Determination method and determination system for depth of gas-halogen interface of sediment salt cavern

Abstract

The embodiment of the invention provides a method and system for determining the depth of a gas-halogen interface of a sediment salt cavern, and belongs to the field of salt cavern gas storage construction engineering. The determination method comprises the following steps: determining the descending depth of the gas-brine interface along with the time change according to the initial depth of the gas-brine interface, the brine discharge flow of a brine discharge well and the cavity form above the sediment surface of a sediment salt cavern; under the condition that the descending depth is smaller than or equal to the sediment surface depth of the sediment salt cavern, the pressure loss coefficient of brine flowing through sediment is determined; and under the condition that the descending depth is greater than the sediment surface depth, determining the target depth of the gas-halogen interface. The technical problem that the gas-brine interface of the sediment salt-cavern gas storage cannot be effectively predicted due to the fact that the form of the cavity below the sediment surface cannot be measured in the gas injection and brine discharge process is solved, and the operability of sediment gap utilization of the sediment salt-cavern gas storage is greatly improved. The method has the advantages of being easy to operate, low in cost, good in economical efficiency, good in reliability and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of salt cavern gas storage construction engineering, and particularly to a method and a system for determining the depth of the gas-halogen interface of a sedimentary salt cavern. Background Art

[0002] Underground salt cavern storage is one of the main ways of energy storage and is widely used for the storage of energy such as petroleum, natural gas, hydrogen, and compressed air.

[0003] In China, salt rock is mainly stratified salt rock. During the process of solution cavity formation by water, a large amount of insoluble sediment accumulates at the bottom of the cavity. For salt rock layers with a high content of insoluble substances, the volume of the sediment is very large and occupies most of the cavity space. At present, the cavity above the sediment surface is mainly used for gas storage, and the brine above the sediment surface is discharged by the method of gas injection and brine drainage; this method results in the waste of most of the cavity volume below the sediment surface, and the cavity utilization rate is low.

[0004] Experimental results show that about 52.4% of the sediment space is filled with brine. By gas injection and brine drainage, about 8.21% of the brine in the sediment space can be displaced, and this part of the space is vacated for gas storage. In order to improve the cavity utilization rate and increase the gas storage space, fully discharging the brine in the sediment voids is the key to using sediment for gas storage.

[0005] In order to prevent gas from spraying out of the brine drainage well and causing production safety accidents, the position of the gas-halogen interface must be higher than the position of the brine drainage well nozzle. However, there is currently no reliable and feasible method to monitor the gas-halogen interface in real time during the process of gas injection and brine drainage using the sediment voids of the salt cavern gas storage. The prior art can only obtain the cavity shape above the sediment surface, while the cavity volume shape below the sediment surface is unknown. This makes it difficult to predict the position of the gas-halogen interface during gas injection and brine drainage in the sedimentary salt cavern gas storage, and the safety risk of gas injection and brine drainage construction is high. Summary of the Invention

[0006] The purpose of the embodiments of the present invention is to provide a method and a system for determining the depth of the gas-halogen interface of a sedimentary salt cavern. The determination method can be applied to the construction of a sedimentary salt cavern gas storage, and can predict the gas-halogen interface in real time during the implementation of double-well gas injection and brine drainage, prevent gas from overflowing from the brine drainage well, and avoid causing production safety accidents.

[0007] To achieve the above object, an embodiment of the present invention provides a method for determining the depth of the gas-halide interface in a sedimentary salt cavern. The determination method includes: determining the depth of the gas-halide interface that decreases over time based on the initial depth of the gas-halide interface, the drainage flow rate of the drainage well, and the cavity shape above the sediment surface of the sedimentary salt cavern, where the initial depth of the gas-halide interface is lower than the lower end of the gas injection well; in the case where the depth of decrease is less than or equal to the depth of the sediment surface of the sedimentary salt cavern, determining the pressure loss coefficient of the brine flowing through the sediment based on the depth of decrease, the gas injection pressure of the gas injection well, the drainage pressure of the drainage well, the pressure loss during the drainage process of the drainage well, and the path length of the brine flowing through the sediment in the sedimentary salt cavern; and in the case where the depth of decrease is greater than the depth of the sediment surface, determining the target depth of the gas-halide interface based on the pressure loss coefficient, the gas injection pressure of the gas injection well, the drainage pressure of the drainage well, the pressure loss during the drainage process of the drainage well, the depth of the sediment surface, and the path length of the brine flowing through the sediment.

[0008] Optionally, determining the depth of the gas-halide interface that decreases over time includes: determining the area of each cross-section in a plurality of cross-sections in the vertical direction of the sedimentary salt cavern according to the cavity shape of the sedimentary salt cavern; determining the depth of decrease of the gas-halide interface at each set interval time according to the drainage flow rate of the drainage well and the area of each cross-section; and determining the depth of the gas-halide interface that decreases over time according to the depth of decrease at each set interval time.

