In-situ infiltration enhancement system and method for low-permeability contaminated sites

Abstract

The present invention relates to an in-situ permeability enhancement system and method for low-permeability contaminated sites. The permeability enhancement system comprises: a drilling device, a nitrogen preparation device, a liquid nitrogen preparation device, a water supply device and a controller. The drilling device comprises: a drill rod, a drill bit, a temperature sensor, a pressure sensor and a water content sensor. A liquid nitrogen injection channel is provided inside the drill rod, and a heat-insulating oil channel is provided outside the liquid nitrogen injection channel. The drill rod also has a clean water injection channel and a high-pressure nitrogen channel. The drill bit is a spiral drill bit, which is arranged at the front end of the drill rod. The drill bit is provided with a plurality of liquid nitrogen perforations, a plurality of clean water injection holes and a plurality of high-pressure nitrogen perforations. The system can adapt to the permeability enhancement of low-permeability contaminated sites with high, medium and low water contents, and can realize the permeability enhancement of low-permeability contaminated sites with high efficiency, continuity, high degree of automation and applicable to various geological environments. The system and method can provide support for site remediation after permeability enhancement, thereby solving the problems of poor applicability, difficulty in permeability enhancement and high cost of permeability enhancement technology for contaminated sites.

Description

Technical Field

[0001] The present invention relates to the technical field of contaminated site remediation, and in particular to an in-situ permeability enhancement system and method for a low-permeability contaminated site. Background Art

[0002] In recent years, a series of site remediation technologies have been developed using physical, chemical or biological methods to transfer, transform, absorb, degrade or convert toxic and harmful pollutants into harmless substances. According to the different disposal sites, it can be divided into in-situ remediation and ex-situ remediation. However, compared with the disadvantages of large engineering workload and high cost of ex-situ remediation, in-situ remediation without moving the contaminated soil has become a hot spot in site remediation research due to its advantages of low investment, simple construction and little impact on the surrounding environment.

[0003] In-situ remediation technologies include in-situ leaching, vapor phase extraction (SVE), multiphase extraction (MPVE), in-situ thermal desorption, biodegradation, in-situ chemical reduction oxidation (ISCO), in-situ solidification stabilization and phytoremediation. Studies have found that these in-situ remediation technologies have problems such as long remediation cycles, incomplete or excessive treatment, and low treatment effects in low-permeability contaminated sites in engineering applications, which to a certain extent limit the promotion and application of remediation technologies. The reason why in-situ remediation of low-permeability contaminated sites is limited is that the dense structure and low porosity of the contaminated body make it difficult for remediation agents or pollutants to quickly migrate or remove through their original cracks, affecting the effect of remediation. Fracturing permeability enhancement technology is considered to be an effective method to increase the permeability of low-permeability contaminated sites and to coordinate with other remediation methods to improve the remediation effect.

[0004] Pressure fracturing technology built on energy extraction refers to a method of applying pressure media to expand primary fractures and add new fractures. According to different media, it can be divided into hydraulic fracturing and pneumatic fracturing technology. Although hydraulic fracturing technology has been widely used in the permeability enhancement of high-stress dense sandstone and shale, it is difficult to achieve ideal results due to its large water consumption, serious secondary pollution, and high clay content in formations. In low-permeability contaminated formations, most of the rock and soil materials are clay with low tensile strength and high plasticity, silty clay or silty soft soil, and weakly cemented sand with high water-sensitive mineral content. Therefore, hydraulic fracturing is difficult to adapt to low-permeability contaminated sites. For this reason, pneumatic fracturing technology using high-pressure gas as a medium has been developed. The process can generally be described as injecting air (or other gases) into the contaminated site formation at sufficient pressure and flow rate to produce artificial fractures. Once established, the fractures increase the permeability of the formation. From the perspective of transport mechanism, these fractured pore networks transform the medium transport from a diffusion process to a convection-diffusion process, making the removal or treatment of pollutants faster and more effective. Compared with hydraulic fracturing, pneumatic fracturing usually has a faster crack propagation rate, no fracturing fluid contamination, and in clay, with the assistance of supporting materials, it can make up for the closure of cracks after propagation. Therefore, previous studies have shown that pneumatic fracturing technology is considered to be a cost-effective and enhanced method for in-situ treatment of low-permeability contaminated sites.

