CN112610275A - Comprehensive evaluation index system and design method for gas production rate of salt cavern gas storage - Google Patents
Comprehensive evaluation index system and design method for gas production rate of salt cavern gas storage Download PDFInfo
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Abstract
The invention discloses a comprehensive evaluation index system and a design method for gas production rate of a salt cavern gas storage, which comprises the following steps of dividing the salt cavern gas storage into a cavity part, a pipe column system part and a wellhead station part from bottom to top, and respectively comprehensively researching factors influencing the gas production rate of the gas storage from the three aspects: firstly, the stability and the volume of the cavity are shrunk, secondly, the tubular column is eroded, corroded and vibrated, and thirdly, hydrate and condensate water are generated; aiming at the factors, a gas production rate determination method for avoiding adverse effects is provided, the minimum value under each constraint factor is taken as the maximum gas production rate of the gas storage, so that economic benefits are guaranteed or the gas production rate is improved as far as possible according to the operation requirements of the gas storage, and an emergency response is provided to distribute the gas production rate in the whole service life of the gas storage. The factors studied by the present invention are very comprehensive and basically include all the constituent structures and types of the salt cavern gas storage which can be seen at present, and all the stability and safety problems which can be encountered and are related to the gas production rate of the gas storage.
Description
Technical Field
The invention belongs to the technical field of salt cavern gas storage, and particularly relates to a comprehensive evaluation index system and a design method for gas production rate of a salt cavern gas storage, which are suitable for determining gas production rate parameters of underground gas storage such as natural gas storage, compressed air energy storage, hydrogen storage and the like.
Background
The salt cavern is an underground storage facility formed in a water-soluble mode in deep salt mine, has good sealing performance and stable chemical property, has good damage self-healing capacity, and is an internationally recognized ideal place for oil and gas storage and industrial waste disposal. At present, about 1500 salt caverns for storing various substances exist in the world, and the salt cavern gas storage 107 in service is mainly distributed in developed regions such as America, Canada, Europe and the like, and the effective storage capacity is as high as 2896 multiplied by 108m3Mainly used for natural gas storage and peak regulation, and also comprises a small amount of compressed air energy storage and CO2And H2Etc. storage of the hydrocarbon compounds. The salt cavern gas storage is also a clean energy conversion technology, and has wide application prospect in the fields of flow battery power stations and the like.
Compared with other types of gas storage, the salt cavern gas storage is more flexible in injection and production modes, large in single-day injection and gas production amount, and quicker in emergency response. At present, scholars at home and abroad focus more research on key warehouse building technologies such as site selection and corrosion of a warehouse, and a set of mature and reliable methods is not formed as key parameters for injection and production operation control of salt cavern gas storage due to lack of research on warehouse operation technologies, especially determination of gas production rate. Only sporadic wide reports exist, most typically, the temperature and pressure parameters of the well mouth are mainly observed in the natural gas production process specified by (SY 6826-2010) salt cavern underground gas storage safety technical regulation, and measures for preventing the formation of the well mouth hydrate are taken; in addition, the contraction and deformation of the cavities of Wuhan rock-soil institute Chenfeng and the like of Chinese academy of sciences also give a recommended value of the gas production rate of the salt cavern gas storage.
However, with engineering practice and understanding of the operation technology of the salt cavern gas storage, the discovery is deepened: gas reservoirs with different gas production rates have great differences in operation and peak shaving performance such as stability, working gas amount, service safety, service life and the like. The expression is as follows: the working gas volume extracted at high strength is hundreds of thousands or even hundreds of thousands of squares less than that extracted at low strength; the gas storage of high-strength gas production is easy to have the problems of instability, cracks and the like under the conditions of rapid temperature and internal pressure change; the low gas production rates do not fully exploit the rapid response advantages of salt cavern reservoirs over other types of reservoirs and have the uneconomical disadvantage. Furthermore, current knowledge of the maximum gas production rate of salt cavern gas reservoirs is in the face of knowledge. The reference is mainly based on the volume shrinkage of the molten cavity, the problems of the safety of the pipe column, the operation condition and the like are not basically considered, and the reference factors are gradually recognized to be not the only important indexes influencing the gas production rate of the gas storage. Therefore, in order to adapt to the development trend and market demand of the salt cavern gas storage, a set of comprehensive gas production rate evaluation method which can exert the advantages of the salt cavern gas storage to the maximum extent on the basis of ensuring the stability and safety of the gas storage is reasonably made, and the method also becomes one of the serious problems of the future salt cavern gas storage construction.
