Regulation and control method and system for fractured surrounding rock freezing circle of underground natural gas storage cavern

Abstract

The embodiment of the invention provides a regulation and control method and system for a fissure surrounding rock freezing circle of an underground natural gas storage cavern, and the method comprises the steps: selecting a rock mass excavation roadway to form a storage cavern of liquefied natural gas, and taking the freezing circle formed by freezing surrounding rock fissure water as a sealing structure; setting the storage pressure in the tunnel and the storage temperature of the liquefied natural gas in a pressurized storage state, setting the temperature of the outer contact surface of the heat-insulating layer, and determining the thickness of the heat-insulating layer through thermodynamic calculation based on the evaporation loss requirement; a water replenishing roadway and a water replenishing hole are arranged above the storage cavern, and a water draining roadway and a water draining hole are arranged below the storage cavern and the storage cavern; checking the efficiency of the groundwater control process through a multi-stage water pumping and draining test, and optimizing the arrangement of drill holes in a low-efficiency area; controlling drainage until the fissure water is drained to a target state; and storing the liquefied natural gas, expanding the freezing circle to the target isotherm, stopping drainage, and forming the freezing circle. According to the invention, gas storage and waste underground space utilization are promoted.

Description

Technical Field

[0001] This application relates to the technical field of cryogenic liquefied natural gas (LNG) storage, specifically to a method and system for controlling the frozen zone of fractured surrounding rock in underground natural gas storage. Background Technology

[0002] Global natural gas utilization is continuously increasing, leading to a strong demand for gas storage facilities. Construction primarily utilizes depleted oil and gas reservoirs and salt caverns, but site selection is severely limited by geological conditions, resulting in poor site suitability and slow construction progress. Only by rapidly advancing gas storage projects can the pressure of natural gas pipeline supply gaps be addressed and natural gas supply guaranteed. In particular, the supply capacity of liquefied natural gas (LNG) is insufficient, and there is an urgent need to reduce the construction costs of new LNG storage facilities. Based on the current development of tank construction technology, the trend towards larger LNG storage tanks is becoming increasingly apparent. Cryogenic underground LNG storage, as a new technology, can achieve a single tank capacity of up to one million cubic meters.

[0003] Compared to above-ground and underground storage tanks, cryogenic underground liquefied natural gas (LNG) storage tanks are safer, more environmentally friendly, and require less land. Their economic advantages become more pronounced as storage capacity increases: the investment for above-ground LNG storage is approximately 10 yuan per cubic meter; for gas reservoir-type storage, it's about 8 yuan per cubic meter; and for underground LNG storage, the investment is expected to drop to 6 yuan per cubic meter. With the increasing number of LNG receiving terminals built along the coast, available port resources are becoming increasingly limited, while cryogenic underground LNG storage offers a wide range of site selection options and promising development prospects.

[0004] Currently, the technical details regarding the control of the freezing zone range in underground cryogenic liquefied natural gas (LNG) storage facilities (especially at the 0°C isotherm) are not yet fully developed, both domestically and internationally. Therefore, there is an urgent need to develop a scheme that can dynamically evolve and regulate the freezing zone of fractured surrounding rock in cryogenic LNG storage facilities. This would provide support for the construction of gas storage facilities in areas with the most concentrated gas consumption and where facility construction is difficult, and would have significant implications for natural gas reserves and energy structure transformation. Summary of the Invention

[0005] This application proposes a method and system for regulating the frozen zone of fractured surrounding rock in underground natural gas storage facilities, in order to overcome the deficiencies of the prior art.

[0006] According to a first aspect of the embodiments of this application, a method for regulating the frozen zone of fractured surrounding rock in an underground natural gas storage facility is provided, comprising: The rock mass was selected to excavate tunnels to form storage chambers for liquefied natural gas, and the frozen zone formed by the freezing of water in the surrounding rock fissures was used as a sealing structure. Set the storage pressure inside the cavern and the storage temperature of liquefied natural gas under pressurized storage conditions, as well as the temperature of the outer contact surface of the insulation layer, and determine the thickness of the insulation layer through thermodynamic calculations based on the evaporation loss requirements. A water supply tunnel and water supply hole are provided above the storage cavern, and a drainage tunnel and drainage hole are provided below the storage tank and the storage cavern; The efficiency of the groundwater control process was verified through multi-stage pumping and drainage tests, and the borehole layout in inefficient areas was optimized. Control the drainage until the fissure water is drained to the target state; The process involves storing liquefied natural gas and extending the freezing zone to the target isotherm, stopping drainage, and forming the freezing zone.

[0007] In some embodiments, the selection of rock mass for excavating tunnels to form liquefied natural gas storage chambers includes: The storage site is selected based on the distribution of natural gas users, the location of gas pipelines, or the location of liquefied natural gas terminals; Ensure that the geological conditions of the reservoir site meet the following requirements: no regional fault zones, uniaxial compressive strength of rock mass ≥30MPa, and permeability coefficient <10. -7 Geological conditions at m / s; The tunnel is excavated within the rock mass of the reservoir site, which meets the geological conditions described above, and a sealing layer, an insulation layer, and a concrete lining layer are installed in layers to form the storage cavern for storing the liquefied natural gas.

[0008] In some embodiments, the provision of a water replenishment tunnel and water replenishment hole above the storage chamber includes: At least two water supply tunnels and multiple water supply holes are provided within a range of 15-25 meters above the storage chamber. The diameter of each water replenishment hole is 90-110 mm, and the depth of each water replenishment hole is less than or equal to 100 m. Multiple water replenishment holes are staggered at intervals of 10-15 m, and a rock mass blank area of ​​more than or equal to 2 m is reserved between adjacent water replenishment holes.

[0009] In some embodiments, the provision of drainage tunnels and drainage holes below the storage tank and the storage chamber includes: At least two external drainage tunnels shall be constructed within a range of 10-15 meters below the storage tank; An internal drainage tunnel is provided below the storage chamber; The external drainage tunnel and the internal drainage tunnel are connected by multiple drainage holes, and the multiple drainage holes are connected to one internal drainage tunnel and two external drainage tunnels with a slope of greater than or equal to 1%.