[0009] Optionally, determining the depth of decrease of the gas-halide interface at each set interval time includes: according to the drainage flow rate Q 卤 of the drainage well and the area A i of each cross-section in the plurality of cross-sections, determining the depth of decrease Δh of the gas-halide interface at each set interval time Δt by the following formula:

[0010]

[0011] Δh = m·a,

[0012] where a is the interval distance between two adjacent cross-sections in the plurality of cross-sections, i is the serial number of each cross-section in the plurality of cross-sections, and m is the number of cross-sections spanned by the gas-halide interface at each set interval time Δt.

[0013] Optionally, the determination method further includes: in the case where the depth of decrease is less than or equal to the depth of the sediment surface of the sedimentary salt cavern, determining the sum of the initial depth of the gas-halide interface and the depth of decrease as the target depth of the gas-halide interface at the target time.

[0014] Optionally, the pressure loss of the brine drainage well during the brine drainage process is determined by the following steps: determining the friction factor along the length of the brine drainage well according to the inner pipe radius, inner pipe roughness of the brine drainage well, and the flow velocity of the brine; and determining the pressure loss of the brine drainage well during the brine drainage process according to the inner pipe radius of the brine drainage well, the length of the brine drainage well, the friction factor along the length, and the flow velocity of the brine.

[0015] Optionally, determining the friction factor along the length of the brine drainage well includes: according to the inner pipe radius r 卤 of the brine drainage well, the inner pipe roughness ε, and the flow velocity v 卤 of the brine, determining the friction factor λ 卤 along the length of the brine drainage well by the following formula

[0016]

[0017] where ρ 卤 is the density of the brine, and μ 卤 is the viscosity of the brine.

[0018] Optionally, determining the pressure loss of the brine drainage well during the brine drainage process includes: according to the inner pipe radius r 卤 of the brine drainage well, the length L 排卤管 of the brine drainage well, the friction factor λ 卤 along the length, and the flow velocity v 卤 of the brine, determining the pressure loss P 阻 of the brine drainage well during the brine drainage process by the following formula

[0019]

[0020] A 卤 = πr 卤 2 ,

[0021] where ρ 卤 is the density of the brine, and A 卤 is the cross-sectional area of the inner pipe of the brine drainage well.

[0022] Optionally, determining the pressure loss coefficient of the brine flowing through the sediment includes: according to the descent depth h gb of the gas-brine interface, the gas injection pressure P 气 of the gas injection well, the brine drainage pressure P 卤 of the brine drainage well, the pressure loss P 阻 of the brine drainage well during the brine drainage process, and the path length L 沉渣, the pressure loss coefficient k of the brine flowing through the sediment is determined by the following formula:

[0023]

[0024] where ρ 卤 is the density of the brine, ρ 气 is the density of the injected gas, and g is the acceleration due to gravity.

[0025] Optionally, determining the target depth of the gas-brine interface includes: according to the pressure loss coefficient k, the injection pressure P of the injection well 气 , the brine discharge pressure P of the brine discharge well 卤 , the pressure loss P during the brine discharge process of the brine discharge well 阻 , the depth H0 of the sediment surface and the path length L of the brine flowing through the sediment 沉渣 , the target depth h of the gas-brine interface is determined by the following formula 目标 :

[0026]

[0027] where ρ 卤 is the density of the brine, ρ 气 is the density of the injected gas, and g is the acceleration due to gravity.

[0028] On the other hand, the present invention provides a determination system for the depth of the gas-brine interface of a sediment salt cavern. The determination system includes: a first determination device for determining the decreasing depth of the gas-brine interface varying with time according to the initial depth of the gas-brine interface, the brine discharge flow rate of the brine discharge well, and the cavity shape above the sediment surface of the sediment salt cavern, wherein the initial depth of the gas-brine interface is lower than the lower end of the injection well; a second determination device for, when the decreasing depth is less than or equal to the depth of the sediment surface of the sediment salt cavern, determining the pressure loss coefficient of the brine flowing through the sediment according to the decreasing depth, the injection pressure of the injection well, the brine discharge pressure of the brine discharge well, the pressure loss during the brine discharge process of the brine discharge well, and the path length of the brine flowing through the sediment in the sediment salt cavern; and a third determination device for, when the decreasing depth is greater than the depth of the sediment surface, determining the target depth of the gas-brine interface according to the pressure loss coefficient, the injection pressure of the injection well, the brine discharge pressure of the brine discharge well, the pressure loss during the brine discharge process of the brine discharge well, the depth of the sediment surface, and the path length of the brine flowing through the sediment.

[0029] Through the above technical solution, the present invention solves the technical problem that under the gas injection and brine drainage process, the cavity shape below the sediment surface cannot be measured, resulting in the inability to effectively predict the gas-brine interface of the sediment salt cavern gas storage reservoir, and greatly improves the operability of the utilization of the sediment voids in the sediment salt cavern gas storage reservoir. The present invention has the characteristics of simple operation, low cost, good economy, and good reliability.

