A method for segmented forced current cathodic protection of the outer wall of a casing of an oil and gas well

Abstract

The present application relates to oil and gas well downhole casing outer wall anticorrosion technical field, disclose a kind of oil and gas well casing outer wall segmented forced current cathodic protection method, to oil and gas well casing adopts segmented forced current cathodic protection.The present application solves the uneven distribution of cathodic protection current problem existing in prior art.

Description

Technical Field

[0001] This invention relates to the field of corrosion protection technology for the outer wall of downhole casing in oil and gas wells, specifically a method for segmented forced current cathodic protection of the outer wall of oil and gas well casing. Background Technology

[0002] Oil and gas well casing outer wall protection generally relies on anti-corrosion coatings and cement layers. However, anti-corrosion coatings are easily damaged during oil and gas well casing construction, and cement layers are prone to cracking due to geological factors, allowing corrosive media to penetrate. Both of these protective layers can lead to severe corrosion of the oil and gas well casing outer wall. To extend the life of oil and gas wells, cathodic protection of the casing outer wall is necessary. Common cathodic protection methods for oil and gas well casing outer walls include the following:

[0003] 1. Sacrificial anode protection method. This method requires installing sacrificial anode blocks on the outer wall of the oil and gas well casing and placing them downhole together with the casing to ensure uniform distribution of the electric field lines. Since sacrificial anodes are consumed over time, they will eventually deplete after a certain number of years. However, due to the high cost and difficulty of replacing anodes, replacement is generally abandoned, leading to corrosion of the oil and gas well casing.

[0004] 2. Forced current cathodic protection is employed, with the auxiliary anode being a deep-well anode bed. This method requires drilling a separate deep well near the protected well and installing the auxiliary anode, resulting in significant investment. This method relies on an ideal state of uniform geological conditions, similar to the cathodic protection principle of common shallow horizontal pipelines. Common shallow horizontal pipelines exhibit good cathodic protection because the differences in shallow geological conditions along the pipeline are not significant, allowing for controllable distribution of the shallow protection electric field. However, oil and gas well casings often penetrate vertically to considerable depths, some approaching 10,000 meters, penetrating various complex geological layers, including multiple water-blocking and electrical-breaking layers. The varying oxidizability of different substances in each geological layer leads to severe macro-cell corrosion between layers and severely uneven distribution of the cathodic protection current electric field, deviating significantly from the ideal state. Therefore, the actual cathodic protection effect is severely uneven; some areas are underprotected and prone to corrosion perforation, while others are overprotected, resulting in hydrogen evolution and potentially hydrogen embrittlement or cathodic stripping.

[0005] 3. Based on Method 2 above, the cathodic protection power supply equipment adopts a pulsed power supply, replacing the previous DC protection current with pulsed current. The pulsed current is essentially a combination of AC and DC components. The AC component of the current penetrates geological layers with higher resistance more easily, thus optimizing the uniformity of the protective electric field. However, the DC component of the current is still significantly affected by the differences in geological layers underground, therefore the optimization effect on the uniformity of the electric field is limited, and the improvement in protection effect is also limited. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention provides a method for segmented forced current cathodic protection of the outer wall of oil and gas well casing, which solves the problem of uneven cathodic protection current distribution in the prior art.

[0007] The technical solution adopted by the present invention to solve the above problems is:

[0008] A method for segmented forced current cathodic protection of the outer wall of oil and gas well casing, wherein segmented forced current cathodic protection is applied to the oil and gas well casing.

[0009] As a preferred technical solution, segmented protection is achieved by electrically connecting a common cathode and different anodes to the oil and gas well casing.

[0010] As a preferred technical solution, different protection parameters are set according to the physicochemical characteristics of different geological layers where each anode is located.

[0011] As a preferred technical solution, during construction, holes are drilled from the inner wall outward in the inner wall of the casing of oil and gas wells in different geological layers downhole, and the anode bed is buried outside the casing and cement layer through the holes. Then, the anode cable is connected through the inside of the casing to the anode terminal of the corresponding forced current cathodic protection power supply equipment on the ground.