Disclosure of Invention
Based on the above, the invention aims to provide a comprehensive evaluation index system and a design method for the gas production rate of a salt cavern gas storage, which firstly provide a comprehensive evaluation index system and a design method for the gas production rate of the salt cavern gas storage, wherein the salt cavern gas storage is layered according to the structure, and a plurality of factors influencing the maximum gas production rate of the gas storage are researched one by one from the safety aspects of a cavity, a pipe column, underground equipment and a wellhead station respectively, the importance of each factor is analyzed, and the maximum gas production rate comprehensive evaluation system which is mainly suitable for the salt cavern type natural gas storage is further obtained.
The technical conception of the invention is as follows: the salt cavern gas storage is structurally layered from bottom to top in an all-round way as shown in figure 1a, and comprises a cavity part, a pipe column system part (figure 1b) and a wellhead station part. From these three aspects, a number of factors affecting the gas production rate of a gas storage reservoir are studied comprehensively, including: firstly, the stability and the volume of the cavity are contracted; erosion, corrosion and vibration of the pipe column; and generating hydrate and condensate water. Aiming at several factors, a gas production rate determination method for avoiding adverse effects is provided, and a comprehensive evaluation index system and a design method for the gas production rate of the salt cavern gas storage are further provided.
In order to further achieve the purpose, the invention adopts the following technical scheme: a comprehensive evaluation index system and a design method for gas production rate of a salt cavern gas storage comprise the following steps:
classifying and judging the functions, operation conditions and stability of salt cavern gas storage
When designing a salt cavern gas storage to be determined for gas production rate distribution scheme, firstly judging the function of the gas storage according to the classification standard of the salt cavern gas storage; secondly, the construction and positioning of the gas storage are carried out, and then the stability state of the gas storage is judged according to the cavity shape, the sediment content, the top plate state and the service life condition; finally, grading according to the stability of the gas storage cavity, wherein economic benefits need to be ensured, and emergency response function needs also need to be met; further analyzing the decisive factors influencing the maximum gas production rate of the salt cavern gas storage;
setting a gas production rate scheme, solving the operating thermodynamic parameter changes of the salt cavern gas storage system, namely the cavity part and the shaft, at different gas production rates, and solving by adopting an analytical method or thermodynamic numerical simulation to provide basic calculation data for safety constraint conditions of the gas storage at different gas production rates;
determining optimal gas production rate distribution scheme from cavity safety angle
Firstly, determining an optimal gas production rate scheme based on software platforms flac3d and abaqus according to a numerical simulation method, namely firstly researching the physical and mechanical property strength and constitutive relation of salt rocks in a gas storage area to be built; secondly, establishing a numerical analysis model according to the stratum information; thirdly, setting a gas production rate scheme according to the positioning of the gas storage and the market demand, carrying out dynamic rheological simulation of the gas storage in the gas production depressurization stage and the whole service life, and finally analyzing the deformation distribution of the surrounding rock damage area, the cavity wall displacement distribution and the surrounding rock stress distribution of the salt cavity of the gas storage and the volume shrinkage rate of the solution cavity to obtain an optimal gas production rate distribution scheme;
determining maximum gas production rate from the angle of safety of pipe column and underground equipment
Factors influencing the safety of the underground pipe column and equipment of the gas storage mainly comprise erosion and corrosion of the pipe column and the equipment, and in addition, the vibration of the pipe column can also influence the safety of a pipe column system of the gas storage; in the specific production operation, the safety conditions of the pipe column and the underground equipment at different gas production rates are judged according to the following calculation and judgment formulas;
4.1 erosion
Calculating the erosion flow rate by adopting the standard of APIRP 14E, and combining a gas state equation and hydromechanics knowledge to obtain the erosion yield of the gas production tubular column:
in the formula: v. ofcIs the erosion flow rate, m/s; c is an empirical constant; rhomFor the density of the mixed gas under specific working conditions，kg/m3(ii) a r is the relative density of the gas, and is dimensionless; p is the flow pressure of the pipe column, MPa; z is a gas compression constant and has no dimension; t is the gas temperature, K; d is the inner diameter of the tubular column, m; qscFor the erosion yield, m3/d。
The conservative C value of the salt cavern gas storage is recommended to be 100-150;