[0010] In some embodiments, the method further includes: Multiple upper and lower drainage holes are provided within a 10-meter radius around the storage chamber. Each of the above and below drainage holes includes an upper drainage hole and a lower drainage hole. The upper drainage hole is drilled from the water replenishment tunnel, and the lower drainage hole is drilled from the drainage tunnel. The spatial overlap depth of the multiple above and below drainage holes is greater than or equal to 5 meters.

[0011] In some implementations, the verification of the efficiency of the groundwater control process through multi-stage pumping and drainage tests includes: Control the closure of all boreholes to measure the initial water head of the groundwater, with a measurement cycle of 3-4 days; The system controls the opening of some boreholes to drain water and tests the drainage efficiency. Specifically, the upward-facing boreholes are controlled to use gravity drainage, and the downward-facing boreholes are controlled to activate submersible pumps. Control the opening of all boreholes to drain water and verify the drainage capacity; The control system simulates heavy rain conditions by injecting water into the water replenishment tunnel, and tests the maximum drainage capacity.

[0012] In some embodiments, controlling drainage until the fissure water is drained to the target state includes: Drainage is controlled until the fissure water is drained to a state where the groundwater level drops to a predetermined depth below the cavern floor, wherein the predetermined depth ranges from 8 to 10 meters.

[0013] In some embodiments, storing liquefied natural gas and extending the freeze zone to the target isotherm, stopping drainage, and forming the freeze zone includes: The liquefied natural gas is stored; After storing the liquefied natural gas, the location of the frozen zone is detected by azimuth measurement until the frozen zone extends to the target isotherm, at which point the drainage is stopped to restore groundwater and form the frozen zone.

[0014] According to a second aspect of this application, a control system for the frozen zone of fractured surrounding rock in an underground natural gas storage facility is provided, comprising: The storage construction module is used to select rock mass excavation tunnels to form liquefied natural gas storage chambers, and to use the freezing ring formed by the freezing of water in the surrounding rock fissures as a sealing structure; The parameter setting module is used to set the storage pressure inside the cave and the storage temperature of liquefied natural gas under pressurized storage conditions, as well as the temperature of the outer contact surface of the insulation layer, and to determine the thickness of the insulation layer through thermodynamic calculations based on the evaporation loss requirements. A circulation layout module is used to set up a water replenishment tunnel and water replenishment hole above the storage cavern, and to set up a drainage tunnel and drainage hole below the storage tank and the storage cavern; The efficiency verification module is used to verify the efficiency of the groundwater control process through multi-stage pumping and drainage tests, and to optimize the borehole layout in inefficient areas. The construction preparation module is used to control drainage until the fissure water is drained to the target state; A dynamic control module is used to store liquefied natural gas and extend the freezing zone to the target isotherm, stop drainage, and form the freezing zone.

[0015] In some embodiments, the storage cavern includes, from the inside out, a sealing layer, an insulation layer, a concrete lining layer, the freezing ring, and the surrounding rock; The storage pressure inside the storage chamber ranges from 1 MPa to 3 MPa, the storage temperature for liquefied natural gas ranges from -120°C to -100°C, and the temperature of the outer contact surface of the insulation layer ranges from -50°C to -30°C.

[0016] The beneficial effects of the method and system for regulating the frozen zone of fractured surrounding rock in underground natural gas storage according to the embodiments of this application include at least the following: This application embodiment forms a natural sealing barrier through rock tunnels and utilizes the self-expansion property of fracture water upon freezing to create an adaptive freezing zone, significantly improving the structural stability of the storage facility. Simultaneously, it reduces sensitivity to geological conditions, allowing for flexible site selection in stable rock strata areas, overcoming the geographical limitations of traditional storage facilities. By combining pressurized storage with optimized temperature gradient settings, the temperature difference between the inside and outside of the tunnel is effectively reduced, minimizing cold energy loss. The insulation layer thickness is dynamically calculated based on evaporation loss requirements, precisely balancing insulation performance and economy, reducing long-term operational energy consumption from the source. A highly efficient hydraulic control network is formed through upper and lower partitioned water supply and drainage tunnels and boreholes (upper water supply, lower drainage). The staggered borehole design ensured the integrity of the rock mass structure, and spatial collaborative control enabled the directional flow of fissure water, providing a foundation for the dynamic evolution of the frozen zone. Multi-stage pumping and drainage tests accurately identified inefficient areas, and targeted drilling increased system reliability. Dynamic optimization design ensured efficient groundwater drainage during construction and precise replenishment during operation, balancing engineering safety and long-term sealing requirements. Phased drainage control enabled gradual drainage of fissure water, creating a dry environment for cavern construction. After storage, combined with frozen end monitoring data, the replenishment and drainage system was activated and deactivated according to location, promoting the directional infiltration of groundwater into the cooling rock mass to form a complete frozen zone, achieving dynamic and precise control of the sealing structure. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the method for controlling the frozen zone of fractured surrounding rock in an underground natural gas storage facility according to an embodiment of this application. Figure 2 This is a schematic diagram of the structure of an underground cryogenic liquefied natural gas storage facility according to an embodiment of this application; Figure 3 This is a graph showing the boiling point and pressure of liquefied natural gas in a saturated state according to an embodiment of this application. Figure 4 This is a temperature field simulation cloud map of cryogenic storage of liquefied natural gas at ambient pressure, according to an embodiment of this application. Figure 5 This is a temperature field simulation cloud map of liquefied natural gas stored at low temperature and pressure, as described in an embodiment of this application. Figure 6 This is a schematic diagram of the structure of the groundwater control system for a cryogenic liquefied natural gas storage facility according to an embodiment of this application; Figure 7 This is a schematic diagram of the first step of freeze zone control in an embodiment of this application; Figure 8 This is a schematic diagram of the second step of freeze zone adjustment in an embodiment of this application; Figure 9 This is a schematic diagram of the third step of freeze zone adjustment in an embodiment of this application; Figure 10 This is a schematic diagram of the fourth step of freeze zone adjustment in an embodiment of this application; Figure 11 This is a schematic diagram of the fifth step of freeze zone adjustment in an embodiment of this application; Figure 12 This is a schematic diagram of the sixth step of freeze zone adjustment in an embodiment of this application; Figure 13 This is a schematic diagram of the control system for the frozen zone of fractured surrounding rock in an underground natural gas storage facility, according to an embodiment of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0019] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0020] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0021] In the description of the embodiments of the present invention, it should be noted that the terms "inner", "outer", "upper", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0022] This application discloses a method for controlling the frozen zone of fractured surrounding rock in underground natural gas reservoirs. This method is based on the method for controlling the frozen zone of fractured surrounding rock in underground natural gas reservoirs. (See attached document.) Figure 1 As shown, the method includes steps 110-160.