[0030] Other features and advantages of the embodiments of the present invention will be described in detail in the subsequent specific implementation part. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings are used to provide a further understanding of the embodiments of the present invention, and constitute a part of the specification. Together with the following specific implementation manners, they are used to explain the embodiments of the present invention, but do not constitute a limitation to the embodiments of the present invention. In the drawings:

[0032] Figure 1 is a schematic flow chart of a method for determining the depth of the gas-brine interface of a sediment salt cavern according to an embodiment of the present invention;

[0033] Figure 2 is a schematic structural diagram of a system for determining the depth of the gas-brine interface of a sediment salt cavern according to an embodiment of the present invention;

[0034] Figure 3 is a schematic diagram of a gas injection and brine drainage system for a sediment salt cavern according to an embodiment of the present invention.

[0035] DESCRIPTION OF THE REFERENCE NUMERALS

[0036] 1 - Gas compressor; 2 - Gas flowmeter; 3 - Gas pressure gauge; 4 - Gas thermometer; 5 - Gas injection well valve; 6 - Inner pipe of the gas injection well; 7 - Gas injection well; 8 - Casing of the gas injection well; 9 - Gas; 10 - Gas-brine interface; 11 - Salt cavern cavity; 12 - Sediment; 13 - Brine; 14 - Brine drainage well; 15 - Casing of the brine drainage well; 16 - Inner pipe of the brine drainage well; 17 - Brine drainage well valve; 18 - Brine flowmeter; 19 - Brine pressure gauge; 20 - Brine thermometer; 21 - Brine concentration meter; 22 - First communication cable; 23 - Second communication cable; 24 - Computer. DETAILED DESCRIPTION OF THE INVENTION

[0037] The following will describe in detail the specific implementation manners of the embodiments of the present invention with reference to the drawings. It should be understood that the specific implementation manners described herein are only used to illustrate and explain the embodiments of the present invention, and are not used to limit the embodiments of the present invention.

[0038] The present invention first provides a method for determining the depth of the gas-liquid interface in a sediment salt cavern, which can be applied to the construction of a sediment salt cavern gas storage reservoir to predict the gas-liquid interface in real time during the implementation of gas injection and brine drainage through two wells. The sediment salt cavern gas storage reservoir mainly uses two wells for gas injection and brine drainage. One injection well is used for gas injection, and the other brine drainage well is used for brine drainage. During the gas injection and brine drainage operation, try to remove the brine in the upper part of the sediment and the voids in the sediment through these two wells, that is, inject high-pressure gas into the injection well to displace the brine out of the brine drainage well.

[0039] Specifically, as Figure 1 shown, the determination method may include steps S110-S130.

[0040] Step S110, determine the depth of decline of the gas-liquid interface varying with time according to the initial depth of the gas-liquid interface, the brine drainage flow rate of the brine drainage well, and the cavity shape above the sediment surface of the sediment salt cavern.

[0041] Among them, the initial depth of the gas-liquid interface should be lower than the lower end of the injection well to ensure that the depth of decline of the gas-liquid interface is related to the cavity. If the initial depth of the gas-liquid interface is higher than the lower end of the injection well, the inner diameter of the injection well should be introduced to calculate the depth of decline of the gas-liquid interface.

[0042] In one embodiment, the determination of the depth of decline of the gas-liquid interface varying with time in step S110 may include:

[0043] Step S111, determine the area of each cross-section in a plurality of cross-sections of the sediment salt cavern in the vertical direction according to the cavity shape of the sediment salt cavern.

[0044] Specifically, the cavity shape above the sediment surface of the sediment salt cavern can be obtained by sonar cavity measurement, and according to the cavity shape of the sediment salt cavern, the sediment salt cavern can be divided into a plurality of cross-sections at a set interval in the vertical direction, and then the area of each cross-section among the plurality of cross-sections can be determined. Among them, when the cavity shape of the sediment salt cavern is approximately cylindrical or frustum-shaped, each cross-section is approximately circular, and the area of the cross-section can be calculated according to the radius of each cross-section.

[0045] Step S112, determine the depth of decline of the gas-liquid interface within each set interval time according to the brine drainage flow rate of the brine drainage well and the area of each cross-section.

[0046] Specifically, according to the brine drainage flow rate Q 卤 of the brine drainage well and the area A i of each cross-section among the plurality of cross-sections, the depth of decline Δh of the gas-liquid interface within each set interval time Δt can be determined by the following formula:

[0047]

[0048] Δh = m·a,

[0049] where a is the distance between two adjacent cross-sections among a plurality of cross-sections, i is the serial number of each cross-section among the plurality of cross-sections, and m is the number of cross-sections spanned by the gas-halide interface within each set time interval Δt.

[0050] Step S113: Determine the depth of descent of the gas-halide interface varying with time according to the depth of descent within each set time interval.

[0051] Specifically, according to the depth of descent Δh within each set time interval Δt, the depth of descent h of the gas-halide interface within the target time can be determined by the following formula gb :

[0052]

[0053] where j is the monitoring serial number of the set time interval Δt, and n is the number of monitoring times.

