Anode ground bed suitable for Loess Plateau region and construction method thereof

Abstract

The present application relates to the field of cathodic protection technology and discloses an anode groundbed suitable for the Loess Plateau region and a method for constructing the same. The anode groundbed comprises an anode and an anode groundbed filler. The anode is arranged inside a deep well and connected to a power source via a cable. The power source is located outside the deep well. The anode groundbed filler is filled in the anode active area inside the deep well. The anode groundbed filler comprises 5-10% by mass of a water absorbent, 10-20% by mass of a strong electrolyte, 70-85% by mass of a carbon backfill, and 2-5% by mass of a pH neutralizer. The present application achieves the reconstruction of the anode groundbed structure through the combined effect of the anode groundbed filler, which can effectively improve the working environment of the anode, reduce the anode grounding resistance, increase the anode output current, and thereby enhance the protection effect of the cathode.

Description

Technical Field

[0001] The present application relates to the field of oil drilling technology, in particular to the field of cathodic protection, and more specifically to an anode bed suitable for the Loess Plateau region and a construction method thereof. Background Art

[0002] With the continued development of oil and gas fields in the Loess Plateau, the number of oil and water well casing damage caused by corrosive water layers has been increasing year by year, with an average of over 200 new casing damage wells added each year. This has directly impacted the efficient development of oil and gas fields and the increase and stability of production. Currently, forced current cathodic protection technology is an effective measure to inhibit casing corrosion.

[0003] Due to the unique geographical environment of the Loess Plateau, characterized by perennial drought and low rainfall, and a low groundwater level, the soil resistivity is generally high, reaching over 300Ω•m. Wells are typically drilled to depths of 200-250m, and are completed in open-hole conditions, making wellbore collapse and anode bed failure more likely. Consequently, the unique local geographical environment often results in low anode bed conductivity and high ground resistance, which severely impacts the effectiveness of cathodic protection systems and wastes significant energy.

[0004] At present, there are many studies on the structure of cathodic protection devices, such as the publication number CN205934026U

[0005] The utility model patent discloses a cathodic protection device for marine risers. The device achieves electrical conduction between the anode and the steel pipe through the water-absorbing and moisturizing properties of the water-absorbing resin, and then realizes the operation of the cathodic protection system through the connection of metal wires. It has its own water replenishment and storage system, which effectively ensures the normal operation of the system under waterless conditions.

[0006] The above-mentioned prior art proposes a sacrificial anode cathodic protection device, which achieves the purpose of sacrificing the anode and protecting the cathode by adding a filler layer structure with a water absorption function. Since this technology belongs to the sacrificial anode cathodic protection technology, it is not suitable for the special geographical environment of the Loess Plateau. Summary of the Invention

[0007] In order to solve the problems and shortcomings existing in the above-mentioned prior art, the present application proposes an anode bed and a construction method for cathodic protection of oil and water well casings that are particularly suitable for the Loess Plateau region. The present application realizes the reconstruction of the anode bed structure through the comprehensive effect of backfill material, which can effectively improve the working environment of the anode, reduce the anode grounding resistance, increase the anode output current, and thereby enhance the protection effect of the cathode.

[0008] In order to achieve the above-mentioned invention objectives, the technical solutions of this application are as follows:

[0009] An anode ground bed suitable for use in the Loess Plateau region comprises an anode, which is arranged inside a deep well and connected to a power supply via a cable, the power supply being located outside the deep well. The invention is characterized in that the invention also comprises an anode ground bed filler, which is filled in the anode active area inside the deep well. The anode ground bed filler comprises 5 to 10% by mass of a water absorbent, 10 to 20% by mass of a strong electrolyte, 70 to 85% by mass of a carbon backfill material, and 2 to 5% by mass of a pH neutralizer.

[0010] Preferably, the water absorbent includes one or more of the following substances, including acrylamide-acrylate copolymer cross-linked product, starch grafted acrylate copolymer cross-linked product, and water-absorbing resin (SAP).

