Method and system for reconstructing a liquefied natural gas storage based on abandoned mine galleries

Abstract

The application provides a method and system for reconstructing a liquefied natural gas storage based on an abandoned mine roadway, the method comprising: selecting an abandoned mine roadway with qualified surrounding rock stability and constructing a double gas-tight barrier; transforming a section of the abandoned mine roadway into a trapezoidal structure with a preset angle and constructing a support unit based on an anchor rod, a concrete lining layer, the surrounding rock and the transformed section; laying a composite tank wall structure composed of a stainless steel membrane and an insulation layer on an inner surface of a roadway of the abandoned mine roadway, so as to provide insulation and double gas-tight barrier functions and ensure the sealing property and thermal efficiency of low-temperature liquefied natural gas storage; arranging a process operation platform on a top of a chamber of the abandoned mine roadway and arranging a pump pit below the process operation platform; and arranging an underground water control unit around the storage, so as to drain fissure water of a rock mass during a construction period and restore saturation of the rock mass to form a frozen circle during an operation period. The application solves the problem of underground construction stability of a natural gas storage.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of abandoned well roadway reconstruction, and in particular to a method and system for reconstructing a liquefied natural gas (LNG) storage based on an abandoned well roadway. BACKGROUND

[0002] At present, the demand for natural gas is growing rapidly, and the construction of natural gas storage mainly adopts two forms of depleted oil and gas reservoirs and salt caves, but their site selection is severely limited by geological conditions, and the site suitability is poor, and the construction of the gas storage is slow.

[0003] Only by rapidly promoting the construction of gas storage projects can the gap in the supply of natural gas pipeline networks be adjusted to ensure the supply of natural gas. In particular, the capacity of liquefied natural gas is insufficient, and the construction cost of new liquefied natural gas storage needs to be reduced. With the continuous growth of global natural gas utilization and the development of storage tank construction technology, the trend of large-scale liquefied natural gas storage tanks is more and more obvious, and the construction technology of a single tank with a capacity of 27x10 4 cubic meters has matured, and the largest underground storage tank has reached a capacity of 25x10 4 cubic meters, and the low-temperature underground liquefied natural gas storage as a new technology can reach a single tank capacity of one million cubic meters. Compared with the above-ground and underground storage tank forms, the underground low-temperature liquefied natural gas storage is more secure, environmentally friendly, and occupies less land, and its economic advantage is more obvious as the storage capacity increases: the investment in ground liquefied natural gas storage is about 10 yuan / cubic meter; the investment in gas reservoir type storage is about 8 yuan / cubic meter; and the investment in underground liquefied natural gas storage is expected to be reduced to 6 yuan / cubic meter. With the increasing number of liquefied natural gas receiving stations in coastal areas, the available port resources are becoming more and more limited, and the low-temperature underground liquefied natural gas storage utilizes abandoned mine resources, especially in inland areas where mines are widely distributed, and the range of site selection is wide, and the development prospect is broad. However, this technology is still in the blank field.

[0004] At present, the reconstruction of low-temperature liquefied natural gas storage based on abandoned well roadways is still in its infancy at home and abroad, and there is no mature construction case or core technology. Therefore, it is urgent to create a construction device for reconstructing low-temperature liquefied natural gas storage based on abandoned well roadways, which provides a suitable optimization scheme for the use of a large amount of abandoned underground space in areas with the most concentrated gas consumption and difficult gas storage construction. SUMMARY

[0005] The present application proposes a method and system for reconstructing a liquefied natural gas storage based on an abandoned well roadway to solve the defects of the prior art.

[0006] According to a first aspect of an embodiment of the present application, a method for reconstructing a liquefied natural gas storage based on an abandoned well roadway is provided, comprising:

[0007] selecting a waste well roadway with a surrounding rock stability meeting a standard, and constructing a double gas-tight barrier;

[0008] reforming a section of the waste well roadway into a trapezoidal structure with a preset angle, for adapting to installation requirements of a thin film material of a stainless steel membrane, and constructing a support unit based on an anchor rod, a concrete lining layer, the surrounding rock, and the reformed section, for ensuring stability of a cavern structure and construction safety;

[0009] laying a composite tank wall structure composed of a stainless steel membrane and a thermal insulation layer on an inner surface of the roadway of the waste well roadway, for providing thermal insulation and double gas-tight barrier functions and ensuring sealing and thermal efficiency of low-temperature liquefied natural gas storage;

[0010] providing a process operation platform on a top of the cavern of the waste well roadway, and providing a pump pit below the process operation platform for installing a submersible pump;

[0011] arranging an underground water control unit around the storage, for dewatering rock fissure water during a construction period and restoring rock saturation to form a permafrost during an operation period.

[0012] In some embodiments, the double gas-tight barrier includes a first layer barrier and a second layer barrier, and the constructing the double gas-tight barrier includes:

[0013] constructing the first layer barrier as a stainless steel membrane, and constructing the second layer barrier as a permafrost formed by frozen underground water;

[0014] providing a thermal insulation layer, a water-resisting layer, and a concrete lining layer between the first layer barrier and the second layer barrier.

[0015] In some embodiments, the method further includes:

[0016] providing a corrugated structure on a surface of the stainless steel membrane, a corrugation pitch of the corrugated structure being 400-700 mm.

