Well construction method for fixed-depth precision heating electrode well

Abstract

The present invention provides a method for constructing a fixed-depth, precise heating electrode well, comprising the following steps: (1) preparing a metal mesh cage with electrodes, and filling the gap between the electrodes and the metal mesh cage with graphite; (2) sequentially placing the electrodes with the metal mesh cages at the depths required for heating in the wellbore, and filling the gaps between the metal mesh cages and the wellbore wall with iron sand or coarse sand; (3) covering the top of the lowest metal mesh cage with bentonite as a barrier layer, and covering the tops and bottoms of the remaining metal mesh cages with a layer of bentonite as a barrier layer; and (4) filling the non-heated strata in the wellbore with fine sand. The present invention can match the depth of the conductive material position with the position and height of the electrodes, thereby achieving precise, fixed-depth heating of the target stratum, avoiding the drawback of the traditional method of inaccurate heating due to the inaccurate depth of the conductive material filling position, and is conducive to reducing the amount of heated earthwork and lowering heating energy consumption.

Description

Technical Field

[0001] The present invention relates to a fixed-depth precision heating electrode well structure and a highly efficient and economical well construction method thereof. Background Art

[0002] Resistance heating is a highly efficient in-situ thermal desorption technology for removing VOCs and some SVOCs from the environment. It has been widely used internationally and holds broad application prospects in my country. It primarily involves constructing electrode wells at contaminated sites and placing electrodes. Current is then introduced through the electrodes into the ground, flowing between them. Joule heat generated by the soil's inherent electrical resistance raises the underground temperature, promoting the volatilization and solubilization of pollutants. Combined with extraction, pollutants are extracted and transported to surface purification equipment for treatment, achieving remediation.

[0003] Based on the heterogeneity of soil and the discontinuity of underground pollutant distribution, the use of "fixed-depth precision heating" to reduce the amount of heated earthwork and improve energy efficiency is one of the important and feasible ways.

[0004] There are usually two types of traditional fixed-depth heating electrode well structures and well construction methods. One is to place only one long electrode in an electrode well, and then add conductive materials and insulating materials according to the depth range of the heated formation and non-heated formation respectively; the other is to place two or more short electrodes in an electrode well. The position of the electrode is determined according to the depth range of the required heated formation, and then conductive materials are added around the electrodes, and insulating materials are added to the non-heated formation between the electrodes.

[0005] There are two problems with the above two methods of building fixed-depth heating wells: first, the depth setting effect is poor, making it difficult to achieve precise heating; second, the well construction filling process is cumbersome and time-consuming, and high-density conductive materials such as iron sand are used in large quantities, resulting in high costs.

[0006] Placing only a single long electrode in an electrode well and simply filling it with conductive and insulating materials makes it difficult to achieve precise, fixed-depth heating. This is especially true for electrodes located in the saturated zone, where the high moisture content of the soil makes it difficult for the insulating material to effectively insulate. Placing multiple electrodes in a single well has improved fixed-depth heating to some extent, but the actual precision remains unsatisfactory. This is because the process of adding conductive and insulating materials separately into the well makes it difficult to accurately control the depth of the added materials, which can easily lead to a mismatch between the depth of the conductive material and the electrode.

[0007] When multiple heating formations are located within an electrode well, the well construction process requires multiple additions of conductive and insulating materials, making the well filling process cumbersome and time-consuming. To prevent sand layer collapse, mud-walled well construction is currently widely used in China. The mud density is approximately 1.3 kg / L, while the commonly used conductive materials are iron sand or graphite, with densities of approximately 4.1 kg / L and 0.9 kg / L, respectively. Although graphite is used as a conductive material for electrode wells, it has a lower usage, lower well construction costs, more stable chemical properties, and better results. However, due to its lower density than mud, graphite floats on the mud surface and is difficult to sink. Therefore, in order to complete well construction faster, iron sand is often used, resulting in high well construction costs. Summary of the Invention

[0008] The present invention provides a method for constructing a fixed-depth precise heating electrode well, the purpose of which is to improve well construction efficiency, reduce construction costs, achieve fixed-depth precise heating, and reduce heating energy consumption.

[0009] To achieve the above object, the technical solution adopted by the present invention is:

[0010] A method for constructing a fixed-depth, precise heating electrode well, comprising:

[0011] (1) Make a metal mesh cage;

[0012] ① Make a support frame, and then wrap the side and bottom surfaces of the support frame with metal mesh;

[0013] ②Place the electrode in the center of the metal mesh cage and connect the electrode to the water injection pipe and cable;

[0014] ③ Filling the gap between the electrode and the metal mesh cage with graphite. After filling, the top surface of the support frame is sealed with a metal mesh. The particle size of the graphite is larger than the mesh size of the metal mesh.