[0011] Preferably, the strong electrolyte comprises one or more of the following substances, including sodium chloride, potassium chloride, and magnesium chloride.

[0012] Preferably, the carbon backfill material includes one or more of the following substances, including petroleum coke, metallurgical coke, and artificial graphite slag.

[0013] Preferably, the pH neutralizer includes one or more of the following substances, including calcium hydroxide, calcium carbonate, and sodium hydroxide.

[0014] Preferably, the relative density of the carbon backfill material is greater than 1.5 g / cm 3 , particle size range is 3-5mm, and carbon content is >85%.

[0015] Based on the same inventive concept, the present application also proposes a method for constructing an anode bed suitable for the Loess Plateau region. The anode bed constructed by the method is the anode bed suitable for the Loess Plateau region, and specifically comprises the following steps:

[0016] Step S1. Complete deep well drilling operations according to the designed well depth and lower the casing into the rock layer;

[0017] Step S2. Prepare a 3~5% sodium chloride aqueous solution for circulating well washing, with a circulation time of not less than 3 hours;

[0018] Step S3. Prepare the anode bed filler according to the ratio, and mix and stir the anode bed filler evenly;

[0019] Step S4. Put the anode bed filler into a cloth bag, tie the bag tightly and sink it into the bottom of the well;

[0020] Step S5. Lowering the anode into the deep well;

[0021] Step S6: backfill the gap between the anode and the well wall with anode bed filler, and backfill the top of the anode with coke.

[0022] Preferably, in step S4, the thickness of the anode bed filler sunk to the bottom of the well is ≥1 m.

[0023] Preferably, in step S6, the height of the coke backfill exceeds 1 m from the top of the anode.

[0024] Beneficial effects of this application:

[0025] (1) The present application improves the structure of the anode bed and adopts an anode bed filler to fill the gap between the anode and the well wall. The anode bed filler can absorb the water around the anode bed when formation water flows into the wellbore or when water is replenished in the later stage. When there is a lack of water, it can release part of the water to ensure the moisture of the anode bed and reduce the resistivity and grounding resistance.

[0026] (2) The anode bed structure of the present application can prevent the surrounding stratum sand from collapsing and mixing into the anode bed filler, resulting in an increase in the grounding resistance of the anode bed.

[0027] (3) The anode bed filler of the present application increases the electrical conductivity of the entire anode bed, reduces the grounding resistance, and can improve the cathodic protection effect.

[0028] (4) The anode bed filler of the present application can neutralize the acidic gas generated on the anode surface, thereby reducing the chemical corrosion of the anode by the acidic gas.

[0029] (5) The wellbore integrity and the specification selection of carbon backfill material in this application are conducive to the smooth discharge of gas generated during the anode action, avoiding the occurrence of "gas blockage effect" and improving the effect of cathodic protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The foregoing and following detailed description of the present application will become more apparent when read in conjunction with the following drawings, in which:

[0031] Figure 1 This is a schematic diagram of the anode bed structure for this application.

[0032] In the attached figure:

[0033] 1. Rock layer; 2. Anode bed filler; 3. Anode; 4. Groundwater level; 5. Loess layer; 6. Casing; 7. Cable; 8. Steel cable. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the technical solutions in this application, the following will further illustrate the technical solutions for achieving the invention objectives of this application through several specific embodiments. It should be noted that the technical solutions claimed for protection in this application include but are not limited to the following embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without making any creative efforts should fall within the scope of protection of this application.

[0035] Due to the unique geographical environment of the Loess Plateau, characterized by perennial drought and low rainfall, and a low groundwater level, the soil resistivity is generally high, exceeding 300Ω•m. Drilling depths of 200-250m and open-hole completions are designed to be prone to wellbore collapse and anode bed failure. This can easily lead to low conductivity and high ground resistance in the anode bed, severely compromising the effectiveness of the cathodic protection system and wasting significant energy.