[0017] In some embodiments, the waste well roadway with a surrounding rock stability meeting a standard is a main roadway with a gentle slope roadway, and the reforming a section of the waste well roadway into a trapezoidal structure with a preset angle includes:

[0018] performing anchor rod support construction and grouting reinforcement treatment on a support weak area of the waste well roadway, wherein anchor rod holes and grouting holes are arranged at a preset pitch and depths of the anchor rod holes and the grouting holes are greater than a cavern structure size;

[0019] performing reinforced concrete lining on the waste well roadway to generate the concrete lining layer.

[0020] In some embodiments, the slope of the gentle slope tunnel does not exceed 5%, the corner angles of the trapezoidal structure are limited to 90° and 135°, the length of the anchor bolt is 2.5 meters, the spacing between the anchor bolts is 1.5 meters × 1.5 meters, and the thickness of the concrete lining layer is not less than 100 millimeters.

[0021] In some embodiments, the insulation layer is composed of plywood, polyurethane foam, elastic sealant, and a moisture-proof layer from the inside out; the method further includes:

[0022] The moisture-proof layer is applied to the concrete wall to prevent water vapor penetration.

[0023] In some embodiments, the groundwater control unit includes an upper water replenishment subunit and a lower drainage subunit, and the deployment of the groundwater control unit around the reservoir includes:

[0024] The water supply holes of the upper water supply subunit and the drainage holes of the lower drainage subunit are arranged in a ring within a predetermined distance range around the cavern of the storage tank.

[0025] In some embodiments, the process operation platform and the tank wall structure of the pump pit that contact the liquefied natural gas are both composite tank wall structures composed of a stainless steel membrane and the insulation layer.

[0026] According to a second aspect of this application, a system for converting abandoned shafts into liquefied natural gas storage facilities is provided, comprising:

[0027] The dual-barrier construction module is used to select abandoned shafts and tunnels with acceptable surrounding rock stability and construct dual airtight barriers.

[0028] The tunnel section modification module is used to modify the cross-section of the abandoned tunnel into a trapezoidal structure with a preset angle to adapt to the installation requirements of the stainless steel membrane material, and to construct a support unit based on anchor bolts, concrete lining layer, surrounding rock and the modified cross-section to ensure the stability of the tunnel structure and construction safety.

[0029] The roadway surface paving module is used to lay a composite tank wall structure consisting of a stainless steel membrane and an insulation layer on the inner surface of the roadway in the abandoned mine roadway, in order to provide insulation and a double airtight barrier function and ensure the sealing and thermal efficiency of the cryogenic liquefied natural gas storage.

[0030] The operating platform and pump pit construction module is used to set up a process operating platform on the top of the cavern in the abandoned shaft, and to set up a pump pit for installing a submersible pump below the process operating platform.

[0031] The water control unit deployment module is used to deploy groundwater control units around the reservoir, which are used to drain the fissure water in the rock mass during the construction period and to restore the rock mass to saturation during the operation period to form a cryosphere.

[0032] In some embodiments, the system further comprises:

[0033] The integrated tank wall structure comprises the stainless steel membrane, the thermal insulation layer, the reinforced concrete lining layer and the surrounding rock arranged from inside to outside.

[0034] A gas phase pipeline and a feed pipe are used to connect the storage.

[0035] The method and system for reconstructing a liquefied natural gas storage based on an abandoned mine roadway according to the embodiments of the present application have at least the following beneficial effects:

[0036] By selecting an abandoned mine roadway with stable surrounding rock and constructing a double gas-tight barrier, the existing geological conditions can be effectively utilized to reduce the risk of building a storage, ensuring long-term structural stability and operational safety. The double sealing design of the stainless steel membrane and the ice sheet significantly improves the anti-leakage performance of the liquefied natural gas storage. By transforming the cross-section of the abandoned mine roadway into a preset angle trapezoidal structure to adapt to the installation of the stainless steel membrane, the accurate deployment and sealing integrity of the membrane material are ensured. The support unit integrates the self-stability of the surrounding rock and reinforcement measures, strengthens the support of the cavern structure, prevents collapse during construction, and ensures safety. By laying a composite tank wall structure on the inner surface of the roadway, the synergistic effect of the stainless steel membrane and the thermal insulation layer is utilized to achieve efficient thermal insulation to reduce the evaporation loss of liquefied natural gas. The double gas-tight barrier mechanism enhances the overall sealing performance, optimizes the thermal efficiency and operational reliability of the low-temperature storage environment. The process operation platform set at the top of the cavern facilitates equipment installation and maintenance operations, improving the convenience of inspection and maintenance. The pump pit below supports the stable installation of the submersible pump, ensuring the continuity and operational efficiency of the liquefied natural gas transportation process. By laying the groundwater control unit to drain fissure water during construction to create a dry construction environment, water pressure interference is reduced. During the operation period, the rock mass saturation forms an ice sheet, which utilizes the natural freezing barrier to enhance the sealing effect and reduce the long-term maintenance requirements. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 FIG. 1 is a flowchart of the method for reconstructing a liquefied natural gas storage based on an abandoned mine roadway according to the embodiments of the present application;

[0038] Figure 2 FIG. 3 is a schematic diagram of underground site selection for reconstructing a liquefied natural gas storage based on an abandoned mine roadway according to the embodiments of the present application;

[0039] Figure 3 FIG. 5 is a schematic diagram of storage construction for reconstructing a liquefied natural gas storage based on an abandoned mine roadway according to the embodiments of the present application;

[0040] Figure 4 FIG. 7 is a schematic diagram of the cross-section of the low-temperature liquefied natural gas storage of the reconstructed abandoned mine roadway according to the embodiments of the present application.

