Well building method for deep well in polluted site investigation and monitoring well

Abstract

The invention belongs to the technical field of polluted site environment investigation, and particularly relates to a well building method for a deep well in polluted site investigation and a monitoring well, and the well building method comprises the following steps: S1, determining a monitoring well site, drilling a hole to a first target depth for the first time at the monitoring well site to obtain a first well hole, and in the process of drilling the hole for the first time, synchronously following a sleeve; s2, the first well hole is washed with clear water, pre-mixed cement paste is injected into the bottom of the hole through a grouting pipe, and the interior of the casing pipe and an annular space between the first well hole and the casing pipe are filled from bottom to top; and S3, after the cement paste stands for a preset time, a water stop barrier is obtained, a hole is drilled in the water stop barrier in the casing pipe for the second time to a second target depth, a second well hole is obtained, and the monitoring well is manufactured. By constructing the water stop barrier, the quality and safety of deep well construction can be ensured.

Description

Technical Field

[0001] This invention belongs to the technical field of environmental investigation of contaminated sites, and specifically relates to a method for constructing deep wells and a monitoring well in the investigation of contaminated sites. Background Technology

[0002] In environmental investigations and risk assessments of contaminated sites, groundwater is a crucial pathway for pollutant migration. The investigation process typically follows a "from shallow to deep" principle: first, monitoring wells are constructed in shallow aquifers for sampling and analysis. If the shallow groundwater levels are within acceptable limits, no further investment is needed to investigate deeper groundwater; conversely, if shallow groundwater contamination is confirmed, deeper monitoring wells must be constructed to determine the vertical distribution and depth of the contamination.

[0003] Currently, there are two main models for the construction of deep groundwater monitoring wells: (1) Constructing multi-layer monitoring wells at once: Constructing multi-layer monitoring wells that can simultaneously monitor multiple shallow and deep aquifers at the initial stage of the investigation. The disadvantage of this method is that if the shallow groundwater is not polluted, the construction, sampling and subsequent sample analysis costs of the deep monitoring wells will be wasted, resulting in an unnecessary economic burden. If the shallow groundwater is polluted, this method can easily cause the polluted groundwater in the shallow layer to migrate to the deeper layer, increasing environmental risks and subsequent remediation costs.

[0004] (2) Direct construction of conventional single-layer deep wells: When deep data is required, drilling is carried out directly to the target depth, and materials such as bentonite are used for interlayer water sealing. Under complex hydrogeological conditions (such as the presence of confined water, quicksand layers, etc.), drilling to the deep layer at one time can easily cause problems such as borehole wall collapse and cross-contamination between different aquifers, and the reliability of conventional water sealing materials faces challenges in the high-pressure environment at depth.

[0005] Therefore, existing technologies lack a dedicated method that can flexibly adapt to phased investigation decisions, control costs, and ensure the quality of deep well construction and water-stopping effects. Summary of the Invention

[0006] One of the objectives of this invention is to overcome the shortcomings of the prior art and provide a method for constructing deep wells in contaminated site investigations. By constructing a water-stopping barrier, the quality and safety of deep well construction can be ensured.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for constructing deep wells in contaminated site investigations includes the following steps: S1. Determine the monitoring well site. Drill a hole to the first target depth at the monitoring well site to obtain the first well. During the second drilling process, the casing is advanced synchronously. S2. Use clean water to wash the first wellbore, and inject the pre-mixed cement slurry into the bottom of the hole through the grouting pipe to fill the inside of the casing and the annular space between the first wellbore and the casing from bottom to top. S3. After the cement slurry has been left to stand for a predetermined time, a water-stop barrier is obtained. A second hole is drilled on the water-stop barrier inside the casing to the second target depth to obtain the second well hole, thus creating a monitoring well.

[0008] Preferably, in step S3, the second wellbore is washed with clean water, and the well pipe, filter pipe and sedimentation pipe are connected in sequence along the axis to form a continuous pipe string. The pipe string is then lowered into the second wellbore with the sedimentation pipe as the starting point.

[0009] Preferably, in step S3, before lowering the filter pipe, the filter pipe is wrapped with at least three layers of 120-mesh nylon mesh, and then the nylon mesh is fixed.

[0010] Preferably, in step S3, the well casing is made of multiple pipe bodies connected by a direct connector. Before the casing string is lowered, each pipe body is measured and arranged in sequence, and the length of the well casing is obtained based on the measurement data.