[0012] As a preferred technical solution, during construction, holes are drilled from the inner wall outward in the inner wall of the oil and gas well casing in different geological layers downhole, and test pieces are buried in the oil and gas well casing and outside the cement layer through the holes. Then, the zero-position cable is connected through the inside of the oil and gas well casing to the zero-position terminal of the corresponding forced current cathodic protection power supply equipment on the ground.

[0013] As a preferred technical solution, the test piece has the same material and protection measures as the oil and gas well casing.

[0014] As a preferred technical solution, after construction is completed, insulating and anti-corrosion materials are used to seal the edge gaps of the holes.

[0015] As a preferred technical solution, a trial run is conducted after construction is completed. Based on the power-off potential difference and power-on current feedback between the test piece and the reference electrode, it is determined whether the oil and gas well casing section corresponding to the geological layer of the test piece meets the set protection requirements.

[0016] As a preferred technical solution, after determining whether the oil and gas well casing section corresponding to the geological layer of the test piece meets the set protection requirements, the protection potential is adjusted to enable the oil and gas well casing to obtain the best protection state.

[0017] As a preferred technical solution, oil and gas well casing includes one or more of the following: casing for oil and gas production wells, casing for gas injection wells, or casing for water injection wells.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) Compared with the background technology methods two and three, it avoids the problem of uneven distribution of cathodic protection current caused by different resistivities of geological layers, makes the protection electric field uniform and controllable, and eliminates the phenomenon of under-protection or over-protection.

[0020] (2) Compared with the background technology methods two and three, it solves the problem of severe macrocell corrosion caused by the difference in oxidative properties of different substances in different geological layers;

[0021] (3) Compared with the background technology methods two and three, no additional deep well is drilled outside the protected well to install the anode ground bed, thus reducing costs;

[0022] (4) Compared with the first method in the background technology, the protection effect is more durable and easier to maintain. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the forced current cathodic protection principle of the outer wall of the casing of an oil and gas well, taking the three geological layers of the oil and gas well as an example.

[0024] Figure 2 A wiring diagram for a single set of cathodic protection power supply equipment;

[0025] Figure 3 This is a circuit connection diagram for a single cathodic protection power supply device that combines the test cathode cable and the zero-position cable.

[0026] The labels and their corresponding names in the attached diagram:

[0027] 1-Cathode protection power supply equipment;

[0028] 2-Cathode terminals of cathodic protection power supply equipment;

[0029] 3-Zero-position terminal of cathodic protection power supply equipment;

[0030] 4-Reference terminals for cathodic protection power supply equipment;

[0031] 5 - Anode terminals of cathodic protection power supply equipment;

[0032] 6-Reference cable;

[0033] 7-Cathode cable;

[0034] 8-Reference electrode;

[0035] 9-Structural boundary;

[0036] 10 - Oil and gas well casing wall;

[0037] 11-Auxiliary anode ground bed;

[0038] 12-Test film;

[0039] 13- Cathode cable of the test piece;

[0040] 14-Syroscope;

[0041] 15-Ammeter;

[0042] 16 - Zero-position cable of the test piece;

[0043] 17 - Large resistance;

[0044] 18 - The cathode cable and zero-position cable after the test pieces are combined. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0046] Example 1

[0047] like Figures 1 to 3 As shown, to address the problems of high cost and operational difficulty in sacrificial anode replacement during existing oil and gas well casing corrosion protection, as well as the issues of under-protection and over-protection caused by uneven forced current cathodic protection, this invention discloses a method for segmented forced current cathodic protection of the outer wall of oil and gas well casing. This method employs segmented forced current cathodic protection for the oil and gas well casing, but without disconnecting the casing with an insulating joint. Instead, it uses a common cathode with different anodes for segmented protection. Each anode is configured with different protection parameters based on the physicochemical characteristics of its respective geological layer, resulting in a more uniform and controllable protective electric field distribution. During implementation, holes are drilled from the inner wall of the protected casing outwards, and auxiliary anodes are placed outside the casing through these holes. Different anode parameters are set according to the differences in geological strata, facilitating segmented protection and reducing costs.