[0015] (2) Place the electrodes with metal mesh cages in the wellbore at the depth required for heating, and fill the gap between the metal mesh cages and the well wall with iron sand or coarse sand;

[0016] (3) The top of the lowest metal mesh cage is covered with a barrier layer, and the top and bottom of the remaining metal mesh cages are each covered with a barrier layer;

[0017] (4) The non-heated strata in the wellbore are filled with fine sand or original soil.

[0018] The method for constructing a fixed-depth precision heating electrode well comprises the following steps: a wellhead sleeve is provided at the wellhead of the wellbore, the wellhead sleeve is inserted into the sand layer and fixed by pouring cement mortar; the water injection pipe and cable are respectively passed through the wall holes of the wellhead sleeve and connected to the ground.

[0019] The method for constructing a fixed-depth precision heating electrode well, wherein: the mesh diameter of the metal mesh is 1-2 mm, and the graphite is in flake or granular form with a particle size of 3-5 mm.

[0020] The method for constructing a fixed-depth precision heating electrode well, wherein: the support frame is composed of a support ring and support ribs made of carbon steel, and the support ring and the support ribs are connected by electric welding; the support rings are distributed at equal intervals along the center axis of the electrode, and the support ribs are distributed at equal intervals along the circumference of the electrode. The support frame is cylindrical, and the metal mesh seals the outer circumference and two end faces of the support frame.

[0021] The method for constructing a fixed-depth, precise heating electrode well comprises the following steps: only one electrode is placed in a metal mesh cage.

[0022] The method for constructing a fixed-depth precision heating electrode well, wherein: the water injection pipe is made of polytetrafluoroethylene, the cable is wrapped with a glass fiber tube at the part passing through the electrode, and the water injection pipe and cable are both resistant to acid and alkali corrosion.

[0023] The method for constructing a fixed-depth precision heating electrode well, wherein: an equipotential layer is formed between the cement mortar and the fine sand or original soil.

[0024] The method for constructing a fixed-depth precision heating electrode well, wherein: the wellhead sleeve is made of an insulating material such as PVC or PPR.

[0025] The method for constructing a fixed-depth precision heating electrode well, wherein: the coarse sand is quartz sand.

[0026] The method for constructing a fixed-depth precision heating electrode well, wherein: the barrier layer is bentonite or clay balls.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. It can match the depth of the conductive material with the position and height of the electrode, thereby achieving precise depth heating of the target formation. This avoids the disadvantage of traditional methods that cannot accurately heat the conductive material due to inaccurate filling depth, which is beneficial to reducing the amount of heated earthwork and lowering heating energy consumption.

[0029] 2. Improved well construction speed, especially when multiple electrodes need to be installed for heating multiple non-continuous formations. This avoids the time required for separately placing conductive materials and measuring depth, facilitating rapid well construction and preventing hole collapse.

[0030] 3. It solves the problem that graphite floats on the mud and is difficult to sink when using the mud wall protection process due to its low density, greatly reduces the amount of iron sand used, and reduces the cost of well construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the structure of a fixed-depth precision heating electrode well.

[0032] Figure 2 This is a schematic diagram of the production process of a metal mesh cage combined with an electrode. DETAILED DESCRIPTION

[0033] like Figure 1 、 Figure 2 As shown, the present invention provides a fixed-depth precision heating electrode well structure, including a wellbore 1, a metal mesh cage 2, an electrode 3, a water injection pipe 4, a cable 5, graphite 6, bentonite 7, fine sand 8, cement mortar 9, a wellhead sleeve 10, a quick-connect valve 11, iron sand 12, an equipotential layer 13, a cover 14, etc., wherein:

[0034] The wellbore 1 has a diameter of 15 to 30 cm and a depth determined by the depth of the lower edge of the bottommost heated stratum, usually 0.5 to 1.0 m deeper than the lower edge;

[0035] The metal mesh cage 2 is cylindrical and placed in the center of the wellbore 1. Its surface material is a metal mesh 21 (such as wire mesh or stainless steel mesh) with a mesh aperture of 1 to 2 mm. The metal mesh cage 2 contains a support frame, which is composed of a carbon steel support ring 22 and support ribs 23. The support rings 22 and support ribs 23 are connected by electric welding. The number of support rings 22 varies depending on the length of the electrode 3, ranging from 3 to 7, and are evenly spaced along the central axis of the electrode 3. The number of support ribs 23 varies depending on the diameter of the electrode 3, ranging from 4 to 8, and are evenly spaced along the circumference of the electrode 3. The metal mesh 21 is fixed to the support frame at the support ring 22 by iron wire or clamps. The two end faces of the metal mesh cage 2 are also sealed with the metal mesh 21.

