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 r...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.展开更多
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 bu...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.展开更多
The authors regret that the Declaration of Competing Interest for this publication is incomplete.The appropriate Declaration of Competing Interest is as follows.
Salt cavern hydrogen storage(SCHS)is an important component of large-scale underground hydrogen storage,with advantages such as large hydrogen storage capacity and economic feasibility.However,the uniqueness of the sa...Salt cavern hydrogen storage(SCHS)is an important component of large-scale underground hydrogen storage,with advantages such as large hydrogen storage capacity and economic feasibility.However,the uniqueness of the salt cavern structure and the inherent high risk of hydrogen storage pose a potential leakage risk.This study aims to assess the leakage risk of salt cavern hydrogen storage through a comprehensive assessment.First,the three major influencing factors of leakage risk are summarized,taking into account the unique engineering,geological conditions,and operating conditions of salt cavern storage.Subsequently,the salt cavern hydrogen storage leakage risk evaluation index system was established,and the weights of the evaluation indexes were assigned using the combination assignment method.On the basis of the two-dimensional cloud model,a new leakage risk assessment method was proposed.In addition,the risk level assessment of the salt cavern hydrogen storage facility proposed to be constructed in Pingdingshan City,Henan Province,was carried out.Finally,corresponding risk control and preventive measures are proposed.The results of the study are useful and instructive for the safe construction of deep salt cavern hydrogen storage.展开更多
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 tim...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.展开更多
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 stor...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.展开更多
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...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.展开更多
Salt caverns are extensively utilized for storing various substances such as fossil energy,hydrogen,compressed air,nuclear waste,and industrial solid waste.In China,when the salt cavern is leached through single-well ...Salt caverns are extensively utilized for storing various substances such as fossil energy,hydrogen,compressed air,nuclear waste,and industrial solid waste.In China,when the salt cavern is leached through single-well water solution mining with oil as a cushion,engineering challenges arise with the leaching tubing,leading to issues like damage and instability.These problems significantly hinder the progress of cavern construction and the control of cavern shape.The primary cause of this is the flowinduced vibration instability of leaching tubing within a confined space,which results in severe bending or damage to the tubing.This study presents a model experimental investigation on the dynamic characteristics of leaching tubing using a self-developed liquid-solid coupling physical model experiment apparatus.The experiment utilizes a silicone-rubber pipe(SRP)and a polycarbonate pipe(PCP)to examine the effects of various factors on the dynamic stability of cantilevered pipes conveying fluid.These factors include external space constraint,flexural rigidity,medium outside the pipe,overhanging length,and end conditions.The experiments reveal four dynamic response phenomena:water hammer,static buckling,chaotic motion,and flutter instability.The study further demonstrates that the length of the external space constraint has a direct impact on the flutter critical flow velocity of the cantilevered pipe conveying fluid.Additionally,the flutter critical flow velocity is influenced by the end conditions and different external media.展开更多
Large underground caverns are commonly used in variety of applications. In many cases, because of the geomechanical limitations of dimensions and requirement of high volume, several parallel caverns are used. Plastic ...Large underground caverns are commonly used in variety of applications. In many cases, because of the geomechanical limitations of dimensions and requirement of high volume, several parallel caverns are used. Plastic zone integration requires a larger rock pillar distance of theses adjacent caverns while eco- nomic and access reasons require smaller distance. In lran many underground projects are located in West and South West, Asmari formation covers a large part of these regions. The stability of underground spaces that are constructed or will be constructed in this formation has been investigated. A proper cross section based on plastic analysis and a stability criterion has been proposed for each region. Finally, in each case, allowable rock pillar between adjacent caverns with similar dimension was determined with two methods （numerical analysis and fire service law）. Results show that Fire Service Law uses a very con- servative safety factor and it was proposed to use a correction factor for allowable distance based on application of underground space.展开更多