[0005] However, when the groundwater level is shallow and the contaminated site to be repaired is in the capillary zone, saturated zone, or even below the groundwater level, the pneumatic fracturing technology is limited due to the high water content. There are few reports in China on the use of pneumatic fracturing permeability enhancement technology to enhance the repair of low-permeability contaminated sites. A set of application processes is urgently needed to solve the low permeability problem. In addition, the application of pneumatic fracturing technology in some contaminated sites abroad has shown that there are problems such as the difficulty in matching the injection pressure with the target permeability coefficient to be achieved in the repaired formation, and the difficulty in controlling the direction of crack propagation. Summary of the invention

[0006] The present application provides an in-situ permeability enhancement system and method for low-permeability contaminated sites, which solves the technical problem of the lack of pneumatic fracturing permeability enhancement technology to enhance the repair of low-permeability contaminated sites, and realizes a relatively universal permeability enhancement technology and process for low-permeability contaminated sites based on pneumatic fracturing technology.

[0007] The present application provides an in-situ permeability enhancement system for low-permeability contaminated sites, comprising: a drilling device, a nitrogen preparation device, a liquid nitrogen preparation device, a water supply device and a controller.

[0008] The drilling device includes: a drill pipe, a drill bit, a temperature sensor, a pressure sensor and a water content sensor.

[0009] A liquid nitrogen injection channel is provided in the drill pipe, and a heat-insulating oil channel is provided outside the liquid nitrogen injection channel.

[0010] The drill pipe is also provided with a clean water injection channel and a high-pressure nitrogen channel.

[0011] The drill bit is a spiral drill bit, which is arranged at the end of the drill rod. The drill bit is provided with a plurality of liquid nitrogen perforations, a plurality of clean water injection holes and a plurality of high-pressure nitrogen perforations. The liquid nitrogen perforations are connected to the liquid nitrogen injection channel, the clean water injection holes are connected to the clean water injection channel, and the high-pressure nitrogen perforations are connected to the high-pressure nitrogen channel.

[0012] The temperature sensor, pressure sensor and water content sensor are arranged on the drill bit, the temperature sensor detects the temperature of the infiltration position, the pressure sensor detects the pressure of the infiltration position, and the water content sensor detects the water content of the infiltration position;

[0013] The output end of the nitrogen preparation device is connected to the drilling device, and is used to prepare high-pressure nitrogen and send it into the high-pressure nitrogen channel;

[0014] The output end of the liquid nitrogen preparation device is connected to the drilling device, and is used to prepare liquid nitrogen and send it into the liquid nitrogen injection channel;

[0015] The output end of the water supply device is connected to the drilling device for conveying clean water to the clean water injection channel;

[0016] The controller is electrically connected to the temperature sensor, the pressure sensor, the moisture content sensor, the liquid nitrogen preparation device, the nitrogen gas preparation device and the water supply device, and controls the working sequence and working time interval of the liquid nitrogen preparation device, the nitrogen gas preparation device and the water supply device after receiving the temperature, pressure and moisture content information of the permeation position.

[0017] Preferably, the drill bit comprises: a head end, a spiral middle section and a tail end,

[0018] A plurality of clean water injection holes are respectively arranged at the head end and the tail end;

[0019] A plurality of liquid nitrogen perforations are arranged on the outer side of the threads of the spiral middle section, and a plurality of high-pressure nitrogen perforations are arranged on the inner side of the threads of the spiral middle section;

[0020] The temperature sensor and the pressure sensor are arranged at the position where the head end is combined with the spiral middle section; the temperature sensor and the pressure sensor are also arranged at the position where the tail end is combined with the spiral middle section;

[0021] The water content sensor is arranged on the spiral middle section.

[0022] Preferably, the head end is provided with 1 or 2 clean water injection holes;

[0023] The tail end is provided with 3 to 6 clean water injection holes;

[0024] The length of the spiral middle section is 0.2 to 0.8 meters;

[0025] The liquid nitrogen perforations are arranged at equal intervals, the number of which is controlled at 20 to 40 per meter, and the phase angle between the liquid nitrogen perforations is 30 to 90 degrees;

[0026] The arrangement spacing, number and phase angle between holes of the high-pressure nitrogen perforations are the same as those of the liquid nitrogen perforations.