[0023] Step 110: Select a rock mass to excavate a tunnel to form a storage cavern for liquefied natural gas (hereinafter referred to as the cavern), and use the frozen ring formed by the freezing of water in the surrounding rock fissures as a sealing structure.

[0024] In this application, the storage cavern is the basic physical structure of the storage tank, forming a direct space for liquefied natural gas through the sealing and insulation material of the rock tunnel lining; while the storage tank of this application is a complete engineering system including the main cavern body, the groundwater control system, and the freeze zone control system.

[0025] One of the objectives of this step in the application is to select a suitable location for an underground cryogenic liquefied natural gas (LNG) storage facility. The criteria for determining suitability include whether user needs are met, geological conditions, and supporting infrastructure. For example, this can be achieved by excavating tunnels within the rock mass and lining the tunnel surfaces with insulation, sealing, and other materials to store cryogenic liquefied natural gas (LNG) underground.

[0026] In addition, the location of underground cryogenic liquefied natural gas (LNG) storage facilities can be determined by comprehensively considering factors such as the needs of natural gas users, the source of LNG, and transportation conditions. Typically, they are located in areas with a high concentration of users, reliable gas pipeline networks, or near large LNG terminals.

[0027] In some embodiments, the selection of rock mass excavation tunnels to form liquefied natural gas storage caverns includes: selecting a storage site based on the distribution of natural gas users, gas pipeline networks, or the location of liquefied natural gas terminals; ensuring that the geological conditions of the storage site meet the requirements of no regional fault zones, uniaxial compressive strength of rock mass ≥30MPa, and permeability coefficient <10. -7 The geological conditions of the reservoir site are met; the tunnel is excavated in the rock mass of the reservoir site that meets the geological conditions and a sealing layer, an insulation layer and a concrete lining layer are installed in layers to form the storage cavern for storing the liquefied natural gas.

[0028] For example, the geological conditions for selecting sites for underground cryogenic liquefied natural gas (LNG) storage facilities typically need to meet the following requirements: no regional fault zones pass through the storage site area, there are few fault fracture zones, the fault displacement is small, and it has no impact on the safety of the storage facility; the rock strata are stably distributed, and the seismic intensity is less than 7 degrees; the rock has high strength and quality, and the uniaxial compressive strength is usually higher than 30 MPa in most areas; the rock mass has low permeability, and the permeability coefficient is usually less than 10 in most areas. -7 m / s. (See attached table) Figure 2 The diagram shows the construction structure of an underground cryogenic liquefied natural gas storage facility. The excavated cavern is constructed from the inside out with a sealing layer, an insulation layer, a concrete lining layer, a freezing zone, and surrounding rock.

[0029] In some embodiments, the freezing ring of this application is an important sealing structure for cryogenic liquefied natural gas. Because the interior of the cavern stores cryogenic liquefied natural gas, even with insulation in the tank wall structure, groundwater will continuously flow from warmer to cooler areas and freeze under the influence of temperature gradients. The water in the fissures freezes, increasing in volume by 1.09 times and causing frost heave, which in turn causes the fissures to expand and form a freezing ring. The freezing ring is a crucial sealing structure for underground cryogenic liquefied natural gas storage facilities.

[0030] Step 120: Set the storage pressure inside the cavern and the storage temperature of liquefied natural gas under pressurized storage conditions, and set the temperature of the outer contact surface of the insulation layer. Based on the evaporation loss requirements, determine the thickness of the insulation layer through thermodynamic calculations.

[0031] In some implementations, to reduce cooling energy consumption and improve storage efficiency, the storage pressure inside the underground cryogenic liquefied natural gas (LNG) storage cavern is set at 1 MPa-3 MPa, the LNG storage temperature inside the cavern is set at -120 to -100°C, and the temperature of the outer contact surface of the insulation layer is set at -50°C to -30°C. Based on the requirements of evaporation loss rate (BOR), leakage and insulation performance are balanced through thermodynamic calculations to ultimately determine the thickness of the insulation layer. It is worth noting that the above parameters can be calculated and determined based on the energy consumption limits for actual applications to determine the working pressure, storage temperature, contact surface temperature, and insulation layer thickness of the LNG cavern.

[0032] According to relevant research in the embodiments of this application, if the underground cryogenic liquefied natural gas storage facility adopts a cryogenic atmospheric pressure storage mode, the storage temperature of the liquefied natural gas in the cave is -162°C and the storage pressure is basically atmospheric pressure. Due to the convective heat transfer effect, the cold energy dissipation of the freezing zone is relatively serious, initially even reaching 12kW / d, and the freezing zone is very large, with a diameter even exceeding 8 meters.

[0033] This application embodiment achieves safe storage of cryogenic liquefied natural gas at higher temperatures by employing a pressurized storage mode, thereby significantly reducing system energy consumption. The theoretical basis of this design lies in the physical property that the boiling point of methane, the main component of cryogenic liquefied natural gas, increases with increasing pressure, as shown in the following relationship: Figure 3 As shown in the figure, at atmospheric pressure (approximately 0.1 MPa), the boiling point of methane is approximately -162°C, which is the typical storage temperature for cryogenic liquefied natural gas (LNG). According to the curve shown, when the storage pressure inside the cavern is increased to 3 MPa, the boiling point of methane correspondingly rises to approximately -100°C. This means that at this pressure, maintaining the cryogenic LNG at -100°C or higher effectively prevents boiling. Therefore, this invention sets the storage temperature to -100°C, reducing the temperature difference between the cryogenic LNG and the surrounding rock environment from over 160°C to approximately 100°C. This reduction in temperature difference directly decreases the heat flux density transferred to the cavern through the insulation layer, fundamentally reducing the evaporation loss (BOR) of the cryogenic LNG. This not only lowers the extreme requirements for the insulation performance of the insulation layer but also significantly reduces the reliquefaction energy consumption required to handle the evaporated gas. Furthermore, the controllable freezing zone reduces the cold energy loss from surrounding rock cooling, improving the overall energy efficiency and construction economy of the storage facility from multiple dimensions.