[0054] Step S120: When the depth of descent is less than or equal to the depth of the sediment surface in the sediment salt cavern, determine the pressure loss coefficient of the brine flowing through the sediment according to the depth of descent, the gas injection pressure of the gas injection well, the brine discharge pressure of the brine discharge well, the pressure loss during the brine discharge process of the brine discharge well, and the path length of the brine flowing through the sediment in the sediment salt cavern.

[0055] Among them, the cavity shape above the sediment surface can be obtained by sonar cavity measurement, and the position of the gas-halide interface during gas injection and brine discharge above the sediment surface can be predicted in real time according to the volume of the discharged brine. However, sonar cannot enter the sediment, and the volume shape of the cavity below the sediment surface is unknown. This makes it difficult to predict the position of the gas-halide interface during gas injection and brine discharge in the sediment salt cavern gas storage, and the safety risk of gas injection and brine discharge construction is high. Therefore, step S120 needs to be introduced to realize the real-time inversion of the sediment permeability coefficient by using the basic parameters of the salt cavern, the cavity shape and the real-time monitoring data of gas injection and brine discharge, so as to obtain the real permeability coefficient of the sediment, and infer the position of the gas-halide interface by using the relationship between the gas pressure and the brine discharge flow rate during the gas injection and brine discharge process below the sediment surface.

[0056] In one embodiment, the pressure loss during the brine discharge process of the brine discharge well in step S120 can be determined by the following steps:

[0057] Step S121: Determine the friction coefficient along the length of the brine discharge well according to the inner pipe radius, inner pipe roughness of the brine discharge well, and the flow rate of the brine.

[0058] Specifically, according to the inner pipe radius r of the brine discharge well 卤 , the inner pipe roughness ε, and the flow rate v of the brine卤 , the friction coefficient λ along the length of the brine discharge well is determined by the following formula 卤 :

[0059]

[0060] where ρ 卤 is the density of the brine, and μ 卤 is the viscosity of the brine.

[0061] Step S122: Determine the pressure loss during the brine discharge process of the brine discharge well according to the inner pipe radius of the brine discharge well, the length of the brine discharge well, the friction coefficient along the length, and the flow velocity of the brine.

[0062] Specifically, the pressure loss P during the brine discharge process of the brine discharge well can be determined according to the inner pipe radius r 卤 of the brine discharge well, the length L 排卤管 of the brine discharge well, the friction coefficient λ along the length 卤 and the flow velocity v 卤 of the brine by the following formula 阻 :

[0063]

[0064] A 卤 = πr 卤 2 ,

[0065] where ρ 卤 is the density of the brine, and A 卤 is the cross-sectional area of the inner pipe of the brine discharge well.

[0066] Specifically, the determination of the pressure loss coefficient of the brine flowing through the sediment can include:

[0067] Determine the pressure loss coefficient k of the brine flowing through the sediment according to the descending depth h gb of the gas-brine interface, the gas injection pressure P 气 of the gas injection well, the brine discharge pressure P 卤 of the brine discharge well, the pressure loss P 阻 during the brine discharge process of the brine discharge well, and the path length L 沉渣 of the brine flowing through the sediment by the following formula

[0068]

[0069] where ρ 卤 is the density of the brine, ρ 气 is the density of the injected gas, and g is the acceleration due to gravity.

[0070] Step S130, when the descending depth is greater than the depth of the sediment surface, determine the target depth of the gas-liquid interface according to the pressure loss coefficient, the gas injection pressure of the gas injection well, the brine drainage pressure of the brine drainage well, the pressure loss during the brine drainage process of the brine drainage well, the depth of the sediment surface, and the path length of the brine flowing through the sediment.

[0071] Specifically, according to the pressure loss coefficient k, the gas injection pressure P of the gas injection well 气 , the brine drainage pressure P of the brine drainage well 卤 , the pressure loss P during the brine drainage process of the brine drainage well 阻 , the depth H0 of the sediment surface, and the path length L of the brine flowing through the sediment 沉渣 , determine the target depth h of the gas-liquid interface by the following formula 目标 :

[0072]

[0073] where ρ 卤 is the density of the brine, ρ 气 is the density of the injected gas, and g is the acceleration due to gravity.

[0074] In one embodiment, the determination method may further include:

[0075] Step S140, when the descending depth is less than or equal to the depth of the sediment surface of the sediment salt cavern, determine the sum of the initial depth of the gas-liquid interface and the descending depth as the target depth of the gas-liquid interface within the target time.

[0076] The effects achieved by the present invention are as follows:

[0077] The present invention provides a method for real-time monitoring of the gas-liquid interface during the process of using gas injection and brine drainage in the sediment voids of a salt cavern gas storage reservoir, which is applied to the real-time prediction of the gas-liquid interface during the implementation of using double-well gas injection and brine drainage in the utilization of sediment voids in the construction of a salt cavern gas storage reservoir. The sediment salt cavern gas storage reservoir mainly uses two wells for gas injection and brine drainage, one well for gas injection and the other well for brine drainage. During the gas injection and brine drainage operation, try to drain the brine in the upper part of the sediment and the sediment voids, inject high-pressure gas into the gas injection well, and displace the brine out. When injecting gas and draining brine above the sediment surface, the position of the gas-liquid interface can be predicted in real time according to the volume of the drained brine. For the prediction of the gas-liquid interface in the sediment, the present invention uses the basic parameters of the salt cavern, the cavity shape, and the real-time monitoring data of gas injection and brine drainage to realize the real-time inversion of the sediment permeability coefficient, so as to obtain the true permeability coefficient of the sediment, and use the relationship between the gas pressure and the brine drainage flow rate during the gas injection and brine drainage process below the sediment surface to infer the position of the gas-liquid interface.

