A design method of oil storage cavern with double-side end entry

Abstract

The application provides a design method of a double-side end hole entering oil storage cavern, which comprises the steps of site selection and geological survey, main cavern parameter determination, construction roadway layout and excavation, water curtain system construction, main cavern layer-by-layer excavation, finishing and sealing, and can greatly shorten the length of construction roadway and the length of single-end tunneling, reduce the engineering investment and greatly improve the construction efficiency. The method of the application directly enters the main cavern from both ends, skips the process of excavating long-distance branch construction roadway, can enter the main cavern in advance and early expose the adverse geological conditions. The connecting port of the construction roadway and the main cavern is arranged at the two ends of the main cavern, and the sealing plug is correspondingly arranged at the end position. The geological conditions of this area are relatively complete, the excavation disturbance is small, the risk of seepage is effectively reduced, and the water sealing safety of the cavern is improved.

Description

Technical Field

[0001] This invention belongs to the field of underground water-sealed cavern technology, specifically relating to a design method for an oil storage cavern with double-sided end entrances. Background Technology

[0002] Water-sealed underground caverns are currently recognized internationally as the primary method for large-scale strategic oil reserves. Their principle involves using water pressure from rock fissures below the groundwater level to seal oil and gas within the cavern. Oil storage caverns typically employ extra-large cross-sections, with single caverns reaching lengths of 800-1000 meters and heights of approximately 30 meters. To meet the stability requirements of the surrounding rock, layered and segmented excavation methods are often used.

[0003] With changes in the international energy landscape and the rapid growth in domestic oil reserve demand, the government has placed higher demands on the construction period of underground water-sealed cavern projects. Early construction cycles for these projects were generally 50-60 months, but have now been gradually increased to 40-50 months. Given that the current drilling and blasting method is the only viable option, how to further shorten the construction period and ensure projects are put into operation on schedule has become a pressing technical challenge in this field.

[0004] Currently, the traditional construction tunnel layout method for underground water-sealed caverns is as follows: Figure 1 As shown, the "middle entry" scheme is commonly used: after the construction tunnel is excavated from the surface, a branch construction tunnel leads into the main tunnel from the middle (a certain distance from the end wall). This arrangement has the following technical drawbacks: First, the construction tunnels are long and involve a large amount of work. Because the branch construction tunnels need to connect from the middle of the main tunnel, the total length of the construction tunnels increases, and the corresponding amount of excavation, grouting, and support such as anchor bolts also increases, which not only increases construction costs but also prolongs the construction period.

[0005] Secondly, the long single-heading excavation distance of the main tunnel leads to low construction efficiency. After entering the main tunnel using the intermediate entry method, it is necessary to excavate at both ends simultaneously. However, one end is relatively long from the end wall, resulting in a long single-heading excavation length (usually up to 400-500m). This makes the main tunnel excavation process cumbersome, construction organization and coordination difficult, and overall construction efficiency constrained.

[0006] Third, the delayed entry into the main tunnel is detrimental to the treatment of unfavorable geological conditions. Because a long construction tunnel must be excavated before entering the main tunnel, the main tunnel is exposed late, and unfavorable geological conditions such as fracture zones and densely jointed zones cannot be detected and treated in a timely manner. If sudden geological problems are encountered in the later stages of excavation, it will seriously affect the construction progress and project safety.

[0007] Fourth, a sealing plug needs to be installed at the intersection of the branch construction roadway and the main tunnel, as this location poses a risk of seepage around the tunnel. In the traditional layout, the intersection of the branch construction roadway and the main tunnel is located in the middle of the tunnel body. A concrete sealing plug needs to be installed at the intersection later. Due to the large excavation disturbance and stress concentration in this area, seepage around the tunnel is prone to occur, affecting the water seal safety of the tunnel.

[0008] In summary, existing underground water-sealed cavern construction tunnel layouts have significant shortcomings in terms of schedule control, workload optimization, and geological risk prevention. How to optimize the construction tunnel layout, shorten the single-heading excavation length, and excavate into the main cavern earlier to reveal geological conditions, while ensuring the volume of the oil storage cavern and the stability of the surrounding rock, has become a pressing technical problem for those skilled in the art. Summary of the Invention