[0034] See attached document Figures 4-5 As shown in the figure, this application embodiment further models and compares the temperature distribution of the storage under different storage conditions. As can be seen from the figure, after 90 days of storage at normal pressure and low temperature, the 0°C isotherm of the freezing zone expands to about 8 meters, while after 90 days of storage at low temperature and pressure, the 0°C isotherm of the freezing zone expands to about 3 meters.

[0035] In this embodiment of the application, after using a pressure of 3MPa for storage, the storage temperature of liquefied natural gas in the cave is -100℃. Considering the frost heave damage to the concrete lining layer and the surrounding rock layer, the temperature of the outer contact surface of the insulation layer is further set to -40℃.

[0036] In one exemplary embodiment, the thickness of the insulation layer is ultimately determined by balancing leakage and heat transfer performance through thermodynamic calculations based on the required evaporation loss rate.

[0037] For example, in a specific embodiment, the required evaporation loss rate for the underground cryogenic liquefied natural gas (LNG) storage facility can be clearly defined first. Typically, the required evaporation loss rate for surface LNG storage tanks is between 0.05% and 0.15%, but can also be determined based on the construction scale and economic requirements of the underground cryogenic LNG storage facility. This embodiment is designed according to an evaporation loss rate limit of 0.1% (i.e., daily evaporation not exceeding 0.1% of the storage volume), and the heat leakage limit is calculated accordingly to derive the insulation layer thickness. The specific calculation process includes: first, calculating the volume V of the cryogenic LNG storage facility (V = 10 × 10⁻⁶). 4 m 3); secondly, the contact surface temperature T 接触面 The temperature was set to -40℃ and the temperature of the liquefied natural gas inside the cave was T. 液化天然气 Set to -100℃ and measure the density ρ of liquefied natural gas. 液化天然气 (ρ) 液化天然气 =450kg / m 3 ) and determination of latent heat of vaporization L v (L) v =510kJ / kg= 51×10 4 J / kg); and then the thickness of the insulation layer is obtained based on the calculated mass flow rate and heat leakage limit.

[0038] For example, calculating mass flow rate includes calculating daily evaporation and converting daily evaporation into mass flow rate Q. evap For example, daily evaporation = BOR × V / 100 = 100m³ 3 / d; converted to mass flow rate is Q. evap = 100m 3 / d×450kg / m 3 =45000kg / d.

[0039] For example, calculating the heat leakage limit includes: Calculate the heat input Q corresponding to the evaporation rate. in =Q evap ×L v =45000 kg / d × 510000 J / kg; After further standardizing the time unit to seconds, Q in =45000×510000 / 86400≈265625W.

[0040] For example, the insulation layer thickness d is derived based on the following formula: ; Where d is the thickness of the insulation layer, in meters; The temperature difference between the inside and outside of the insulation layer of a cryogenic liquefied natural gas storage facility; The unit is K, which is 60K in this embodiment; k is the thermal conductivity, with the unit being W / (m·K). The polyurethane foam insulation structure used in this embodiment has a thermal conductivity of 0.015 W / (m·K); A is the surface area of ​​the underground cavern, which is also the total heat dissipation area, with the unit being m². 2 In this embodiment, it is approximately 50,000m 2 Q in This represents the heat input corresponding to the evaporation rate, in W. In this embodiment, it is calculated to be 265625 W.

[0041] In one exemplary embodiment, ,in, These are the contact surface temperature and the liquefied natural gas temperature, respectively.

[0042] In summary, the insulation layer thickness d in this embodiment is calculated as follows: .

[0043] In addition, this embodiment of the application also considers the uncertainties such as material aging and construction errors, and the preferred safety margin is 1.2. Finally, the thickness of the insulation layer in this embodiment is 200 mm.

[0044] Step 130: A water replenishment tunnel and water replenishment hole are provided above the storage cavern, and a drainage tunnel and drainage hole are provided below the storage tank and the storage cavern.

[0045] In some embodiments, setting up water replenishment tunnels and water replenishment holes above the storage cavern includes: setting up at least two water replenishment tunnels and multiple water replenishment holes within a range of 15-25 meters above the storage cavern, wherein the diameter of each water replenishment hole is in the range of 90-110 mm, and the depth of each water replenishment hole is less than or equal to 100 meters; the multiple water replenishment holes are staggered at intervals of 10-15 meters, and a rock mass blank area of ​​more than or equal to 2 meters is maintained between adjacent water replenishment holes.

[0046] In some embodiments, the provision of drainage tunnels and drainage holes below the storage tank and the storage cavern includes: providing at least two external drainage tunnels within a range of 10-15 meters below the storage tank (see attached diagram). Figure 6-12 (As shown in the attached diagram); an internal drainage tunnel is constructed below the storage chamber (see attached diagram). Figure 6-12 (As shown in the diagram), the external drainage tunnel and the internal drainage tunnel are connected by multiple drainage holes, which connect one internal drainage tunnel and two external drainage tunnels with a slope of ≥1%. The connection between the internal and external drainage tunnels is a systematic hydraulic connection achieved through a network of drainage holes. Specifically, the drainage hole arrangement logic includes, for example, one internal drainage tunnel located below the storage cavern primarily for directly collecting seepage water from the cavern foundation, while two external drainage tunnels located around the storage area collect regional groundwater; multiple drainage holes are arranged radially (slope ≥1%), extending from the internal drainage tunnel in different directions and connecting to the two external drainage tunnels, forming a branching network of "center-to-periphery flow". Water flow path design includes, for example, the construction of drainage holes in the rock mass by inclined drilling (the slope ensures gravity flow), so that water in the internal tunnels can be naturally guided to the external tunnels through the boreholes; the borehole connection points adopt a branching or manifold design (such as setting up a water collection pit in the internal tunnels and connecting each external tunnel through the borehole branches) to ensure that there are no dead corners in hydraulic coverage.