[0078] Therefore, the present invention solves the technical problem that the prior art cannot measure the cavity shape below the sediment surface, resulting in the inability to effectively predict the gas-liquid interface during gas injection and brine drainage in the sediment salt cavern gas storage reservoir, greatly improving the operability of the utilization of the sediment voids in the salt cavern gas storage reservoir, and having the characteristics of simple operation, low cost, good economy, and good reliability.

[0079] On the other hand, the present invention also provides a determination system 200 for the depth of the gas-liquid interface of a sediment salt cavern, as Figure 2 shown, the determination system may include:

[0080] A first determination device 210, configured to determine the depth of the gas-liquid interface decreasing with time according to the initial depth of the gas-liquid interface, the brine drainage flow rate of the brine drainage well, and the cavity shape above the sediment surface of the sediment salt cavern, wherein the initial depth of the gas-liquid interface is lower than the lower end of the gas injection well;

[0081] A second determination device 220, configured to determine the pressure loss coefficient of the brine flowing through the sediment according to the decreasing depth, the gas injection pressure of the gas injection well, the brine drainage pressure of the brine drainage well, the pressure loss during the brine drainage process of the brine drainage well, and the path length of the brine flowing through the sediment in the sediment salt cavern when the decreasing depth is less than or equal to the sediment surface depth of the sediment salt cavern; and

[0082] A third determination device 230, configured to determine the target depth of the gas-liquid interface according to the pressure loss coefficient, the gas injection pressure of the gas injection well, the brine drainage pressure of the brine drainage well, the pressure loss during the brine drainage process of the brine drainage well, the sediment surface depth, and the path length of the brine flowing through the sediment when the decreasing depth is greater than the sediment surface depth.

[0083] Regarding the beneficial effects of the determination system for the depth of the gas-liquid interface of a sediment salt cavern provided by the present invention, reference may be made to the description of the determination method for the depth of the gas-liquid interface of a sediment salt cavern above, and details will not be repeated here.

[0084] Example 1:

[0085] Figure 3 Shows a schematic diagram of a system for gas injection and brine drainage using the determination method and determination system of the present invention.

[0086] Specifically, the gas injection and brine drainage system includes the following components: a compressor 1, a gas flowmeter 2, a gas pressure gauge 3, a gas thermometer 4, a gas injection well valve 5, a gas injection well 7, gas 9, a salt cavern cavity 11, sediment 12, brine 13, a brine drainage well 14, a brine drainage well valve 17, a brine flowmeter 18, a brine pressure gauge 19, a brine thermometer 20, a brine concentration gauge 21, a first communication cable 22, a second communication cable 23, and a computer 24. The gas injection well consists of an inner pipe 6 of the gas injection well and a casing 8 of the gas injection well.

[0087] Among them, a compressor 1, a gas flowmeter 2, a gas pressure gauge 3, a gas thermometer 4, an injection well valve 5, and an injection well 7 are connected. During gas injection for brine drainage, the compressor 1 provides pressure to inject gas into the inner pipe 6 of the injection well, driving the brine in the cavity into the brine drainage well 14. The gas flowmeter 2 monitors the gas flow rate, the gas pressure gauge 3 monitors the gas pressure, the gas thermometer 4 monitors the gas temperature, and the injection well valve 4 controls the opening and closing of the injection well.

[0088] Among them, the brine drainage well 14 is composed of an inner pipe 16 of the brine drainage well and a casing 15 of the brine drainage well. The brine drainage well 14, a brine drainage well valve 17, a brine flowmeter 18, a brine pressure gauge 19, a brine thermometer 20, and a brine concentration gauge 21 are connected in sequence. During gas injection for brine drainage, the brine enters the inner pipe 16 of the brine drainage well from the cavity and flows through the brine drainage well valve 17, the brine flowmeter 18, the brine pressure gauge 19, the brine thermometer 20, and the brine concentration gauge 21. The brine drainage well valve 17 is used to control the opening and closing of the brine drainage well, the brine flowmeter 18 is used to monitor the brine flow rate, the brine pressure gauge 19 is used to monitor the brine pressure, the brine thermometer 20 is used to monitor the brine temperature, and the brine concentration gauge 21 is used to monitor the brine concentration.