[0027] Preferably, the liquid nitrogen preparation device is a highly integrated vehicle-mounted liquid nitrogen preparation device, which provides compressed air through an air compressor, purifies the compressed air through a multi-stage filter, separates nitrogen and oxygen from the purified compressed air through a high-pressure drive membrane separation module, and produces the liquid nitrogen through a pressurized cooling nitrogen liquefaction module.

[0028] Preferably, the nitrogen preparation device is a vehicle-mounted nitrogen booster, and the vehicle-mounted nitrogen booster is connected to the nitrogen output end of the high-pressure drive membrane separation module;

[0029] The vehicle-mounted nitrogen boosting device cools and boosts the nitrogen sent by the high-pressure drive membrane separation module to obtain the high-pressure nitrogen. The temperature of the cooling and boosting process is controlled at 4 to 10° C., and the pressure is controlled at 10 to 30 MPa.

[0030] Preferably, the nitrogen preparation device is connected to a proppant supply device; the proppant supply device mixes the proppant into the high-pressure nitrogen; the compressive strength of the proppant is 1 to 10 MPa; and the particle size of the proppant is 20 to 60 meshes.

[0031] Based on the same invention, the present application also provides an in-situ infiltration enhancement method for a low-permeability contaminated site, which is implemented by the in-situ infiltration enhancement system for a low-permeability contaminated site, comprising:

[0032] The well arrangement is set to a plum blossom-shaped well arrangement, the central well is a permeability enhancement well, and the four wells around the permeability enhancement well are gas extraction wells; the well spacing of the plum blossom-shaped well arrangement is controlled to be 2 to 8 meters;

[0033] The drilling device is drilled to the permeability target position, and the water content of the permeability target position is determined by the water content sensor.

[0034] When the water content of the target permeability enhancement position is greater than 35%, the construction sequence is: liquid nitrogen injection through the liquid nitrogen perforation of the drill bit, well soaking, clean water injection plugging through the clean water injection hole of the drill bit, high-pressure nitrogen fracturing through the high-pressure nitrogen perforation of the drill bit, and the drilling device is withdrawn 30 to 100 cm and then the above steps are repeated in sequence;

[0035] When the water content of the target permeability enhancement position is greater than 20% and less than or equal to 35%, the construction sequence is: injecting clean water through the clean water injection hole of the drill bit, injecting liquid nitrogen through the liquid nitrogen perforation of the drill bit, soaking the well, then injecting clean water through the clean water injection hole of the drill bit to seal, performing high-pressure nitrogen fracturing through the high-pressure nitrogen perforation of the drill bit, and repeating the above steps in sequence after the drilling device is withdrawn by 30 to 100 cm;

[0036] When the water content of the target permeability enhancement position is less than or equal to 20%, the construction sequence is: injecting clean water through the clean water injection hole of the drill bit, injecting liquid nitrogen through the liquid nitrogen perforating of the drill bit, performing high-pressure nitrogen fracturing through the high-pressure nitrogen perforating of the drill bit, and repeating the above steps in sequence after the drilling device is withdrawn 30 to 100 cm.

[0037] Preferably, when the water content of the target location for permeability enhancement is greater than 35%,

[0038] The pressure of the liquid nitrogen injection is controlled to be 0.5 kPa to 5 MPa, and the application time is 10 to 30 seconds;

[0039] The soaking time is controlled to be 3 to 10 minutes;

[0040] The pressure of the clean water injection plugging is controlled to be 10-100 kPa, and the application time is 5-10 s;

[0041] The pressure of the high-pressure nitrogen fracturing is controlled to be 1-30 MPa, and the application time is 5-20 seconds.

[0042] Preferably, when the water content of the target position for permeability enhancement is greater than 20% and less than or equal to 35%,

[0043] The pressure of the clean water injection is controlled to be 10-100 kPa, and the application time is 3-5 s;

[0044] The pressure of the liquid nitrogen injection is controlled to be 0.5 kPa to 5 MPa, and the application time is 5 to 20 seconds;

[0045] The soaking time is controlled to be 1 to 3 minutes;

[0046] The pressure of the clean water injection plugging is controlled to be 10-100 kPa, and the application time is 3-8 s;

[0047] The pressure of the high-pressure nitrogen fracturing is controlled to be 1-30 MPa, and the application time is 5-20 seconds.

