另一部分来自夹层蠕变,且纯盐岩蠕变率高于夹层,横向应变率大于夹层。根据试验结果,拟合试验曲线得出了盐岩夹层蠕变经验公式,由最小二乘法得到盐岩夹层蠕变经验公式拟合参数;并分析了曲线特征,建立了盐岩夹层蠕变理论模型,得出了盐岩夹层的粘弹塑性本构方程,为盐岩矿床油气储库的稳定性分析提供了依据。

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。

岩盐地下油气储库群稳定分析及连锁破坏的地质力学模型试验

层状盐岩中油气储库群的整体稳定及其连锁破坏机制的研究对油气储库的安全运行有着及其重要的意义。采用小块体和低强度黏接剂建立地下储库的地质力学模型,以小块体来模拟岩体的变形特性,块体之间的低强度黏接剂模拟岩体的强度特性。泥岩夹层采用脱水石膏薄片模拟。模拟四洞室储库群在不同压强下的注采循环过程。通过埋设在模型内部的位移计和应变片自动跟踪监测洞室群及基础的位移和应变随注采压强的变化规律,研究采气方式、内压大小和泥岩夹层对储库群整体稳定性的影响。结果表明,单溶腔采注气对洞室群稳定性和连锁破坏有显著影响,泥岩夹层对洞群稳定影响很小。

地下储气库建设技术研究现状及建议

为了及时把握地下储气库建设技术研究现状,系统地梳理了枯竭油气藏储气库、盐穴储气库、含水层构造储气库的建设及垫底气的设计、提高地下储气库有效储量和生产能力的相关技术、地面系统自动化控制等地下储气库通用技术研究现状及其应用情况。结论认为,我国地下储气库建设技术的研究现状可概括为:国内枯竭气藏建库技术基本成熟;枯竭油藏建库技术尚在摸索之中;盐穴储气库建库技术取得了长足的进步;含水层构造储气库的研究才刚起步。进而提出了我国今后一段时期地下储气库建设的相关建议:①枯竭油气藏仍是我国地下储气库建设的主要类型,应关注相关技术的发展;②盐穴储气库的相关技术需要持续关注,但应当将主要研究力量放在相对薄弱的技术环节上;③我国含水层构造储气库的建设应学习、消化国外相关技术,针对具体的地质条件,加快对注排机理、渗透机理、建库方式、建库周期、井网部署、方案设计和施工技术等的研究;④应高度重视地下储气库建设相关标准、规范的建立;⑤应高度重视地下储气库运行的风险管理。

地下储氢技术研究综述

为了应对气候变化,需要加快能源转型,大幅度提高可再生能源在能源体系中占比。发展地下储氢技术是克服可再生能源波动性和间歇性的有效方法。回顾了地下储氢技术的研究现状,讨论了地下储氢技术特点,介绍了地下储氢主要地质构造及其工业应用,总结得出:地下储氢技术总体上仍然处在发展初级阶段;与地面储氢相比,地下储氢具有储能容量大、储存时间长、储能成本低、储存更安全等优势;不同储氢技术发展及应用程度不同;地下储氢具有技术和经济上的可行性,能否大规模应用关键取决于电解制氢成本能否降低的论断。

模拟盐穴储气库条件下含Cr石油套管腐蚀选材研究

针对某盐穴储气库工程地质条件进行选材,采用高温高压釜模拟试验对4种不同Cr含量石油套管进行腐蚀性能评价,并对腐蚀产物及表面形貌进行研究。研究结果表明,随着Cr含量的提高,腐蚀产物膜厚度减小,腐蚀产物膜中Cr元素发生明显富集,腐蚀速率逐渐降低,抗点蚀性能得到改善。13Cr石油套管腐蚀试验后表面有轻微腐蚀产物,清洗后表面光亮如初,腐蚀速率为0.1011mm/y,明显优于其它材质,符合储气库选材需求。

盐岩溶腔油气储库建造研究

在整理国内外盐岩溶腔油气储库建造研究有关资料的基础上,论述了盐岩溶腔的主要用途及非常规用途,从而确立盐岩溶腔是石油、天然气储备和包括核废料在内的有毒、有害废物处置的理想场所,被称为“高度战略安全的储备库”。进而论述了盐岩溶腔油气储库的建造技术及油气储库溶腔稳定性的研究现状,表明油气储库溶腔的稳定性主要由油气储库的类型、盐岩的力学特性、油气储库运行压力和盖层的厚度来决定。