[0089] Among them, a first communication cable 22 is connected to the gas flowmeter 2, the gas pressure gauge 3, and the gas thermometer 4, and a second communication cable 23 is connected to the brine flowmeter 18, the brine pressure gauge 19, the brine thermometer 20, and the brine concentration gauge 21 for collecting and transmitting monitoring data. The first communication cable 22 and the second communication cable 23 are connected to a computer 24 for storing and analyzing data. A data storage system and a data analysis and processing system are respectively installed in the computer 24. The data storage system is used to store all monitoring data. The data analysis and processing system processes the monitoring data, imports the data into a mathematical model for calculation to obtain the permeability coefficient of the sediment; imports data such as the gas injection pressure and the brine drainage flow rate into a gas-brine interface prediction model to predict the depth of the gas-brine interface.

[0090] Embodiment 2:

[0091] This embodiment also provides a real-time prediction method for the gas-brine interface, which is applied to the process of using gas injection and brine drainage for the sediment voids in a sediment salt cavern gas storage. The real-time prediction method specifically includes the following steps:

[0092] 1) Obtain the basic parameters of the sediment salt cavern gas storage:

[0093] Among them, obtaining the basic parameters of the sediment salt cavern gas storage includes the burial depth, height, diameter, shape, volume of the salt cavern cavity, the distance between the injection well and the brine drainage well, the sediment height, the sediment surface burial depth, the inner pipe diameter of the injection well, the inner pipe diameter of the brine drainage well, and the roughness of the inner pipe of the brine drainage well, etc.

[0094] 2) Install a gas injection and brine drainage data monitoring device:

[0095] According to Figure 3 install relevant components in the gas injection and brine drainage system. Specifically, it is necessary to install devices such as gas flow meters, gas pressure gauges, gas thermometers, brine flow meters, brine pressure gauges, brine thermometers, brine concentration gauges, the first communication cable, the second communication cable, and computers.

[0096] 3) Obtain gas injection and brine drainage monitoring data:

[0097] Start the compressor and begin the gas injection and brine drainage operation. Obtain the injection pressure P 气 , gas flow rate Q 气 , gas temperature T 气 , brine drainage flow rate Q 卤 , brine outlet pressure P 卤 , brine temperature T 卤 , and brine concentration C 卤 through the gas flow meter, gas pressure gauge, gas thermometer, brine flow meter, brine pressure gauge, brine thermometer, and brine concentration gauge respectively, and transmit the above data to the computer for storage and analysis through the communication cable.

[0098] 4) Calculate the pressure loss coefficient of brine in the sediment:

[0099] Utilize the brine drainage flow rate Q 卤 and the cavity shape above the sediment surface to obtain the depth of the gas-liquid interface drop within a single data monitoring time interval:

[0100]

[0101] In the formula, Δh is the depth of the gas-liquid interface drop within a single data monitoring time interval, with the unit of m; Q 卤 is the brine drainage flow rate, with the unit of m 3 / s; Δt is the recording time interval, with the unit of s; r is the cavity radius or the inner radius of the pipe in the gas injection well. When the gas-liquid interface is in the wellbore section, it is the inner radius of the pipe in the gas injection well, and when the gas-liquid interface enters the cavity, it is the cavity radius.

[0102] Accumulate the depth of the gas-liquid interface drop in each time interval to obtain the depth of the gas-liquid interface:

[0103]

[0104] In the formula, h gb is the depth of the gas-liquid interface, with the unit of m; H0 is the depth of the sediment surface, with the unit of m; j is the serial number of the monitoring data record; n is the total number of records.

[0105] According to the gas injection and brine drainage principle, at the gas-liquid interface, the gas-liquid pressure is balanced, and we get:

[0106] P 气+G 气 =P 卤 +G 卤 +P 阻 +P 损 (3)

[0107] In the formula, P 气 is the gas pressure monitored by the gas pressure gauge, with the unit of Pa; G 气 is the pressure caused by the self-weight of the gas, with the unit of Pa; P 卤 is the brine pressure monitored by the brine pressure gauge, with the unit of Pa; G 卤 is the pressure caused by the self-weight of the brine, with the unit of Pa; P 阻 is the pressure loss caused by the frictional resistance along the way during the movement of the brine in the brine discharge well string, with the unit of Pa; P 损 is the pressure loss caused by the movement of the brine in the sediment, with the unit of Pa.

[0108] Among them, the pressure caused by the self-weight of the gas is:

[0109] G 气 =ρ 气 gh gb (4)

[0110] In the formula, ρ 气 is the gas density, with the unit of kg / m 3 ; g is the acceleration of gravity, with the unit of N / kg.

[0111] Among them, the pressure caused by the self-weight of the brine is:

[0112] G 卤 =ρ 卤 gh gb (5)

[0113] In the formula, ρ 卤 is the brine density, with the unit of kg / m 3 .

[0114] Among them, the pressure loss caused by the frictional resistance along the way during the movement of the brine in the brine discharge well string is:

[0115]

[0116] In the formula, r 卤 is the inner radius of the brine discharge inner pipe, with the unit of m; A 卤 is the cross-sectional area of the brine discharge inner pipe, with the unit of m 2 ; r 卤 is the brine flow velocity, with the unit of m / s; λ 卤 is the frictional resistance coefficient along the way; L 排卤管 is the length of the brine discharge pipe, with the unit of m.