[0048] Preferably, when the water content of the target position for permeability enhancement is less than or equal to 20%,

[0049] The pressure of the clean water injection is controlled to be 10-100 kPa, and the application time is 5-12 s;

[0050] The pressure of the liquid nitrogen injection is controlled to be 0.5 kPa to 1 MPa, and the application time is 1 to 3 seconds;

[0051] The pressure of the high-pressure nitrogen fracturing is controlled to be 1-30 MPa, and the application time is 5-20 seconds.

[0052] Preferably, when the distance between the permeability enhancement target position and the ground is greater than 30 m, the pressure of the high-pressure nitrogen fracturing is controlled to be 20-30 MPa;

[0053] When the distance between the permeability enhancement target position and the ground is greater than 10m and less than or equal to 30m, the pressure of the high-pressure nitrogen fracturing is controlled to be 10-20MPa;

[0054] When the distance between the permeability enhancement target position and the ground is less than or equal to 10 m, the pressure of the high-pressure nitrogen fracturing is controlled to be 1-10 MPa.

[0055] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages:

[0056] The present application is based on the principles of liquid nitrogen fracturing and pneumatic fracturing, and provides an in-situ permeability enhancement system for low-permeability contaminated sites consisting of a drilling device, a nitrogen preparation device, a liquid nitrogen preparation device, a water supply device and a controller; when the drill pipe of the drilling device advances to the target formation, the controller controls the sequence of liquid nitrogen injection, high-pressure nitrogen input, well soaking, and clean water freezing and plugging according to the water content and pressure sensor equipped on the drill bit, and applies time and pressure, which can adapt to the permeability enhancement of low-permeability contaminated sites with high, medium and low water contents, and can achieve efficient, continuous, highly automated permeability enhancement of low-permeability contaminated sites suitable for various geological environments, and the system and method can provide support for site remediation after permeability enhancement, thereby solving the problems of poor applicability, difficulty in permeability enhancement, and high cost of permeability enhancement technology for contaminated sites. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0058] Figure 1 A schematic diagram of the restoration work of the in-situ infiltration enhancement system for a low-permeability contaminated site provided in an embodiment of the present application;

[0059] Figure 2 An enlarged cross-sectional view of a drill pipe of a drilling device in an in-situ permeability enhancement system for a low-permeability contaminated site provided in an embodiment of the present application;

[0060] Figure 3 A schematic diagram of the structure of a drill bit of a drilling device in an in-situ permeability enhancement system for a low-permeability contaminated site provided in an embodiment of the present application;

[0061] Figure 4 A well layout process diagram for an in-situ permeability enhancement method for a low-permeability contaminated site provided in an embodiment of the present application;

[0062] Figure 5 A technical schematic diagram of in-situ infiltration enhancement for low-permeability contaminated sites provided in an embodiment of the present application.

[0063] (The components represented by the reference numerals in the attached drawings are: 1 nitrogen preparation device, 2 liquid nitrogen preparation device, 3 drilling device, 4 controller, 5 drill rod, 6 drill bit, 7 temperature sensor, 8 pressure sensor, 9 water content sensor, 61 head end, 62 spiral middle section, 63 tail end, 64 clean water injection hole, 65 liquid nitrogen perforation, 66 high pressure nitrogen perforation) DETAILED DESCRIPTION

[0064] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0065] See attached Figures 1 to 3 The present application provides an in-situ permeability enhancement system for low-permeability contaminated sites, comprising: a drilling device 3, a nitrogen preparation device 1, a liquid nitrogen preparation device 2, a water supply device and a controller 4.