[0009] The purpose of this invention is to solve the problems mentioned in the background section. This invention provides the following technical solution: a method for designing an oil storage cavern with double-sided end entrances, comprising the following steps: S1. Screening of underground water-sealed cavern reservoir site options, conducting geological surveys and obtaining geological information for the selected sites; performing numerical simulations and field tests to analyze the stability of the surrounding rock and the characteristics of the seepage field; S2. Based on the geological survey and the field test conclusions, determine the axial direction, cross-sectional type, length and cross-sectional dimensions of the main tunnel, and determine the layout and elevation of the water curtain tunnel; S3. Set up the construction tunnel entrance according to the layout parameters of the main tunnel. Excavate the first main construction tunnel and the second main construction tunnel from the surface. The two construction tunnels extend to the front of the first end and the second end of the main tunnel, respectively. After turning through the bend, excavate the branch construction tunnels to enter the main tunnel from the first end and the second end, respectively, so as to realize simultaneous entry from both ends of the main tunnel. S4. When the main construction roadway is excavated to the elevation of the water curtain roadway, the branch roadway connecting the main construction roadway and the water curtain roadway is excavated, and the excavation and support construction of the water curtain roadway is carried out. S5. Using the construction passages that have been entered at both ends of the main tunnel in step S3, start excavating the main tunnel in layers from the first end and the second end simultaneously. S6. After completing all the excavation work of the main tunnel, remove the temporary rock steps at one end, exit the tunnel from the other end, and set concrete sealing plugs at both ends of the main tunnel.

[0010] More preferably, step S5 specifically includes: S51. Excavate the upper layer of the main cavern, and enter other main caverns in the same tank area through the upper connecting roadways at both ends of the main cavern to carry out upper layer construction; S52. After the upper layer excavation is completed, the full-section rock steps reserved inside the end of the main tunnel are used as built-in ramps. The middle layer excavation working face of the main tunnel is entered through the built-in ramps to carry out the middle layer excavation of the main tunnel. The middle layer connecting roadway is used to enter other main tunnels in the same tank area to complete the middle layer construction. S53. After the middle layer excavation is completed, the built-in inclined ramp is used to continue the slope to enter the lower layer excavation face of the main chamber, and the lower layer excavation of the main chamber is carried out. The lower layer connecting roadway is used to enter other main chambers in the same tank area to complete the lower layer construction.

[0011] More preferably, the cross-sectional shape of the first main construction tunnel and the second main construction tunnel in step S3 is a straight-walled circular arch, and the cross-sectional dimensions are determined according to the requirements for the passage and transportation of construction equipment.

[0012] More preferably, the upper connecting tunnel, the middle connecting tunnel and the lower connecting tunnel mentioned in step S5 are all set inside the main tunnel, which are used to connect different main tunnels in the same tank area to realize the synchronous construction of each tunnel in the tank area.

[0013] Further preferably, in step S1, the site selection scheme for the underground water-sealed cavern reservoir is determined by oil source, surface water system, lithology, topography, transportation and supporting conditions; the acquisition of geological information specifically includes the acquisition of information on topography, stratigraphy, geological structure and hydrogeological conditions.

[0014] More preferably, in step S3, the entrance to the construction tunnel is located in a location with good surface geological conditions, small excavation volume, and open construction site.

[0015] A further preferred embodiment is that, in step S3, during the process of excavating the first and second main construction tunnels from the ground surface downwards, the two construction tunnels are excavated in parallel along the axis of the main tunnel, and the elevation is gradually reduced to be close to the elevation of the main tunnel roof.

[0016] The present invention also provides an oil storage cavern system with double-ended entrances, comprising: At least one main cavern, the main cavern having a first end and a second end, and the main cavern having an internal ramp located inside the end of the main cavern for connecting different excavation elevation layers of the main cavern; The first main construction tunnel and the second main construction tunnel extend from the ground surface to the first end of the main cavern and are directly connected to the first end. The second main construction tunnel extends from the ground surface to the second end of the main cavern and are directly connected to the second end, forming a construction passage that can be entered from both ends of the main cavern. A water curtain system, including a water curtain tunnel and a branch tunnel connecting the construction tunnel and the water curtain tunnel; The connecting tunnel system includes upper, middle and lower connecting tunnels located inside the main tunnel chambers, used to connect different main tunnel chambers within the same tank area.

[0017] Further preferably, the built-in ramp is a full-section rock step ramp, located inside the end of the main tunnel, with a slope that meets the requirements for the passage of construction equipment; the first main construction tunnel and the second main construction tunnel are provided with arc-shaped bends near the end of the main tunnel, so that the axis of the construction tunnel turns to face the end of the main tunnel.