[0041] Figure 5 A structure diagram of a stainless steel film fold of an embodiment of the present application;

[0042] Figure 6 A structure diagram of a heat preservation layer of an embodiment of the present application;

[0043] Figure 7 A structure diagram of an operation platform of an embodiment of the present application;

[0044] Figure 8 A structure diagram of a system for reconstructing a liquefied natural gas storage based on abandoned mine roadway of an embodiment of the present application. DETAILED DESCRIPTION

[0045] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some but not all of the embodiments of the present application. The components of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations.

[0046] Therefore, the following detailed description of the embodiments of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed embodiments of the present application, but only represents selected embodiments of the embodiments of the present application. Based on the embodiments in the embodiments of the present application, other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the embodiments of the present application.

[0047] It can be noted that similar reference numerals and letters represent similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0048] In the description of the embodiments of the present application, it should be noted that the directions or position relationships indicated by the terms “in”, “out”, “up”, etc. are based on the directions or position relationships shown in the drawings, or the directions or position relationships in which the product of the present application is usually placed, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the indicated device or element must have a preset direction, be constructed and operated in a preset direction, and therefore cannot be understood as limiting the embodiments of the present application.

[0049] The embodiments of the present application disclose a method for reconstructing a liquefied natural gas storage based on abandoned mine roadway, which is executed by a system for reconstructing a liquefied natural gas storage based on abandoned mine roadway. Referring to FIG. 1, Figure 1 As shown in the figure, the method comprises steps 110-150.

[0050] Step 110, selecting a surrounding rock stability qualified abandoned mine roadway, and constructing a double gas-tight barrier.

[0051] The surrounding rock stability qualified abandoned mine roadway is a main roadway with a gentle slope, specifically a main trunk roadway in a mine system that undertakes the main transportation or ventilation function. The application preferably selects a main roadway with good surrounding rock stability as a core passage of the mine; the stability qualified means that the stability and volume requirements of the liquefied natural gas storage modification need to be met.

[0052] In some embodiments, the double gas-tight barrier includes a first layer barrier and a second layer barrier.

[0053] In some embodiments, the construction of the double gas-tight barrier includes: constructing the first layer barrier as a stainless steel membrane, and constructing the second layer barrier as a permafrost circle formed by frozen underground water. The stainless steel membrane adopts Mark III stainless steel or NO96 invar steel, and the thickness is 1.2-1.5 mm.

[0054] In some embodiments, a thermal insulation layer, a waterproof layer and a concrete lining layer are arranged between the first layer barrier and the second layer barrier to achieve the function of low-temperature and airtight storage of liquefied natural gas.

[0055] In some embodiments, the method further includes: arranging a corrugated structure on the surface of the stainless steel membrane, and the corrugated structure has a corrugated spacing of 400-700 mm.

[0056] Exemplarily, a traffic shaft is also arranged in the target area near the main roadway, which is used as a pipeline access passage of the subsequent low-temperature liquefied natural gas storage. The target area can be determined according to the actual construction situation.

[0057] Step 120, the cross section of the abandoned mine roadway is modified into a trapezoidal structure with a preset angle, which is used to adapt to the installation requirements of the thin film material of the stainless steel membrane, and a support unit is constructed based on the anchor rod, the concrete lining layer, the surrounding rock and the modified cross section, which is used to ensure the stability of the cavern structure and the safety of the construction.

[0058] In some embodiments, the modification of the cross section of the abandoned mine roadway into a trapezoidal structure with a preset angle includes: anchor rod support construction and grouting reinforcement treatment are performed on the weak support area of the abandoned mine roadway; the abandoned mine roadway is reinforced with reinforced concrete lining to generate the concrete lining layer.

[0059] Exemplarily, the anchor rod holes and the grouting holes are arranged at a preset interval, and the depth of the anchor rod holes and the grouting holes is greater than the size of the cavern structure.

[0060] For example, engineering practice uses percentage slope rather than angle, and the slope of the gentle slope tunnel does not exceed 5% (for example, the vertical height change range does not exceed 5 meters for every 100 meters of horizontal distance) to reduce the difficulty of reconstruction, and the slope is best when it is close to 0°.

[0061] For example, the corner angles of the trapezoidal structure are limited to 90° and 135°. For instance, when converting abandoned mine shafts into cryogenic liquefied natural gas storage facilities, due to the installation angle limitations of the sealing stainless steel membrane, the mine shafts need to be excavated or filled into a trapezoidal structure, with the angles of each side controlled to 90° and 135°. During support, the self-stabilizing capacity of the surrounding rock and the existing support structure are fully utilized, supplemented by support methods such as anchor bolts and concrete lining.