4.2 Corrosion
The corrosion problem evaluation research of the maximum gas production rate of the salt cavern gas storage is carried out by combining the production working condition of the salt cavern gas storage and adopting a de Waard semi-empirical model:
in the formula, VcIs the corrosion rate, mm/a; t is the gas temperature, K;
is CO2Partial pressure, kPa;
4.3 vibration
The critical rate of the vibration of the tubular column and the parts which are easy to generate buckling vibration can be researched by means of a numerical simulation tool, generally, the gas production rate of the salt cavern gas storage is conservative, and the maximum conservative value is recommended to be 0.55 MPa/d;
determining the maximum gas production rate from the safety angle of the wellhead station
Judging whether the natural gas hydrate is generated or not and the water production rule of the condensate water at different gas production rates according to the following calculation and judgment formulas;
5.1 hydrate
Predicting the generation of hydrate in the gas production stage of the salt cavern gas storage by adopting a Kata graphical method, wherein the regression relation is as follows:
th＝7.4833lnp+20.8358lnΔg-0.9306lnΔglnp-43.5339 (9)
in the formula:
p-pressure, KPa;
th-hydrate formation temperature, ° c;
Δg-the relative density of the gas;
5.2 condensate Water
The saturated water content of the natural gas of the salt cavern gas storage is calculated by adopting a handsome formula, the formula is suitable for real natural gas with the temperature of 0-200 ℃ and the pressure of 5-100 MPa, and the influence of acid gas components and salt content on the water content of the natural gas is considered, so that the water production rule of condensate water in the gas production process can be accurately predicted, and the gas production rate of the salt cavern gas storage is evaluated:
wherein:
when Tc < Tsw
When Tc > Tsw
In the formula:
q-saturated water content of natural gas, g/m3；
Psw-the saturated vapor pressure of water, MPa;
Pgeneral assembly-total pressure of natural gas, MPa;
PCcritical pressure of water vapor, PC＝22.12MPa；
TCCritical temperature of water vapor, TC＝647.3K；
Tsw-the temperature of the saturated water vapour, K;
w is the content of salts in natural gas;
sixthly, on the basis of the step III, further drawing a chart of the gas production rate of the salt cavern gas storage under each constraint factor, and taking the minimum value under each constraint factor as the maximum gas production rate of the gas storage, so that economic benefits are guaranteed or the gas production rate is improved as far as possible according to the operation requirements of the gas storage, and an emergency response is provided to distribute the gas production rate in the whole service period of the gas storage.
The 6 steps are linked, and the design method is designed to analyze all factors which possibly influence the gas production rate of the gas storage, so that the minimum gas production rate value under several constraint conditions is taken under each safety constraint condition of the gas storage, and the safe and efficient operation of the gas storage is ensured.
Compared with the prior art, the invention has the following beneficial effects:
firstly, the salt cavern gas storage is subjected to all-dimensional top-down structural layering, and a plurality of factors influencing the gas production rate of the gas storage are researched from the safety of a cavity, a pipe column, underground equipment and a wellhead station, and the method comprises the following steps: the stability and the volume shrinkage of the cavity, the erosion, the corrosion and the vibration of the pipe column and the underground equipment, and the generation of hydrate and condensate water in the wellhead station.
Secondly, the research factors are very comprehensive, all the composition structures and types of the salt cavern gas storage which can be seen at present are basically included, and all the stability and safety problems which are possibly met and are related to the gas production rate of the gas storage are solved.
And in addition, when processing underground salt cavern storage of gases such as compressed air energy storage, hydrogen storage, carbon dioxide sealing and the like, corresponding adjustment and further detailed research are suggested according to the ideas and methods of the text when processing the gas production rate critical threshold values of different gases under different constraint indexes, so that a gas production rate distribution scheme suitable for the salt cavern gas storage under a specific working condition can be obtained.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings needed for the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a schematic structural diagram of a salt cavern gas storage system, wherein FIG. 1a is a schematic structural layer sign diagram of the salt cavern gas storage, and FIG. 1b is a detailed structural diagram of a pipe column system of the salt cavern gas storage;
FIG. 2 is a schematic diagram of the classification of the function and type of the salt cavern type gas storage according to the invention;
FIG. 3 is a schematic diagram of a method for determining an optimal gas production rate of a gas storage reservoir according to numerical simulation of the present invention;
FIG. 4 is a schematic diagram of a comprehensive evaluation index system and a design method for gas production rate of the salt cavern gas storage.