[0011] Preferably, in step S3, after the tubing is lowered, filter material with a particle size of 2-4 mm is used to evenly fill the area around the well pipe. The well pipe is shaken during filling, and a steel ruler is used to measure in real time. The measurement data of the steel ruler is compared with the length of the well pipe to ensure that the filter material is filled to 50-60 cm above the top of the filter pipe, thus obtaining a filter material layer.

[0012] Preferably, in step S3, dry bentonite balls with a particle size of 30-40 mm are filled above the filter material layer to obtain the first water-stopping layer, and then hydrated bentonite or bentonite slurry with a particle size of 20-40 mm is filled above the first water-stopping layer to a distance of 40-60 cm from the ground to obtain the second water-stopping layer.

[0013] Preferably, in step S1, actual hydrogeological data is obtained to determine the first target depth, wherein the first target depth needs to penetrate the shallow water layer and enter the top of the impermeable layer.

[0014] Preferably, in step S3, a second target depth is obtained based on the data of the first target depth. The second target depth needs to pass through the water-stopping barrier and water-proof layer inside the casing and finally reach the predetermined depth of the deep target aquifer.

[0015] Preferably, in step S3, the diameter of the first well hole is 168~220mm, and the diameter of the second well hole is 110mm.

[0016] Preferably, in step S3, cement slurry is filled above the second water-stopping layer to obtain a sealing layer, a well platform is built above the sealing layer, and a well cover is added to the top of the well pipe.

[0017] The second objective of this invention is to overcome the shortcomings of the prior art and provide a monitoring well, comprising a first wellbore, a casing, a water-stop barrier, a second wellbore, a well pipe, a filter pipe, and a sedimentation pipe. The casing is installed inside the first wellbore, and the water-stop barrier is filled inside the casing and between the casing and the inner wall of the first wellbore. The second wellbore passes sequentially through the water-stop barrier located inside the casing and extends to the bottom of the casing. The well pipe, the filter pipe, and the sedimentation pipe are sequentially connected and are all disposed in the second wellbore. In the wellbore, both the filter pipe and the sedimentation pipe are located below the casing. The filter pipe is located between the well pipe and the sedimentation pipe, and a nylon mesh is wrapped around its outer side. A filter material layer is provided between the well pipe and the filter pipe located below the casing and the inner wall of the second wellbore. A first water-stopping layer, a second water-stopping layer, and a sealing layer are arranged sequentially from bottom to top between the well pipe and the inner wall of the second wellbore. A well platform is provided around the top of the casing and the well pipe. A well cover is provided on the top of the well pipe.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The phased two-stage drilling process breaks down deep well construction into two physically separate and time-interval steps: the formation of the water barrier and well construction, thus enabling reliable construction on demand. 2. Hole diameter matching and center positioning: The matching design of the first and second drilling ensures that the second drilling can be successfully carried out in the center of the cement column, and leaves a sufficiently thick cement ring to ensure the water-stopping effect. 3. Cement grout, as the core material for deep water sealing, forms a rigid barrier after hardening compared to traditional bentonite, with stronger impermeability and is suitable for dealing with deep confined water. 4. The sleeve is not removed, which simplifies the construction and improves the integrity and reliability of the water-stop structure. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic flowchart of a method for constructing deep wells in a contaminated site investigation, as disclosed in an embodiment of this application. Figure 2This is one of the schematic diagrams illustrating the steps of a deep well construction method for contaminated site investigation disclosed in an embodiment of this application; Figure 3 This is the second schematic diagram of the steps of a method for constructing a deep well in a contaminated site investigation disclosed in an embodiment of this application; Figure 4 This is a schematic diagram of the structure of a monitoring well disclosed in an embodiment of this application.

[0021] The components are: 1. First wellbore; 2. Casing; 3. Water-stop barrier; 4. Second wellbore; 5. Well pipe; 6. Filter pipe; 7. Sedimentation pipe; 8. Nylon mesh; 9. Filter media layer; 10. First water-stop layer; 11. Second water-stop layer; 12. Sealing layer; 13. Well platform; 14. Well cover. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] The terms “comprising” and “having”, and any variations thereof, in this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0024] The core idea of ​​this invention is secondary drilling with intermediate water sealing. By dividing the construction of a deep well into two independent drilling stages, the first drilling is not for direct well construction, but to form a localized, vertically upward cement slurry water-stopping barrier 3. After the water-stopping barrier 3 has solidified, a second drilling is performed at its center, penetrating the barrier to the deeper target aquifer and completing the well construction process. This method separates the decision-making process for deep well construction from that for shallow exploration in time, and ensures the quality and safety of deep well construction by first constructing the water-stopping structure.

