A method for brine treatment, gas storage, and cavity expansion in a salt cavern.

Abstract

This invention belongs to the field of salt cavern gas storage engineering, specifically disclosing a method for brine treatment, gas storage, and cavity expansion in salt caverns. The method integrates brine absorption, gas storage, and expansion in two salt caverns, A and B. Through the formation of a hydraulic fracturing network and pressure drive by the brine, rapid in-situ absorption of large volumes of brine can be achieved on an engineering scale, significantly improving brine absorption efficiency. Furthermore, hydraulic fracturing modifies the cavity of salt cavern A, increasing the brine storage space in the reservoir, allowing for more efficient and larger-volume brine discharge from salt cavern B, expanding its usable space, and increasing the construction volume of salt cavern B as a compressed air storage facility. In addition, the method reduces or even eliminates the energy consumption and facility investment required for large-scale surface brine concentration and evaporation or long-distance transportation, significantly reducing processing costs.

Description

Technical Field

[0001] This invention belongs to the field of salt cavern gas storage engineering, specifically relating to a method for brine treatment, gas storage, and cavity expansion of a salt cavern. Background Technology

[0002] During conventional mining of onshore salt mines, the continuous dissolution process often creates underground salt cavities ranging in size from hundreds of thousands of cubic meters. These cavities are perpetually filled with saturated brine with extremely high salt concentrations, far exceeding the capacity of typical surface or industrial wastewater treatment systems. Traditional technologies such as evaporation crystallization, ion exchange, or membrane separation are not only energy-intensive and costly per unit area, but also require large-scale equipment, occupy a large area, and have long operating cycles, making it difficult to meet the demand for rapid treatment and disposal of large volumes of high-salinity brine.

[0003] Currently, my country is launching a series of underground gas storage projects using salt caverns and compressed air energy storage (CAES) facilities, aiming to utilize existing or abandoned salt caverns for large-scale gas storage. To efficiently convert these salt caverns into CAES storage facilities, the residual saturated brine within the caverns must first be replaced or deeply treated. However, traditional brine treatment processes are insufficient in terms of economics, energy consumption, land occupation, and processing efficiency to obtain sufficiently large gas storage salt caverns, failing to meet the requirements for gas storage facility construction and storage space capacity.

[0004] Therefore, how to safely and efficiently dispose of large volumes of high-concentration brine is a key technical challenge that urgently needs to be overcome and solved in the construction of salt cavern gas storage and compressed air energy storage projects. Summary of the Invention

[0005] In view of the problems of high-concentration and large-volume brine treatment difficulties and insufficient gas storage space in salt caverns mentioned above, the present invention will provide a method for brine treatment, gas storage and cavity expansion of salt caverns.

[0006] To achieve the above objectives, the following technical solutions are specifically included: This invention provides a method for brine treatment, gas storage, and cavity expansion in salt caverns, comprising the following steps: S1. Construct a brine reinjection system, which includes a fracturing pump system, a brine mixer, and a real-time monitoring and control system. S2. Set up a brine injection channel in the formation of the target salt cavern A, and obtain the formation fracturing pressure P of the target salt cavern A. b ; S3. Inject gas into the upper part of the cavity of the target salt cave B and discharge brine from the target salt cave B, so that the target salt cave B expands the space for storing gas. S4. Using the brine reinjection system described in step S1, the brine described in step S3 is injected into the brine injection channel described in step S2 in a segmented injection manner, so that the target salt cave A can absorb the brine and expand the formation volume. The segmented injection includes the following three stages: In the first stage, the initial pressure of the injected brine is 0; in the second stage, the pressure of the injected brine gradually increases to P. b This causes the formation of the target salt cavern A to fracture; in the third stage, the pressure of the injected brine is reduced to (0.1-0.6) × P. b Continue until the brine is completely added.