[0117] Among them, the friction coefficient along the way is calculated according to the following formula:

[0118]

[0119] In the formula, μ 卤 is the viscosity of the brine, with the unit of Pa·s; ε is the inner pipe roughness of the brine discharge well, with the unit of m.

[0120] Among them, the pressure loss caused by the friction along the way when the brine moves in the pipe string of the brine discharge well is:

[0121] P 损 = kL 沉渣 (8)

[0122] In the formula, L 沉渣 is the total length of the path that the brine flows through the sediment, with the unit of m; k is the sediment pressure loss coefficient, with the unit of Pa / m.

[0123] In summary, according to the monitoring data of the gas injection pressure and the brine discharge flow rate during gas injection and brine discharge above the sediment surface, the pressure loss coefficient of the brine in the sediment can be calculated:

[0124]

[0125] 5) Prediction of the depth of the gas-brine interface below the sediment surface:

[0126] When the gas-brine interface enters below the sediment surface, the pressure loss of the brine in the sediment is:

[0127] P 损 = k[L 沉渣 -(h gb -H0)], (h gb > H0) (10)

[0128] By monitoring the relationship between the gas pressure and the brine discharge flow rate, the depth of the gas-brine interface is calculated in real time:

[0129]

[0130] In summary, by calculating and recording the monitoring data, and calculating and displaying the position of the gas-brine interface in real time. Thus, the present invention can realize predicting and obtaining the position of the gas-brine interface during the process of gas injection and brine discharge using the voids of the sediment in the salt cavern gas storage reservoir, including the positions of the gas-brine interfaces above and below the sediment surface, and assisting in judging the risk of gas entering the brine discharge well.

[0131] In summary, the content of the present invention mainly includes: aiming at the problem that it is difficult to quantitatively predict the position of the gas-halide interface during the gas injection and brine drainage process in the sediment voids of salt cavern gas storage reservoirs, the present invention provides a real-time prediction method for the gas-halide interface during gas injection and brine drainage in sediment salt cavern gas storage reservoirs. A mathematical model of the gas injection pressure and brine drainage flow rate during the gas injection and brine drainage process in the sediment salt cavern gas storage reservoir is established. Through the monitoring data of the gas pressure and brine flow rate above the sediment surface and the sonar cavity monitoring data, the pressure loss coefficient when the brine flows in the sediment is determined; according to the monitoring data of the gas pressure and brine flow rate of the gas injection and brine drainage below the sediment surface, the position of the gas-halide interface is predicted in real time.

[0132] The effects achieved by the present invention are as follows: The present invention provides a real-time prediction method for the gas-halide interface during gas injection and brine drainage in sediment salt cavern gas storage reservoirs. By using the basic parameters of the salt cavern, the cavity shape, and the real-time monitoring data of gas injection and brine drainage, the real-time inversion of the sediment permeability coefficient is realized, so as to obtain the true permeability coefficient of the sediment; by using the relationship between the gas pressure and the brine drainage flow rate during the gas injection and brine drainage process below the sediment surface, the position of the gas-halide interface is inferred. The present invention solves the technical problem that the cavity shape below the sediment surface cannot be measured in the prior art, resulting in the inability to effectively predict the gas-halide interface during gas injection and brine drainage in sediment salt cavern gas storage reservoirs, greatly improving the operability of the utilization of sediment voids in salt cavern gas storage reservoirs, and having the characteristics of simple operation, low cost, good economy, and good reliability.

[0133] It should also be noted that the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, commodity or device. Without further limitation, the element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method, commodity or device including the element.

[0134] The above are only the embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the scope of the claims of the present application.

Claims

1. A method for determining the depth of the gas-halide interface in a sedimentary salt cavern, characterized in that, The determination method includes: Determining the depth of decline of the gas-halogen interface varying with time according to the initial depth of the gas-halogen interface, the brine discharge flow rate of the brine discharge well, and the cavity shape above the sediment surface of the sediment salt cavern, wherein the initial depth of the gas-halogen interface is lower than the lower end of the gas injection well; When the depth of decline is less than or equal to the depth of the sediment surface of the sediment salt cavern, determining the pressure loss coefficient of the brine flowing through the sediment according to the depth of decline, the gas injection pressure of the gas injection well, the brine discharge pressure of the brine discharge well, the pressure loss during the brine discharge process of the brine discharge well, and the path length of the brine flowing through the sediment in the sediment salt cavern; and When the depth of decline is greater than the depth of the sediment surface, determining the target depth of the gas-halogen interface according to the pressure loss coefficient, the gas injection pressure of the gas injection well, the brine discharge pressure of the brine discharge well, the pressure loss during the brine discharge process of the brine discharge well, the depth of the sediment surface, and the path length of the brine flowing through the sediment.