Detailed Description
In order to more clearly illustrate the embodiments of the present invention and/or the technical solutions in the prior art, the following description will explain specific embodiments of the present invention with reference to the accompanying drawings. It is obvious that the drawings in the following description are only examples of the invention, and that for a person skilled in the art, other drawings and embodiments can be derived from them without inventive effort.
As shown in fig. 1-4, a comprehensive evaluation index system and design method for gas production rate of salt cavern gas storage comprises the following steps:
classifying and judging the functions, operation conditions and stability of salt cavern gas storage
When designing a salt cavern gas storage to be determined for gas production rate distribution scheme, firstly, judging and analyzing the functions of the gas storage, such as natural gas storage, compressed air energy storage or energy gas storage of hydrogen and the like, according to the salt cavern gas storage function and type classification standard shown in fig. 2; secondly, the construction and positioning of the gas storage, including peak regulation and supply or strategic emergency storage in commercial operation; finally, the stability state of the gas storage is judged according to the form, sediment content, top plate state and service life condition of the gas storage, and the stability state is mainly represented as follows: such as the shape stability state and the volume shrinkage rate of a spherical cavity, a pear-shaped cavity and a part of irregular cavity are superior to those of a cylindrical or cubic cavity under the same condition; the sediment has certain resistance to the deformation of the molten cavity, and can inhibit the deformation of the salt cavity; the stability of the cavity with insufficient strength of the top plate or the surrounding rock is poor, the service time of the gas storage is more than 5-10 years, the deformation of the cavity tends to be stable, and the stability of the gas storage is not a decisive factor for determining the maximum gas production rate of the gas storage under the condition that the internal pressure of the cavity in operation does not change greatly. On the basis of the analysis, the gas storage cavity is classified according to the stability, so that the economic benefit needs to be ensured, and the gas storage cavity also needs to have the requirements of an emergency response function and the like; further analyzing the decisive factors influencing the maximum gas production rate of the salt cavern gas storage;
and secondly, setting different gas production rate schemes, solving the operating thermodynamic parameter changes of the salt cavern gas storage system, namely the cavity part and the shaft, under different gas production rates, and solving by adopting an analytical method or thermodynamic numerical simulation, wherein basic calculation data are provided for the safety constraint conditions of the gas storage system under different gas production rates by referring to research results of Takayama Tanfei and Chenjian of China academy.
Determining optimal gas production rate distribution scheme from cavity safety angle
Generally speaking, the stability of a cavity of a gas storage is poor, or the gas storage needs to ensure economic benefits, the working gas amount is increased, the bottom gas is reduced, and when the volume shrinkage is reduced as much as possible, the optimal gas production rate scheme is determined according to a numerical simulation method strictly based on a software platform, such as flac3d, abaqus and the like, and the operation steps can be carried out according to the numerical simulation steps shown in fig. 3, namely, the physical and mechanical properties of the formation salt rock in the region of the gas storage to be built, such as strength, constitutive relation and the like, are researched; secondly, establishing a numerical analysis model according to the stratum information; thirdly, setting a gas production rate scheme according to the positioning of the gas storage and the market demand, carrying out dynamic rheological simulation of the gas storage in the gas production depressurization stage and the whole service life, and finally analyzing the deformation distribution of the surrounding rock damage area, the cavity wall displacement distribution and the surrounding rock stress state of the salt cavity of the gas storage and the volume shrinkage rate of the solution cavity to obtain the optimal gas production rate distribution scheme. The method is obtained according to the prior practice and the research result of numerical simulation: the gas production rate schemes are combined before, during and after the operation of the gas storage respectively in the high-pressure state and the low-pressure state, namely, the gas storage is combined by adopting the gas production rate schemes of high-pressure high-production, low-pressure low-production, low-speed production in the early stage and high-speed production in the medium and later stages, so that the volume shrinkage of the gas storage within the service life (30a) can be reduced as much as possible, the effective storage capacity is increased, the production working gas amount is larger, the advantage of rapid peak regulation can be realized in the high-pressure state of the gas storage, and the economic benefit of a gas storage system is improved.
