A method for preventing seawater intrusion in an underground cavern near the sea

Abstract

The invention discloses a method for preventing seawater intrusion in an underground cavern near a sea. The method utilizes the correlation between the risk of seawater intrusion and the hydrological and geological conditions, and not only adjusts the determination method and standard of the risk of seawater intrusion in a targeted manner, and makes a preliminary and re-determination of the risk level of seawater intrusion based on this, but also considers the factors affecting the risk of seawater intrusion more comprehensively, thereby significantly improving the accuracy of determining the risk of seawater intrusion; and also makes a targeted adjustment to the prevention and control measures based on the determination result, thereby making the prevention and control measures more targeted, and avoiding excessive prevention and control caused by inappropriate prevention and control measures under the premise of ensuring effective prevention of seawater intrusion, that is, saving the cost and resources of prevention and control, and shortening the construction period, and is suitable for large-scale application and promotion in the project of preventing seawater intrusion in underground caverns near sea.

Description

Technical Field

[0001] The invention relates to the technical field of underground engineering, and in particular to a method for preventing seawater intrusion into a seaside underground cavern. Background Art

[0002] Seawater intrusion refers to the phenomenon that the natural freshwater groundwater level drops due to the construction of underground caverns in areas near the coast, resulting in the destruction of the balance between seawater and freshwater, causing seawater to flow into the caverns through faults or dense joints, resulting in large amounts of water seepage and gushing in the caverns. Therefore, when designing and constructing underground caverns in areas near the coast, the problem of seawater intrusion must be considered.

[0003] In order to facilitate the transportation and storage of crude oil, underground oil depots are usually built in coastal areas, and the natural and abundant underground fresh water is used to seal the oil stored in the underground oil depot. When selecting a site for the construction of an underground oil depot, in order to avoid seawater intrusion, a location with good stratum conditions and a certain distance from the coast is usually selected, thereby reducing the risk of seawater intrusion. However, affected by many factors such as topography, environment, cost and transportation, not all underground oil depots meet the above site selection requirements. Among them, the site selection of some underground oil depots is close to the coast and there are water flow channels such as fault fracture zones, which pose a greater risk of seawater intrusion. Therefore, how to accurately and effectively identify the risk level of seawater intrusion and formulate protective measures based on this has become the key to whether such underground oil depots can operate normally and safely. Summary of the invention

[0004] The invention aims to overcome the defects of the existing methods for preventing seawater intrusion, that is, the poor accuracy of judging the risk of seawater intrusion and the poor protection effect against seawater intrusion, and proposes a method for preventing seawater intrusion in underground caverns near the sea. The method not only adjusts the judgment method and standard of the seawater intrusion risk in a targeted manner, and makes a preliminary judgment and a re-judgment of the seawater intrusion risk level based on this, but also makes a targeted adjustment to the prevention and control measures based on the judgment result, thereby significantly improving the accuracy of judging the risk of seawater intrusion; and making the prevention and control measures more targeted, and more suitable for large-scale application and promotion in the seawater intrusion prevention project of underground caverns near the sea.

[0005] In order to achieve the above object, the present invention provides a method for preventing seawater intrusion in an underground cavern near the sea, comprising the following steps:

[0006] (1) Combine the freshwater level, seawater elevation and geological information data of the reservoir area with the structural data of the underground cavern to establish a three-dimensional seepage field model of the reservoir area. Use the three-dimensional seepage field model to analyze the water level changes and seepage laws of groundwater during cavern construction, and obtain the water level of natural freshwater after cavern excavation. Based on the water level of natural freshwater, make a preliminary assessment of the risk of seawater intrusion into the underground cavern.

[0007] (2) Based on the results of the initial assessment, monitoring holes are set up on the fault fracture zone and / or crack-intensive zone on the seaward side of the ground periphery of the reservoir area to monitor the water level and water quality in the monitoring holes; based on the monitoring results, the risk of seawater intrusion into the underground cavern is reassessed outside the cavern;

[0008] After the underground cavern is excavated, the real geological conditions and hydrological data of the fault fracture zone and / or the fissure-intensive zone on the sea side are obtained from underground using advance drilling technology, geological radar technology and transient electromagnetic or infrared water exploration technology; the risk of seawater intrusion into the underground cavern is re-evaluated in the cave based on the real geological conditions and hydrological data;

[0009] (3) Based on the results of the re-evaluation inside and outside the cave, corresponding prevention and control measures are selected during the construction of the underground cave to prevent seawater from invading the underground cave.