[0048] To overcome the shortcomings of the prior art, the present invention provides a method for segmented forced current cathodic protection of the outer wall of oil and gas well casing.

[0049] The technical solution adopted in this invention is:

[0050] 1. Segmented forced current cathodic protection is adopted for oil and gas well casing, but it is not necessary to disconnect the oil and gas well casing with insulating joints. Instead, segmented protection is carried out by using a common cathode with different anodes. Each anode is set with different protection parameters according to the physicochemical characteristics of its different geological layers, so that the distribution of the protection electric field is more uniform and controllable.

[0051] 2. In the implementation of this method, the auxiliary anode must be installed outside the outer wall of the well casing to protect the outer wall of the casing. Background methods two and three involve drilling a separate well outside the oil and gas well to install the auxiliary anode, which is not conducive to installing multiple auxiliary anodes with different parameters according to geological stratification for segmented protection. This method, however, involves drilling holes outward from the inner wall of the casing of the well being protected, and installing multiple different anodes according to the actual geological conditions, which facilitates segmented protection and reduces costs.

[0052] A method for segmented forced current cathodic protection of the outer wall of oil and gas well casing is disclosed. The oil and gas well casing is protected by segmented forced current cathodic protection, but it is not necessary to disconnect the oil and gas well casing with an insulating joint. Instead, segmented protection is carried out by using a common cathode with different anodes. Each anode is set with different protection parameters according to the physicochemical characteristics of the different geological layers in which it is located.

[0053] Preferably, the casing of oil and gas wells includes the casing of oil and gas production wells, the casing of gas injection wells, or the casing of water injection wells.

[0054] Preferably, holes are drilled from the inner wall outward in the casing of oil and gas wells in different geological layers downhole, and the anode bed is buried outside the oil and gas well casing and cement layer through the holes. Then, the anode cable is connected through the inside of the oil and gas well casing to the anode terminal of the corresponding forced current cathodic protection power supply equipment on the ground.

[0055] Preferably, holes are drilled from the inner wall outwards into the casing of oil and gas wells in different geological layers downhole. Test pieces are then embedded in the casing and outside the cement layer through these holes. A zero-position cable is then connected through the inside of the casing to the zero-position terminal of the corresponding forced current cathodic protection power supply on the surface. The test pieces should have the same material and protection measures as the oil and gas well casing.

[0056] Preferably, after the oil and gas well casing opening is completed, the gaps at the edge of the opening need to be sealed with insulating and anti-corrosion material.

[0057] Preferably, a trial run is conducted after construction is completed. At this time, the oil and gas well casing section corresponding to the geological layer of the test piece should be judged based on the feedback of the power-off potential difference and power-on current between the test piece and the reference electrode to obtain appropriate protection. Then, the protection potential can be adjusted to obtain the best protection state.

[0058] Compared with the existing sacrificial anode protection method, the protection effect is more durable and easier to maintain; compared with the existing forced current cathodic protection method, it avoids the problem of uneven cathodic protection current distribution caused by different resistivities of different geological layers, making the protection electric field uniform and controllable, and eliminating under-protection and over-protection phenomena; it solves the problem of severe macrocell corrosion caused by the difference in oxidizability of different substances in different geological layers; it eliminates the need to drill a deep well outside the protected well to install an anode ground bed, thus reducing costs.

[0059] Example 2

[0060] like Figures 1 to 3 As shown, as a further optimization of Embodiment 1, this embodiment also includes the following technical features based on Embodiment 1:

[0061] A method for segmented forced current cathodic protection of the outer wall of an oil and gas well casing, such as Figure 1 , Figure 2 Taking a certain oil and gas well with a geological layer of three layers as an example: the geological layer is divided into upper, middle and lower layers. The upper layer contains oxidizing minerals and has a high oxygen content. The middle layer is a dense water-resistant layer. The lower layer contains oil and gas resources and some reducing minerals. Figure 1 The exhibition also showcased the formation boundary line 9, the casing wall of the oil and gas well 10, the auxiliary anode bed 11, and the anode cables that are individually connected to the anode terminals of their respective cathodic protection power supply equipment.