[0007] In the method of this invention, brine is discharged from salt cavern B by gas injection and brine discharge. Simultaneously, the cavity left after the brine discharge from salt cavern B is used to store gas, achieving the purpose of gas storage. The discharged brine is injected into the target salt cavern A. While absorbing the brine, the brine is hydraulically fracturing the salt cavern formation by staged pressurization, forming a network of interconnected fractures and expanding the volume of salt cavern A. Continuous brine injection maintains formation pore pressure, keeping fractures and high-permeability channels unobstructed. This significantly expands the reservoir's usable space, improves brine absorption efficiency, and enables the rapid reinjection of a larger volume of brine into salt cavern A. Furthermore, the staged pressurization method effectively controls the injection pressure and flow rate, allowing for controlled fracture expansion and efficient brine absorption in salt cavern A while preventing fractures from breaching non-target strata. This ensures that the injection process causes no pollution or adverse effects on the surface or adjacent aquifers. Because salt cavern A can efficiently hold a large volume of brine, this allows for the discharge of a large amount of brine from salt cavern B, providing more space for gas storage. This achieves directional expansion of the gas storage space in salt cavern B, increasing the volume of gas stored there. Therefore, the method of this invention integrates brine absorption, gas storage, and expansion in both salt caverns A and B. By forming a hydraulic fracturing network and pressure-driven action, rapid in-situ absorption of large volumes of brine can be achieved on an engineering scale, significantly improving brine absorption efficiency. Furthermore, hydraulic fracturing modifies the cavity of salt cavern A, increasing the brine storage space in the reservoir, allowing for the discharge of more brine from salt cavern B more efficiently, expanding usable space, and increasing the construction volume of salt cavern B as a compressed air storage facility. In addition, the method of this invention can reduce or even avoid the energy consumption and facility investment required for large-scale surface brine concentration and evaporation or long-distance transportation, significantly reducing processing costs.

[0008] Preferably, in step S1, the fracturing pump system includes a high-pressure hydraulic fracturing pump. The fracturing pump provides the power for brine injection, so that the pressure of the injected brine reaches the pressure of the fractured formation.

[0009] Preferably, in step S1, the real-time monitoring and control system includes at least one of a pressure gauge, a flow meter, and a microseismic monitoring sensor. The pressure gauge and flow meter are used to monitor the pressure and flow rate of fluids such as brine, water, or gas, facilitating the control of fluid velocity and energy.

[0010] Preferably, in step S1, the brine mixer includes a static mixer or a circulating mixing tank. The brine mixer is used to store and pre-treat the raw brine discharged from the salt cavern B.

[0011] Preferably, in step S2, the brine injection channel includes multiple clusters of perforations, each cluster having 3 or more perforations; more preferably, the brine injection channel includes N clusters of perforations, each cluster of perforations including m perforations, where N is 2-50, more preferably 3-10; and m is 3-10, more preferably 4-6.

[0012] The brine injection channel, as the injection well for brine, exhibits a clustered perforation distribution and meets the required airtightness, which is conducive to achieving controllable fracture initiation, directional fracture propagation, and distributed, efficient brine absorption in salt cavern formations.

[0013] Preferably, the injection channel includes a matching casing and sealing components. The brine injection channel has also undergone formation pressure testing and gas tightness testing. The injection channel is connected to the fracturing pump system in the brine reinjection system.

[0014] Preferably, in step S2, the formation fracturing pressure P of the target salt cavern A is obtained. b The process includes the following steps: First, the in-situ stress and pore pressure of the target salt cavern A are obtained based on field tests, and then the formation fracture pressure P is calculated using the Hubbert-Willis expression or the Haimson-Fairhurst expression. b The pre-tested fracturing pressure of the target salt cavern A formation is beneficial for controlling the pressure in the subsequent staged pressurization method, making the formation fracturing initiation controllable and the brine absorption more stable and efficient.

[0015] More preferably, the Hubbert-Willis expression is: P b =3σ h -σ H +σ T -p0; In the formula, P b For formation fracture pressure, σ h σ is the minimum horizontal stress in the formation. H σ represents the maximum horizontal stress in the formation. T p0 is the initial formation pore pressure, where p is the tensile strength of the rock. More preferably, the Haimson-Fairhurst expression is: P b =(3σ h -σ H +σ T -2ηp0) / 1-η; In the formula, P b For formation fracture pressure, σ h σ is the minimum horizontal stress in the formation. H σ represents the maximum horizontal stress in the formation. T η is the tensile strength of the rock, p0 is the initial formation pore pressure, and η is the porosity coefficient.