[0018] A further preferred embodiment is that a concrete sealing plug is provided at the end of the main cavern to seal the cavern after construction is completed.

[0019] Compared with existing technologies, the oil storage cavern design method provided by this invention, which involves entering the cavern from both ends of the main cavern and combining it with an innovative design of built-in inclined ramps, has achieved the following beneficial effects by changing the traditional "middle entry" construction roadway layout: First, it significantly shortens the length of construction tunnels, reducing project investment.

[0020] This invention abandons the traditional method of entering the main tunnel from the middle section using branch construction roadways. Instead, it replaces most of the branch construction roadways with ramps installed inside the main tunnel, allowing direct entry from both ends of the main tunnel. Engineering examples have verified that this method can shorten the total excavation mileage of the construction roadway by approximately 30% to 40%, correspondingly reducing the amount of excavation, grouting, and anchor bolt support required, thus significantly lowering construction costs.

[0021] Second, shortening the length of single-heading tunneling significantly improves construction efficiency.

[0022] Traditional methods of entering the main tunnel via the middle approach require excavation from both ends, with a single-ended excavation length of 400-500m at one end. This invention employs a double-ended entry method, excavating simultaneously from both ends of the main tunnel towards the middle, reducing the single-ended excavation length by approximately 50%, to only 200-250m. Construction organization is smoother, main tunnel excavation efficiency is increased by 50%-80%, and the main tunnel construction period can be reduced by 9-16 months. For the entire tunnel project, this shortens the construction cycle by 15%-20%, effectively solving the technical challenge of tight deadlines.

[0023] Third, enter the main cavern in advance to expose unfavorable geological conditions as early as possible.

[0024] This invention allows for direct entry into the main tunnel from both ends, bypassing the process of excavating long-distance branch tunnels, and enabling upper-level excavation to begin approximately 6-8 months earlier. This allows for the early exposure of adverse geological conditions such as fractured zones and densely jointed zones, providing ample time for geological risk assessment and emergency response, and preventing project delays and safety accidents caused by encountering unfavorable geological formations later on.

[0025] Fourth, optimize the arrangement of sealing plugs to effectively reduce the risk of seepage around the plug.

[0026] In traditional layouts, the intersection of the branch construction tunnel and the main tunnel is located in the middle of the tunnel body. A concrete sealing plug needs to be installed at this intersection later. This area is prone to seepage channels due to significant excavation disturbance and stress concentration. This invention places the connection between the construction tunnel and the main tunnel at both ends of the main tunnel, with the sealing plugs correspondingly placed at the ends. The geological conditions in this area are relatively intact, and excavation disturbance is minimal, effectively reducing the risk of seepage around the tunnel and improving the water seal safety of the tunnel. Attached Figure Description

[0027] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a plan view of the underground cavern layout in an embodiment of the present invention; Figure 3 This is a cross-sectional view of section AA in the plan view of the underground cavern layout of an embodiment of the present invention; Figure 4 This is a cross-sectional view of section BB in the plan view of the underground cavern layout of an embodiment of the present invention; In the diagram, 1. Main tunnel; 2. Construction tunnel entrance; 3. First main construction tunnel; 4. Second main construction tunnel; 5. First end; 6. Second end; 7. Water curtain tunnel; 8. Curved bend; 9. Branch tunnel; 10. Upper connecting tunnel; 11. Middle connecting tunnel; 12. Lower connecting tunnel; 13. Branch construction tunnel; 14. Internal ramp. Detailed Implementation

[0028] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1 This embodiment provides a design method for an oil storage cavern with double-ended entrances, such as... Figure 1 The method flowchart of the present invention includes the following steps: S1. Screening of underground water-sealed cavern reservoir sites: Geological surveys are conducted at selected sites to obtain geological information. The selection of sites is determined based on oil source, surface water system, lithology, topography, transportation, and supporting conditions. Geological information obtained specifically includes topography, stratigraphy, lithology, geological structure, and hydrogeological conditions. Numerical simulations and field tests are performed to analyze the stability of the surrounding rock and the characteristics of the seepage field.

[0030] S2. Based on the geological survey and the field test results, determine the axial direction, cross-sectional type, length and cross-sectional dimensions of the main tunnel 1, and determine the location and elevation of the water curtain tunnel 7.