[0062] Under normal circumstances, the upper and lower layers are in a state of equal positive and negative charge, separated by the middle layer, making it difficult for matter to exchange or influence each other. After the oil and gas well is drilled through, the casing connects the electron channels of the upper and lower layers, causing oxidizing minerals and oxygen in the upper layer to gain electrons through the casing, while reducing minerals in the lower layer provide electrons. The difference in charged ion concentration between the upper and lower layers drives the exchange of positive and negative charges, forming a battery circuit. Therefore, electrons continuously flow into the casing from the lower layer, while iron ions flow into the surrounding medium, forming macrocell corrosion.

[0063] On the other hand, if the background technology method two or three is adopted instead of the segmented cathodic protection method, the resistivity of the upper and lower layers is relatively small, while the resistivity of the middle water-proof layer is relatively large. If the anode ground bed is placed in the upper or middle layer, the middle and lower layer sleeves are difficult to protect; if the anode ground bed is placed in the lower layer, the middle layer sleeve is difficult to protect, and the upper layer sleeve is directly protected by the macro cell current.

[0064] According to the method of this invention, holes can be drilled from the inside out for the upper, middle, and lower layers of oil and gas well casing, and auxiliary anodes and test pieces can be placed separately. The test pieces should have the same material and protective measures as the oil and gas well casing. Since the continuous sections of the oil and gas well casing cannot be tested separately, test pieces can only be used to replace the oil and gas well casing for segmented testing.

[0065] Each of the upper, middle, and lower anodes is connected to the anode terminal 5 of the corresponding cathodic protection power supply equipment through an independent anode cable.

[0066] Each of the upper, middle, and lower test pieces is connected to the zero-position terminal 3 of the corresponding cathodic protection power supply equipment through an independent zero-position cable.

[0067] All cathode protection power supply equipment's cathode terminals 2 share a single cathode cable connected to the conduit.

[0068] All reference terminals 4 of the cathodic protection power supply equipment share a single reference cable 6 connected to the buried reference electrode.

[0069] Since the test pieces should receive the same forced current cathodic protection as the oil and gas well casing, each of the upper, middle, and lower layers of test pieces is connected to the shared cathodic cable on the ground via an independent cathodic cable 7. However, this cathodic cable needs to automatically disconnect during power-off testing; therefore, a thyristor 14 is added to each cable. The control electrode of the thyristor is connected to the corresponding anode through a large resistor 17, and its on / off state is controlled by the anode potential. Simultaneously, an ammeter should be connected in series with the cathodic cable connected to each test piece to monitor the protective current of that test piece.

[0070] The oxidizing properties of the surrounding environment in geological formations are a major factor contributing to casing corrosion in oil and gas wells. This example utilizes cathodic protection power supply equipment 1, which takes this factor into account. The equipment repeatedly energizes and de-energizes the anode and cathode. When energized, the cathode supplies electrons to the surrounding environment, locally reducing its density. When de-energized, the equipment automatically detects the electrode potential of the surrounding environment using a reference electrode 8 as a baseline. Essentially, this detects whether the cathode provides sufficient electrons to the surrounding environment during energization, and whether it reduces the thin layer of surrounding environment adjacent to the cathode to an acceptable range. When the electrode potential of the adjacent thin layer of surrounding environment decreases to an appropriate level, it no longer corrodes the cathode. Therefore, the de-energization potential can characterize whether the cathode has received adequate protection.

[0071] In this embodiment, each of the upper, middle, and lower layers is equipped with independent cathodic protection power supply equipment, test pieces, and anodes to provide corresponding protection based on the different oxidation characteristics of each layer. The corresponding cathodic protection parameters are calculated according to the different geological parameters of each layer, and specific details can be found in relevant standards as follows:

[0072] Calculation of casing resistance in oil and gas wells (refer to GB / T 21448-2017 formula for calculating pipeline resistance)

[0073]

[0074] In the formula:

[0075] R s —Pipeline resistance, Ω / m;

[0076] ρ t —Resistivity of steel, Ω·mm 2 / m;

[0077] D p —Outer diameter of the pipe, in meters;

[0078] δ—Pipe wall thickness, mm.