[0010] The invention discloses a method for preventing seawater intrusion in an underground cavern near a sea. The method utilizes the correlation between the risk of seawater intrusion and the hydrological and geological conditions. The method and standard for determining the risk of seawater intrusion are adjusted in a targeted manner, and the risk level of seawater intrusion is initially and re-determined based on the method and standard. The factors affecting the risk of seawater intrusion are considered more comprehensively, thereby significantly improving the accuracy of determining the risk of seawater intrusion. The method also adjusts the prevention and control measures in a targeted manner based on the result of the determination, thereby making the prevention and control measures more targeted. Under the premise of ensuring effective prevention of seawater intrusion, the method avoids excessive prevention and control caused by inappropriate prevention and control measures, thereby saving the cost and resources of prevention and control and shortening the construction period. The method is suitable for large-scale application and promotion in seawater intrusion prevention projects in underground caverns near sea.

[0011] Wherein, in step (1), the freshwater level, seawater elevation and geological information data of the reservoir area can be obtained through geological survey; the reservoir area refers to the area used for building an underground cavern.

[0012] Wherein, in step (1), the geological information at least includes topography, landform, stratum and fracture zone information; the geological information is a necessary factor for constructing a three-dimensional seepage field model. By analyzing the three-dimensional seepage field model, more accurate analysis and preliminary judgment results can be obtained.

[0013] Wherein, in step (1), the initial judgment standard is: when the water level of natural fresh water is lower than the seawater elevation, the risk of seawater intrusion into the underground cavern is initially judged to be high; when the water level of natural fresh water is not lower than the seawater elevation, the risk of seawater intrusion into the underground cavern is initially judged to be low; the initial judgment standard can make a more accurate and faster initial judgment on the risk of seawater intrusion, thereby providing guidance for subsequent steps, making the method of preventing seawater intrusion more effective, more targeted, and lowering the cost of prevention and control.

[0014] Among them, in step (2), preferably, the method for setting the monitoring holes is: when the risk of seawater intrusion into the underground cavern is initially judged to be low, the detection holes are set at a distance of 15-25m; when the risk of seawater intrusion into the underground cavern is initially judged to be high, the monitoring holes are set at a distance of 5-10m. The preferred method for setting the monitoring holes can save construction time and cost on the basis of ensuring the accuracy of the judgment, and is more suitable for promotion and application.

[0015] Among them, in step (2), preferably, the depth of the monitoring hole is 1-2m lower than the bottom surface of the underground cavern, and the hole diameter is 150-200mm; the preferred monitoring hole parameters result in more accurate monitoring results, better monitoring effects, and more suitable construction period and cost.

[0016] Wherein, in step (2), the standard for re-judgment outside the cave is: when the water level in the monitoring hole is lower than the water level of natural fresh water predicted by the seepage analysis, and / or when the water quality corrosivity in the monitoring hole is judged to be weak, medium or strong, then the risk of seawater intrusion into the underground cavern is judged to be high; otherwise, the risk of seawater intrusion into the underground cavern is judged to be low. The standard for re-judgment outside the cave can more accurately and quickly re-judge the risk of seawater intrusion outside the cave, thereby providing guidance for subsequent prevention and control measures, making the method of preventing seawater intrusion more effective, more targeted and with lower prevention and control costs.

[0017] In step (2), the standard for the in-tunnel re-judgment is as follows: when there is no water in the advance drilling hole or the water quality is judged to be non-corrosive, the in-tunnel re-judgment risk of seawater intrusion into the underground cavern is zero; when the water output of a single advance drilling hole is ≤10 L / min, the water quality inspection shows that the corrosiveness is slight and the rock mass is relatively intact-intact, the in-tunnel re-judgment risk of seawater intrusion into the underground cavern is low; when the water output of a single advance drilling hole is ≥30 L / min, the water quality inspection shows that the corrosiveness is medium or strong and the rock mass is relatively broken-broken, the in-tunnel re-judgment risk of seawater intrusion into the underground cavern is high; in other cases, the in-tunnel re-judgment risk of seawater intrusion into the underground cavern is medium; the standard for the in-tunnel re-judgment can more accurately and quickly re-judge the risk of seawater intrusion in the cave, thereby providing guidance for subsequent prevention and control measures, making the method of preventing seawater intrusion more effective and targeted, and reducing the prevention and control cost.