Determining maximum gas production rate from the angle of safety of pipe column and underground equipment
The salt cavern gas storage system comprises a cavity, a shaft (pipe column and underground equipment) and a wellhead station (as shown in figure 1 a), wherein the cavity comprises gas, residual brine and a proper amount of sediments, the shaft mainly comprises an injection and production pipe column (as shown in figure 1b), a packer, a guide shoe, a seat joint, a control pipeline and the like, and the wellhead mainly comprises a safety valve, a restrictor, a flow divider, a flow nipple and other pipeline systems (as shown in figure 1 a).
The factors that the gas production rate affects the safety of the underground pipe column and the equipment of the gas storage mainly include erosion and corrosion of the pipe column and the equipment, and in addition, the vibration of the pipe column may also affect the safety of a pipe column system of the gas storage. In the specific production operation, the safety conditions of the pipe column and the underground equipment at different gas production rates are analyzed and judged as follows.
4.1 erosion
The erosion flow rate is calculated by adopting the standard of APIRP 14E, and the model has high accuracy, is simple and easy to implement and is widely accepted in the industry. And (3) combining a gas state equation and hydromechanics knowledge to obtain the erosion yield of the gas production pipe column:
in the formula: v. ofcIs the erosion flow rate, m/s; c is an empirical constant; rhomThe density of the mixed gas in kg/m under specific working conditions3(ii) a r is the relative density of the gas, and is dimensionless; p is the flow pressure of the pipe column, MPa; z is a gas compression constant and has no dimension; t is the gas temperature, K; d is the inner diameter of the tubular column, m; qscFor the erosion yield, m3/d。
C is mainly formed by CO in natural gas2、H2S and water vapor content, solid particles, column materials, inner diameter and the like, and recommended values are given in the APIRP 14E standard, but research shows that the recommended values are slightly conservative. More representative values of C are typically selected from historical production data. In oil gas development and gas reservoir type gas storage, the value of C is generally 100-150, the C value of the salt cavern gas storage is recommended to be 100-150 when being conserved, and the production working condition and historical data of the gas storage are specifically referred.
4.2 Corrosion
Corrosion, one of the common problems of downhole equipment, is caused annuallyThe economic loss is as high as trillion. The salt cavern gas storage injection and production wells generally adopt at the same time, the throughput is large, the service cycle is long, and therefore the method is used for treating condensate water, drilling residual liquid and CO2、H2Under the repeated action of S and other substances, the corrosion perforation and even the fracture of a pipe column or underground equipment are easily caused, and the operation safety of the gas storage is directly threatened. The corrosion type of the gas production pipe column of the salt cavern gas storage is mainly CO2Caused electrochemical corrosion and erosion corrosion, and CO2Partial pressure, gas production rate and liquid water are the determining factors causing corrosion failure of the pipe column.
To avoid corrosion failure of the pipe string, decades of CO international developments have been made2Corrosion studies, from tests and mechanisms, different prediction models were proposed, respectively. Roughly divided into three categories: the method comprises the following steps of firstly, an experience model, secondly, a semi-experience model and thirdly, a mechanism model. Known examples are Norsok M506 empirical model in Norway, the empirical equation for erosion in Petroleum Engineers, DE Waard semi-empirical prediction model, and Ohio mechanistic model. The corrosion problem evaluation research of the maximum gas production rate of the salt cavern gas storage is carried out by combining the production working condition of the salt cavern gas storage and adopting a de Waard semi-empirical model which has the widest application range and the most complete consideration factors.
In the formula, VcIs the corrosion rate, mm/a; t is the gas temperature, K;
is CO2Partial pressure, kPa.