[0047] In some embodiments, the method further includes: setting up a plurality of upper and lower drainage holes within a 10-meter radius around the storage cavern, wherein each upper and lower drainage hole includes an upper drainage hole and a lower drainage hole, the upper drainage hole being drilled from the water replenishment tunnel, the lower drainage hole being drilled from the drainage tunnel, and the spatial overlap depth of the plurality of upper and lower drainage holes being greater than or equal to 5 meters.

[0048] In one exemplary embodiment, the cryogenic liquefied natural gas storage facility utilizes a groundwater control system to regulate the freezing zone. (See attached diagram.) Figure 6 As shown, based on engineering experience and considering drainage efficiency, at least two water replenishment tunnels are typically installed at an elevation of 15-25 meters above the cryogenic liquefied natural gas (LNG) cavern. Water replenishment holes are drilled between the replenishment tunnels, with a diameter of 90-110 mm and a length not exceeding 100 meters. The spacing between the water replenishment holes is usually between 10-15 meters, and they should be staggered. A minimum of 2 meters of rock mass clearance should be left between adjacent water replenishment holes to avoid excessive rock mass damage caused by complete penetration. At least two drainage tunnels are installed at an elevation of 10-15 meters below the cryogenic LNG storage, and one internal drainage tunnel is installed below the cryogenic LNG cavern to divert groundwater outside the concrete lining layer of the cavern to the internal drainage tunnel. Simultaneously, one external drainage tunnel is constructed on each side of the cryogenic liquefied natural gas (LNG) cavern. The internal and external drainage tunnels are connected by drainage holes with a slope of no less than 1%, the final slope of which can be calculated based on the specific tunnel elevation. Additionally, upper and lower drainage holes are installed within a 10-meter radius around the cryogenic LNG storage facility. The upper drainage holes are drilled from the upper water replenishment tunnel, and the lower drainage holes are drilled from the lower drainage tunnel. The spatial overlap depth of the upper and lower drainage holes should preferably exceed 5 meters to achieve efficient groundwater drainage during construction.

[0049] Step 140: Verify the efficiency of the groundwater control process through multi-stage pumping and drainage tests, and optimize the borehole layout in inefficient areas.

[0050] In some implementations, the efficiency of the groundwater control process is verified through a multi-stage pumping and drainage test, which includes: controlling the closure of all boreholes to measure the initial water head of the groundwater for a period of 3 to 4 days, the purpose of which is to measure during the period of stable seepage; controlling the opening of some boreholes to drain water and verify the drainage efficiency, wherein the upward boreholes are controlled to use gravity drainage and the downward boreholes are controlled to use submersible pumps; controlling the opening of all boreholes to drain water and verify the drainage capacity; and controlling the injection of water into the water replenishment tunnel to simulate heavy rain conditions and test the maximum drainage capacity.

[0051] For example, in a specific implementation process, the efficiency of the groundwater control process is verified through pumping and drainage tests to ensure the dual objectives of draining groundwater during construction and replenishing groundwater during operation. In areas with low efficiency, the drilling density of drainage holes should be increased, and the final layout scheme of the groundwater control system is determined. This application's groundwater control process also fully considers the seepage characteristics of natural groundwater systems and combines numerical simulation, theoretical calculations, and engineering practice experience, adopting a dynamic design and dynamic construction model. The final groundwater control system scheme should be determined based on the pumping and drainage system tests.

[0052] For example, the test of the pumping and drainage process in this application satisfies the following requirements: verifying the hydraulic connectivity of the groundwater control system, detecting potential uncontrolled hydrogeological areas, determining whether to add additional pumping and drainage holes to improve system efficiency, and ensuring the dual objectives of draining groundwater during construction and replenishing groundwater during operation.

[0053] For example, as shown in Table 1 below, the test method for the pumping and drainage system consists of four stages. The first stage is to measure the initial water head to determine the changes in water head at each well; the second and third stages are to check the pumping and drainage efficiency; and the fourth stage is to simulate drainage conditions during heavy rain to evaluate the maximum drainage capacity of the drainage system.

[0054] Table 1: Test Stages of the Pumping and Drainage System

[0055] In the experiment shown in Table 1 above, the efficiency of the groundwater control process was judged based on the seepage volume in the low-temperature liquefied natural gas cavern, the changes in pressure and flow rate of each borehole, and the changes in seepage points in the cavern. The groundwater control process was optimized as needed, and seepage prevention and reduction measures such as grouting and sealing were also appropriately added.

[0056] For example, the phased pumping and drainage process test of this application satisfies the comprehensive judgment of the following multiple principles: if the pressure of the closed drainage hole in the second stage is lower than that in the first stage, it indicates that the working efficiency of the adjacent opened drainage hole is high and no additional hole is needed for the time being; otherwise, it indicates that the working efficiency of the opened drainage hole is low and an additional hole is needed to improve the local drainage efficiency; if the pressure of each drainage hole drops to zero in the third stage, it indicates that the working efficiency is high and no additional hole is needed for the time being; otherwise, an additional hole should be added near a drainage hole that still has pressure to improve the local drainage efficiency; if the pressure of each drainage hole drops to zero in the fourth stage, it indicates that the working efficiency is high and no additional hole is needed for the time being; otherwise, an additional hole should be added near a drainage hole that still has pressure to improve the local drainage efficiency; if the flow rate of a water supply hole above the reservoir in the fourth stage is significantly lower than the average water supply flow rate, it should be considered to add a water supply hole nearby to improve the local water supply capacity; after each hole is drilled and filled, a simple local pumping and drainage system test should be carried out to verify the local pumping and drainage efficiency. This application enables the layout of a groundwater control system (used to execute the groundwater control process of an underground cryogenic liquefied natural gas storage facility) through the above steps.