[0018] Among them, the water quality corrosiveness identification standard is carried out with reference to the "Corrosiveness Evaluation" in the "Geotechnical Engineering Investigation Code GB50021-2001" (2009 edition).

[0019] Among them, the rock mass condition identification standard is based on the "Qualitative Classification of Rock Integrity" in the "Geotechnical Engineering Investigation Code GB50021-2001" (2009 edition).

[0020] Among them, in step (3), the corresponding relationship between the results of the re-judgment inside the cave and the re-judgment outside the cave and the prevention and control measures is:

[0021]

[0022] Among them, preferably, the grouting materials for the radial grouting and advance grouting are ordinary cement slurry or ultrafine cement slurry with a water-cement ratio of 0.8-1:1; the grouting pressure is 2-3MPa greater than the water pressure of the drilled water; before grouting, the surrounding rock within a range of ≥5m around the underground cavern needs to be water-blocked and reinforced; the preferred grouting conditions have a better effect on the prevention and control of seawater intrusion.

[0023] Among them, the setting method of the fresh water partition is: setting an injection hole in the direction of seawater in the underground cavern, and introducing natural fresh water into the injection hole, and ensuring that the pressure difference between the natural fresh water head and the seawater head is greater than the minimum head required for the fresh water partition; the minimum head required for the fresh water partition is predicted by analyzing the water level changes and seepage laws of groundwater during the cavern construction process using a three-dimensional seepage field model; through the setting of the fresh water partition, seawater intrusion can be better prevented, with stronger targeting and lower prevention and control costs.

[0024] Among them, preferably, the minimum distance between the water injection hole and the edge of the underground cavern is not less than 20m; the diameter of the water injection hole is 110-150mm, and the spacing between the water injection holes is 10-20m; the preferred water injection hole parameters have better freshwater isolation effect, are more targeted, and have lower prevention and control costs.

[0025] Among them, preferably, the prevention and control measures also include the use of one or more of early-strength anti-seepage and corrosion-resistant shotcrete, multiple anti-corrosion anchor rods and waterproof concrete structures; the preferred prevention and control measures have better prevention and control effects on seawater intrusion.

[0026] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0027] 1. The method for preventing seawater intrusion in an underground cavern near the sea of ​​the present invention adjusts the determination method and standard of seawater intrusion risk in a targeted manner, and makes an initial and re-determination of the seawater intrusion risk level based on the method, and considers the factors affecting the seawater intrusion risk more comprehensively, thereby significantly improving the accuracy of determining the seawater intrusion risk.

[0028] 2. The method for preventing seawater intrusion in underground caverns near the sea of ​​the present invention makes targeted adjustments to the prevention and control measures based on the judgment results, thereby making the prevention and control measures more targeted. Under the premise of effectively preventing seawater intrusion, the method can avoid excessive prevention and control caused by inappropriate prevention and control measures, thereby saving the cost and resources of prevention and control and shortening the construction period.

[0029] 3. The method of preventing seawater intrusion in underground caverns near the sea of ​​the present invention has high accuracy in risk assessment, the selected prevention and control measures are highly targeted and have good prevention and control effects, and the method is simple and highly operational, which provides technical guarantee for the safe construction and operation of underground cavern projects and is suitable for large-scale application and promotion in projects to prevent seawater intrusion in underground caverns near the sea. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic flow chart of a method for preventing seawater intrusion in an underground cavern near the sea according to the present invention;

[0031] Figure 2 It is a schematic diagram of the three-dimensional seepage field model of the present invention;

[0032] Figure 3 It is a schematic diagram of the monitoring hole arrangement of the present invention;

[0033] Figure 4 It is a schematic diagram of the arrangement of the water injection holes of the present invention.

[0034] Markings in the figure: 1-seawater; 2-coastline; 3-fault fracture zone and / or fissure-intensive zone; 4-monitoring hole; 5-underground cavern; 6-tunnel; 7-water injection hole; 8-fresh water. DETAILED DESCRIPTION

[0035] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0036] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] Example 1

[0038] Project Name: Huizhou Petroleum Cavern

[0039] Project description: Huizhou National Underground Oil Storage Depot is the second phase of the national crude oil strategic reserve construction project. It is built under the mountain of Tanyebei, Renshan Town, Huidong County, Huizhou City, Guangdong Province, covering an area of ​​about 106.7 hectares. The cavern is designed to have a petroleum storage capacity of 5 million cubic meters. The Huizhou Underground Water Seal Oil Storage Depot project mainly includes two parts: underground engineering and ground auxiliary facilities engineering. The underground engineering mainly includes construction tunnels, water curtain systems, underground oil storage caverns and operating shafts.