[0036] The electrode 3 is placed in the center of the metal mesh cage 2. The diameter of the electrode 3 is 6.3 to 21.6 cm and the length is 2 to 6 m. The length is determined according to the thickness of the heated stratum, and is preferably 3 m. It is appropriate to place one electrode 3 in one metal mesh cage 2.

[0037] The vertical placement and number of the metal mesh cage 2 and its electrodes 3 in the well are determined according to the location and number of the required heated formations. The maximum number of electrodes 3 placed in one electrode well is no more than 6.

[0038] The electrode 3 is equipped with a water injection pipe 4 and a cable 5, which can respectively introduce water (or electrolyte, reagent, etc.) and current into the electrode 3; the water injection pipe 4 is made of polytetrafluoroethylene and can withstand temperatures above 200°C; the cable 5 is wrapped with a glass fiber tube at the portion passing through the electrode 3, which can withstand temperatures above 300°C and voltages above 1.5kV; the water injection pipe 4 and cable 5 are both resistant to acid and alkali corrosion;

[0039] The gap between the metal mesh cage 2 and the electrode 3 is filled with graphite 6, and the thickness of the gap in the radial direction is 3 to 5 cm. The graphite 6 is in the form of flakes or particles with a particle size of 3 to 5 mm, so that it is easy for the electrode 3 to be injected with water or drugs and then enter the surrounding soil through the particle pores.

[0040] The gap between the metal mesh cage 2 and the well wall is filled with iron sand 12 (or coarse sand, such as quartz sand), the particle size of the iron sand 12 is 2 to 3 mm, and the thickness of the gap in the radial direction is about 1 to 2 cm;

[0041] The top and bottom of the metal mesh cage 2 are filled with bentonite 7 (or clay balls) as a barrier layer. The vertical thickness of the barrier layer is about 0.5 μm. This prevents water injected through the electrode 3 or steam generated around the electrode 3 from migrating upward or downward along the permeable filler, thereby promoting horizontal flow of water or steam and promoting heat transfer and diffusion by convection.

[0042] The depth range of the non-heated stratum is filled with insulating materials with relatively high resistance, such as fine sand 8 (or original soil);

[0043] Fill cement mortar 9 from the wellhead surface to 20-30 cm below the ground to fix the wellhead sleeve 10;

[0044] There is an equipotential layer between the cement mortar 9 and the fine sand 8. The equipotential layer 13 is a metal mesh or graphite, preferably a metal mesh 21, which is connected to the equipotential layer in the surrounding soil to reduce the step voltage and protect the electrical safety of ground personnel.

[0045] The wellhead sleeve 10 is made of an insulating material such as PVC or PPR, with a pipe diameter of 110 to 150 mm. There are two holes on the pipe wall, which are used to allow the water injection pipe 4 and the cable 5 to pass through respectively; the top of the wellhead sleeve 10 is equipped with a cover 14 to facilitate related operations when connecting or removing the cable 5; the total length of the wellhead sleeve 10 is about 80 cm, of which the height above the ground is 40 cm, and the underground part is 40 cm. The underground part passes through the cement mortar 9 and the equipotential layer and is inserted into the fine sand 8.

[0046] It can be seen from this that the present invention also provides a method for constructing a fixed-depth, precise heating electrode well, comprising the following steps:

[0047] (1) According to the parameters such as the depth range of the heating formation, the diameter of the electrode 3 and the well diameter, a metal mesh cage 2 is manufactured;

[0048] ① Weld the support ribs 23 to the support ring 22, then wrap the support ribs 23 with the metal mesh 21, and fix the metal mesh 21 with wire or a clamp and seal the bottom;

[0049] ② Place the electrode 3 in the center of the metal mesh cage 2. The electrode 3 is connected to the water injection pipe 4 and the cable 5;

[0050] ③ Fill the gap between the electrode 3 and the metal mesh cage 2 with graphite 6. After filling, seal the top of the metal mesh cage 2 with a metal mesh 21 and a wire or a clamp.

[0051] (2) Based on the maximum heating depth, use mud wall protection and other technologies to construct the well;

[0052] (3) Place electrodes 3 in order from bottom to top according to the location of the heated formation:

[0053] ① Use a crane or other equipment to place the electrode 3 with the metal mesh cage 2 to the specified depth, and fit the water injection pipe 4 and cable 5 along the well wall;

[0054] ② Add a certain amount of iron sand 12 (or coarse sand) into the well to fill the gap between the metal mesh cage 2 and the well wall;

[0055] ③ Fill the well with bentonite balls to cover the electrode 3 to a thickness of about 50 cm;

[0056] ④ Fill the well with fine sand 8 to a certain height so that it fills the non-heated formation;