[0016] Preferably, in step S2, the stratum depth of the target salt cavern A is 50-200m. The stratum selected for salt cavern A should have a large thickness, a stable top plate, good isolation from the aquifer, and an intact aquitard; the salt cavern should have a regular geometry and no risk of leakage from active faults or fissures; the on-site construction conditions should allow for the installation of a high-pressure brine injection channel (injection well) and monitoring facilities, and the burial depth of the brine injection channel is generally in the range of several hundred meters to several kilometers.

[0017] Preferably, in step S3, the gas in the injected gas includes air.

[0018] Preferably, in step S4, the brine further undergoes pretreatment, including dilution and stirring, in a brine mixer placed in the brine reinjection system described in step S1. The original saturated brine in the salt mine is diluted (mixed with fresh water) to a certain proportion, and homogenized using a static mixer or circulating mixing tank to avoid stratification or localized high-concentration areas in the brine, thereby reducing the risk of crystallization and precipitation during the brine reinjection into the reservoir.

[0019] Preferably, in step S4, the mass concentration of the brine is calculated based on the mass percentage of NaCl it contains, with the brine mass concentration being w1 and the saturated brine mass concentration being w2, where w1 accounts for 40%-95% of w2. To reduce the risk of crystallization blockage between the injection pipeline and the formation in the brine injection channel, the diluted brine concentration should preferably be maintained within the range of 40%-95% of the brine saturation (more preferably 50%-80%). Furthermore, static and dynamic sedimentation tests at room temperature or downhole temperature, as well as small-well test injections, can be performed before on-site injection to determine the optimal ratio and injection rate, further mitigating the risk of blockage. If the brine concentration discharged from salt cavern B is not saturated, the brine can be directly injected into salt cavern A without dilution.

[0020] Preferably, in step S4, the mass concentration of the brine is 10wt%-15wt%.

[0021] Preferably, in step S4, the pressure of the brine injected in the second stage is gradually increased to P. b During the process, the pressure of the injected brine can be increased to P in multiple stages. b For example, the pressure of the injected brine can be increased to P in 3-8 stages. b More specifically, the pressure of the injected brine was increased from 0 to (0.5-0.85)×P b Then increase it to (0.90-0.94)×P b Continue to increase to (0.95-0.99)×P b Finally, it was increased to P. b .

[0022] More preferably, the average rate of brine injection in the second stage is v1, and the average rate of brine injection in the third stage is v2, satisfying: v2 > v1; more specifically, satisfying: v2 = (1-2) × v1; even more preferably, v1 is 0.5-1.5m. 3 / min, where v2 is 1.5-3m 3 / min.

[0023] Compared with existing technologies, the present invention has the following beneficial effects: The method of the present invention integrates the brine absorption, gas storage and expansion of two salt caverns A and B. By forming a hydraulic fracture network and pressure drive through the brine, it can achieve rapid in-situ absorption of large-volume brine on an engineering scale, significantly improving the brine absorption efficiency. Moreover, the hydraulic fracturing achieves cavity modification of salt cavern A, increasing the brine storage space in the reservoir, allowing more brine to be discharged from salt cavern B more efficiently, expanding the usable space and increasing the construction volume of salt cavern B as a compressed air storage facility. In addition, the method of the present invention can reduce or even avoid the energy consumption and facility investment required for large-scale surface brine concentration and evaporation or long-distance transportation, resulting in a significant reduction in processing costs. Attached Figure Description

[0024] Figure 1 This is a flowchart of the integrated method for brine treatment, gas storage, and cavity expansion of a salt cavern according to the present invention. Detailed Implementation

[0025] To better illustrate the purpose, technical solution, and advantages of this invention, specific embodiments will be used to further explain the invention below. Unless otherwise specified, the experimental methods used in the embodiments and / or comparative examples are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available. Obviously, the described embodiments are only a part of the embodiments of this invention, not all of them. Based on the described embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0026] Example 1 A method for brine treatment, gas storage, and cavity expansion in a salt cavern, the process flow diagram of which is shown below. Figure 1 As shown, the specific steps include the following: S1. The brine reinjection system consists of a surface-mounted high-pressure hydraulic fracturing pump system, a circulating mixing tank, a high-pressure delivery pipeline, an injection well (extending underground), and a real-time monitoring and control system. The high-pressure hydraulic fracturing pump system provides the injection power; the circulating mixing tank mixes the brine with clean water; the high-pressure delivery pipeline connects the fracturing pump system to the injection well; the injection well consists of a surface injection port (wellhead) and an underground channel, and is equipped with sealing components such as casing and packers; the real-time monitoring and control system includes pressure gauges, flow meters, and microseismic monitoring sensors. The pressure gauges and flow meters monitor the brine flowing into the injection well, and the microseismic monitoring sensors are placed in appropriate underground locations to detect underground vibrations.