4.3 vibration
The vibration of the gas production pipe column of the salt cavern gas storage is a fluid-solid coupling phenomenon which is subjected to multiple constraints such as seat sealing, oil protection, flowing gas flow and the like in a limited space, and the dynamic behavior of the gas production pipe column is very complex due to factors such as gas compressibility, temperature pressure fluctuation, frictional resistance and the like. When the gas flow velocity is very high and reaches a certain order of magnitude or the gas frequency is close to the natural frequency of the pipe column, the pipe column is subjected to great dynamic pressure, so that the bow-shaped transverse buckling or axial frequent vibration occurs. Once vibration occurs, extrusion collision and shaking of pipe strings between the pipe columns and the casing pipes can undoubtedly cause damage to the pipe strings and the casing pipes, threads are loosened, seat sealing is loosened seriously, and accidents such as leakage of a gas storage warehouse, breakage of the pipe columns, well falling and the like can be caused. However, on the premise of ensuring stable and economic production of the salt cavern gas storage, the gas production rate is generally conservative, the maximum of the current conservative value is recommended to be 0.55MPa/d (refer to the report of Houzheng of Claus talge university in Germany, the research of numerical simulation of the gold jar gas storage, the Chenfeng of Chinese academy and the research of indoor physical models of Liujian of Shandong university and the like), the problem of dynamic instability is difficult to occur or basically does not occur in a multi-constraint gas production string, so in the normal and stable production of the salt cavern gas storage, the influence of critical vibration rate can be not considered, and in order to ensure the comprehensiveness of the analysis factors, quantitative description is made on the vibration problem of the tubular column, if it is necessary to specially analyze the vibration or buckling problem of the pipe column, simulation or research of related theories can be carried out by means of numerical software, the numerical software adopts ANSYS or Fluent research, and the research method refers to the research results of a professor team of the fame of the Chinese university of petroleum Yan.
Determining the maximum gas production rate from the safety angle of the wellhead station
The gas production rate mainly influences the safety of a wellhead station by influencing the temperature and pressure distribution in a wellhead and a shaft of a gas storage reservoir, and the safety factors of the wellhead station, which are mainly influenced for a natural gas storage reservoir, are hydrate generation blockage and excessive generation of condensate water which may occur in the wellhead station. In the specific production operation, the following analysis mainly aims at different gas production rates to judge whether the natural gas hydrate is generated or not and the water production rule of the condensed water.
5.1 hydrate
The hydrate is a potential factor influencing the safe operation of the gas storage, and the hydrate can be generated when the temperature and pressure conditions for forming the hydrate are reached in the operation process of the gas storage due to the residual brine in the dissolving cavity. The hydrate is an ice crystal-like solid substance and is formed by hydrating natural gas components and liquid water. The gas storage device is easy to form at rough positions, elbows and valves near a wellhead, can influence the yield, and can seriously block the cross section of a shaft to cause the stop of the gas storage device.
The prediction research of water and matters is not mature, and the Kata graphical method, the Bonom empirical formula method, the van der Waal-Platteuw thermodynamic model and the Motiee relational expression are the most widely applied methods at present. The Kata graphical method is adopted to predict the generation of the hydrate in the gas production stage of the salt cavern gas storage, and practice proves that the method is high in accuracy, can be popularized in the production of the salt cavern gas storage, and is used as one of important evaluation indexes of the maximum gas production rate of the gas storage.
The regression relationship is as follows:
th＝7.4833lnp+20.8358lnΔg-0.9306lnΔglnp-43.5339 (9)
in the formula
p-pressure, KPa;
th-hydrate formation temperature, ° c;
Δg-gas relative density.
5.2 condensate Water
The residual brine has non-negligible influence on the injection and production of the salt cavern gas storage, and according to investigation, the amount of water which cannot be discharged from the cavity can generally reach hundreds or even tens of thousands of squares, and is enough for humidifying natural gas for decades. Therefore, under high temperature and high pressure, part of brine is always evaporated and mixed in natural gas in a gaseous state or a mist-like liquid droplet state, so that the natural gas in the cavity is in a water content saturated or nearly saturated state. In the gas production stage, when the temperature of gas is reduced to the dew point of natural gas water, the distillation action of the long-distance pipe column causes the supersaturated part of the water content of the natural gas to be condensed in the pipe column to precipitate dew, so that liquid desalted water is gradually produced and adsorbed on the surface of the pipe column in the form of a water film, thereby reducing the flow section and increasing the resistance. When more condensate water is produced, the condensate water can flow back to the bottom of the well along the pipe wall, a casing shoe and a salt layer of an open hole section are dissolved, and a groove is formed, so that the damages of loosening and instability of the pipe column and the casing shoe, gas leakage and the like are caused.