To ensure the airtightness of salt cavern oil storage in layered salt rock,this study investigates the porosity and permeability characteristics and seepage laws of the surrounding rock of the storage caverns under th...To ensure the airtightness of salt cavern oil storage in layered salt rock,this study investigates the porosity and permeability characteristics and seepage laws of the surrounding rock of the storage caverns under the erosion of crude oil and brine.Salt rock,interlayer,and cap rock samples from the Jintan salt cavern storage in Jiangsu,China,were used.The porosity and permeability changes of the samples were measured under different static water pressures,different erosion times,and different working conditions(crude oil erosion and brine erosion).Finally,based on the theory of single-phase liquid stable seepage,liquid seepage models for interlayer and cap rock were established.The results show that the porosity and permeability parameters of the surrounding rock are not affected by stress changes under different working conditions.The wetting of crude oil covers the pore structure inside the surrounding rock,enhancing its airtightness macroscopically and thus favoring the long-term airtightness of the salt cavern oil storage.In contrast,brine erosion destroys the pore structure inside the surrounding rock,severely deteriorating its airtightness macroscopically,which seriously affects the lifespan of the storage cavern and is detrimental to the long-term airtightness of the salt cavern oil storage.Based on the assumption of single-phase liquid stable seepage,the leakage of the storage cavern was calculated.The calcu-lations of gas and liquid leakage were corrected according to the airtightness standards of gas storage caverns and combined with existing simulation parameters,which to some extent proved the accuracy of the liquid seepage models for interlayer and cap rock.展开更多
Underground Thermal Energy Storage(UTES)store unstable and non-continuous energy underground,releasing stable heat energy on demand.This effectively improve energy utilization and optimize energy allocation.As UTES te...Underground Thermal Energy Storage(UTES)store unstable and non-continuous energy underground,releasing stable heat energy on demand.This effectively improve energy utilization and optimize energy allocation.As UTES technology advances,accommodating greater depth,higher temperature and multi-energy complementarity,new research challenges emerge.This paper comprehensively provides a systematic summary of the current research status of UTES.It categorized different types of UTES systems,analyzes the applicability of key technologies of UTES,and evaluate their economic and environmental benefits.Moreover,this paper identifies existing issues with UTES,such as injection blockage,wellbore scaling and corrosion,seepage and heat transfer in cracks,etc.It suggests deepening the research on blockage formation mechanism and plugging prevention technology,improving the study of anticorrosive materials and water treatment technology,and enhancing the investigation of reservoir fracture network characterization technology and seepage heat transfer.These recommendations serve as valuable references for promoting the high-quality development of UTES.展开更多
Salt cavern energy storage technology contributes to energy reserves and renewable energy scale-up.This study focuses on salt cavern gas storage in Jintan to assess the long-term stability of its surrounding rock unde...Salt cavern energy storage technology contributes to energy reserves and renewable energy scale-up.This study focuses on salt cavern gas storage in Jintan to assess the long-term stability of its surrounding rock under frequent operation.The fatigue test results indicate that stress holding significantly reduces fatigue life,with the magnitude of stress level outweighing the duration of holding time in determining peak strain.Employing a machine learning approach,the impact of various factors on fatigue life and peak strain was quantified,revealing that higher stress limits and stress holding adversely impact the fatigue index,whereas lower stress limits and rate exhibit a positive effect.A novel fatigue-creep composite damage constitutive model is constructed,which is able to consider stress magnitude,rate,and stress holding.The model,validated through multi-path tests,accurately captures the elasto-viscous behavior of salt rock during loading,unloading,and stress holding.Sensitivity analysis further reveals the time-and stress-dependent behavior of model parameters,clarifying that strain changes stem not only from stress variations but are also influenced by alterations in elasto-viscous parameters.This study provides a new method for the mechanical assessment of salt cavern gas storage surrounding rocks.展开更多