[0027] S2. Salt Layer Geological Condition Screening and Reinjection Channel Design: To ensure the controllability and long-term safe storage of brine injection, the following technical requirements should be met simultaneously, and the layout and dimensions of the brine injection channels should be determined according to the following process: (a) Select a suitable brine injection salt cavern based on geological and well location requirements, and mark it as target salt cavern A; in particular, the selected salt cavern strata should be preliminarily assessed based on parameters such as the burial depth of the salt cavern top, roof thickness, pillar width, block faults, salt-bearing layer thickness, and interlayer sealing performance. Determine the salt cavern conditions by conducting sonar cavity probing, geophysical drilling, and sealing performance assessment, ensuring that its roof is stable, well isolated from the aquifer, and the aquitard is intact. In this embodiment, the average stratum thickness is 50-200m; the salt cavern geometry is regular, with no risk of leakage from active faults or fissures; the on-site construction conditions allow for the installation of high-pressure injection wells and monitoring facilities, and the burial depth of the salt cavern top is 600-1000m.

[0028] (b) Overall configuration of the injection channel: An injection well is installed in the target salt cavern A, with a pipe embedded in the well. Within the well section, perforations are arranged in clusters along the pipe according to the distribution of geostress and producing formation, with a total of 3 clusters, each with 4 perforations arranged at 90° phase. Simultaneously, the well is segmented, and a multi-stage packer with internal sealing is installed in each segment. A check valve is also installed within the well to maintain well pressure. The packers provide mechanical isolation between the segments and between different segments, and their interaction with the check valve prevents brine outflow. This injection channel configuration enables controlled fracture initiation, directional fracture propagation, and distributed absorption. Before formal injection, formation pressure and gas tightness tests are conducted on the injection well (brine injection channel) to confirm wellbore integrity and sealing.

[0029] S3, Obtain formation fracture pressure Pb Based on the in-situ stress and pore pressure of salt cavern A obtained from field logging / core data, the formation fracture pressure P of salt cavern A is calculated using the Hubbert-Willis expression or the Haimson-Fairhurst expression. b .

[0030] The Hubbert-Willis expression is given by equation (1), which is based on linear elasticity and assumes that there is no pore pressure transmission in the near-wellbore region. Therefore, it is applicable to non-permeable conditions. P b =3σ h -σ H +σ T -p0(1); In the formula, P b For formation fracture pressure, σ h σ is the minimum horizontal stress in the formation. H σ represents the maximum horizontal stress in the formation. T p0 is the tensile strength of the rock and p0 is the initial formation pore pressure.

[0031] For formations with porosity-elastic coupling and fluid permeability, Haimson and Fairhurst proposed a porosity-elastic modified fracturing pressure Haimson-Fairhurst (H–F) expression (2) based on Biot's porosity-elasticity theory: P b =(3σ h -σ H +σ T -2ηp0) / 1-η(2; In the formula, P b For formation fracture pressure, σ h σ is the minimum horizontal stress in the formation. H σ represents the maximum horizontal stress in the formation. T η is the tensile strength of the rock, p0 is the initial formation pore pressure, and η is the porous elastic coefficient. η depends on material parameters such as the Biot coefficient α and the Poisson ratio ν. It is used to characterize the correction effect of pore pressure on effective stress, and its specific value can be selected and determined according to the actual situation.