Based on the method, the research results of the water content of natural gas commonly used at home and abroad are researched, the saturated water content of the natural gas of the salt cavern gas storage is calculated by adopting a handsome formula, the formula is suitable for real natural gas with the temperature of 0-200 ℃ and the pressure of 5-100 MPa, and the influence of acid gas components and the salt content on the water content of the natural gas is considered. Therefore, the water production rule of the condensed water in the gas production process can be accurately predicted, and the gas production rate of the salt cavern gas storage is evaluated.
Wherein:
when Tc < Tsw
When Tc > Tsw
In the formula:
q-saturated water content of natural gas, g/m3；
Psw-the saturated vapor pressure of water, MPa;
Pgeneral assembly-total pressure of natural gas, MPa;
PCcritical pressure of water vapor, PC＝22.12MPa；
TCCritical temperature of water vapor, TC＝647.3K；
Tsw-the temperature of the saturated water vapour, K;
w is the content of salts in natural gas;
And obtaining the gas production rate distribution scheme in the whole service life of the gas storage.
Sixthly, on the basis of the step (III), a gas production rate determination method for avoiding adverse effects is provided for all the factors, and the gas production rate of the salt cavern gas storage under all the constraint factors can be respectively drawn through the indexes, so that the minimum value under the constraint of all the factors is taken as the maximum gas production rate of the gas storage. According to the operation requirements of the gas storage, such as the requirement of ensuring economic benefit, or the requirement of improving the gas production rate as much as possible and having emergency response, the gas production rate scheme of the gas storage in the whole service period is distributed.
FIG. 4 combines the above factors to obtain a conventional process for gas production rate allocation for salt cavern gas reservoirs. When designing a distribution scheme of gas production rate of the salt cavern gas storage, firstly classifying the gas storage, secondly setting a gas production rate scheme according to construction positioning and requirements of the gas storage, thirdly evaluating the construction positioning and stability state of the gas storage, and finally calculating and analyzing the gas production rate of the salt cavern gas storage and the selected three constraint conditions, and taking the maximum gas production rate of the salt cavern gas storage as the minimum value of each safety index, thereby further realizing the gas production rate scheme distribution of a specific salt cavern gas storage. It should be noted that when the stability of the gas storage is poor or economic benefit needs to be guaranteed, the operation of the gas storage can be guaranteed according to the optimal gas production rate obtained by the cavity safety constraint condition by means of numerical simulation, in addition, when the stability of the gas storage is good and the gas production rate needs to be improved, the cavity safety can be regarded as having no limit on the maximum gas production rate of the gas storage, the gas production rate can be an arbitrary value, the minimum value of the maximum gas production rate is taken under all other constraint conditions, and the efficient and stable operation of the gas storage can be realized.
It should be noted that the evaluation and calculation formulas of the 5 indexes of erosion, corrosion, vibration, hydrate and condensate water are applicable to most of the salt cavern gas storage for gas storage, in particular to the salt cavern gas storage for natural gas storage, and on the basis of other gas storage, related results which are more appropriate and accurate and have wider application range are selected to carry out comprehensive evaluation research on the gas production rate of the gas storage when different production working conditions are processed according to different physical and chemical properties of the other gas storage.
The above examples are only preferred embodiments of the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications may be made to the above-described embodiments, and not all embodiments may be exhaustive. All obvious changes and modifications of the technical scheme of the invention are within the protection scope of the invention.