[0025] In one embodiment of the present invention, a method for constructing deep wells in a contaminated site investigation is provided, comprising the following steps: S1. At the determined monitoring well site, a drilling rig is used to drill a first borehole to the first target depth, obtaining the first wellbore 1. During the first drilling, the casing 2 is simultaneously advanced. Before the first drilling, a pre-drilling is performed at the monitoring well site. When drilling reaches the easily collapsible depth, the casing 2 is simultaneously advanced, i.e., the casing 2 is immediately lowered after drilling to the easily collapsible depth to prevent borehole collapse. This allows the invention to be applied to loose formations, with the easily collapsible depth being 5-6m. The depth of the first drilling should penetrate the shallow aquifer that needs to be isolated and enter the top of the relatively stable aquitard. The first target depth needs to be determined according to the actual hydrogeological conditions; for example, the first target depth can be 15m. During the drilling process, core samples at different depths are arranged sequentially, and the drilling depth can be dynamically adjusted according to the state of the core samples. The simultaneous advancement of the casing 2 can be achieved by advancing the casing 2 1m for every 1m of drilling depth, thereby avoiding borehole collapse.

[0026] S2. After drilling to the first target depth, borehole wall cleaning begins. The first borehole 1 is rinsed with clean water to remove mud and drill cuttings, ensuring a clean borehole wall and creating conditions for good bonding between the cement slurry and the formation. The rinsing time is determined by the color of the rinse water, or a turbidity meter can be used to monitor the rinse water. After rinsing, cement slurry is injected. Pre-mixed cement slurry is injected into the bottom of the borehole through a grouting pipe, filling the inside of the casing 2 and the annular space between the first borehole 1 and the casing 2 from bottom to top. The water-cement ratio of the cement slurry is preferably 0.5~0.6. After the cement slurry injection is completed, the casing 2 is not removed but remains buried underground as part of the permanent structure. This strengthens the water-stop barrier 3 and avoids potential damage to the cement structure if the casing is pulled out.

[0027] S3. After the cement grout injection is completed, it needs to be left to cure. The cement grout should be left to cure for a predetermined time, at least 48 hours, to form a water-stop barrier 3, ensuring the cement grout fully hardens and reaches the predetermined strength, forming a solid cement column water-stop barrier 3. A second borehole is then drilled into the water-stop barrier 3 inside the casing 2 to the second target depth, resulting in a second wellbore 4, thus creating a monitoring well. At the center of the hardened cement column formed after the first drilling, a second borehole is drilled using a smaller diameter drill bit. This second borehole will penetrate the cement column and the underlying aquitard, ultimately reaching the predetermined depth of the deep target aquifer. The preferred drill bit diameter for the first borehole is 168-220 mm, and the preferred drill bit diameter for the second borehole is 110 mm.

[0028] In one embodiment, in step S3, after the second drilling, the borehole wall is cleaned again. Clean water is used to perform a second rinsing of the second wellbore 4 to ensure cleanliness inside the well. The rinsing time is determined by the color of the rinse water, or a turbidity meter can be used to monitor the rinse water and determine the timing of the second rinsing. The well pipe 5, filter pipe 6, and sedimentation pipe 7 are connected sequentially along their centerlines to form a continuous tubing string. The tubing string is lowered into the second wellbore 4, starting with sedimentation pipe 7. The well pipe 5 is a PVC pipe with an outer diameter of 63mm and an inner diameter of 57mm. The filter pipe 6 is a slotted pipe, with the slotted position of the filter pipe 6 determined according to the target aquifer. The sedimentation pipe 7 is 50cm long.

[0029] Specifically, in one embodiment, in step S3, before the filter pipe 6 is lowered, a 120-mesh nylon mesh 8 is used to wrap the filter pipe 6 in at least three layers, and then the nylon mesh 8 is fixed.

[0030] Specifically, in one embodiment, in step S3, the well pipe 5 is made of multiple pipe bodies connected by a direct connector. Before lowering the pipe string, the hole depth is corrected according to the actual drilling data. Each pipe body is measured and arranged in sequence, and the length of the well pipe 5 is obtained based on the measurement data to ensure that the lowering depth and the installation position of the filter pipe 6 are accurate. The lowering speed of the well pipe 5 should not be too fast, for example, it can be 5~10 meters / minute. After the pipe is lowered, the well pipe 5 is straightened and fixed, and the well pipe 5 is aligned with the borehole axis.