[0057] ⑤Add 7 balls of bentonite into the well again, with a thickness of about 50cm;

[0058] ⑥ Repeat steps ① to ③ above to install the electrode 3 of the second heating depth;

[0059] ⑦ Repeat steps ④ to ⑥ until multiple electrodes 3 are installed;

[0060] ⑧Insert the wellhead sleeve 10 into the sand layer 20-30 cm from the wellhead, and gather the water injection pipes 4 and cables 5 of each electrode 3 into the pipe; then pour cement mortar 9 to fix the sleeve;

[0061] ⑨ Pass the water injection pipe 4 and the cable 5 through the two wall holes of the wellhead sleeve 10 respectively, and connect them to the ground water injection pipe 4 and the cable 5 through the quick valve 11 and the copper pipe respectively.

[0062] Advantages of the present invention:

[0063] Compared with the traditional well construction process of first placing the electrode 3 and then placing the conductive material, the present invention binds the conductive material and the electrode 3 through the metal mesh cage 2, which has the following advantages:

[0064] 1. It can match the depth of the conductive material with the position and height of the electrode, thereby achieving precise depth heating of the target formation. This avoids the disadvantage of traditional methods that cannot accurately heat the conductive material due to inaccurate filling depth, which is beneficial to reducing the amount of heated earthwork and lowering heating energy consumption.

[0065] 2. Improved well construction speed, especially when multiple electrodes need to be installed for heating multiple non-continuous formations. This avoids the time required for separately placing conductive materials and measuring depth, facilitating rapid well construction and preventing hole collapse.

[0066] 3. It solves the problem that graphite floats on the mud and is difficult to sink when using the mud wall protection process due to its low density, greatly reduces the amount of iron sand used, and reduces the cost of well construction.

Claims

1. A method for constructing a fixed-depth, precise heating electrode well, characterized in that: include: (1) Make a metal mesh cage; ① Make a support frame, and then wrap the side and bottom surfaces of the support frame with metal mesh; ②Place the electrode in the center of the metal mesh cage and connect the electrode to the water injection pipe and cable; ③ Filling the gap between the electrode and the metal mesh cage with graphite. After filling, the top surface of the support frame is sealed with a metal mesh. The particle size of the graphite is larger than the mesh size of the metal mesh. (2) Place the electrodes with metal mesh cages in the wellbore at the depth required for heating, and fill the gap between the metal mesh cages and the wellbore wall with iron sand or coarse sand; (3) The top of the lowest metal mesh cage is covered with a barrier layer, and the tops and bottoms of the remaining metal mesh cages are each covered with a barrier layer; (4) The non-heated strata in the wellbore are filled with fine sand or original soil.

2. The method for constructing a fixed-depth, precise heating electrode well according to claim 1, characterized in that: A wellhead sleeve is provided at the wellhead of the wellbore, and the wellhead sleeve is inserted into the sand layer and fixed by pouring cement mortar; the water injection pipe and the cable respectively pass through the wall holes of the wellhead sleeve and are connected to the ground.

3. The method for constructing a fixed-depth, precise heating electrode well according to claim 1, characterized in that: The mesh size of the metal mesh is 1-2 mm, and the graphite is in the form of flakes or particles with a particle size of 3-5 mm.

4. The method for constructing a fixed-depth, precise heating electrode well according to claim 1, characterized in that: The support frame is composed of a support ring and support ribs made of carbon steel, and the support ring and the support ribs are connected by electric welding; the support rings are distributed at equal intervals along the center axis of the electrode, and the support ribs are distributed at equal intervals along the circumference of the electrode. The support frame is cylindrical, and the metal mesh seals the outer circumference and two end faces of the support frame.

5. The method for constructing a fixed-depth, precise heating electrode well according to claim 1, characterized in that: Only one electrode is placed in a metal mesh cage.

6. The method for constructing a fixed-depth, precise heating electrode well according to claim 1, characterized in that: The water injection pipe is made of polytetrafluoroethylene, and the cable is wrapped with a glass fiber tube at the part passing through the electrode. The water injection pipe and the cable are both resistant to acid and alkali corrosion and high temperature.

7. The method for constructing a fixed-depth, precise heating electrode well according to claim 2, characterized in that: An equipotential layer is formed between the cement mortar and the fine sand or original soil.

8. The method for constructing a fixed-depth, precise heating electrode well according to claim 2, characterized in that: The wellhead sleeve is made of insulating material such as PVC or PPR.

9. The method for constructing a fixed-depth, precise heating electrode well according to claim 1, characterized in that: The coarse sand is quartz sand.

10. The method for constructing a fixed-depth, precise heating electrode well according to claim 1, characterized in that: The barrier layer is bentonite or clay balls.

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