[0032] S4. Gas Injection and Brine Discharge of Salt Cavern B: Select a salt cavern similar to salt cavern A and suitable for subsequent gas storage (including requirements for sealing and storage space), designating it as target salt cavern B. Install gas injection and brine discharge channels (including the installation of corresponding tubing) for target salt cavern B. The gas injection channel should be positioned so that the injected gas is located at the upper part of the salt cavern B cavity. The brine discharge channel should descend from the ground to the lower part of the salt cavern B cavity, near the upper surface of the insoluble sediment at the bottom of the salt cavern. Both the gas injection and brine discharge channels should be equipped with necessary valves, isolation devices, real-time monitoring equipment, and sealing components to ensure the normal operation of gas injection and brine discharge. Connect the compressor and brine extraction equipment to the gas injection and brine discharge channels on the ground, respectively. The brine extraction equipment should be equipped with corresponding delivery pipelines to transport the subsequently extracted brine to the circulating mixing tank in the brine reinjection system of salt cavern A. After setting up the gas injection channel and the brine discharge channel, the cavity shape, structure, sealing performance, and wellbore integrity of the salt cavern B after the gas injection channel are evaluated. Once the salt cavern B passes the evaluation and meets the actual operational requirements, compressed air is injected into the upper part of the salt cavern B through the compressor and the gas injection channel. The top or high-level gas injection of the salt cavern B forms a gas phase, which forms a gas-liquid interface with the liquid surface of the brine. The pressure of the continuously injected compressed air on the gas-liquid interface causes the brine to be discharged from underground to the surface through the low-level brine discharge channel and transported to the circulating mixing tank in the brine reinjection system of the salt cavern A for temporary storage. If the discharged brine meets the actual injection requirements, it can also be directly input into the injection well of the salt cavern A. Because the brine concentration in the salt cavern B in this embodiment is high, direct injection into the salt cavern A may cause blockage of the injection well or channel. Therefore, pretreatment is required in the circulating mixing tank before reinjection. As compressed air is continuously injected to store compressed air and brine is continuously discharged, the gas-liquid interface gradually decreases, the volume of compressed air stored in salt cavern B gradually increases, and the gradual discharge of brine allows the space in salt cavern B that originally contained brine to be used as a space to contain gas, thus increasing the volume of gas that can be contained, which significantly expands the gas storage space of salt cavern B; until the gas-liquid interface in salt cavern B is controlled to reach the gas phase volume that the salt cavern B is designed to contain, the cavity morphology, gas-liquid interface height and usable volume are then verified by measuring the cavity and downhole interface using sonar.

[0033] In this step, the salt cavern B achieves the in-situ brine discharge and absorption process, as well as the efficient storage of compressed air and the directional expansion of the gas storage chamber through "high-level gas injection and low-level brine discharge".

[0034] S5. Brine Dilution: The brine from salt cavern B, transported to the circulating mixing tank in the brine reinjection system, is tested for brine concentration to confirm it is saturated. It is then mixed with fresh water and thoroughly stirred in the circulating mixing tank to ensure uniform concentration and good fluidity. The original saturated brine in salt cavern B has a NaCl saturation of 26.4 wt% at 25°C. Pretreated brine is obtained by mixing brine and fresh water at a 1:1 mass ratio, with a NaCl mass fraction of 13.2 wt%. Static and dynamic sedimentation tests at ambient / downhole temperatures, as well as a small-well injection test, are conducted before on-site injection to ensure smooth injection at this concentration.

[0035] S6. Brine is reinjected into salt cavern A for digestion: The fracturing pump system in the brine reinjection system is started, and the pretreated brine is injected into the injection well in stages at a constant rate, with the injection process being fully monitored.

[0036] The segmented injection process includes the following three stages: In the first stage, the initial pressure of the injected brine is 0.

[0037] In the second stage, the brine flow rate in the fracturing pump system is controlled (the average injection rate of brine is 1 m). 3 The pressure of the brine injection is kept constant ( / min), and the pressure is gradually increased to P. b There is no limit to the number of times the pressure is gradually increased, but it is preferable to set it to be done in 4 or more steps. For example, the brine injection pressure is increased from 0 to 0.8 × P. b Then from 0.8×P b Increased to 0.85×P b Increase it to 0.9×P b Then continue to increase it to 0.95×P b Finally, it was increased to P. b Increase to P b Subsequently, on the one hand, if a sudden drop in the pressure of the injected brine occurs within a short period of time (for example, a sudden drop in the brine injection pressure ≥1.0 MPa or compared to P), b The decrease in brine injection pressure is ≥5%×P b These can all serve as indicators or signals of a sudden pressure drop, or the appearance of a clear inflection point / plateau in the pressure curve of brine injection (pressure criterion); on the other hand, if the microseismic sensor detects a sudden increase in the microseismic event rate or energy within the target layer (microseismic criterion), it can be determined that there is a fracture in the formation of salt cavern A, and the fractures therein have started and are propagating; in addition, if the pressure of brine injection shows a plateau or multiple sudden drops, the fracture mode and propagation direction should be further analyzed in conjunction with the microseismic location and pressure derivative to determine whether the formation of salt cavern A and its fractures have started.