[0062] For example, the anchor bolt is 2.5 meters long and the anchor bolts are spaced 1.5 meters by 1.5 meters; the thickness of the concrete lining layer is not less than 100 millimeters.

[0063] It is worth noting that, in this application embodiment, the stability of the surrounding rock and the durability of the support structure were assessed before the abandoned mine shaft was renovated. Based on anchor bolt support and grouting reinforcement measures, the weakness of the support structure during mining was avoided. After the abandoned mine shaft underwent the above reinforcement treatment, a stainless steel membrane was used as the first barrier for the airtightness of the tank, and frozen groundwater (cryosphere) as the second airtightness barrier. An insulation layer, a waterproof layer, and a concrete lining layer were respectively installed between the two barriers to achieve the function of low-temperature, sealed storage of liquefied natural gas. Furthermore, the above parameters can be calculated based on the actual construction scale and land acquisition area during application, and the working pressure, diameter, and layout scheme of the gas storage chamber can be further determined.

[0064] In one specific exemplary embodiment, reference is made to the appendix. Figure 2 As shown, an abandoned mine shaft was selected and converted into a medium-sized test chamber with a volume of 60 cubic meters. The slope of the main shaft was approximately 3‰. About 200 meters from the main shaft, there was an auxiliary shaft leading directly to the surface, which could serve as a passage for subsequent process pipelines. Before the conversion of the abandoned mine shaft, the stability of the surrounding rock and the durability of the support structure were assessed. For example, anchor bolt support and grouting reinforcement measures were adopted to improve the weak support structure during mining. The spacing between rows and rings of anchor bolt holes and grouting holes was 2 meters. The depth of anchor bolt holes and grouting holes should be greater than the height or span of the chamber. The drilling length was typically 4-5 meters, and ordinary Portland cement was preferred as the grouting material. (See attached diagram.) Figure 3 As shown, after the abandoned shaft is reinforced, a stainless steel membrane is used as the first barrier to ensure the airtightness of the tank, and frozen groundwater (cryosphere) is used as the second barrier. An insulation layer, a waterproof layer, and a concrete lining layer are installed between the two barriers to achieve the function of low-temperature, airtight storage of liquefied natural gas.

[0065] The application can make full use of the self-stability of the surrounding rock and the existing support structure during support, supplemented by support means such as anchor rods and lining concrete. In addition, based on the limitation of existing materials, in order to reduce the difficulty and cost of procurement and maintenance, the original cross section of the abandoned shaft and roadway is transformed into a trapezoidal top by excavation or filling with lining concrete.

[0066] In a specific example embodiment, reference is made to the drawings in which Figure 4 As shown in the drawings, the top of the abandoned shaft and roadway is transformed into a trapezoidal top by lining concrete, and the lost storage space is supplemented by expanding the roadway floor. According to the calculation, the roadway floor of the abandoned shaft and roadway needs to be vertically excavated by 0.2 meters. The original cross section size of the roadway is about 2.7 meters wide by 2.9 meters high, and after the transformation, the storage space cross section circumference is about 7.55 meters, the net area is about 3.88 square meters, the effective storage area is about 3.06 square meters, and the length of the 6 cubic medium-sized experimental chamber is about 19 meters. During support, the self-stability of the surrounding rock and the existing support structure are fully utilized, supplemented by support means such as anchor rods and lining concrete. It can be specifically divided into primary support and secondary lining. Among them, the primary support includes: the excavation of the operation platform, the pump pit and the sealing plug key groove, and after excavation, the anchor rod support is carried out by using C22 anchor rod. The floor excavation does not need to be supported by anchor rod. The anchor rod is a full-length bonded type cement mortar anchor rod, the thickness of the anchor rod protection layer is not less than 20 millimeters, and the end is equipped with a steel backing plate and a nut (the nut must be tightened after the anchor rod installation is completed). The anchor rod is made of ordinary mortar anchor rod made of HRB400 grade hot-rolled steel bar, the end is exposed by 50 millimeters, the cement mortar used for the anchor rod has a strength grade of M25, the steel backing plate is made of Q235B steel, and has a size of 150*150*8 millimeters, and is fastened by M22 nut. Among them, the secondary lining includes: the thickness of the shaft and roadway reinforced concrete lining layer is about 100 millimeters, the concrete material is C30 low temperature concrete, the steel bar is low temperature steel bar, and the minimum thickness of the protection layer is 40 millimeters. The thickness of the reinforced concrete lining layer of the operation platform is about 350 millimeters, the lining concrete can be prefabricated in the factory, assembled on site, or poured on site, and the construction conditions are determined. The lining concrete is preferably provided with a construction joint every 6 meters, and is subjected to waterproof treatment.

[0067] Step 130, a composite tank wall structure composed of a stainless steel membrane and a thermal insulation layer is laid on the inner surface of the roadway of the abandoned shaft and roadway, for providing thermal insulation and double air-tight barrier functions and ensuring the sealing and thermal efficiency of the low-temperature liquefied natural gas storage.

[0068] Among them, the inner surface of the roadway of the abandoned shaft and roadway refers to all the inner surfaces including the floor, wall and top of the roadway.