[0079] Calculation of the protection radius of a single anode to a pipeline (refer to the formula for calculating the protection radius in GB / T 21448-2008)

[0080]

[0081] In the formula:

[0082] L p —Pipeline protection radius, in meters;

[0083] ΔV—The difference between the maximum protection potential and the minimum protection potential, in V;

[0084] D p —Outer diameter of the pipe, in meters;

[0085] J S —Protection current density, A / m 2 ;

[0086] R s —Pipeline resistance, Ω / m.

[0087] Grounding resistance calculation (refer to Dwight's formula for calculating the grounding resistance of multi-branch vertical shallow buried anode ground beds):

[0088]

[0089] In the formula: R v - Vertical anode grounding resistance, Ω;

[0090] ρ – Soil resistivity, Ω·m;

[0091] L a - Auxiliary anode length (including packing), m;

[0092] D a - Auxiliary anode diameter (including packing), m;

[0093] S – Anode spacing, m;

[0094] N – Number of auxiliary anodes, only.

[0095] Grounding resistance calculation (refer to the calculation formula for grounding resistance of deep well anode groundbed GB / T21448-2008):

[0096]

[0097] In the formula: R v1 - Anode grounding resistance, Ω;

[0098] ρ – Soil resistivity, Ω·m;

[0099] L a - Auxiliary anode length (including packing), m;

[0100] t – Auxiliary anode burial depth (distance from top of packing material to ground surface), m;

[0101] D a - Auxiliary anode diameter (including packing), m.

[0102] Calculation of protection current (refer to the protection current calculation formula GB / T 21448-2008)

[0103] I = πD p ×Js×L p

[0104] Where: I—protection current, A;

[0105] D p —Outer diameter of the pipe, in meters;

[0106] J S —Protection current density, A / m 2 ;

[0107] L p —Protective pipe length, in meters.

[0108] Calculation of device output current

[0109] I = κ L ×I

[0110] Where: I—protection current, A;

[0111] κ L —Design coefficient, generally taken as 2-3.

[0112] Anode cable resistance calculation

[0113] R1=ρ1·L1

[0114] In the formula:

[0115] R1—Resistance of the anode cable, in Ω;

[0116] ρ1—Anode cable resistivity, Ω / m;

[0117] L1—Length of anode cable, in meters.

[0118] Calculation of cathode transition resistance (refer to the cathode transition resistance calculation formula GB / T 21448-2008)

[0119]

[0120] In the formula:

[0121] R c —Cathode transition resistance, Ω;

[0122] R t —Resistivity of the anti-corrosion coating transition, Ω·m;

[0123] r t —Pipeline resistance, Ω / m;

[0124] L—Length of the protected pipe, in meters.

[0125] Calculation of DC rated output voltage (refer to the formula for calculating DC rated output voltage in GB / T21448-2008)

[0126] V = I(R) h +R1+R c )+V r

[0127] In the formula:

[0128] V—DC output voltage, V;

[0129] I—Protective current, A;

[0130] R h —Auxiliary anode grounding resistance, Ω;

[0131] R1—Resistance of the anode cable, in Ω;

[0132] R c —Cathode transition resistance, Ω;

[0133] V r —The back electromotive force of the auxiliary anode ground bed is generally 2V.

[0134] Calculation of lifespan for high-silicon cast iron anodes

[0135]

[0136] W a =n×ρ a

[0137] In the formula:

[0138] T a —Auxiliary anode design life, a;

[0139] W a —Total mass of auxiliary anode, kg;

[0140] ω a — Consumption rate of auxiliary anode, kg / (A·a);

[0141] I—Protective current, A;

[0142] K—Auxiliary anode utilization coefficient, taken as 0.7 to 0.85;

[0143] n – Number of anodes;

[0144] ρ a - Mass of a single anode; kg.