[0036] Based on this, this application proposes an anode bed and its construction method that are particularly suitable for the Loess Plateau region. By improving the structure of the traditional anode bed, it can effectively improve the working environment of the anode, reduce the anode grounding resistance, increase the anode output current, and thus enhance the cathodic protection effect.

[0037] Example 1

[0038] In order to facilitate the understanding of the technical solution of this application, this application first introduces the structure of the anode bed. This embodiment discloses an anode bed suitable for the Loess Plateau region. Figure 1 The anode bed mainly includes an anode and an anode bed filler. The anode and the anode bed filler are both arranged inside a deep well. Due to the special geographical environment of the Loess Plateau, the drilling depth is generally deep, and the designed well depth is generally greater than 200m. The anode and the anode bed filler are both arranged in the rock stratum of the deep well. Above the rock stratum is a soil layer structure. The anode is connected to a power supply located outside the deep well through a cable. The anode bed filler is filled in the anode active area inside the deep well. A casing is also provided in the deep well. The tail end of the casing passes through the deep well rock layer for 5-10 meters, mainly used to prevent the loess layer from collapsing. Furthermore, the anode bed filler is mainly composed of the following substances, including 5~10% by mass of a water absorbent, 10~20% by mass of a strong electrolyte, 70~85% by mass of a carbon backfill and 2~5% by mass of a pH neutralizer.

[0039] In this embodiment, the relative density of the selected carbon backfill material should be greater than 1.5 g / cm 3 , the particle size of the carbon backfill material should be in the range of 3-5 mm, and the carbon content should be greater than 85%.

[0040] In this embodiment, it should be noted that the water absorbent is acrylamide-acrylate copolymer cross-linked material with a mass percentage of 8%; the strong electrolyte is potassium chloride with a mass percentage of 10%; the carbon backfill material is petroleum coke with a mass percentage of 75%; and the pH neutralizer is calcium carbonate with a mass percentage of 7%.

[0041] In this embodiment, it should also be noted that the anode of the present application is a pre-packaged anode structure, which is composed of an anode body and a pre-installed anode tube arranged on the outer layer of the anode body.

[0042] Example 2

[0043] This embodiment discloses an anode bed suitable for the Loess Plateau region. The difference between this embodiment and Example 1 is that the water absorbent is a starch grafted acrylate copolymer cross-linked product, with a mass percentage of 10%; the strong electrolyte is potassium chloride, with a mass percentage of 15%; the carbon backfill material is petroleum coke, with a mass percentage of 70%; and the pH neutralizer is calcium carbonate, with a mass percentage of 5%.

[0044] Example 3

[0045] This embodiment discloses an anode bed suitable for the Loess Plateau region. The difference between this embodiment and Example 1 is that the water absorbent is a water-absorbing resin (SAP) with a mass percentage of 10%; the strong electrolyte is sodium chloride with a mass percentage of 10%; the carbon backfill material is petroleum coke with a mass percentage of 75%; and the pH neutralizer is sodium hydroxide with a mass percentage of 5%.

[0046] Example 4

[0047] This embodiment discloses an anode bed suitable for the Loess Plateau region. The difference between this embodiment and Example 1 is that the water absorbent is a mixture of acrylamide-acrylate copolymer cross-linked product and starch grafted acrylate copolymer cross-linked product, wherein the mass percentage of acrylamide-acrylate copolymer cross-linked product is 5%, and the mass percentage of starch grafted acrylate copolymer cross-linked product is 5%; the strong electrolyte is potassium chloride, the mass percentage of which is 15%; the carbon backfill material is petroleum coke, the mass percentage of which is 70%; and the pH neutralizer is calcium carbonate, the mass percentage of which is 5%.

[0048] Example 5

[0049] This embodiment discloses an anode ground bed suitable for use in the Loess Plateau region. This embodiment differs from Example 1 in that the water absorbent is a mixture of an acrylamide-acrylate copolymer cross-linked product and a water-absorbing resin (SAP), wherein the mass percentage of the acrylamide-acrylate copolymer cross-linked product is 5%, and the mass percentage of the water-absorbing resin (SAP) is 5%; the strong electrolyte is potassium chloride, with a mass percentage of 10%; the carbon backfill material is petroleum coke, with a mass percentage of 75%; and the pH neutralizer is calcium carbonate, with a mass percentage of 5%.