2. The determination method according to claim 1, wherein The determination of the depth of decline of the gas-halogen interface varying with time includes: Determining the area of each cross-section in a plurality of cross-sections in the vertical direction of the sediment salt cavern according to the cavity shape of the sediment salt cavern; Determining the depth of decline of the gas-halogen interface at each set interval time according to the brine discharge flow rate of the brine discharge well and the area of each cross-section; and Determining the depth of decline of the gas-halogen interface varying with time according to the depth of decline at each set interval time.

3. The determination method according to claim 2, wherein The determination of the depth of decline of the gas-halogen interface at each set interval time includes: According to the brine discharge flow rate Q of the brine discharge well 卤 and the area A of each of the plurality of cross-sections i , the following formula is used to determine the depth of descent Δh of the gas-brine interface within each set time interval Δt: Δh = m·a, where a is the interval distance between two adjacent cross-sections among the plurality of cross-sections, i is the serial number of each cross-section among the plurality of cross-sections, and m is the number of cross-sections spanned by the gas-halogen interface within each set interval time Δt.

4. The determination method according to any one of claims 1 to 3, characterized in that The determination method further includes: when the depth of decline is less than or equal to the depth of the sediment surface of the sediment salt cavern, determining the sum of the initial depth of the gas-halogen interface and the depth of decline as the target depth of the gas-halogen interface at the target time.

5. The determination method according to claim 1, characterized in that The pressure loss during the brine discharge process of the brine discharge well is determined by the following steps: Determining the friction factor along the length of the brine discharge well according to the inner pipe radius, inner pipe roughness of the brine discharge well, and the flow velocity of the brine; and Determining the pressure loss during the brine discharge process of the brine discharge well according to the inner pipe radius of the brine discharge well, the length of the brine discharge well, the friction factor along the length, and the flow velocity of the brine.

6. The determination method according to claim 5, characterized in that The determination of the friction factor along the length of the brine discharge well includes: According to the inner pipe radius r of the brine drainage well 卤 , the inner pipe roughness ε, and the flow velocity v of the brine 卤 , the friction factor λ along the length of the brine drainage well is determined by the following formula 卤 : Among them, ρ 卤 is the density of the brine, and μ 卤 is the viscosity of the brine.

7. The determination method according to claim 5, characterized in that, The determination of the pressure loss during the brine discharge process of the brine discharge well includes: According to the inner pipe radius r of the brine drainage well 卤 , the length L of the brine drainage well 排卤管 , the friction coefficient λ along the way 卤 and the flow velocity v of the brine 卤 , the pressure loss P during the brine drainage process of the brine drainage well is determined by the following formula 阻 : A 卤 ＝πr 卤 2 ， Among them, ρ 卤 is the density of the brine, and A 卤 is the cross-sectional area of the inner pipe of the brine discharge well.

8. The determination method according to claim 1, wherein The determination of the pressure loss coefficient of the brine flowing through the sediment includes: According to the descending depth h of the gas-halogen interface gb , the gas injection pressure P of the gas injection well 气 , the brine drainage pressure P of the brine drainage well 卤 , the pressure loss P during the brine drainage process of the brine drainage well 阻 and the path length L of the brine flowing through the sediment 沉渣 , the pressure loss coefficient k of the brine flowing through the sediment is determined by the following formula: Among them, ρ 卤 is the density of the brine, ρ 气 is the density of the injected gas, and g is the acceleration due to gravity.

9. The determination method according to claim 1, characterized in that The determination of the target depth of the gas-halogen interface includes: According to the pressure loss coefficient k, the gas injection pressure P of the gas injection well 气 , the brine discharge pressure P of the brine discharge well 卤 , the pressure loss P during the brine discharge process of the brine discharge well 阻 , the depth H0 of the sediment surface and the path length L of the brine flowing through the sediment 沉渣 , the target depth h of the gas-brine interface is determined by the following formula 目标 : Among them, ρ 卤 is the density of the brine, ρ 气 is the density of the injected gas, and g is the acceleration due to gravity.

10. A system for determining the depth of the gas-halogen interface in a sedimentary salt cavern, characterized in that, The determination system includes: The first determination device is configured to determine the depth of the decline of the gas-halide interface over time according to the initial depth of the gas-halide interface, the brine discharge flow rate of the brine discharge well, and the cavity shape above the sediment surface of the sediment salt cavern, wherein the initial depth of the gas-halide interface is lower than the lower end of the gas injection well; The second determination device is configured to, when the depth of the decline is less than or equal to the depth of the sediment surface of the sediment salt cavern, determine the pressure loss coefficient of the brine flowing through the sediment according to the depth of the decline, the gas injection pressure of the gas injection well, the brine discharge pressure of the brine discharge well, the pressure loss during the brine discharge process of the brine discharge well, and the path length of the brine flowing through the sediment in the sediment salt cavern; and The third determination device is configured to, when the depth of the decline is greater than the depth of the sediment surface, determine the target depth of the gas-halide interface according to the pressure loss coefficient, the gas injection pressure of the gas injection well, the brine discharge pressure of the brine discharge well, the pressure loss during the brine discharge process of the brine discharge well, the depth of the sediment surface, and the path length of the brine flowing through the sediment.

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