Claims (1)
1. A comprehensive evaluation index system and a design method for gas production rate of a salt cavern gas storage are characterized by comprising the following steps:
classifying and judging the functions, the operation conditions and the stability state of the salt cavern gas storage:
when designing a salt cavern gas storage for determining a gas production rate distribution scheme, firstly judging the functions of the gas storage according to the classification standard of the salt cavern gas storage; secondly, the construction and positioning of the gas storage are carried out, and then the stability state of the gas storage is judged according to the cavity shape, the sediment content, the top plate state and the service life; finally, grading according to the stability of the gas storage cavity, wherein economic benefits need to be ensured, and emergency response function needs also need to be met; further analyzing the decisive factors influencing the maximum gas production rate of the salt cavern gas storage;
setting a gas production rate scheme, solving the operating thermodynamic parameter changes of the salt cavern gas storage system, namely the cavity part and the shaft, at different gas production rates, and solving by adopting an analytical method or thermodynamic numerical simulation to provide basic calculation data for safety constraint conditions of the gas storage at different gas production rates;
determining a gas production rate distribution scheme from the cavity safety angle:
firstly, determining a gas production rate scheme based on software platforms flac3d and abaqus according to a numerical simulation method, namely firstly researching the physical and mechanical property strength and constitutive relation of salt rocks in a gas storage area to be built; secondly, establishing a numerical analysis model according to the stratum information; thirdly, setting a gas production rate scheme according to the positioning of the gas storage and the market demand, carrying out dynamic rheological simulation of the gas storage in the gas production depressurization stage and the whole service life, and finally analyzing the deformation distribution of the surrounding rock damage area, the cavity wall displacement distribution and the surrounding rock stress distribution of the salt cavity of the gas storage and the volume shrinkage rate of the solution cavity to obtain an optimal gas production rate distribution scheme;
determining the maximum gas production rate from the angle of the safety of the pipe column and the underground equipment:
factors influencing the safety of the underground pipe column and the equipment of the gas storage reservoir by the gas production rate comprise erosion and corrosion of the pipe column and the equipment and vibration of the pipe column, and in the specific production operation, the safety conditions of the underground pipe column and the underground equipment at different gas production rates are judged according to the following calculation and judgment formulas;
4.1 erosion:
calculating the erosion flow rate by adopting the standard of APIRP 14E, and combining a gas state equation and hydromechanics knowledge to obtain the erosion yield of the gas production tubular column:
in the formula: v. ofcIs the erosion flow rate, m/s; c is an empirical constant; rhomThe density of the mixed gas in kg/m under specific working conditions3(ii) a r is a gas phaseNo dimension for density; p is the flow pressure of the pipe column, MPa; z is a gas compression constant and has no dimension; t is the gas temperature, K; d is the inner diameter of the tubular column, m; qscFor the erosion yield, m3/d。
Taking the C value of the salt cavern gas storage as 100-150;
4.2 corrosion:
the method is characterized in that a de Waard semi-empirical model is adopted to evaluate and research the corrosion problem of the gas production rate of the salt cavern gas storage by combining the production working condition of the salt cavern gas storage:
in the formula, VcIs the corrosion rate, mm/a; t is the gas temperature, K;
is CO2Partial pressure, kPa;
4.3, vibration:
researching the critical rate of the vibration of the tubular column and the position which is easy to generate buckling vibration by a numerical simulation tool;
determining the maximum gas production rate from the safety angle of the wellhead station:
judging whether the natural gas hydrate is generated or not and the water production rule of the condensate water at different gas production rates according to the following calculation and judgment formulas;
5.1 hydrate:
predicting the generation of hydrate in the gas production stage of the salt cavern gas storage by adopting a Kata graphical method, wherein the regression relation is as follows:
th＝7.4833lnp+20.8358lnΔg-0.9306lnΔglnp-43.5339 (9)
in the formula:
p-pressure, KPa;
th-hydrate formation temperature, ° c;
Δg-the relative density of the gas;
5.2 condensate water:
the saturated water content of the natural gas of the salt cavern gas storage is calculated by adopting a handsome formula, the formula is suitable for real natural gas with the temperature of 0-200 ℃ and the pressure of 5-100 MPa, the influence of acid gas components and salt content on the water content of the natural gas is considered, the water production rule of condensate water in the gas production process is predicted, and the gas production rate of the salt cavern gas storage is evaluated:
wherein:
when Tc < Tsw
When Tc > Tsw
In the formula:
q-saturated water content of natural gas, g/m3；
Psw-the saturated vapor pressure of water, MPa;
Pgeneral assembly-total pressure of natural gas, MPa;
PCcritical pressure of water vapor, PC＝22.12MPa；
TCCritical temperature of water vapor, TC＝647.3K；
Tsw-the temperature of the saturated water vapour, K;
w is the content of salts in natural gas;
sixthly, on the basis of the step III, further drawing a chart of gas production rate of the salt cavern gas storage under each constraint factor, taking the minimum value under each constraint factor as the maximum gas production rate of the gas storage, and according to the operation requirement of the gas storage, the method is a scheme for ensuring economic benefit or improving the gas production rate and having emergency response to distribute the gas production rate in the whole service period of the gas storage.
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