[0057] Step 150: Control the drainage until the fissure water is drained to the target state.

[0058] In some embodiments, controlling drainage until the fissure water is drained to the target state includes controlling drainage until the fissure water is drained to a state that lowers the groundwater level to a predetermined depth below the cavern floor, wherein the predetermined depth ranges from 8 to 10 meters.

[0059] Step 160: Store the liquefied natural gas and extend the frozen zone to the target isotherm, stop draining and form the frozen zone.

[0060] In some embodiments, storing liquefied natural gas and extending the frozen zone to the target isotherm, stopping drainage, and forming the frozen zone includes: storing the liquefied natural gas; performing azimuth detection of the location of the frozen zone after storing the liquefied natural gas, and stopping drainage after extending the frozen zone to the target isotherm to restore groundwater and form the frozen zone.

[0061] Specifically, this application regulates the freezing zone through a groundwater control system. In the early stages of construction, drainage is initiated to deplete the fissure water in the rock mass, creating a dry environment for construction. Once the cryogenic liquefied natural gas is stored in the cavern tank and the freezing zone has advanced to near the 0°C isotherm, drainage is stopped and groundwater is restored to form the freezing zone.

[0062] For example, the construction steps for regulating the frozen zone using a groundwater control system can be divided into the following steps 151-156.

[0063] Step 151, refer to the appendix Figure 7As shown, before constructing the cryogenic liquefied natural gas (LNG) cavern, groundwater in the surrounding rock is drained, lowering the groundwater level to 8-10 meters below the cavern floor. Drainage can be achieved by installing dewatering wells on the surface, or by converting the function of the upper water supply tunnels and wells into pumping systems, using pumps to remove water from the surrounding rock fissures.

[0064] Step 152, refer to the appendix Figure 8 As shown, during the excavation of the cryogenic liquefied natural gas cavern, groundwater in the surrounding rock was continuously drained to reduce the risk of cavern excavation.

[0065] Step 153, refer to the appendix Figure 9 As shown, after the civil construction of the cryogenic liquefied natural gas cavern is completed, the tank wall sealing system and the inlet and outlet shaft pipelines are installed. During this period, the groundwater in the surrounding rock of the cryogenic liquefied natural gas cavern is still drained to reduce the damage of groundwater static pressure to the surrounding rock and support structure.

[0066] Step 154, refer to the appendix Figure 10 As shown, cryogenic liquefied natural gas (LNG) begins to be stored inside the cavern. From inside the cavern, the freezing point continuously conducts outwards, and combined with monitoring data from surrounding temperature sensors, this continues until the freezing point reaches near the preset 0°C isotherm. During this period, groundwater in the surrounding rock of the cryogenic LNG cavern is continuously drained to prepare for the subsequent formation of the freeze zone.

[0067] Step 155, refer to the appendix Figure 11 As shown, due to the uneven heat conduction, when the monitoring data in all directions around the low-temperature liquefied natural gas storage facility show that the freezing point has been transmitted to the vicinity of the 0℃ isotherm in this location, the drainage system in that location is stopped, and the water replenishment hole above is opened. Local groundwater in this location slowly seeps into the cooled rock mass and forms a freezing zone.

[0068] Step 156, refer to the appendix Figure 12 As shown, once the groundwater levels in all directions have recovered and a freezing zone has formed around the cavern, the entire drainage system will be shut down.

[0069] During liquefied natural gas storage, the drainage phase may last for several months or a year, depending on the thermal properties of the surrounding rock and the local hydrogeological characteristics.

[0070] This application embodiment forms a natural sealing barrier through rock tunnels and utilizes the self-expansion property of fracture water upon freezing to create an adaptive freezing zone, significantly improving the structural stability of the storage facility. Simultaneously, it reduces sensitivity to geological conditions, allowing for flexible site selection in stable rock strata areas, overcoming the geographical limitations of traditional storage facilities. By combining pressurized storage with optimized temperature gradient settings, the temperature difference between the inside and outside of the tunnel is effectively reduced, minimizing cold energy loss. The insulation layer thickness is dynamically calculated based on evaporation loss requirements, precisely balancing insulation performance and economy, reducing long-term operational energy consumption from the source. A highly efficient hydraulic control network is formed through upper and lower partitioned water supply and drainage tunnels and boreholes (upper water supply, lower drainage). The staggered borehole design ensured the integrity of the rock mass structure, and spatial collaborative control enabled the directional flow of fissure water, providing a foundation for the dynamic evolution of the frozen zone. Multi-stage pumping and drainage tests accurately identified inefficient areas, and targeted drilling increased system reliability. Dynamic optimization design ensured efficient groundwater drainage during construction and precise replenishment during operation, balancing engineering safety and long-term sealing requirements. Phased drainage control enabled gradual drainage of fissure water, creating a dry environment for cavern construction. After storage, combined with frozen end monitoring data, the replenishment and drainage system was activated and deactivated according to location, promoting the directional infiltration of groundwater into the cooling rock mass to form a complete frozen zone, achieving dynamic and precise control of the sealing structure.

[0071] This application also discloses a control system for the frozen zone of fractured surrounding rock in underground natural gas storage. (See attached document.) Figure 13 As shown, the system includes: a storage construction module 1310, a parameter setting module 1320, a circulation layout module 1330, an efficiency verification module 1340, a construction preparation module 1350, and a dynamic control module 1360.

[0072] The storage construction module 1310 is used to select a rock mass to excavate a tunnel to form a storage cavern for liquefied natural gas, and to use the frozen ring formed by the freezing of water in the surrounding rock fissures as a sealing structure.

[0073] The parameter setting module 1320 is used to set the storage pressure inside the cavern and the storage temperature of liquefied natural gas under pressurized storage conditions, as well as the temperature of the outer contact surface of the insulation layer, and to determine the thickness of the insulation layer through thermodynamic calculations based on the evaporation loss requirements.

[0074] The circulation layout module 1330 is used to set up a water replenishment tunnel and water replenishment hole above the storage cavern, and to set up a drainage tunnel and drainage hole below the storage cavern and the storage tank.