[0066] The drilling device 3 is a vehicle-mounted drilling device. The drilling device 3 includes: a drill rod 5, a drill bit 6, a temperature sensor 7, a pressure sensor 8 and a water content sensor 9, see the attached Figure 2 The drill rod 5 is provided with a liquid nitrogen injection channel inside, and an insulating oil channel is provided outside the liquid nitrogen injection channel, and the insulating oil plays an insulating role on the liquid nitrogen; the drill rod 5 is also provided with a clean water injection channel and a high-pressure nitrogen channel. A multi-layer casing structure is provided inside the drill rod 5, specifically: the center of the drill rod 5 is the liquid nitrogen injection channel, the insulating oil channel is sleeved outside the liquid nitrogen injection channel, the clean water injection channel is sleeved outside the insulating oil channel, and the high-pressure nitrogen channel is sleeved outside the clean water injection channel. The diameter selection range of the drill rod 5 is

[0067] The drill bit 6 is a spiral drill bit, which is arranged at the front end of the drill rod 5. The drill bit 6 is provided with a plurality of liquid nitrogen perforations 65, a plurality of clean water injection holes 64 and a plurality of high-pressure nitrogen perforations 66. The liquid nitrogen perforations 65 are connected to the liquid nitrogen injection channel, the clean water injection holes 64 are connected to the clean water injection channel, and the high-pressure nitrogen perforations 66 are connected to the high-pressure nitrogen channel.

[0068] The temperature sensor 7, the pressure sensor 8 and the water content sensor 9 are arranged on the drill bit 6. The temperature sensor 7 detects the temperature at the infiltration position, the pressure sensor 8 detects the pressure at the infiltration position, and the water content sensor 9 detects the water content at the infiltration position.

[0069] The output end of the nitrogen preparation device 1 is connected to the drilling device 3, which is used to prepare high-pressure nitrogen and send it into the high-pressure nitrogen channel; the output end of the liquid nitrogen preparation device 2 is connected to the drilling device 3, which is used to prepare liquid nitrogen and send it into the liquid nitrogen injection channel; the output end of the water supply device is connected to the drilling device 3, which is used to transport clean water to the clean water injection channel.

[0070] The controller 4 is electrically connected to the temperature sensor 7, the pressure sensor 8, the moisture sensor 9, the liquid nitrogen preparation device 2, the nitrogen preparation device 1 and the water supply device, and controls the working sequence and working time interval of the liquid nitrogen preparation device 2, the nitrogen preparation device 1 and the water supply device after receiving the temperature, pressure and moisture information of the permeability enhancement position. The control principle of the controller 4 is: the drill rod 5 advances to the target position, and the moisture content and soil pressure of the permeability enhancement position are determined by the moisture sensor 9 and the pressure sensor 8. According to the well layout process and the monitored geological condition parameters, the time interval and sequence of liquid nitrogen, nitrogen pneumatic permeability enhancement and clean water injection plugging are set, and the ground displacement, downhole temperature, pressure and moisture content changes are monitored to feedback the permeability enhancement effect and make real-time adjustments.

[0071] For further information, see Appendix Figure 3The drill bit 6 includes: a head end 61, a spiral middle section 62 and a tail end 6, a plurality of clean water injection holes 64 are respectively arranged at the head end 61 and the tail end 63; a plurality of liquid nitrogen perforations 65 are arranged on the outer side of the thread of the spiral middle section 62, and a plurality of high-pressure nitrogen perforations 66 are arranged on the inner side of the thread of the spiral middle section 62; a temperature sensor 7 and a pressure sensor 8 are arranged at the position where the head end 61 and the spiral middle section 62 are combined; a temperature sensor 7 and a pressure sensor 8 are also arranged at the position where the tail end 63 and the spiral middle section 62 are combined; a water content sensor 9 is arranged on the spiral middle section 62. As a preferred embodiment, the head end 61 is provided with 1 or 2 clean water injection holes 64; the tail end 63 is provided with 3 to 6 clean water injection holes 64; the length of the spiral middle section 62 is 0.2 to 0.8 meters; the liquid nitrogen perforations 65 are arranged at equal intervals, the number is controlled at 20 to 40 per meter, and the phase angle between the liquid nitrogen perforations 65 is 30 to 90°; the arrangement spacing, number and phase angle between the high-pressure nitrogen perforations 66 are the same as those of the liquid nitrogen perforations 65.

[0072] Furthermore, the liquid nitrogen preparation device 2 is a highly integrated vehicle-mounted liquid nitrogen preparation device, which provides compressed air through an air compressor, purifies the compressed air through a multi-stage filter, separates nitrogen and oxygen from the purified compressed air through a high-pressure drive membrane separation module, and the separated nitrogen is pressurized and cooled by a nitrogen liquefaction module to produce liquid nitrogen.