[0038] In the third stage, after confirming the fracturing of the salt cavern A stratum, the pressure of the injected brine was reduced to 0.3 × P. b And maintaining this pressure constant, the average rate of brine injection is 2m. 3 The injection rate is maintained at 1000 m / min until the predetermined volume of brine to be absorbed is reached. Once this is achieved, the injection is stopped, and the final injection volume and wellhead pressure data are recorded for subsequent performance evaluation.

[0039] Simultaneously, comprehensive monitoring is required throughout the entire brine injection process, including microseismic monitoring, wellhead and bottom hole pressure monitoring, and environmental monitoring. This is to obtain real-time monitoring results of microseismic activity, pressure, and flow rate, and to adjust the brine injection process based on the monitoring results. Specifically, in microseismic monitoring, microseismic monitoring instruments need to be deployed around the salt cavern to locate the seismic source activity triggered by the injection in real time, monitor the extent of hydraulic fracture propagation, prevent fractures from penetrating non-target strata, and enable synchronous initiation and uniform extension of clusters within the segment, increasing the complexity and volume of artificial fractures. During wellhead and bottom hole pressure monitoring, the pressure and flow rate changes of the injected brine need to be recorded in real time to observe sudden pressure changes or flow anomalies. In environmental monitoring, surface displacement and groundwater quality are monitored to ensure that the injection process does not pollute or adversely affect the surface or adjacent aquifers.

[0040] In addition, after the brine is injected, the well pressure is maintained by using packers and check valves. Combined with the self-healing and sealing properties of the salt layer itself, the brine is safely and securely stored in a closed manner, preventing pollution to the surface and adjacent aquifers.

[0041] S7. Evaluation of Brine Absorption Effectiveness: After injection, a comprehensive evaluation is conducted on the changes in injection volume and effective salt cavern volume, as well as formation isolation, using methods such as sonar cavity measurement, pressure recovery tests, tracer and chemical monitoring, microseismic monitoring, and surface monitoring. If no anomalies are detected in the tracer and surrounding aquifers, and no abnormal microseismic events are observed in the pressure recovery curve, it is determined that the injection has been effectively absorbed and the salt layer is in an acceptable storage state. Simultaneously, before brine injection, a numerical simulation model is typically constructed to simulate formation pressure changes and fracture morphology evolution during the brine reinjection process. After brine absorption, the brine reinjection process is simulated again to obtain formation pressure changes. If the brine reinjection curves from the previous and subsequent simulations are consistent, it is determined that the injection has been effectively absorbed and the salt layer is in an acceptable storage state.

[0042] Traditional brine injection methods require a low injection rate throughout the process to maximize brine volume in the salt cavern. Excessive injection rate leads to a surge in formation pore pressure, resulting in a lower injected brine volume. Specifically, regarding the geology of salt cavern A in this embodiment, numerical simulation calculations show that if traditional brine injection methods are used (without formation fracturing), the theoretical maximum average injection rate for a single well in salt cavern A is 0.1 m / s².3 Based on a cumulative brine injection rate of / min over 30 days, the theoretical maximum volume of brine injected into salt cavern A is 0.1 × 60 × 24 × 30 = 4320 m³. 3 As injection continues, the pore pressure around the wellbore rises and eventually approaches the critical pressure for formation fracturing. At this point, it is no longer possible to continue injecting fluid at this rate; that is, the maximum injection volume of brine using the conventional method is approximately 4320 m³. 3 .