[0031] Specifically, in one embodiment, in step S3, after the tubing is lowered, filter media is filled. Filter media with a particle size of 2-4 mm is evenly filled around the perimeter of the well pipe 5, avoiding filling from a single direction. The well pipe 5 is shaken while filling to prevent bridging during filter media filling. During the filter media filling process, a steel ruler is used for real-time measurement, and the measurement data is compared with the length of the well pipe 5 to ensure that the filter media is filled to 50-60 cm above the top of the filter pipe 6, preferably 50 cm, resulting in a filter media layer 9. The filter media layer 9 is used to filter the groundwater entering the well pipe 5, resulting in better water quality of the detected deep groundwater. The filter media can be quartz sand.

[0032] Specifically, in one embodiment, in step S3, after the filter material is filled, a sealing and water-stopping process is performed to prevent external water above the filter material layer 9 from entering the well through the filter material layer 9. To ensure the water-stopping effect, spherical bentonite with a diameter of 20-40 mm is selected and filled in two sections. The first section is filled with dry bentonite balls with a particle size of 30-40 mm above the filter material layer 9 to obtain the first water-stopping layer 10. Then, water-added bentonite or bentonite slurry with a particle size of 20-40 mm is filled above the first water-stopping layer 10 to a distance of 40-60 cm from the ground, preferably 50 cm, to obtain the second water-stopping layer 11. By setting the first water-stopping layer 10 and the second water-stopping layer 11, it is possible to effectively avoid shallow water from polluting the deep water that needs to be monitored.

[0033] Specifically, in one embodiment, in step S1, actual hydrogeological data is acquired to obtain a first target depth, wherein the first target depth needs to penetrate the shallow water layer and enter the top of the impermeable layer.

[0034] Specifically, in one embodiment, in step S3, a second target depth is obtained based on the data of the first target depth, wherein the second target depth needs to pass through the water-stopping barrier 3 and the water-proof layer inside the casing 2, and finally reach the predetermined depth of the deep target aquifer.

[0035] Specifically, in one embodiment, in step S3, the diameter of the first well hole 1 is 168~220mm, and the diameter of the second well hole 4 is 110mm.

[0036] Specifically, in one embodiment, in step S3, cement slurry is filled above the second water-stopping layer 11 to the ground surface to obtain a sealing layer 12. The sealing layer 12 is used to prevent surface water from seeping into the well hole and to avoid affecting the monitoring results. A well platform 13 is built above the sealing layer 12, a well cover is added to the top of the well pipe 5, and four safety pillars are set around the well pipe 5 to protect the well pipe 5 and serve as a warning.

[0037] In another embodiment of the present invention, a monitoring well is provided, comprising a first wellbore 1, a casing 2, a water-stop barrier 3, a second wellbore 4, a well pipe 5, a filter pipe 6, and a sedimentation pipe 7. The casing 2 is installed inside the first wellbore 1, and the water-stop barrier 3 is filled inside the casing 2 and between the casing 2 and the inner wall of the first wellbore 1. The second wellbore 4 passes sequentially through the water-stop barrier 3 located inside the casing 2 and extends to the bottom of the casing 2. The well pipe 5, the filter pipe 6, and the sedimentation pipe 7 are sequentially connected and are all disposed in the second wellbore 4. Water pipe 6 and sedimentation pipe 7 are both located below casing 2. Filter pipe 6 is located between well pipe 5 and sedimentation pipe 7. Nylon mesh 8 is wrapped around the outside of filter pipe 6. Filter material layer 9 is provided between well pipe 5, filter pipe 6 and sedimentation pipe 7 located below casing 2 and the inner wall of the second well hole 4. A first water-stopping layer 10, a second water-stopping layer 11 and a sealing layer 12 are arranged sequentially from bottom to top between the inner walls of well pipe 5 and the second well hole 4. A well platform 13 is provided around the top of casing 2 and well pipe 5. A well cover 14 is provided on the top of well pipe 5.

[0038] Clearly, this invention breaks down deep well construction into two physically separate and time-separated steps: the formation of the water-stop barrier and well construction, thus providing a foundation for on-demand and reliable construction. The matching design of the first and second borehole diameters ensures that the second borehole can be successfully drilled at the center of the cement column, leaving a sufficiently thick cement ring to guarantee the water-stopping effect. As the core material for deep water-stopping, cement grout, compared to traditional bentonite, forms a rigid barrier after hardening, exhibiting stronger impermeability and making it suitable for dealing with deep confined water. The casing is not removed, simplifying construction and improving the integrity and reliability of the water-stopping structure.

[0039] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0040] It should be understood that the phrase "one embodiment" or "an embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of this application. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Those skilled in the art should also recognize that the embodiments described in the specification are optional embodiments, and the actions and modules involved are not necessarily essential to this application.

[0041] In the various embodiments of this application, it should be understood that the sequence number of each process does not necessarily imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0042] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on this invention are within the scope of protection of this invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the invention.