[0073] The nitrogen preparation device 1 is a vehicle-mounted nitrogen boosting device, which is connected to the nitrogen output end of the high-pressure drive membrane separation module; the vehicle-mounted nitrogen boosting device refrigerates and pressurizes the nitrogen sent into the high-pressure drive membrane separation module to obtain high-pressure nitrogen, and the temperature of the refrigeration and pressurization process is controlled at 4 to 10°C, and the pressure is controlled at 10 to 30MPa.

[0074] Furthermore, the nitrogen preparation device 1 may be connected to a proppant supply device. As required, the proppant may be mixed into the high-pressure nitrogen through the proppant supply device during the high-pressure nitrogen cracking process; the compressive strength of the proppant is 1 to 10 MPa; and the particle size of the proppant is 20 to 60 meshes.

[0075] Based on the same invention, see Appendix Figure 4 and 5 The present application also provides an in-situ infiltration enhancement method for a low-permeability contaminated site, which is implemented by the above-mentioned in-situ infiltration enhancement system for a low-permeability contaminated site, comprising:

[0076] See attached Figure 4 The well layout method is set to a plum blossom-shaped well layout method, the central well is a seepage well, and the four wells around the seepage well are gas extraction wells; the well spacing in the plum blossom-shaped well layout method is controlled to be 2 to 8 meters.

[0077] The drilling device 3 is advanced to the target permeability enhancement position, and the water content of the target permeability enhancement position is determined by the water content sensor 9.

[0078] The construction sequence is determined according to the moisture content of the target location for infiltration, which can be divided into three situations:

[0079] 1. When the water content at the target position of permeability enhancement is greater than 35%, the construction sequence is: liquid nitrogen injection through the liquid nitrogen perforation 65 of the drill bit 6, well soaking, clean water injection plugging through the clean water injection hole 64 of the drill bit 6, high-pressure nitrogen fracturing through the high-pressure nitrogen perforation 66 of the drill bit 6, and the drilling device 3 is withdrawn by 30 to 100 cm and then the above steps are repeated in sequence.

[0080] 2. When the water content at the target position of permeability enhancement is greater than 20% and less than or equal to 35%, the construction sequence is: inject clean water through the clean water injection hole 64 of the drill bit 6, inject liquid nitrogen through the liquid nitrogen perforation 65 of the drill bit 6, soak the well, then inject clean water through the clean water injection hole 64 of the drill bit 6 to seal, perform high-pressure nitrogen fracturing through the high-pressure nitrogen perforation 66 of the drill bit 6, and repeat the above steps after the drilling device 3 is withdrawn by 30 to 100 cm.

[0081] 3. When the water content at the target permeability enhancement position is less than or equal to 20%, the construction sequence is: inject clean water through the clean water injection hole 64 of the drill bit 6, inject liquid nitrogen through the liquid nitrogen perforation 65 of the drill bit 6, perform high-pressure nitrogen fracturing through the high-pressure nitrogen perforation 66 of the drill bit 6, and repeat the above steps after the drilling device 3 is withdrawn by 30 to 100 cm.

[0082] In the first case, when the water content at the target permeability enhancement position is greater than 35%, the pressure of liquid nitrogen injection is controlled to be 0.5kPa~5Mpa, and the application time is 10~30s; the soaking time is controlled to be 3~10min; the pressure of clean water injection plugging is controlled to be 10~100kPa, and the application time is 5~10s; the pressure of high-pressure nitrogen fracturing is controlled to be 1~30Mpa, and the application time is 5~20s.

[0083] In the second case, when the water content at the target permeability enhancement position is greater than 20% and less than or equal to 35%, the pressure of clean water injection is controlled to be 10-100 kPa, and the application time is 3-5 s; the pressure of liquid nitrogen injection is controlled to be 0.5 kPa-5 MPa, and the application time is 5-20 s; the soaking time is controlled to be 1-3 min; the pressure of clean water injection plugging is controlled to be 10-100 kPa, and the application time is 3-8 s; the pressure of high-pressure nitrogen fracturing is controlled to be 1-30 MPa, and the application time is 5-20 s.