[0069] In some embodiments, the insulation layer is composed of plywood, polyurethane foam, elastic mortar, and a moisture barrier layer from the inside out. Polyurethane foam, due to its high thermal resistance, is used as the main insulation component. The polyurethane foam thickness is approximately 200 mm, thereby controlling the temperature of the insulation structure between the membrane and the concrete wall, as well as the temperature of the concrete structure, to be no lower than -50°C.

[0070] In some embodiments, the method further includes applying the moisture barrier to the concrete wall to prevent water vapor penetration.

[0071] For example, the stainless steel membrane is made of Mark III stainless steel or NO96 Invar steel, with a thickness of 1.2-1.5 mm. The insulation layer consists of plywood, polyurethane foam, elastic mortar, and a moisture-proof layer. The bottom, walls, and top of the tunnel all adopt a structure of stainless steel membrane and insulation layer. The tank wall structure, from the inside out, consists of stainless steel membrane, insulation layer, reinforced concrete lining layer, and surrounding rock, mainly relying on the two sealing designs of stainless steel membrane and cryosphere. The stainless steel membrane can be used only to contain liquefied natural gas and does not bear the load independently; the pressure of the liquefied natural gas is borne by the lining wall and surrounding rock. The stainless steel membrane is made of Mark III stainless steel or NO96 Invar steel, with a thickness of 1.2-1.5 mm. The stainless steel membrane has a pleated structure with a pleat spacing of 400-700 mm, as shown in the attached diagram. Figure 5 As shown, the film structure, formed by mold pressing, possesses ductility and can absorb shrinkage deformation under low-temperature conditions. The stainless steel membrane's sealing function includes, but is not limited to: the inner stainless steel film possesses both liquid and airtightness, its form being a double-layered orthogonal corrugated grid, functioning similarly to a bellows, allowing for bidirectional contraction / expansion under varying temperature conditions. The inner film is composed of stainless steel film sheets welded to the protective layer, with the film sheets overlapping and welded together. The entire inner film is densely welded to ensure the airtightness of the maintenance system.

[0072] For example, refer to the appendix. Figure 6 As shown, the insulation layer consists of plywood, polyurethane foam, elastic sealant, and a moisture barrier. Polyurethane foam, with its high thermal resistance, is the primary insulation component, approximately 200 mm thick. The plywood layers above and below the polyurethane foam provide a secure connection. The elastic sealant is used for leveling the concrete wall and connecting the wall to the plywood. The moisture barrier (approximately 2.5 mm thick) is applied to the concrete wall and is airtight, preventing liquid water or water vapor from penetrating the insulation layer during use. The functions of the insulation layer include, but are not limited to: ensuring the concrete structure remains at a temperature no lower than -50°C through the insulation structure between the membrane and the concrete wall; and transferring the lateral pressure of the liquefied natural gas from the inner layer to the concrete wall, thus requiring a certain load-bearing capacity. The insulation space of the insulation layer, from the inner layer (inner membrane) to the outer layer (moisture barrier), is completely sealed and permanently placed within the liquefied natural gas layer for easy monitoring.

[0073] Step 140: A process operation platform is set on the top of the cavern in the abandoned shaft, and a pump pit for installing a submersible pump is set below the process operation platform.

[0074] Among them, the top of the abandoned shaft and tunnel is equipped with a process operation platform for the installation and maintenance of equipment such as valves and instruments entering the tunnel. Below the operation platform is a pump pit for installing equipment such as submersible pumps. This pump pit is a vertical shaft pump pit.

[0075] In some embodiments, the process operation platform and the tank wall structure of the pump pit that are in contact with liquefied natural gas are both composite tank wall structures composed of a stainless steel membrane and the insulation layer.

[0076] To prevent liquefied natural gas (LNG) leakage, all fluid inlet and outlet pipelines and instrument connections within the storage facility are connected from the top of the tank. The converted cryogenic LNG storage facility in the abandoned mine shaft is equipped with at least one feed pipe, which is inserted into the storage facility via a vertical feed pipe. The operator can adjust the LNG feed rate by manipulating the feed valve at the top of the storage facility. The LNG storage tank is connected to other pipelines within the station via a vapor phase pipeline to transport the vaporized gas generated within the storage facility and the gas generated by the station's surface system to the venting system. No gas is emitted during normal operation.

[0077] For example, refer to the appendix. Figure 7 As shown, in this embodiment, the original shaft is excavated, and an operating platform (including a lining structure with a lining thickness of 350 mm) measuring 4.0 meters (length) × 4.0 meters (width) × 2.7 meters (height) is constructed for the installation and maintenance of equipment such as valves and instruments entering the tunnel. A pump pit can be set below the operating platform for installing equipment such as submersible pumps. For ease of later testing, a pump cylinder size of DN500 is recommended, and the pump pit size is recommended to be 1200 mm × 1200 mm × 500 mm.

[0078] Step 150: Deploy groundwater control units around the reservoir to drain fissure water in the rock mass during construction and to restore rock mass saturation to form a cryosphere during operation.

[0079] In some implementations, the groundwater control unit includes an upper water replenishment subunit and a lower drainage subunit.

[0080] In some embodiments, the deployment of groundwater control units around the reservoir includes: arranging the water supply holes of the upper water supply subunit and the drainage holes of the lower drainage subunit in a ring within a predetermined distance range around the cavern of the reservoir.