[0031] S3. Based on the layout parameters of the main tunnel 1, the construction tunnel entrance 2 is set in a location with good surface geological conditions, minimal excavation volume, and an open construction site. The first main construction tunnel 3 and the second main construction tunnel 4 are excavated from the surface. These two tunnels extend to the front of the first end 5 and the second end 6 of the main tunnel 1, respectively. After turning at bends, branch construction tunnels 13 are excavated and enter the main tunnel 1 from the first end 5 and the second end 6, respectively, enabling simultaneous entry from both ends of the main tunnel 1. The cross-sectional shape of the first main construction tunnel 3 and the second main construction tunnel 4 in step S3 is a straight-walled circular arch, and the cross-sectional dimensions are determined according to the requirements for the passage and transportation of construction equipment. During the excavation of the first main construction tunnel 3 and the second main construction tunnel 4 downwards from the surface, the two tunnels are excavated parallel to each other along the axis of the main tunnel 1, gradually decreasing in elevation to near the top elevation of the main tunnel 1.

[0032] S4. When the main construction roadway is excavated to the elevation of the water curtain roadway 7, the branch roadway 9 connecting the main construction roadway and the water curtain roadway 7 is excavated, and the excavation and support construction of the water curtain roadway 7 is carried out.

[0033] S5. Utilizing the construction passages already accessed at both ends of the main tunnel 1 in step S3, begin layered excavation of the main tunnel 1 simultaneously from the first end 5 and the second end 6. Step S5 specifically includes: S51. Excavate the upper layer of the main tunnel 1, and enter other main tunnels in the same tank area through the upper connecting roadways 10 at both ends of the main tunnel to carry out upper layer construction.

[0034] S52. After the upper layer excavation is completed, the full-section rock steps reserved inside the end of the main tunnel 1 are used as the built-in ramp 14. The middle layer excavation working face of the main tunnel 1 is entered through the built-in ramp 14 to carry out the middle layer excavation of the main tunnel 1. The middle layer connecting roadway 11 is used to enter other main tunnels in the same tank area to complete the middle layer construction.

[0035] S53. After the middle layer excavation is completed, the built-in ramp 14 is used to continue the slope to enter the lower excavation face of the main chamber 1 to carry out the lower excavation of the main chamber 1, and enter other main chambers in the same tank area through the lower connecting roadway 12 to complete the lower layer construction.

[0036] The upper connecting tunnel 10, the middle connecting tunnel 11 and the lower connecting tunnel 12 mentioned in step S5 are all located inside the main cavern 1, and are used to connect different main caverns 1 in the same tank area to realize the synchronous construction of each cavern in the tank area.

[0037] S6. After completing all the excavation work of the main tunnel 1, remove the temporary rock steps at one end, exit the tunnel from the other end, and set concrete sealing plugs at both ends of the main tunnel 1.

[0038] Example 2 I. Project Overview This embodiment takes the design of a groundwater-sealed cavern project as an example. This embodiment provides a design method for an oil storage cavern with double-ended entrances, combined with... Figure 2 The underground cavern layout plan in this embodiment Figure 3 The plan view of the underground cavern layout of this embodiment, and the AA section cross-section view and Figure 4 The BB section cross-section diagram in the underground cavern layout plan of this embodiment is used for illustration.

[0039] like Figure 2 As shown in this embodiment, the underground engineering section mainly consists of 4 sets of caverns, each containing 2 main chambers, totaling 8 main chambers 1. Each main chamber 1 adopts a straight-walled, three-centered circular arch cross-section, with a span of 20m and a height of 30m. The total length of the 8 main chambers is approximately 11,000m, and the floor elevation of main chamber 1 is -100m. The water curtain system includes 6 water curtain tunnels 7 and 2 water curtain traffic tunnels. The floor elevation of water curtain tunnels 7 is -40m, and they adopt a 7m × 6.5m straight-walled, circular arch cross-section, with a total length of approximately 4,500m. The construction tunnels adopt a 10m × 9m straight-walled, circular arch cross-section, with a total length of approximately 7,500m.

[0040] II. Site Selection and Geological Survey Step S1: Screen the site options for the underground water-sealed cavern reservoir, conduct geological surveys and obtain geological information for the selected sites; perform numerical simulations and field tests to analyze the stability of the surrounding rock and the characteristics of the seepage field.

[0041] In this embodiment, the basic principles for the construction land of underground water-sealed cavern projects stipulated by the state are first followed, and factors such as oil source, surface water system, lithology, topography, support, transportation and support conditions are considered to select a suitable site.