[0040] Project geological conditions: The strata in the reservoir area are relatively simple, basically the Quaternary Holocene system (Q) strata, and the rest are Late Jurassic intrusive rocks. The intrusive rocks (T3S) are mainly monzogranite, among which the caves are mainly located in the medium weathered and slightly weathered layers, with hard rocks and good integrity. There are small-scale quartz veins, quartz porphyry and diabase veins interspersed.

[0041] Project hydrological conditions: The groundwater depth is 0.5 to 49 meters, the elevation is 15.78 to 206.69 meters, and the groundwater level is obviously controlled by the terrain and is relatively abundant and stable. According to the geological survey report, the groundwater level in the reservoir area is stable, and the reservoir area has groundwater covering the entire reservoir area. The loose layer on the surface has a good replenishment effect on the underlying bedrock fissure water.

[0042] The structure and situation of underground caverns: The caverns are divided into 5 groups with a total of 10 oil storage caverns. Two main caverns in each group are connected to form a tank through a construction branch tunnel. The main cavern roof elevation is -30m, the floor elevation is -60m, the design length is about 930m, the cave axis direction is 70° north-east, and the single cave capacity is about 500,000m 3 The main cavern is 20m wide and 30m high, with a straight-walled circular arch cross-section.

[0043] Specific steps of the method to prevent seawater intrusion (see the flowchart for Figure 1 ):

[0044] (1) Based on the freshwater level, seawater elevation and geological information data of the reservoir area and the structural data of the underground cavern, a three-dimensional seepage field model of the reservoir area is established (see Figure 2 ); The three-dimensional seepage field model was used to analyze the water level changes and seepage laws of groundwater during the cavern construction process. It was found that the water level of natural fresh water after the cavern excavation was more than 10m above sea level. Based on the water level of natural fresh water, the risk of seawater intrusion into the underground cavern was initially judged, and the initial judgment result was low intrusion risk;

[0045] (2) Based on the results of the initial assessment, monitoring holes (25 m apart; 1.5 m below the bottom of the underground cavern and with a hole diameter of 180 mm) were set up on the fault fracture zone and / or fissure-intensive zone on the seaward side of the ground periphery of the reservoir area to monitor the water level and water quality. Based on the monitoring results (the water level was 15 m above sea level and the water quality was non-corrosive), the risk of seawater intrusion into the underground cavern was reassessed outside the cavern, and the result of the reassessment outside the cavern was low.

[0046] After the underground cavern was excavated, the real geological conditions and hydrological data of the fault fracture zone and / or the fissure-intensive zone on the sea side were obtained from underground using advance drilling technology, geological radar technology and infrared water detection technology. Based on the real geological conditions and hydrological data (the water output of a single hole is 15L / min, the corrosiveness of the water quality inspection is judged as non-corrosive; the rock mass is intact-relatively intact), the risk of seawater intrusion into the underground cavern was re-evaluated in the cave, and the result of the in-cave re-evaluation was that there was no risk of seawater intrusion;

[0047] (3) Based on the results of the re-evaluation inside the cave (no risk of seawater intrusion) and the re-evaluation outside the cave (low risk of seawater intrusion), anti-seawater intrusion measures were not considered when constructing the underground cavern.

Claims

1. A method for preventing seawater intrusion in an underground cavern near the sea, characterized in that: The following steps are involved: (1) Combine the freshwater level, seawater elevation and geological information data of the reservoir area with the structural data of the underground cavern to establish a three-dimensional seepage field model of the reservoir area. Use the three-dimensional seepage field model to analyze the water level changes and seepage laws of groundwater during cavern construction, and obtain the water level of natural freshwater after cavern excavation. Based on the water level of natural freshwater, make a preliminary assessment of the risk of seawater intrusion into the underground cavern. (2) Based on the results of the initial assessment, monitoring holes are set up on the fault fracture zone and / or crack-intensive zone on the seaward side of the ground periphery of the reservoir area to monitor the water level and water quality in the monitoring holes; based on the monitoring results, the risk of seawater intrusion into the underground cavern is reassessed outside the cavern; After the underground cavern is excavated, the real geological conditions and hydrological data of the fault fracture zone and / or the fissure-intensive zone on the sea side are obtained from underground using advance drilling technology, geological radar technology and transient electromagnetic or infrared water exploration technology; the risk of seawater intrusion into the underground cavern is re-evaluated in the cave based on the real geological conditions and hydrological data; (3) Based on the results of the re-evaluation inside and outside the cave, corresponding prevention and control measures are selected during the construction of the underground cave to prevent seawater from invading the underground cave.