[0075] The efficiency verification module 1340 is used to verify the efficiency of the groundwater control process through multi-stage pumping and drainage tests, and to optimize the borehole layout in inefficient areas.

[0076] Construction preparation module 1350 is used to control drainage until the fissure water is drained to the target state.

[0077] The dynamic control module 1360 is used to store liquefied natural gas and extend the freezing zone to the target isotherm, stop drainage and form the freezing zone.

[0078] In some embodiments, the storage chamber includes, from the inside out, a sealing layer, an insulation layer, a concrete lining layer, the freezing zone, and the surrounding rock.

[0079] In some embodiments, the storage pressure inside the storage chamber ranges from 1 MPa to 3 MPa, the storage temperature for liquefied natural gas ranges from -120°C to -100°C, and the temperature of the outer contact surface of the insulation layer ranges from -50°C to -30°C.

[0080] This application addresses the current situation where existing gas storage technologies mainly focus on construction types such as surface membrane tanks, salt cavern gas storage facilities, and depleted gas reservoir storage facilities. Surface membrane tanks are costly and small in scale, while salt cavern gas storage facilities and depleted gas reservoir storage facilities are greatly limited by geological structure, geographical resources, and location, making it difficult to meet the needs of large-scale underground gas storage construction in severely gas-deficient areas of East and South China. This application creates a dynamic evolution and control system for the frozen zone of fractured surrounding rock in cryogenic liquefied natural gas (LNG) storage facilities. This system has significant advantages in both time and spatial scales, representing the optimal approach for long-term, large-scale gas storage and is of great significance. This application also solves the problems of existing gas storage and low-temperature LNG storage technologies. The existing methods for storing cryogenic liquefied natural gas (LNG) suffer from limitations such as small scale, high cost, and constraints related to geological conditions and geographical location. This invention effectively addresses the challenges of sealing and stability in cryogenic LNG storage facilities, particularly the difficulty in effectively controlling the 0°C isotherm. It presents a dynamic evolution and control system for the frozen zone in fractured surrounding rock of cryogenic LNG storage facilities. The system details the functional design of various individual components, from site selection, working pressure and temperature settings, insulation layer calculations, and the frozen zone control system, to crucial auxiliary designs such as efficiency testing and construction procedures for the groundwater control system. This system requires only the selection of materials with moderate strength and relatively high stability. High underground space can meet all construction requirements, has extremely high tolerance for geological conditions, and is widely applicable. This application's embodiment optimizes key parameters such as underground storage pressure, liquefied natural gas storage temperature, and contact surface temperature, shortening the 0℃ isotherm range to reduce cold energy consumption and improve storage efficiency. By setting up a groundwater control system and dividing it into a six-step method for regulating the freezing zone, it achieves precise control of the dynamic evolution of the freezing zone, effectively solving the sealing and stability problems of low-temperature liquefied natural gas storage facilities caused by the difficulty in effectively controlling the 0℃ isotherm. The device parameters can be appropriately adjusted according to actual working conditions, offering significant optimization potential. The embodiments can be applied not only to liquefied natural gas (LNG) storage but also to cryogenic liquefied petroleum gas (LPG) storage, which is of great value for the comprehensive utilization of space in natural gas reserves and the transformation of energy structure. The embodiments of this application, through the comprehensive use of various underground structures, individual units and materials, have the advantages of large scale, strong targeting, high reliability, convenient operation, low cost and wide applicability. They can be quickly applied to the construction of underground space for comprehensive utilization of LNG and LPG storage facilities, effectively reducing the storage cost of cryogenic LNG, improving the economic benefits of storage construction, and thus promoting the healthy development of the gas storage and underground space comprehensive utilization industry chain.

[0081] This application also discloses an electronic device that integrates the above-mentioned control system for the frozen zone of fractured surrounding rock in underground natural gas storage, for implementing the above-mentioned control method for the frozen zone of fractured surrounding rock in underground natural gas storage.

[0082] This application has the advantages of high relevance, high reliability, convenient operation, low cost, and wide applicability. It solves the problems of small scale, high cost, and geographical limitations of existing liquefied natural gas (LNG) storage facilities. It has invented a complete system solution, from the functional design of different individual units such as the site selection of cryogenic LNG storage facilities, working pressure and temperature setting, insulation layer calculation, and freezing zone control system, to important auxiliary designs such as the efficiency test and construction steps of the groundwater control system. It only requires the selection of underground space with moderate strength and high stability to meet all construction requirements. It has extremely high tolerance for geological conditions and a wide range of applications. This application provides a complete set of technologies and solutions for the dynamic evolution and regulation of the frozen zone in fractured surrounding rock of cryogenic liquefied natural gas (LNG) storage facilities. This promotes the long-term, large-scale storage of natural gas and LNG and ensures energy security. Based on the construction principles of cryogenic LNG storage facilities and the functional requirements of the frozen zone in cryogenic liquid storage, this application provides a complete system solution from the perspective of engineering practice. It covers the functional design of different individual units, such as the site selection of cryogenic LNG storage facilities, working pressure and temperature settings, insulation layer calculation, and frozen zone control system, as well as important auxiliary designs such as the efficiency test and construction steps of the groundwater control system. All construction requirements can be met by selecting underground spaces with moderate strength and high stability. It has a very high tolerance for geological conditions and is applicable to various scenarios with different engineering geology, hydrogeology, and underground engineering layouts. By integrating various underground units, structures, and devices, this method provides a large-scale, highly targeted, highly reliable, easy-to-operate, low-cost, and widely applicable approach for the dynamic evolution and regulation of the frozen zone in fractured surrounding rock of cryogenic liquefied natural gas (LNG) storage facilities. It can be rapidly applied to various natural gas storage and LNG industry chain construction projects, effectively reducing the storage costs of natural gas and LNG, improving economic efficiency, and thus promoting the healthy development of the gas storage and abandoned underground space utilization industry chain.

[0083] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of this application, and this application is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this application, and these modifications and improvements are also considered to be within the scope of protection of this application.