[0084] In the third case, when the water content at the target permeability enhancement position is less than or equal to 20%, the pressure of clean water injection is controlled to be 10-100 kPa, and the application time is 5-12 s; the pressure of liquid nitrogen injection is controlled to be 0.5 kPa-1 MPa, and the application time is 1-3 s; the pressure of high-pressure nitrogen fracturing is controlled to be 1-30 MPa, and the application time is 5-20 s.

[0085] Furthermore, when the distance between the permeability target position and the ground is greater than 30m, the pressure of high-pressure nitrogen fracturing is controlled to be 20-30MPa; when the distance between the permeability target position and the ground is greater than 10m and less than or equal to 30m, the pressure of high-pressure nitrogen fracturing is controlled to be 10-20MPa; when the distance between the permeability target position and the ground is less than or equal to 10m, the pressure of high-pressure nitrogen fracturing is controlled to be 1-10MPa.

[0086] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An in-situ infiltration enhancement system for low-permeability contaminated sites, characterized in that: include: Drilling equipment, nitrogen preparation equipment, liquid nitrogen preparation equipment, water supply equipment and controller, The drilling device comprises: a drill pipe, a drill bit and a water content sensor. A liquid nitrogen injection channel is provided in the drill pipe, and a heat-insulating oil channel is provided outside the liquid nitrogen injection channel. The drill pipe is also provided with a clean water injection channel and a high-pressure nitrogen channel. The drill bit is a spiral drill bit, which is arranged at the end of the drill rod. The drill bit is provided with a plurality of liquid nitrogen perforations, a plurality of clean water injection holes and a plurality of high-pressure nitrogen perforations. The liquid nitrogen perforations are connected to the liquid nitrogen injection channel, the clean water injection holes are connected to the clean water injection channel, and the high-pressure nitrogen perforations are connected to the high-pressure nitrogen channel. The water content sensor is arranged on the drill bit, and the water content sensor detects the water content at the permeability increase position; The output end of the nitrogen preparation device is connected to the drilling device, and is used to prepare high-pressure nitrogen and send it into the high-pressure nitrogen channel; The output end of the liquid nitrogen preparation device is connected to the drilling device, and is used to prepare liquid nitrogen and send it into the liquid nitrogen injection channel; The output end of the water supply device is connected to the drilling device for conveying clean water to the clean water injection channel; The controller is electrically connected to the moisture content sensor, the liquid nitrogen preparation device, the nitrogen gas preparation device and the water supply device, and controls the working sequence and working time interval of the liquid nitrogen preparation device, the nitrogen gas preparation device and the water supply device after receiving the moisture content information of the permeation increase position; The drill bit comprises: a head end, a spiral middle section and a tail end, A plurality of clean water injection holes are respectively arranged at the head end and the tail end; A plurality of liquid nitrogen perforations are arranged on the outer side of the threads of the spiral middle section, and a plurality of high-pressure nitrogen perforations are arranged on the inner side of the threads of the spiral middle section; The moisture content sensor is arranged on the spiral middle section; The head end is provided with 1 or 2 clean water injection holes; The tail end is provided with 3 to 6 clean water injection holes; The length of the spiral middle section is 0.2 to 0.8 meters; The liquid nitrogen perforations are arranged at equal intervals, the number of which is controlled at 20 to 40 per meter, and the phase angle between the liquid nitrogen perforations is 30 to 90 degrees; The arrangement spacing, number and phase angle between the high-pressure nitrogen perforations are the same as those of the liquid nitrogen perforations; The liquid nitrogen preparation device is a highly integrated vehicle-mounted liquid nitrogen preparation device, which provides compressed air through an air compressor, purifies the compressed air through a multi-stage filter, separates nitrogen and oxygen from the purified compressed air through a high-pressure drive membrane separation module, and produces liquid nitrogen through a pressurized cooling nitrogen liquefaction module.