2. The method for preventing seawater intrusion according to claim 1, characterized in that: In step (1), the geological information includes topography, landform, stratum and fracture zone information.

3. The method for preventing seawater intrusion according to claim 1, characterized in that: In step (1), the initial judgment standard is: when the water level of natural fresh water is lower than the seawater elevation, the initial judgment risk of seawater intrusion into the underground cavern is high; when the water level of natural fresh water is not lower than the seawater elevation, the initial judgment risk of seawater intrusion into the underground cavern is low.

4. The method for preventing seawater intrusion according to claim 1, characterized in that: In step (2), the monitoring holes are set up in the following manner: when the risk of seawater intrusion into the underground cavern is initially judged to be low, the monitoring holes are set up at a distance of 15-25 m; when the risk of seawater intrusion into the underground cavern is initially judged to be high, the monitoring holes are set up at a distance of 5-10 m.

5. The method for preventing seawater intrusion according to claim 1, characterized in that: In step (2), the monitoring hole depth is 1-2 m below the bottom surface of the underground cavern, and the hole diameter is 150-200 mm.

6. The method for preventing seawater intrusion according to claim 1, characterized in that: In step (2), the standard for re-judgment outside the cave is: when the water level in the monitoring hole is lower than the water level of natural fresh water predicted by the seepage analysis, and / or when the water corrosivity in the monitoring hole is judged to be weak, medium or strong, the risk of seawater intrusion into the underground cavern is judged to be high; otherwise, the risk of seawater intrusion into the underground cavern is judged to be low. The standard for re-judgment outside the cave can more accurately and quickly re-judge the risk of seawater intrusion outside the cave, thereby providing guidance for subsequent prevention and control measures, making the method of preventing seawater intrusion more effective, more targeted and with lower prevention and control costs.

7. The method for preventing seawater intrusion according to claim 1, characterized in that: In step (2), the criteria for the in-tunnel re-judgment are as follows: when there is no water in the advance drilling hole or the water quality is judged to be non-corrosive, the in-tunnel re-judgment risk of seawater intrusion into the underground cavern is zero; when the water output of a single advance drilling hole is ≤10 L / min, the corrosiveness of the water quality inspection is judged to be slight, and the rock mass condition is relatively intact-intact, the in-tunnel re-judgment risk of seawater intrusion into the underground cavern is low; when the water output of a single advance drilling hole is ≥30 L / min, the corrosiveness of the water quality inspection is judged to be medium or strong, and the rock mass condition is relatively broken-broken, the in-tunnel re-judgment risk of seawater intrusion into the underground cavern is high; in other cases, the in-tunnel re-judgment risk of seawater intrusion into the underground cavern is medium.

8. The method for preventing seawater intrusion according to claim 1, characterized in that: In step (3), the corresponding relationship between the results of the re-evaluation inside the cave and outside the cave and the prevention and control measures is:

9. The method for preventing seawater intrusion according to claim 8, characterized in that: The grouting materials for the radial grouting and advance grouting are ordinary cement slurry or ultrafine cement slurry with a water-cement ratio of 0.8-1:1; the grouting pressure is 2-3MPa greater than the water pressure of the drilled water; before grouting, the surrounding rock within a range of ≥5m around the underground cavern needs to be water-blocked and reinforced.

10. The method for preventing seawater intrusion according to claim 8, characterized in that: The method for setting up the freshwater barrier is as follows: drilling holes in the direction of seawater from the underground cavern, and introducing natural fresh water into the holes, and ensuring that the pressure difference between the natural freshwater head and the seawater head is greater than the minimum head required for the freshwater barrier; the minimum head required for the freshwater barrier is predicted by analyzing the water level changes and seepage laws of groundwater during the cavern construction process using a three-dimensional seepage field model.

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