[0050] Resistivity measurement:

[0051] The Wenner method (four-electrode equidistant method) was used to measure the resistivity of the soil and anode bed. The test results are shown in Table 1 below.

[0052] During the resistivity test, the electrode burial depth was 0.1m, and the distance between ground electrodes was 3m. The resistivity was calculated using the following formula:

[0053] ;

[0054] In the formula, R is the measured resistance value and a is the electrode distance.

[0055] Table 1 Resistivity of soil and anode bed on site

[0056]

[0057] Analysis of the experimental data in Table 1 shows that the resistivity of the on-site soil is 199.66 Ω·m. However, the resistivity of the anode bed reconstructed after filler treatment is significantly reduced, reaching a minimum of 12.06 Ω·m. Therefore, the anode bed constructed using the method of this application can effectively reduce the grounding resistance of the anode bed in deep wells, thereby improving the cathodic protection effect.

[0058] Example 6

[0059] Based on the same inventive concept, an embodiment of the present application also proposes a method for constructing an anode bed suitable for the Loess Plateau region. The anode bed constructed by the method is the anode bed suitable for the Loess Plateau region of any of the above embodiments, and the construction method specifically includes the following steps.

[0060] Step S1: Complete deep well drilling operations according to the designed well depth, and lower casing into the rock layer of the deep well.

[0061] In this embodiment, in the Loess Plateau region, the designed drilling depth is generally 200-250 m, and the well is drilled through the loess layer to 20-30 m below the rock layer.

[0062] In this embodiment, it should be noted that the casing is made of concrete. When lowering the casing, the casing needs to penetrate 5-10 meters of the rock layer. The casing is mainly used to prevent the loess layer from collapsing, thereby ensuring the integrity of the wellbore.

[0063] Step S2. Prepare a 3-5% sodium chloride aqueous solution for circulating well washing. The circulation time is not less than 3 hours to ensure that the liquid out of the well is clean and there is no sand at the bottom of the well.

[0064] Step S3. Prepare the anode bed filler according to the corresponding ratio, mix and stir the prepared anode bed filler evenly, and set aside.

[0065] In this embodiment, the anode bed filler mainly consists of 5-10% by mass of a water absorbent, 10-20% by mass of a strong electrolyte, 70-85% by mass of a carbon backfill material, and 2-5% by mass of a pH neutralizer.

[0066] The water absorbent may be one or more of the following substances, including acrylamide-acrylate copolymer cross-linked product, starch grafted acrylate copolymer cross-linked product and water absorbent resin (SAP).

[0067] Water-absorbent polymer (SAP) resin is a highly absorbent resin.

[0068] The strong electrolyte may be one or more of the following substances, including sodium chloride, potassium chloride and magnesium chloride.

[0069] The carbon backfill material can be one or more of the following materials, including petroleum coke, metallurgical coke and artificial graphite slag

[0070] The pH neutralizer may be one or more of the following substances, including calcium hydroxide, calcium carbonate and sodium hydroxide.

[0071] Step S4: Put the configured anode bed filler into a cloth bag, tie the bag tightly and sink it into the bottom of the well.

[0072] In this embodiment, it should be noted that the thickness of the anode bed filler sunk into the well bottom is ≥1 m, that is, the filling thickness of the anode bed filler at the well bottom needs to be greater than or equal to 1 m.

[0073] Step S5: Lower the anode into the deep well.

[0074] In this embodiment, it should be noted that the anode is a pre-packaged structure. When placing the anode, the anode should be placed as close to the center of the deep well as possible.

[0075] In this embodiment, it should also be noted that when lowering the anode, a steel cable is generally used to lower the anode into the well.

[0076] Step S6: backfill the gap between the anode and the well wall with anode bed filler, and backfill the top of the anode with coke.