[0042] Geological exploration work was carried out at the selected reservoir site to obtain the following geological information: Topography and landforms: The reservoir site area is characterized by low mountains and hills with well-developed surface vegetation and a cover layer thickness of about 2-5m; Stratigraphy: The main lithology is granite, with a saturated uniaxial compressive strength of 60-80 MPa, classifying it as hard rock; Geological structure: Two faults, F1 and F2, are developed in the area, intersecting the axis of the main cavern 1 at a large angle. There are three main groups of joints and fissures, with a spacing of 0.3-0.8m. Hydrogeological conditions: Groundwater level depth 15-25m, permeability coefficient 5×10 - 5 cm / s, which meets the requirements for water seal conditions.

[0043] Based on this, three-dimensional numerical simulations and on-site hydrological tests were conducted to analyze the stability of the surrounding rock, displacement and deformation characteristics, and seepage field distribution during the excavation of the cavern complex, providing a basis for subsequent design. Simultaneously, the site was rated according to the requirements of the "Code for Construction of Underground Water-Sealed Caverns" (SY / T 0610-2023), categorized as excellent, medium, and poor.

[0044] III. Determination of Parameters for Main Chamber 1 S2. Based on the geological survey and the field test results, determine the axial direction, cross-sectional type, length and cross-sectional dimensions of the main tunnel 1, and determine the location and elevation of the water curtain tunnel 7.

[0045] Based on the survey and testing conclusions, the following design parameters are determined in this embodiment: The axial direction of the main chamber 1 is determined to be N45°E in order to form a favorable angle with the main structural surface.

[0046] Section type: The section adopts a straight wall three-center circular arch type section. This section type has good stress performance and is conducive to the stability of the surrounding rock.

[0047] Cavern length and cross-sectional dimensions: The length of a single main cavern is 1200-1500m, the cross-sectional span is 20m, and the height is 30m.

[0048] Water curtain tunnel 7 arrangement: Water curtain tunnel 7 is arranged at an elevation of 40m above the main tunnel 1 (i.e., the bottom plate elevation - 40m) to form a water curtain barrier and ensure the water seal of the tunnel.

[0049] IV. Construction Tunnel Layout and Excavation S3. Set up the construction tunnel entrance 2 according to the layout parameters of the main tunnel 1, excavate the first main construction tunnel 3 and the second main construction tunnel 4 from the ground surface, and extend the two construction tunnels to the front of the first end 5 and the second end 6 of the main tunnel 1 respectively. After turning through the bend, excavate the branch construction tunnel 13 to enter the main tunnel 1 from the first end 5 and the second end 5 respectively, so as to realize simultaneous entry from both ends of the main tunnel 1.

[0050] like Figure 2 and Figure 3 As shown, in this embodiment, a main construction tunnel is set up on each of the east and west sides of the main tunnel group 1: The entrance to the construction tunnel 2 is located in a location with favorable surface geological conditions, minimal excavation, and an open construction site. The entrance to the first main construction tunnel 3 is located on the east side of the reservoir area, where the surface is a gentle slope with a thin overburden layer, exposed rock, and an open construction site, facilitating the placement of construction facilities. The entrance to the second main construction tunnel 4 is located on the west side of the reservoir area, also in a location with favorable geological conditions and minimal excavation.

[0051] After selecting the entrance 2 of the construction tunnel, the tunnel excavation operation commenced. Two construction tunnels (the first main construction tunnel 3 and the second main construction tunnel 4) were excavated downwards from the ground surface, advancing parallel to the axis of the main tunnel 1, and gradually lowering the elevation to near the top elevation of the main tunnel 1. During excavation, a 10m × 9m straight-walled circular arch cross-section was adopted; however, the cross-section dimensions could be determined based on the passage and transportation requirements of large dump trucks and excavating equipment.

[0052] When the tunneling reaches the elevation of the roof of the main tunnel 1 (approximately -70m), the two construction tunnels have reached approximately 30m in front of the first end 5 and the second end 5 of the main tunnel 1, respectively. At this point, an arc-shaped bend 8 is installed to turn the axis of the construction tunnels so that they face the end of the main tunnel 1. Then, a short-distance branch construction tunnel 13 (approximately 20-30m long) is excavated to enter the main tunnel from the first end 5 and the second end 6, respectively, thus enabling simultaneous entry from both ends of the main tunnel 1.

[0053] V. Construction of the Water Curtain System S4. When the main construction roadway is excavated to the elevation of the water curtain roadway 7, the branch roadway 9 connecting the main construction roadway and the water curtain roadway 7 is excavated, and the excavation and support construction of the water curtain roadway 7 is carried out.