[0081] One of the purposes of the underground water control unit is to drain fissure water in the rock mass before the construction period and the formation of the freezing circle, so that the fissure water in the bedrock is in an unsaturated state, avoiding the formation of water pressure on the sealing system in the tank, and also creating a dry environment for the construction of the sealing system. During the concrete pouring stage, the main function of the underground water control unit is to reduce the amount of water flowing into the storage tank; during the installation of the sealing system, the function of the drainage system is to reduce humidity; during the early cooling period of operation, the function of the drainage system is to drain the rock mass and reduce the saturation of the rock mass fissures; after the low-temperature dry rock mass reaches a certain range, the function of the drainage system is to restore the saturation of the rock mass and form a freezing circle.

[0082] The main purpose of the underground water control unit is to drain fissure water in the rock mass before the construction period and the formation of the freezing circle, so that the fissure water in the bedrock is in an unsaturated state, avoiding the formation of water pressure on the sealing system in the tank, and also creating a dry environment for the construction of the sealing system. During the concrete pouring stage, the main function of the underground water control unit is to reduce the amount of water flowing into the storage tank; during the installation of the sealing system, the function of the drainage system is to reduce humidity; during the early cooling period of operation, the function of the drainage system is to drain the rock mass and reduce the saturation of the rock mass fissures; after the low-temperature dry rock mass reaches a certain range, the function of the drainage system is to restore the saturation of the rock mass and form a freezing circle.

[0083] For example, the water replenishment subunit and the drainage subunit of the present embodiment are each provided with 4 water replenishment and drainage holes in the range of 5 meters above and below the cavern, with a hole spacing of 5 meters, a hole diameter of 110 millimeters, and an overlapping length of 1 meter. During the low-temperature liquefied natural gas modification of the abandoned well roadway, the water replenishment and drainage holes play a drainage function, extracting the underground water level around the cavern, facilitating on-site construction. During the low-temperature liquefied natural gas trial operation of the abandoned well roadway, the water replenishment and drainage holes are connected to the water replenishment pipeline of the main roadway, playing a water replenishment function, gradually achieving water saturation of the rock mass, and facilitating the formation of the freezing circle.

[0084] In order to provide a complete technology and solution for reconstructing a low-temperature liquefied natural gas storage in an abandoned well roadway, and promote long-term and large-scale storage of natural gas and liquefied natural gas and energy security, according to the construction principle of the low-temperature liquefied natural gas storage reconstructed in the abandoned well roadway and the functional requirements of low-temperature liquid storage, and starting from engineering practice, the embodiment of the application provides a system solution for the site selection of a large roadway of the low-temperature liquefied natural gas storage reconstructed in the abandoned well roadway, the reconstruction structure of the well roadway, the supporting scheme, the tank wall structure of the low-temperature liquefied natural gas storage, and the underground water control unit and other auxiliary facilities, which can meet all construction requirements only by selecting a hard rock stratum with moderate strength, has a high tolerance to geological conditions, and is suitable for different engineering geology, different hydrogeology, different underground engineering layout and other scenes. Through integration of various underground monomers, structures and devices, a large-scale, highly targeted, highly reliable, convenient-to-operate, low-cost and widely applicable method is provided for construction of the low-temperature liquefied natural gas storage reconstructed in the abandoned well roadway, which can be quickly applied to natural gas storage and liquefied natural gas industry chain construction, effectively reduces the storage cost of natural gas and liquefied natural gas, improves economic benefits, and further promotes the healthy development of the gas storage and abandoned underground space utilization industry chain.

[0085] By selecting the abandoned well roadway with qualified surrounding rock stability and constructing a double gas-tight barrier, the embodiment of the application can effectively utilize the existing geological conditions to reduce the risk of building a storage, ensure long-term structural stability and operational safety, and significantly improve the anti-leakage performance of liquefied natural gas storage through the double sealing design of the stainless steel membrane and the frozen circle; the cross section of the abandoned well roadway is reconstructed into a preset angle trapezoidal structure to adapt to the installation of the stainless steel membrane, ensuring the accurate deployment and sealing integrity of the membrane material, the supporting unit integrates the self-stability of the surrounding rock and the reinforcement measures to strengthen the support of the chamber structure, prevent the collapse risk during construction, and ensure the safety of the operation; the composite tank wall structure is laid on the inner surface of the roadway to realize efficient thermal insulation to reduce the evaporation loss of liquefied natural gas by utilizing the synergistic effect of the stainless steel membrane and the thermal insulation layer, the double gas-tight barrier mechanism enhances the overall sealing performance, and the thermal efficiency and operational reliability of the low-temperature storage environment are optimized; the process operation platform is arranged at the top of the chamber to facilitate equipment installation and maintenance operation, which improves the maintenance convenience, and the pump pit below the platform supports the stable installation of the submerged pump to ensure the continuity and operational efficiency of the liquefied natural gas transportation process; the underground water control unit is arranged to drain fissure water during construction to create a dry construction environment, reduce water pressure interference, and restore rock mass saturation to form a frozen circle during operation to utilize the natural frozen barrier to enhance the sealing effect and reduce the long-term maintenance requirements.