2. The in-situ infiltration enhancement system for low-permeability contaminated sites according to claim 1, characterized in that: The nitrogen preparation device is a vehicle-mounted nitrogen booster, and the vehicle-mounted nitrogen booster is connected to the nitrogen output end of the high-pressure drive membrane separation module; The vehicle-mounted nitrogen boosting device cools and boosts the nitrogen sent into the high-pressure drive membrane separation module to obtain the high-pressure nitrogen. The temperature of the cooling and boosting process is controlled at 4-10°C, and the pressure is controlled at 10-30MPa.

3. The in-situ infiltration enhancement system for low-permeability contaminated sites according to claim 2, characterized in that: The nitrogen preparation device is connected to a proppant supply device; the proppant supply device mixes the proppant into the high-pressure nitrogen; the compressive strength of the proppant is 1-10 MPa; and the particle size of the proppant is 20-60 meshes.

4. A method for increasing in-situ permeability of a low-permeability contaminated site, characterized in that: The method is realized by the low-permeability contaminated site in-situ infiltration enhancement system according to any one of claims 1 to 3, comprising: The well layout is set to a plum blossom-shaped well layout, the central well is a permeability enhancement well, and the four wells around the permeability enhancement well are gas extraction wells; the well spacing of the plum blossom-shaped well layout is controlled to be 2 to 8 meters; The drilling device is drilled to the permeability target position, and the water content of the permeability target position is determined by the water content sensor. When the water content of the target permeability enhancement position is greater than 35%, the construction sequence is: liquid nitrogen injection through the liquid nitrogen perforation of the drill bit, well soaking, clean water injection plugging through the clean water injection hole of the drill bit, high-pressure nitrogen fracturing through the high-pressure nitrogen perforation of the drill bit, and the drilling device is withdrawn 30-100 cm and then the above steps are repeated in sequence; When the water content of the target permeability enhancement position is greater than 20% and less than or equal to 35%, the construction sequence is: injecting clean water through the clean water injection hole of the drill bit, injecting liquid nitrogen through the liquid nitrogen perforation of the drill bit, soaking the well, then injecting clean water through the clean water injection hole of the drill bit to seal, performing high-pressure nitrogen fracturing through the high-pressure nitrogen perforation of the drill bit, and then retracting the drilling device by 30-100 cm and then repeating the above steps in sequence; When the water content of the target permeability enhancement position is less than or equal to 20%, the construction sequence is: injecting clean water through the clean water injection hole of the drill bit, injecting liquid nitrogen through the liquid nitrogen perforating of the drill bit, performing high-pressure nitrogen fracturing through the high-pressure nitrogen perforating of the drill bit, and repeating the above steps in sequence after the drilling device is withdrawn 30 to 100 cm.

5. The in-situ infiltration enhancement method for low-permeability contaminated sites according to claim 4, characterized in that: When the water content of the target location for infiltration is greater than 35%, The pressure of the liquid nitrogen injection is controlled to be 0.5 kPa~5 MPa, and the application time is 10~30 s; The soaking time is controlled to be 3 to 10 minutes; The pressure of the clean water injection plugging is controlled to be 10-100 kPa, and the application time is 5-10 s; The pressure of the high-pressure nitrogen fracturing is controlled to be 1-30 MPa, and the application time is 5-20 s.

6. The in-situ infiltration enhancement method for low-permeability contaminated sites according to claim 4, characterized in that: When the water content of the target position of the infiltration is greater than 20% and less than or equal to 35%, The pressure of the clean water injection is controlled to be 10-100 kPa, and the application time is 3-5 s; The pressure of the liquid nitrogen injection is controlled to be 0.5 kPa~5 MPa, and the application time is 5~20 s; The soaking time is controlled to be 1 to 3 minutes; The pressure of the clean water injection plugging is controlled to be 10-100 kPa, and the application time is 3-8 s; The pressure of the high-pressure nitrogen fracturing is controlled to be 1-30 MPa, and the application time is 5-20 s.

7. The in-situ infiltration enhancement method for low-permeability contaminated sites according to claim 4, characterized in that: When the water content of the target position of the permeability increase is less than or equal to 20%, The pressure of the clean water injection is controlled to be 10-100 kPa, and the application time is 5-12 s; The pressure of the liquid nitrogen injection is controlled to be 0.5 kPa~1 MPa, and the application time is 1~3 s; The pressure of the high-pressure nitrogen fracturing is controlled to be 1-30 MPa, and the application time is 5-20 s.

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