Cusp displacement catastrophe theory can be introduced to propose a new method about instability failure of the interbed for gas storage cavern in bedded salt in solution mining.We can calculate initial fracture drawi...Cusp displacement catastrophe theory can be introduced to propose a new method about instability failure of the interbed for gas storage cavern in bedded salt in solution mining.We can calculate initial fracture drawing pace of this interbed to obtain 2D and 3D gas storage shapes at this time.Moreover,Stability evaluation of strength reduction finite element method(FEM)based on this catastrophe theory can used to evaluate this interbed stability after initial fracture.A specific example is simulated to obtain the influence of the interbed depth,cavern internal pressure,and cavern building time on stability safety factor(SSF).The results indicate:the value of SSF will be lower with the increase of cavern building time in solution mining and the increase of interbed depth and also this value remains a rise with the increase of cavern internal pressure Especially,we can conclude that the second-fracture of the interbed may take place when this pressure is lower than 6 MPa or after 6 days later of the interbed after initial fracture.According to above analysis,some effective measures,namely elevating the tube up to the top of the interbed,or changing the circulation of in-and-out lines,can be introduced to avoid the negative effects when the secondfracture of the interbed may occur.展开更多
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 c...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.展开更多
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 ...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.展开更多
A multistage filtering strategy was proposed to target the periodic noise present in the cavity sonar signal of salt cavern gas storage.First,the relevant signal's frequency band range is selected,and the paramete...A multistage filtering strategy was proposed to target the periodic noise present in the cavity sonar signal of salt cavern gas storage.First,the relevant signal's frequency band range is selected,and the parameters of the signal's time-frequency domain are collected using the Short-Time Fourier Transform(STFT).Second,the adaptive Wiener filter is adjusted with windows of variable lengths,completing the first stage of filtering.Lastly,the second stage involves utilizing the wavelet transform to enhance the capacity for filtering periodic noise.The Signal-to-Noise Ratio(SNR)and correlation coefficient are thoroughly estimated to assess the sonar signal after the second stage of filtering,and the Minimum Mean Squared Error(MMSE)is employed to evaluate the impact of the first filtering stage,confirming the effectiveness of the proposed filtering technique.According to various experiments,the method presented in this work effectively suppresses multiple types of noise,improves the accuracy of echo extraction,and enhances the SNR by approximately 10 dB,all while preserving the characteristics of the original signal.展开更多
As a non-renewable rare industrial gas resource,the decreasing production of helium has stimulated the demand for large-scale storage.Dewar tanks,storage tanks and other liquid helium storage methods are difficult to ...As a non-renewable rare industrial gas resource,the decreasing production of helium has stimulated the demand for large-scale storage.Dewar tanks,storage tanks and other liquid helium storage methods are difficult to meet the needs of largescale and long-term storage.Salt caverns have been widely used in gas energy storage due to their low permeability,which has been proven by decades of stable operation of natural gas storage.However,helium has higher permeability under the same storage conditions,and the feasibility of using rock salt for helium storage has not yet been evaluated by mature theories and standards.In addition,an overlooked fact is that the permeability characteristics of rock salt and micro-permeable layers(MPL)are very different,and MPL can provide leakage channels for high-pressure helium.In this paper,a seepage movement model of small molecule gas in MPL is established.Its calculative accuracy and engineering applicability are verified by the seepage test results.The MPL has crystal structure,which makes the permeability change with different confining pressure and gas injection pressure.The change of permeability is caused by the residual brine in the crystal void.The compaction and the increase of flow velocity of salt rock crystal void increase the viscous resistance and decrease the flow velocity.The permeability of nitrogen and helium in the MPL is different,but the difference decreases at high confining pressure and high injection pressure.In deep salt formations with plateau potential stress,the difference of surrounding rock leakage characteristics between helium and natural gas is smaller,and the expected leakage amount of helium is lower.The paper proposes a numerical calculation model suitable for predicting leaks in salt cavern helium storage facilities with known faults and structural planes,completing the assessment of helium leakage in salt caverns considering the gas physical properties,injection and production conditions,operating pressure,and in-situ stress of surrounding rocks.The above achievements can provide technical references for early-stage leakage prediction and parameter optimization in helium storage salt cavern engineering.展开更多
文摘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.
文摘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.
文摘The authors regret that the Declaration of Competing Interest for this publication is incomplete.The appropriate Declaration of Competing Interest is as follows.