[0086] The embodiment of the application also discloses a system for reconstructing a liquefied natural gas storage based on an abandoned well roadway. Figure 8As shown, the system comprises: a double barrier building module 1010, a well and roadway section reconstruction module 1020, a roadway surface laying module 1030, an operation platform and pump pit building module 1040, and a water control unit layout module 1050.

[0087] The double barrier building module 1010 is configured to select a waste well and roadway with qualified surrounding rock stability, and build a double gas-tight barrier.

[0088] The well and roadway section reconstruction module 1020 is configured to reconstruct the section of the waste well and roadway into a trapezoidal structure with a preset angle, so as to adapt to the installation requirement of the film material of the stainless steel film, and build a support unit based on the anchor rod, the concrete lining layer, the surrounding rock, and the reconstructed section, so as to ensure the stability of the cavern structure and the safety of construction.

[0089] The roadway surface laying module 1030 is configured to lay a composite tank wall structure composed of a stainless steel film and a thermal insulation layer on the inner surface of the roadway of the waste well and roadway, so as to provide the functions of thermal insulation and double gas-tight barrier, and ensure the sealing and thermal efficiency of the low-temperature liquefied natural gas storage.

[0090] The operation platform and pump pit building module 1040 is configured to set a process operation platform on the top of the cavern of the waste well and roadway, and set a pump pit for installing a submerged pump below the process operation platform.

[0091] The water control unit layout module 1050 is configured to layout an underground water control unit around the storage, so as to drain the rock fissure water during the construction period and restore the rock saturation to form a frozen circle during the operation period.

[0092] In some embodiments, the system further comprises: a comprehensive tank wall structure including the stainless steel film, the thermal insulation layer, the reinforced concrete lining layer, and the surrounding rock arranged from inside to outside; a gas phase pipeline and a feed pipe for connecting the storage.

[0093] For example, in order to prevent liquefied natural gas from leaking, all fluid inlet and outlet pipelines and all instrument connections in the tank are connected from the top of the tank. The waste well and roadway is reconstructed into a low-temperature liquefied natural gas storage with at least one feed pipe, and the feed is realized by inserting a vertical feed pipe into the tank. The operator can adjust the feed amount of liquefied natural gas by operating the feed valve on the top of the storage. The liquefied natural gas storage is connected to other pipelines in the station through a gas phase pipeline, for transporting the evaporation gas generated in the storage and the gas generated by the ground system in the station to the venting system. No gas is discharged during normal operation, and a pump pit for installing submerged pumps and other equipment is arranged below the operation platform.

[0094] The embodiment of the present application is directed to the fact that there is no construction case of abandoned well roadway reconstruction low-temperature liquefied natural gas storage, and the existing storage technology is mainly concentrated in the construction types of ground film tank, salt cave gas storage, depleted gas reservoir gas storage, etc. The ground film tank has high construction cost and small scale, and the construction of salt cave gas storage and depleted gas reservoir gas storage is greatly limited by geological structure, geographical resources and location, which is difficult to meet the demand of large-scale underground gas storage construction in areas with serious gas shortage. The system based on abandoned well roadway reconstruction liquefied natural gas storage has great advantages in time scale and space scale, is the best way for long-term large-scale gas storage, and has great significance. The embodiment of the present application solves the problems of small scale, high cost, great geological condition and geographical location limitation of the existing gas storage and low-temperature liquefied natural gas storage mode, and layouts the system solution of different monomer function design of abandoned well roadway reconstruction low-temperature liquefied natural gas storage, such as large roadway site selection, roadway reconstruction structure, support scheme, tank wall structure of low-temperature liquefied natural gas storage, and auxiliary facilities such as underground water control unit. Only the underground space with moderate strength of abandoned well roadway needs to be selected to meet all construction requirements, which has high tolerance to geological conditions and wide application range. The tank wall structure of the abandoned well roadway low-temperature liquefied natural gas storage of the embodiment of the present application is in turn stainless steel film, thermal insulation layer, reinforced concrete lining layer, surrounding rock and the like from inside to outside, which together form the sealing structure and force transmission structure of the low-temperature liquefied natural gas chamber. The reinforced concrete lining layer and the surrounding rock mainly bear the pressure of liquefied natural gas, and the stainless steel film and the frozen circle are provided as two gas-tight barriers, which effectively solve the problems of chamber sealing and stability under the high-efficiency operation state of the low-temperature liquefied natural gas storage. The device parameters can be appropriately adjusted according to the actual working condition, and the optimization space is large. The construction device of the abandoned well roadway low-temperature liquefied natural gas storage of the embodiment of the present application can not only be applied to liquefied natural gas storage, but also be applied to abandoned underground space utilization, which has important value for natural gas reserve, underground space comprehensive utilization and energy structure transformation. The embodiment of the present application comprehensively uses various underground structures, monomers and materials, has the advantages of large scale, strong pertinence, high reliability, convenient operation, low cost, wide application range and the like, can be quickly applied to liquefied natural gas storage and abandoned underground space comprehensive utilization and the like, effectively reduces the storage cost of gas and low-temperature liquefied natural gas, improves the economic benefit of the construction of the storage, and further promotes the healthy development of the industry chain of gas storage and underground space comprehensive utilization.

[0095] It can be understood that the above embodiments are only exemplary embodiments adopted for illustrating the principles of the present application, but the present application is not limited thereto. Various modifications and improvements can be made by those skilled in the art without departing from the spirit and essence of the present application, and these modifications and improvements are also considered as the protection scope of the present application.