Claims

1. A method of regulating the frozen zone of a fracture surrounding rock of an underground natural gas reservoir, characterized in that, The method comprises the following steps: selecting a rock mass to excavate a roadway to form a storage cavern for liquefied natural gas, and taking a freezing circle formed by freezing of fissure water in surrounding rock as a sealing structure; setting a storage pressure in the cavern in a pressurized storage state and a storage temperature of liquefied natural gas, and setting a temperature of an outer contact surface of a thermal insulation layer, and determining a thickness of the thermal insulation layer based on a requirement of evaporation loss through thermodynamic calculation; providing a water supplementing roadway and water supplementing holes above the storage cavern, and providing a drainage roadway and drainage holes below the storage cavern and the storage cavern; calculating an efficiency of a groundwater control process through a multi-stage water pumping and drainage test, and optimizing drilling arrangement in a low-efficiency area; controlling drainage until fissure water is dewatered to a target state; stopping drainage and forming the freezing circle after storing liquefied natural gas and expanding the freezing circle to a target isotherm.

2. The method of claim 1, wherein, The step of selecting a rock mass to excavate a roadway to form a storage cavern for liquefied natural gas comprises the following steps: selecting a storage site according to distribution of natural gas users, a gas pipeline network or a liquefied natural gas terminal location; Ensure that the geological conditions of the library address meet the conditions of no regional fault zone, rock mass uniaxial compressive strength ≥ 30 MPa, and permeability coefficient < 10 -7 m / s excavating the roadway in a rock mass at the storage site meeting the geological conditions, and layer by layer lining a sealing layer, a thermal insulation layer and a concrete lining layer to form the storage cavern for storing the liquefied natural gas.

3. The method of claim 1, wherein, The step of providing a water supplementing roadway and water supplementing holes above the storage cavern comprises the following steps: providing at least two water supplementing roadways and a plurality of water supplementing holes in a range of 15-25 meters above the storage cavern, wherein a diameter of each of the water supplementing holes is in a range of 90-110 mm, and a depth of each of the water supplementing holes is less than or equal to 100 meters; the plurality of water supplementing holes are arranged in a staggered manner at a spacing of 10-15 meters, and a rock mass blank area in a range of greater than or equal to 2 meters is reserved between adjacent water supplementing holes.

4. The method of claim 1, wherein, The step of providing a drainage roadway and drainage holes below the storage cavern and the storage cavern comprises the following steps: providing at least two external drainage roadways in a range of 10-15 meters below the storage cavern; providing one internal drainage roadway below the storage cavern; the external drainage roadways and the internal drainage roadway are connected through a plurality of drainage holes, and the plurality of drainage holes are connected to one internal drainage roadway and two external drainage roadways at a slope of greater than or equal to 1%.

5. The method of claim 1, wherein, The method further comprises the following steps: providing a plurality of up and down drainage holes in a range of 10 meters around the storage cavern, wherein each of the up and down drainage holes comprises an upper drainage hole and a lower drainage hole, the upper drainage hole is drilled from the water supplementing roadway, and the lower drainage hole is drilled from the drainage roadway, and a spatial overlapping depth of the plurality of up and down drainage holes is greater than or equal to 5 meters.

6. The method of claim 1, wherein, The step of calculating an efficiency of a groundwater control process through a multi-stage water pumping and drainage test comprises the following steps: controlling to close all the drilling holes to measure an initial water head of the groundwater, and a measurement period is 3-4 days; controlling to open part of the drilling holes to drain water and check drainage efficiency, wherein the drilling holes upward are controlled to adopt self-flow drainage, and the drilling holes downward are controlled to use submersible pumps; controlling to open all the drilling holes to drain water and verify drainage capacity; controlling to execute a simulated heavy rain condition through water injection in the water supplementing roadway, and testing maximum drainage capacity.

7. The method of claim 1, wherein, The step of controlling drainage until fissure water is dewatered to a target state comprises the following steps: The drainage is controlled until the fissure water is dewatered to a state that the groundwater level is lowered to a predetermined depth below the floor of the cavern, wherein the predetermined depth is in a range of 8-10 meters.

8. The method of claim 1, wherein, The liquefied natural gas is stored and the freezing circle is expanded to a target isotherm, the drainage is stopped and the freezing circle is formed. The liquefied natural gas is stored. Azimuth detection of the position of the freezing circle is performed after the liquefied natural gas is stored, and the drainage is stopped after the freezing circle is expanded to the target isotherm, for recovering the groundwater and forming the freezing circle.

9. A control system for the frozen zone of fractured surrounding rock in an underground natural gas storage facility, characterized in that, It comprises: A repository construction module for selecting a rock mass excavation tunnel to form a liquefied natural gas storage cavern, and taking a freezing circle formed by freezing of fissure water in surrounding rock as a sealing structure; A parameter setting module for setting the in-cavern storage pressure and the storage temperature of liquefied natural gas in a pressurized storage state, and setting the temperature of the outer contact surface of the thermal insulation layer, and determining the thickness of the thermal insulation layer based on thermodynamic calculation according to evaporation loss requirements; A flow layout module for setting a water replenishment tunnel and a water replenishment hole above the storage cavern, and setting a drainage tunnel and a drainage hole below the repository and the storage cavern; An efficiency inspection module for testing and calculating the efficiency of the groundwater control process through multi-stage drainage test, and optimizing the drilling arrangement in low-efficiency areas; A construction preparation module for controlling the drainage until the dewatered fissure water reaches a target state; A dynamic regulation and control module for storing liquefied natural gas and expanding the freezing circle to a target isotherm, stopping the drainage and forming the freezing circle.

10. The regulation and control system of the fissure surrounding rock freezing circle of an underground natural gas repository according to claim 9, wherein The storage cavern comprises a sealing layer, a thermal insulation layer, a concrete lining layer, the freezing circle and the surrounding rock arranged from inside to outside; The in-cavern storage pressure of the storage cavern is in a range of 1-3 MPa, the storage temperature of liquefied natural gas is in a range of -120℃ to -100℃, and the outer contact surface temperature of the thermal insulation layer is in a range of -50℃ to -30℃.

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