[0043] In this embodiment, brine is used to first fracturing a single well. The time required before fracturing is short, and the volume of brine absorbed is low and negligible. After formation fracturing, a numerical simulation method similar to the traditional brine injection method described above is used to calculate and evaluate the volume of brine injected into salt cavern A. Furthermore, because formation fracturing significantly increases the formation's seepage channels and movable pore space, the pore pressure is far from reaching the critical value for formation fracture. In fact, the brine injection rate in salt cavern A can be increased to at least 1.0 m³ / s. 3 If the injection rate is above 1.0 / min (as confirmed in the above embodiments), then the cumulative injection volume over 30 days is at least 1.0 × 60 × 24 × 30 = 43200 m³. 3 It can be seen that after fracturing, the volume of brine injected for absorption increases significantly compared to the unfracturing state (approximately more than 10 times that under unfracturing conditions) because it can continue to absorb more fluid.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for brine treatment, gas storage, and cavity expansion in a salt cavern, characterized in that, Includes the following steps: S1. Construct a brine reinjection system, which includes a fracturing pump system, a brine mixer, and a real-time monitoring and control system. S2. Set up a brine injection channel in the formation of the target salt cavern A, and obtain the formation fracturing pressure P of the target salt cavern A. b ; S3. Inject gas into the upper part of the cavity of the target salt cave B and discharge brine from the target salt cave B, so that the target salt cave B expands the space for storing gas. S4. Using the brine reinjection system described in step S1, the brine described in step S3 is injected into the brine injection channel described in step S2 in a segmented injection manner, so that the target salt cave A can absorb the brine and expand the formation volume. The segmented injection includes the following three stages: In the first stage, the initial pressure of the injected brine is 0; in the second stage, the pressure of the injected brine gradually increases to P. b This causes the formation of the target salt cavern A to fracture; in the third stage, the pressure of the injected brine is reduced to (0.1-0.6) × P. b Continue until the brine is completely added.

2. The method for brine treatment, gas storage, and cavity expansion of a salt cavern as described in claim 1, characterized in that, In step S4, the brine is further subjected to a pretreatment process, including dilution and stirring, in the brine mixer described in step S1.

3. The method for brine treatment, gas storage, and cavity expansion of a salt cavern as described in claim 1, characterized in that, In step S4, the mass concentration of the brine is calculated based on the mass percentage of NaCl it contains. The mass concentration of the brine is w1, and the mass concentration of the saturated brine is w2. w1 accounts for 40%-95% of w2.

4. The method for brine treatment, gas storage, and cavity expansion of a salt cavern as described in claim 3, characterized in that, In step S4, the mass concentration of the brine is 10wt%-15wt%.

5. The method for brine treatment, gas storage, and cavity expansion of a salt cavern as described in claim 1, characterized in that, In step S1, the fracturing pump system includes a high-pressure hydraulic fracturing pump, and / or, in step S1, the real-time monitoring and control system includes at least one of a pressure gauge, a flow meter, and a microseismic monitoring sensor.

6. The method for brine treatment, gas storage, and cavity expansion of a salt cavern as described in claim 1, characterized in that, In step S1, the brine mixer includes a static mixer or a circulating mixing tank.

7. The method for brine treatment, gas storage, and cavity expansion of a salt cavern as described in claim 1, characterized in that, In step S2, the brine injection channel includes multiple clusters of perforations, each cluster having three or more perforations; the injection channel includes a matching casing and sealing components; the brine injection channel also undergoes formation pressure testing and gas tightness testing; the injection channel is connected to the fracturing pump system in the brine reinjection system.

8. The method for brine treatment, gas storage, and cavity expansion of a salt cavern as described in claim 1, characterized in that, In step S2, the formation fracturing pressure P of the target salt cavern A is obtained. b The process includes the following steps: First, the in-situ stress and pore pressure of the target salt cavern A are obtained based on field tests, and then the formation fracture pressure P is calculated using the Hubbert-Willis expression or the Haimson-Fairhurst expression. b .

9. The method for brine treatment, gas storage, and cavity expansion of a salt cavern as described in claim 8, characterized in that, The Hubbert-Willis expression is: P b =3σ h -s H +s T -p0; In the formula, P b For formation fracture pressure, σ h σ is the minimum horizontal stress in the formation. H σ represents the maximum horizontal stress in the formation. T p0 is the initial formation pore pressure, where p is the tensile strength of the rock. And / or, the Haimson-Fairhurst expression is: P b =(3σ h -σ H +σ T -2ηp0) / 1-η; In the formula, P b For formation fracture pressure, σ h σ is the minimum horizontal stress in the formation. H σ represents the maximum horizontal stress in the formation. T η is the tensile strength of the rock, p0 is the initial formation pore pressure, and η is the porosity coefficient.

10. The method for brine treatment, gas storage, and cavity expansion of a salt cavern as described in claim 1, characterized in that, In step S3, the gas injected includes air.

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