[0054] When the main construction roadway is excavated to an elevation of -40m (i.e., the bottom elevation of water curtain roadway 7), branch roadways 9 are excavated from the two main construction roadways to enter the designed position of water curtain roadway 7, and the excavation and support construction of water curtain roadway 7 begins. The six water curtain roadways 7 adopt a 7m×6.5m straight wall arched cross section, with a total length of 4500m, and use anchor spraying support to provide water curtain protection for the subsequent excavation of the main tunnel 1.

[0055] VI. Excavation of the main chamber in layers S5. Utilizing the construction channels already accessed at both ends of the main tunnel 1 in step S3, begin layered excavation of the main tunnel 1 simultaneously from the first end 5 and the second end 6. For example... Figure 4 As shown, the main tunnel 1 is 30m high and is being excavated in three layers: upper, middle, and lower, with heights of 10m, 10m, and 10m respectively. The specific excavation process for step S5 is as follows: S51. Excavate the upper layer of the main cavern 1, and enter other main caverns 1 in the same tank area through the upper connecting roadways 10 at both ends of the main cavern 1 to carry out upper layer construction. First, excavate the upper layer (within 10m below the arch) of main caverns 1 (2#, 3#, 6#, and 7#) simultaneously from both ends. After the upper layer excavation is completed, enter the upper connecting roadways 10 set inside the main cavern 1 to carry out upper layer construction of main caverns 1#, 4#, 5#, and 8# in the same tank area, and realize the synchronous excavation of multiple caverns in the same tank area.

[0056] S52. After the upper layer excavation is completed, the pre-reserved full-section rock steps inside the end of the main tunnel 1 are used as an internal ramp 14. The internal ramp 14 is a full-section rock step ramp, located inside the end of the main tunnel 1, with a width the same as the tunnel (20m) and a slope of approximately 8%-10%. It is used to connect the excavation faces at different elevations of the upper, middle, and lower layers. The internal ramp 14 is used to descend into the middle layer excavation face of the main tunnel 1, and the middle layer excavation of the main tunnel 1 (elevation -80m to -90m) is carried out. This includes the middle layer excavation of main tunnels 2#, 3#, 6#, and 7#. Simultaneously, the middle layer connecting roadway 11 is used to enter main tunnels 1#, 4#, 5#, and 8#, completing the middle layer construction of the entire tank area. The middle layer connecting roadway 11 is also used to enter other main tunnels in the same tank area to complete the middle layer construction.

[0057] S53. After the middle layer excavation is completed, the built-in ramp 14 is used to continue the slope to enter the lower excavation working face (-90m to -100m elevation) of the main chamber 1 to carry out the lower excavation of the main chamber 1, and enter other main chambers in the same tank area through the lower connecting roadway 12 to complete the lower layer construction.

[0058] The upper connecting roadway 10, the middle connecting roadway 11, and the lower connecting roadway 12 are all located inside the main cavern 1, used to connect different main caverns 1 within the same tank area, enabling synchronous construction of each cavern within the tank area. Through the aforementioned layered excavation and connecting roadway system, synchronous continuous operation of the upper, middle, and lower levels of the eight main caverns within the same tank area was achieved, significantly improving construction efficiency.

[0059] VII. Finishing and Sealing S6. After completing all the excavation work of the main tunnel 1, remove the temporary rock steps at one end, exit the tunnel from the other end, and set concrete sealing plugs at both ends of the main tunnel 1.

[0060] After the main tunnel 1 has been fully excavated, the temporary rock step (built-in ramp 14) at one end is removed, and all construction equipment and personnel are evacuated from the other end via the construction tunnel. Then, concrete sealing plugs are installed at both ends of the main tunnel 1 (about 2-3m from the end wall). The length of the sealing plugs is determined according to the water pressure. In this embodiment, the length of the sealing plugs is 5m, and C30 concrete is used for pouring. Curtain grouting is set around the perimeter to ensure that the sealing plugs are tightly bonded to the surrounding rock to prevent oil and gas leakage.

[0061] The present invention provides a design method for an oil storage cavern with double-ended entry points. By changing the traditional "middle entry" construction roadway layout, and adopting an innovative design that allows entry from both ends of the main cavern 1 combined with an internal inclined ramp 14, the following beneficial effects are achieved: First, it significantly shortens the length of construction tunnels, reducing project investment.