基金Youth Innovation Promotion Association of the Chinese Academy of Sciences,Grant/Award Number:No.Y2023089Excellent Young Scientists Fund,Grant/Award Number:No.52122403National Natural Science Foundation of China,Grant/Award Number:No.52374069。
文摘Salt cavern hydrogen storage(SCHS)is an important component of large-scale underground hydrogen storage,with advantages such as large hydrogen storage capacity and economic feasibility.However,the uniqueness of the salt cavern structure and the inherent high risk of hydrogen storage pose a potential leakage risk.This study aims to assess the leakage risk of salt cavern hydrogen storage through a comprehensive assessment.First,the three major influencing factors of leakage risk are summarized,taking into account the unique engineering,geological conditions,and operating conditions of salt cavern storage.Subsequently,the salt cavern hydrogen storage leakage risk evaluation index system was established,and the weights of the evaluation indexes were assigned using the combination assignment method.On the basis of the two-dimensional cloud model,a new leakage risk assessment method was proposed.In addition,the risk level assessment of the salt cavern hydrogen storage facility proposed to be constructed in Pingdingshan City,Henan Province,was carried out.Finally,corresponding risk control and preventive measures are proposed.The results of the study are useful and instructive for the safe construction of deep salt cavern hydrogen storage.
基金Supported by the National Natural Science Foundation of China (50779025,50539090)the Open Research Foundation of State Key Laboratory of Hydroscience and Engineering of Tsinghua University (200805331143)
文摘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.
基金the financial supports from Jiangxi Provincial Natural Science Foundation (Grant No. 20212BAB214009, 20212BAB214014)the National Natural Science Foundation of China (Grant No. 51874273)+1 种基金the Key Science and Technology Research Project in Jiangxi Province Department of Education (Grant No. GJJ200634, GJJ200637)the Open Project of State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences (Grant No. Z020016)。
文摘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.
基金Sponsored by the National Natural Science Foundation of China (Grant No. 50676025)National Great Project of Scientific and Technical Supporting Programs Funded by Ministry of Science & Technology of China During the 11th Five-year Plan (Grand No.2006BAB03B09)
文摘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.
基金financial support received from the Open Research Fund of the State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences (Grant No.Z019011)the Shandong Provincial Natural Science Foundation (Grant No.ZR2020QE112)+1 种基金the National Natural Science Foundation of China (No.51874273)the Excellent Young Scientists Fund Program of National Natural Science Foundation of China (No.52122403)。
文摘Salt caverns are extensively utilized for storing various substances such as fossil energy,hydrogen,compressed air,nuclear waste,and industrial solid waste.In China,when the salt cavern is leached through single-well water solution mining with oil as a cushion,engineering challenges arise with the leaching tubing,leading to issues like damage and instability.These problems significantly hinder the progress of cavern construction and the control of cavern shape.The primary cause of this is the flowinduced vibration instability of leaching tubing within a confined space,which results in severe bending or damage to the tubing.This study presents a model experimental investigation on the dynamic characteristics of leaching tubing using a self-developed liquid-solid coupling physical model experiment apparatus.The experiment utilizes a silicone-rubber pipe(SRP)and a polycarbonate pipe(PCP)to examine the effects of various factors on the dynamic stability of cantilevered pipes conveying fluid.These factors include external space constraint,flexural rigidity,medium outside the pipe,overhanging length,and end conditions.The experiments reveal four dynamic response phenomena:water hammer,static buckling,chaotic motion,and flutter instability.The study further demonstrates that the length of the external space constraint has a direct impact on the flutter critical flow velocity of the cantilevered pipe conveying fluid.Additionally,the flutter critical flow velocity is influenced by the end conditions and different external media.
文摘Large underground caverns are commonly used in variety of applications. In many cases, because of the geomechanical limitations of dimensions and requirement of high volume, several parallel caverns are used. Plastic zone integration requires a larger rock pillar distance of theses adjacent caverns while eco- nomic and access reasons require smaller distance. In lran many underground projects are located in West and South West, Asmari formation covers a large part of these regions. The stability of underground spaces that are constructed or will be constructed in this formation has been investigated. A proper cross section based on plastic analysis and a stability criterion has been proposed for each region. Finally, in each case, allowable rock pillar between adjacent caverns with similar dimension was determined with two methods （numerical analysis and fire service law）. Results show that Fire Service Law uses a very con- servative safety factor and it was proposed to use a correction factor for allowable distance based on application of underground space.
基金financial supports of the National Natural Science Foundation of China Youth Science Foundation Project(52204152,52204111,52204153)the Postdoctoral Innovation Talent Support Program(BX2020275)the Postdoctoral Science Foun-dation(2020M683521).