[0077] In this embodiment, it should be noted that when coke is used for backfilling, the height of the coke backfill should exceed the top of the anode by at least 1 m.

[0078] After the deep well construction of this embodiment is completed, the anode active area inside the entire deep well is filled with anode bed fillers.

[0079] The above description is merely a preferred embodiment of the present application and does not constitute any form of limitation to the present application. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present application shall fall within the scope of protection of the present application.

Claims

1. An anode bed suitable for the Loess Plateau region, comprising an anode, the anode being arranged inside a deep well and connected to a power source via a cable, the power source being located outside the deep well, characterized in that: The anode ground bed filler is filled in the anode active area inside the deep well, and the anode ground bed filler includes 5-10% by mass of a water absorbent, 10-20% by mass of a strong electrolyte, 70-85% by mass of a carbon backfill material, and 2-5% by mass of a pH neutralizer; The water absorbent is one or more of acrylamide-acrylate copolymer cross-linked product, starch grafted acrylate copolymer cross-linked product, and water-absorbing resin; The strong electrolyte is one or more of sodium chloride, potassium chloride, and magnesium chloride; The carbon backfill material is one or more of petroleum coke, metallurgical coke, and artificial graphite slag; The pH neutralizer is one or more of calcium hydroxide, calcium carbonate, and sodium hydroxide; The relative density of the carbon backfill material is >1.5g / cm 3 The particle size range of the carbon backfill material is 3-5 mm, and the carbon content of the carbon backfill material is greater than 85%.

2. The anode bed suitable for the Loess Plateau region according to claim 1, characterized in that: The mass percentage of the water absorbing agent is 10%.

3. The anode bed suitable for the Loess Plateau region according to claim 1, characterized in that: The mass percentage of the strong electrolyte is 10%.

4. The anode bed suitable for the Loess Plateau region according to claim 1, characterized in that: The mass percentage of the carbon backfill material is 75%.

5. The anode bed suitable for the Loess Plateau region according to claim 1, characterized in that: The mass percentage of the pH neutralizer is 5%.

6. The anode bed suitable for the Loess Plateau region according to claim 1, characterized in that: The water absorbent is a mixture of acrylamide-acrylate copolymer cross-linked product and starch grafted acrylate copolymer cross-linked product, wherein the mass percentage of acrylamide-acrylate copolymer cross-linked product is 5%, and the mass percentage of starch grafted acrylate copolymer cross-linked product is 5%.

7. The anode bed suitable for the Loess Plateau region according to claim 1, characterized in that: The water absorbent is a mixture of acrylamide-acrylate copolymer cross-linked product and a water absorbent resin, wherein the mass percentage of the acrylamide-acrylate copolymer cross-linked product is 5% and the mass percentage of the water absorbent resin is 5%.

8. A method for constructing an anode bed suitable for the Loess Plateau, characterized in that: The anode ground bed constructed by the method is the anode ground bed suitable for the Loess Plateau region as described in any one of claims 1 to 7, and specifically comprises the following steps: Step S1. Complete deep well drilling operations according to the designed well depth and lower the casing into the rock layer; Step S2. Prepare a 3~5% sodium chloride aqueous solution for circulating well washing, with a circulation time of not less than 3 hours; Step S3. Prepare the anode bed filler according to the ratio, and mix and stir the anode bed filler evenly; Step S4. Put the anode bed filler into a cloth bag, tie the bag tightly and sink it into the bottom of the well; Step S5. Lowering the anode into the deep well; Step S6: backfill the gap between the anode and the well wall with anode bed filler, and backfill the top of the anode with coke.

9. The method for constructing an anode bed suitable for the Loess Plateau region according to claim 8, characterized in that: In step S4, the thickness of the anode bed filler sunk to the bottom of the well is ≥1 m.

10. The method for constructing an anode bed suitable for the Loess Plateau region according to claim 8, characterized in that: In step S6, the height of the coke backfill exceeds 1 m from the top of the anode.

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