[0062] This invention abandons the traditional method of entering the main tunnel from the middle section using branch construction roadways. Instead, it replaces most of the branch construction roadways with ramps 14 built into the main tunnel 1, allowing direct entry from both ends of the main tunnel 1. Engineering examples have verified that this method can shorten the total excavation mileage of the construction roadway by approximately 30% to 40%, correspondingly reducing the amount of excavation work, grouting, and anchor bolt support, thus significantly lowering construction costs.

[0063] Second, shortening the length of single-heading tunneling significantly improves construction efficiency.

[0064] Traditional methods of entering the main tunnel via the middle approach require excavation from both ends, with a single-ended excavation length of 400-500m at one end. This invention employs a double-ended entry method, excavating simultaneously from both ends of the main tunnel towards the middle, reducing the single-ended excavation length by approximately 50%, to only 200-250m. Construction is more streamlined, increasing the excavation efficiency of the main tunnel by 50%-80%, and reducing the construction period of the main tunnel by 9-16 months. For the entire tunnel project, this shortens the construction cycle by 15%-20%, effectively solving the technical challenge of tight deadlines.

[0065] Third, enter the main cavern 1 in advance to expose unfavorable geological conditions as early as possible.

[0066] This invention allows for direct entry into the main tunnel from both ends, bypassing the process of excavating long-distance branch tunnels. This enables upper-level excavation of the main tunnel to begin approximately 6-8 months earlier. This allows for the early exposure of adverse geological conditions such as fractured zones and densely jointed zones, providing ample time for geological risk assessment and emergency response, and preventing project delays and safety accidents caused by encountering unfavorable geological formations later in the project.

[0067] Fourth, optimize the arrangement of sealing plugs to effectively reduce the risk of seepage around the plug.

[0068] In traditional layouts, the intersection of the branch construction tunnel and the main tunnel is located in the middle of the tunnel body. A concrete sealing plug needs to be installed at this intersection later. This area is prone to seepage channels due to significant excavation disturbance and stress concentration. This invention places the connection between the construction tunnel and the main tunnel 1 at both ends of the main tunnel 1, with the sealing plugs correspondingly placed at the ends. The geological conditions in this area are relatively intact, and excavation disturbance is minimal, effectively reducing the risk of seepage around the tunnel and improving the water seal safety of the tunnel.

[0069] Example 3 This embodiment provides an oil storage cavern system with dual-end access, comprising: at least one main cavern 1, each main cavern 1 having a first end 5 and a second end 6, and a built-in ramp 14 provided inside the end of each main cavern 1, the built-in ramp 14 being located inside the end of the main cavern 1 for connecting different excavation elevation layers of the main cavern 1. The built-in ramp 14 is a full-section rock step ramp, located inside the end of the main cavern 1, and its slope meets the requirements for the passage of construction equipment; the first main construction roadway 3 and the second main construction roadway 4 are provided with arc-shaped bends 8 near the end of the main cavern 1, so that the axis of the construction roadway turns directly towards the end of the main cavern 1.

[0070] The first main construction tunnel 3 and the second main construction tunnel 4 extend from the ground surface to the first end 5 of the main tunnel 1 and are directly connected to the first end 1. The second main construction tunnel 4 extends from the ground surface to the second end 6 of the main tunnel 1 and is directly connected to the second end 6, forming a construction passage that can be entered from both ends of the main tunnel 1.

[0071] The water curtain system includes a water curtain tunnel 7 and a branch tunnel 9 connecting the construction tunnel and the water curtain tunnel 7.

[0072] The connecting tunnel system includes an upper connecting tunnel 10, a middle connecting tunnel 11, and a lower connecting tunnel 12, all located inside the main tunnel 1, for connecting different main tunnels 1 within the same tank area. A concrete sealing plug is installed at the end of each main tunnel 1 to seal the tunnel after construction is completed.