文摘To ensure the airtightness of salt cavern oil storage in layered salt rock,this study investigates the porosity and permeability characteristics and seepage laws of the surrounding rock of the storage caverns under the erosion of crude oil and brine.Salt rock,interlayer,and cap rock samples from the Jintan salt cavern storage in Jiangsu,China,were used.The porosity and permeability changes of the samples were measured under different static water pressures,different erosion times,and different working conditions(crude oil erosion and brine erosion).Finally,based on the theory of single-phase liquid stable seepage,liquid seepage models for interlayer and cap rock were established.The results show that the porosity and permeability parameters of the surrounding rock are not affected by stress changes under different working conditions.The wetting of crude oil covers the pore structure inside the surrounding rock,enhancing its airtightness macroscopically and thus favoring the long-term airtightness of the salt cavern oil storage.In contrast,brine erosion destroys the pore structure inside the surrounding rock,severely deteriorating its airtightness macroscopically,which seriously affects the lifespan of the storage cavern and is detrimental to the long-term airtightness of the salt cavern oil storage.Based on the assumption of single-phase liquid stable seepage,the leakage of the storage cavern was calculated.The calcu-lations of gas and liquid leakage were corrected according to the airtightness standards of gas storage caverns and combined with existing simulation parameters,which to some extent proved the accuracy of the liquid seepage models for interlayer and cap rock.
基金supported by the National Nature Science Foundation of China under grant No.42272350the Foundation of Shanxi Key Laboratory for Exploration and Exploitation of Geothermal Resources under grant No.SX202202.
文摘Underground Thermal Energy Storage(UTES)store unstable and non-continuous energy underground,releasing stable heat energy on demand.This effectively improve energy utilization and optimize energy allocation.As UTES technology advances,accommodating greater depth,higher temperature and multi-energy complementarity,new research challenges emerge.This paper comprehensively provides a systematic summary of the current research status of UTES.It categorized different types of UTES systems,analyzes the applicability of key technologies of UTES,and evaluate their economic and environmental benefits.Moreover,this paper identifies existing issues with UTES,such as injection blockage,wellbore scaling and corrosion,seepage and heat transfer in cracks,etc.It suggests deepening the research on blockage formation mechanism and plugging prevention technology,improving the study of anticorrosive materials and water treatment technology,and enhancing the investigation of reservoir fracture network characterization technology and seepage heat transfer.These recommendations serve as valuable references for promoting the high-quality development of UTES.
基金supported by the National Natural Science Foundation of China(Nos.52374078,U24A20616 and 52074043)the Sichuan-Chongqing Science and Technology Innovation Cooperation Program Project(No.2024TIAD-CYKJCXX0011)the Fundamental Research Funds for the Central Universities(No.2023CDJKYJH021)。
文摘Salt cavern energy storage technology contributes to energy reserves and renewable energy scale-up.This study focuses on salt cavern gas storage in Jintan to assess the long-term stability of its surrounding rock under frequent operation.The fatigue test results indicate that stress holding significantly reduces fatigue life,with the magnitude of stress level outweighing the duration of holding time in determining peak strain.Employing a machine learning approach,the impact of various factors on fatigue life and peak strain was quantified,revealing that higher stress limits and stress holding adversely impact the fatigue index,whereas lower stress limits and rate exhibit a positive effect.A novel fatigue-creep composite damage constitutive model is constructed,which is able to consider stress magnitude,rate,and stress holding.The model,validated through multi-path tests,accurately captures the elasto-viscous behavior of salt rock during loading,unloading,and stress holding.Sensitivity analysis further reveals the time-and stress-dependent behavior of model parameters,clarifying that strain changes stem not only from stress variations but are also influenced by alterations in elasto-viscous parameters.This study provides a new method for the mechanical assessment of salt cavern gas storage surrounding rocks.