Claims

1. A method of converting a depleted wellbore into a liquefied natural gas storage reservoir, the method comprising: The method comprises the following steps: ​ selecting a waste well roadway with qualified surrounding rock stability, and constructing a double gas-tight barrier, wherein the double gas-tight barrier comprises a first layer barrier and a second layer barrier, the construction of the double gas-tight barrier comprises: constructing the first layer barrier as a stainless steel membrane, and constructing the second layer barrier as a frozen circle formed by frozen underground water; and setting a thermal insulation layer, a water-resisting layer and a concrete lining layer between the first layer barrier and the second layer barrier; reforming a section of the waste well roadway into a trapezoidal structure with a preset angle, for adapting the installation requirement of the thin film material of the stainless steel membrane, and constructing a support unit based on the anchor rod, the concrete lining layer, the surrounding rock and the reformed section; laying a composite tank wall structure composed of a stainless steel membrane and a thermal insulation layer on the inner surface of the roadway of the waste well roadway; setting a process operation platform on the top of the cavern of the waste well roadway, and setting a pump pit for installing a submersible pump below the process operation platform; arranging a groundwater control unit around the storage, for dewatering rock fissure water during construction and restoring rock saturation to form a frozen circle during operation, wherein the groundwater control unit comprises an upper water supplementing subunit and a lower water draining subunit, and the arrangement of the groundwater control unit around the storage comprises: arranging the water supplementing holes of the upper water supplementing subunit and the water draining holes of the lower water draining subunit in a preset distance range around the cavern of the storage.

2. The method of claim 1, wherein, The method further comprises: setting a wrinkle structure on the surface of the stainless steel membrane, and the wrinkle interval of the wrinkle structure is 400-700 mm.

3. The method of claim 1, wherein the waste roadway of the surrounding rock stability compliance is a large roadway having a gentle slope, characterized in that, The reforming of the section of the waste well roadway into a trapezoidal structure with a preset angle comprises: performing anchor rod support construction and grouting reinforcement treatment on a support weak area of the waste well roadway, wherein anchor rod holes and grouting holes are arranged at a preset interval, and the depth of the anchor rod holes and the grouting holes is greater than the size of the cavern structure; performing reinforced concrete lining of the waste well roadway to generate the concrete lining layer.

4. The method of claim 3, wherein, The slope of the gentle slope roadway is not more than 5%, the angle of the trapezoidal structure is limited to 90° and 135°, the length of the anchor rod is 2.5 m, and the arrangement interval of the anchor rod is 1.5 m x 1.5 m; and the thickness of the concrete lining layer is not less than 100 mm.

5. The method according to claim 1, wherein the thermal insulation layer is composed of plywood, polyurethane foam, elastic mastic, and a moisture barrier layer from the inside to the outside, characterized in that, The method further comprises: applying the moisture-proof layer to the wall surface of the concrete, for blocking water vapor penetration.

6. The method of claim 1, wherein, The tank wall structure of the process operation platform and the pump pit in contact with liquefied natural gas is a composite tank wall structure composed of a stainless steel membrane and a thermal insulation layer.

7. A system for converting a depleted well tunnel into a liquefied natural gas storage reservoir, the system comprising: The method comprises the following steps: a double barrier construction module for selecting a waste well roadway with qualified surrounding rock stability, and constructing a double gas-tight barrier, wherein the double gas-tight barrier comprises a first layer barrier and a second layer barrier, the construction of the double gas-tight barrier comprises: constructing the first layer barrier as a stainless steel membrane, and constructing the second layer barrier as a frozen circle formed by frozen underground water; and setting a thermal insulation layer, a water-resisting layer and a concrete lining layer between the first layer barrier and the second layer barrier; The well roadway section reconstruction module is used to reconstruct the section of the abandoned well roadway into a trapezoidal structure with a preset angle, to adapt the installation requirement of the film material of the stainless steel film, and to construct a support unit based on the anchor rod, the concrete lining layer, the surrounding rock, and the reconstructed section; The roadway surface laying module is used to lay a composite tank wall structure composed of a stainless steel film and a thermal insulation layer on the inner surface of the roadway of the abandoned well roadway; The operation platform and pump pit building module is used to set a process operation platform on the top of the chamber of the abandoned well roadway, and to set a pump pit for installing a submersible pump below the process operation platform; The water control unit laying module is used to lay a groundwater control unit around the storage, to drain the rock fissure water during the construction period and to restore the rock saturation to form a frozen circle during the operation period, wherein the groundwater control unit comprises an upper water supplementing subunit and a lower water draining subunit, and the laying of the groundwater control unit around the storage comprises annularly laying the water supplementing holes of the upper water supplementing subunit and the water draining holes of the lower water draining subunit within a preset distance range around the chamber of the storage.

8. The system for converting a depleted well tunnel into a liquefied natural gas storage reservoir according to claim 7, wherein, The system further comprises: The comprehensive tank wall structure comprises the stainless steel film, the thermal insulation layer, the reinforced concrete lining layer, and the surrounding rock arranged from inside to outside; The gas phase pipeline and the feed pipe are used to connect the storage.

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