Claims

1. A method for constructing deep wells in contaminated site investigations, characterized in that, Includes the following steps: S1. Determine the monitoring well site, and drill to the first target depth at the monitoring well site to obtain the first well hole. During the first drilling process, the casing is advanced synchronously. S2. Use clean water to wash the first wellbore, and inject the pre-mixed cement slurry into the bottom of the hole through the grouting pipe to fill the inside of the casing and the annular space between the first wellbore and the casing from bottom to top. S3. After the cement slurry has been left to stand for a predetermined time, a water-stop barrier is obtained. A second hole is drilled on the water-stop barrier inside the casing to the second target depth to obtain the second well hole, thus creating a monitoring well.

2. The well-construction method for deep wells in contaminated site investigation as described in claim 1, characterized in that, In step S3, the second wellbore is washed with clean water. The well pipe, filter pipe and sedimentation pipe are connected in sequence along the axis to form a continuous tubing string. The tubing string is then lowered into the second wellbore with the sedimentation pipe as the starting point.

3. The method for constructing deep wells in contaminated site investigation as described in claim 2, characterized in that, In step S3, before the filter pipe is lowered, the filter pipe is wrapped with at least three layers of 120-mesh nylon mesh, and then the nylon mesh is fixed.

4. The method for constructing deep wells in contaminated site investigation as described in claim 2, characterized in that, In step S3, the well casing is made of multiple pipe bodies connected by a direct connector. Before the casing string is lowered, each pipe body is measured and arranged in sequence, and the length of the well casing is obtained based on the measurement data.

5. The method for constructing deep wells in contaminated site investigation as described in claim 2, characterized in that, In step S3, after the tubing is lowered, filter material with a particle size of 2-4 mm is used to evenly fill the area around the well pipe. The well pipe is shaken during filling, and a steel ruler is used to measure in real time. The measurement data of the steel ruler is compared with the length of the well pipe to ensure that the filter material is filled to 50-60 cm above the top of the filter pipe, thus obtaining a filter material layer.

6. The well-construction method for deep wells in contaminated site investigation as described in claim 5, characterized in that, In step S3, dry bentonite balls with a particle size of 30-40mm are filled above the filter material layer to obtain the first water-stopping layer. Then, water-added bentonite or bentonite slurry with a particle size of 20-40mm is filled above the first water-stopping layer to a distance of 40-60cm from the ground to obtain the second water-stopping layer.

7. The method for constructing deep wells in contaminated site investigation as described in claim 1, characterized in that, In step S1, actual hydrogeological data is obtained to determine the first target depth, which requires passing through the shallow water layer and entering the top of the impermeable layer.

8. The method for constructing deep wells in contaminated site investigation as described in claim 7, characterized in that, In step S3, a second target depth is obtained based on the data of the first target depth. The second target depth needs to pass through the water-stopping barrier and water-proof layer inside the casing to finally reach the predetermined depth of the deep target aquifer. The diameter of the first wellbore is 168~220mm, and the diameter of the second wellbore is 110mm.

9. The method for constructing deep wells in contaminated site investigation as described in claim 6, characterized in that, In step S3, cement slurry is filled above the second water-stopping layer to obtain a sealing layer. A well platform is built above the sealing layer, and a well cover is added to the top of the well pipe.

10. A monitoring well, characterized in that, The system includes a first wellbore (1), a casing (2), a water-stop barrier (3), a second wellbore (4), a well pipe (5), a filter pipe (6), and a sedimentation pipe (7). The casing (2) is installed inside the first wellbore (1), and the water-stop barrier (3) is filled inside the casing (2) and between the casing (2) and the inner wall of the first wellbore (1). The second wellbore (4) passes through the water-stop barrier located inside the casing (2) and extends to the bottom of the casing (2). The well pipe (5), the filter pipe (6), and the sedimentation pipe (7) are connected in sequence and are all located in the second wellbore (4). The filter pipe (6) and the sedimentation pipe are connected in sequence. (7) All are located below the casing (2). The filter pipe (6) is located between the well pipe (5) and the sedimentation pipe (7). The outer side of the filter pipe (6) is wrapped with nylon mesh (8). A filter material layer (9) is provided between the well pipe (5) below the casing (2) and the filter pipe (6) and the inner wall of the second well hole (4). A first water-stopping layer (10), a second water-stopping layer (11) and a sealing layer (12) are provided from bottom to top between the inner wall of the well pipe (5) and the second well hole (4). A well platform (13) is provided around the top of the casing (2) and the well pipe (5). A well cover (14) is provided on the top of the well pipe (5).

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