文摘Cusp displacement catastrophe theory can be introduced to propose a new method about instability failure of the interbed for gas storage cavern in bedded salt in solution mining.We can calculate initial fracture drawing pace of this interbed to obtain 2D and 3D gas storage shapes at this time.Moreover,Stability evaluation of strength reduction finite element method(FEM)based on this catastrophe theory can used to evaluate this interbed stability after initial fracture.A specific example is simulated to obtain the influence of the interbed depth,cavern internal pressure,and cavern building time on stability safety factor(SSF).The results indicate:the value of SSF will be lower with the increase of cavern building time in solution mining and the increase of interbed depth and also this value remains a rise with the increase of cavern internal pressure Especially,we can conclude that the second-fracture of the interbed may take place when this pressure is lower than 6 MPa or after 6 days later of the interbed after initial fracture.According to above analysis,some effective measures,namely elevating the tube up to the top of the interbed,or changing the circulation of in-and-out lines,can be introduced to avoid the negative effects when the secondfracture of the interbed may occur.
基金supported by the National Science and Technology Major Project of China (Grant Nos 2008ZX05017, 2008ZX05036)the Ex-cellent Doctor Degree Dissertation Training Program of China University of Petroleum (Grant No Z10-10)
文摘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.
基金supported by the National Science and Technology Major Project of China(Grant Nos.2008ZX05017,2008ZX05036)the Excellent Doctor Degree Dissertation Training Program of China University of Petroleum(Grant No.Z10-10)
文摘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.
基金supported by Talent Training&Importing Project of Chinese Academy of Sciences(E455160101).
文摘A multistage filtering strategy was proposed to target the periodic noise present in the cavity sonar signal of salt cavern gas storage.First,the relevant signal's frequency band range is selected,and the parameters of the signal's time-frequency domain are collected using the Short-Time Fourier Transform(STFT).Second,the adaptive Wiener filter is adjusted with windows of variable lengths,completing the first stage of filtering.Lastly,the second stage involves utilizing the wavelet transform to enhance the capacity for filtering periodic noise.The Signal-to-Noise Ratio(SNR)and correlation coefficient are thoroughly estimated to assess the sonar signal after the second stage of filtering,and the Minimum Mean Squared Error(MMSE)is employed to evaluate the impact of the first filtering stage,confirming the effectiveness of the proposed filtering technique.According to various experiments,the method presented in this work effectively suppresses multiple types of noise,improves the accuracy of echo extraction,and enhances the SNR by approximately 10 dB,all while preserving the characteristics of the original signal.
基金supported by the National Natural Science Foundation of China(Grant Nos.42072307,52404066)the Hubei Province Outstanding Youth Fund(Grant No.2021CFA095)+1 种基金the Natural Science Foundation of Wuhan(Grant Nos.2024040701010062,2024040801020255)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDC10020300)。
文摘As a non-renewable rare industrial gas resource,the decreasing production of helium has stimulated the demand for large-scale storage.Dewar tanks,storage tanks and other liquid helium storage methods are difficult to meet the needs of largescale and long-term storage.Salt caverns have been widely used in gas energy storage due to their low permeability,which has been proven by decades of stable operation of natural gas storage.However,helium has higher permeability under the same storage conditions,and the feasibility of using rock salt for helium storage has not yet been evaluated by mature theories and standards.In addition,an overlooked fact is that the permeability characteristics of rock salt and micro-permeable layers(MPL)are very different,and MPL can provide leakage channels for high-pressure helium.In this paper,a seepage movement model of small molecule gas in MPL is established.Its calculative accuracy and engineering applicability are verified by the seepage test results.The MPL has crystal structure,which makes the permeability change with different confining pressure and gas injection pressure.The change of permeability is caused by the residual brine in the crystal void.The compaction and the increase of flow velocity of salt rock crystal void increase the viscous resistance and decrease the flow velocity.The permeability of nitrogen and helium in the MPL is different,but the difference decreases at high confining pressure and high injection pressure.In deep salt formations with plateau potential stress,the difference of surrounding rock leakage characteristics between helium and natural gas is smaller,and the expected leakage amount of helium is lower.The paper proposes a numerical calculation model suitable for predicting leaks in salt cavern helium storage facilities with known faults and structural planes,completing the assessment of helium leakage in salt caverns considering the gas physical properties,injection and production conditions,operating pressure,and in-situ stress of surrounding rocks.The above achievements can provide technical references for early-stage leakage prediction and parameter optimization in helium storage salt cavern engineering.