[0073] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for designing an oil storage cavern with double-ended entrances, characterized in that, Includes the following steps: S1. Screening of underground water-sealed cavern reservoir site options, conducting geological surveys and obtaining geological information for the selected sites; performing numerical simulations and field tests to analyze the stability of the surrounding rock and the characteristics of the seepage field; S2. Based on the geological survey and the field test conclusions, determine the axial direction, cross-sectional type, length and cross-sectional dimensions of the main tunnel, and determine the layout and elevation of the water curtain tunnel; S3. Set up the construction tunnel entrance according to the layout parameters of the main tunnel. Excavate the first main construction tunnel and the second main construction tunnel from the surface. The two construction tunnels extend to the front of the first end and the second end of the main tunnel, respectively. After turning through the bend, excavate the branch construction tunnels to enter the main tunnel from the first end and the second end, respectively, so as to realize simultaneous entry from both ends of the main tunnel. S4. When the main construction roadway is excavated to the elevation of the water curtain roadway, the branch roadway connecting the main construction roadway and the water curtain roadway is excavated, and the excavation and support construction of the water curtain roadway is carried out. S5. Using the construction passages that have been entered at both ends of the main tunnel in step S3, start excavating the main tunnel in layers from the first end and the second end simultaneously. S6. After completing all the excavation work of the main tunnel, remove the temporary rock steps at one end, exit the tunnel from the other end, and set concrete sealing plugs at both ends of the main tunnel.

2. The method for designing an oil storage cavern with double-sided end entrances according to claim 1, characterized in that, Step S5 specifically includes: S51. Excavate the upper layer of the main cavern, and enter other main caverns in the same tank area through the upper connecting roadways at both ends of the main cavern to carry out upper layer construction; S52. After the upper layer excavation is completed, the full-section rock steps reserved inside the end of the main tunnel are used as built-in ramps. The middle layer excavation working face of the main tunnel is entered through the built-in ramps to carry out the middle layer excavation of the main tunnel. The middle layer connecting roadway is used to enter other main tunnels in the same tank area to complete the middle layer construction. S53. After the middle layer excavation is completed, the built-in inclined ramp is used to continue the slope to enter the lower layer excavation face of the main chamber, and the lower layer excavation of the main chamber is carried out. The lower layer connecting roadway is used to enter other main chambers in the same tank area to complete the lower layer construction.

3. The method for designing an oil storage cavern with double-sided end entrances according to claim 1, characterized in that, The first and second main construction tunnels mentioned in step S3 have a straight-walled circular arch shape, and the cross-sectional dimensions are determined according to the requirements for the passage and transportation of construction equipment.

4. The method for designing an oil storage cavern with double-sided end entrances according to claim 2, characterized in that, The upper connecting tunnel, middle connecting tunnel and lower connecting tunnel mentioned in step S5 are all set inside the main tunnel to connect different main tunnels in the same tank area, so as to realize the synchronous construction of each tunnel in the tank area.

5. The method for designing an oil storage cavern with double-sided end entrances according to claim 1, characterized in that, In step S1, the selection of underground water-sealed cavern reservoir sites is determined by oil source, surface water system, lithology, topography, transportation and supporting conditions; the acquisition of geological information specifically includes the acquisition of topography, stratigraphy, geological structure and hydrogeological conditions.

6. The method for designing an oil storage cavern with double-sided end entrances according to claim 1, characterized in that, In step S3, the entrance to the construction tunnel is located in a place with good surface geological conditions, small excavation volume, and open construction site.

7. The method for designing an oil storage cavern with double-sided end entrances according to claim 1, characterized in that, In step S3, during the excavation of the first and second main construction tunnels from the ground surface, the two construction tunnels are excavated in parallel along the axis of the main tunnel, and the elevation is gradually reduced to be close to the elevation of the main tunnel roof.

8. An oil storage cavern system with double-ended entrances, characterized in that, include: At least one main cavern, the main cavern having a first end and a second end, and the main cavern having an internal ramp located inside the end of the main cavern for connecting different excavation elevation layers of the main cavern; The first main construction tunnel and the second main construction tunnel extend from the ground surface to the first end of the main cavern and are directly connected to the first end. The second main construction tunnel extends from the ground surface to the second end of the main cavern and are directly connected to the second end, forming a construction passage that can be entered from both ends of the main cavern. A water curtain system, including a water curtain tunnel and a branch tunnel connecting the construction tunnel and the water curtain tunnel; The connecting tunnel system includes upper, middle and lower connecting tunnels located inside the main tunnel chambers, used to connect different main tunnel chambers within the same tank area.

9. An oil storage cavern system with double-sided end access as described in claim 8, characterized in that, The built-in ramp is a full-section rock step ramp, located inside the end of the main tunnel, with a slope that meets the requirements for the passage of construction equipment; the first and second main construction tunnels have arc-shaped bends near the end of the main tunnel, so that the axis of the construction tunnels turns to face the end of the main tunnel.

10. An oil storage cavern system with double-sided end access according to claim 8, characterized in that, A concrete sealing plug is installed at the end of the main cavern to seal the cavern after construction is completed.

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