[0145] Lifetime calculation of mixed metal oxide anode (MMO / Ti)

[0146]

[0147]

[0148] In the formula:

[0149] T a —Auxiliary anode design life, a;

[0150] I Q —Enhanced current density, 100A / m 2 ;

[0151] I Y —Anode current density, A / m 2 ;

[0152] K—Anode lifetime at enhanced current density, 100A / m 2 This was 10 years ago;

[0153] I—Protective current, A;

[0154] S—Anode area, m 2 .

[0155] The standard referenced in the above-mentioned segmented protection calculation method does not include macrocell corrosion in the calculation. Therefore, a trial run is required after construction. At this time, based on the feedback of the de-energization potential difference and the current flow between the test piece 12 and the reference electrode, it should be determined whether the oil and gas well casing segment corresponding to the geological layer of the test piece has obtained appropriate protection and whether the de-energization potential has been controlled within the design range. At this time, the protection voltage can be increased or decreased for each segment to weaken or strengthen the oxidizing properties of the adjacent thin-layer environmental medium of the corresponding oil and gas well casing, so that the de-energization potential of each segment tends to be consistent.

[0156] Since the cause of macrocell corrosion is the difference in oxidative properties between the upper and lower environmental media, the above process will adjust the oxidative properties of the adjacent thin-layer environmental media in each section of the oil and gas well casing to be more consistent, and will also solve the macrocell corrosion problem.

[0157] Example 3

[0158] like Figures 1 to 3 As shown, this embodiment provides a more detailed implementation method based on Embodiments 1 and 2.

[0159] Generally, the cathode cable and neutral cable of a cathodic protection power supply cannot be used together. This is because the cathodic protection cable carries a larger current than the neutral cable, resulting in a larger voltage drop. This causes the measured potential (current potential) during protection to be lower than expected, leading to insufficient protection voltage provided by the equipment and underprotection. However, in ordinary projects involving relatively shallow buried horizontal pipes or other protected objects, adding a neutral cable is relatively easy, so this problem is usually solved by directly adding a neutral cable.

[0160] However, for oil and gas well casing, the more cables inserted downhole, the narrower the well becomes, thus necessitating a reduction in the number of cables. On the other hand, in Example 1, the judgment of whether the oil and gas well casing is adequately protected is primarily based on the de-energized potential, while the error in the energized potential is less significant than the impact of the macrocell corrosion current, reducing the importance of accurate energized potential measurement. Therefore, the cathode cable 13 and the zero-position cable 16 of the test piece in Example 1 are combined as follows... Figure 3 This can reduce the number of downhole cables to two-thirds, which is more conducive to the normal operation of oil and gas wells.

[0161] After the test cathode cable and zero-position cable are combined (the combined cathode cable and zero-position cable 18), the difference compared to before the combination is that, during the trial operation phase, the protection voltage provided by the cathodic protection power supply is lower than before the combination. Therefore, during the adjustment of the protection voltage, it may be necessary to perform several adjustment operations to bring the de-energization potentials of each segment to a reasonable range and make them consistent. If this error is also estimated based on the reading of the ammeter 15 connected to the test cathode cable during the adjustment process, it may be possible to adjust the de-energization potentials of each segment to a reasonable range and make them consistent more quickly.

[0162] As described above, the present invention can be implemented well.

[0163] All features disclosed in all embodiments of this specification, or steps in all methods or processes implied in the disclosure, may be combined and / or extended or replaced in any way, except for mutually exclusive features and / or steps.

[0164] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Based on the technical essence of the present invention, any simple modifications, equivalent substitutions, and improvements made to the above embodiments within the spirit and principles of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for segmented forced current cathodic protection of the outer wall of an oil and gas well casing, characterized in that, Segmented forced current cathodic protection is adopted for oil and gas well casing. This segmented forced current cathodic protection includes: segmented protection using a common cathode and different anodes electrically connected to the oil and gas well casing, with different protection parameters set according to the physicochemical characteristics of different geological layers where each anode is located; during construction, holes are drilled from the inner wall outwards in the inner wall of the oil and gas well casing in different geological layers downhole, and the anode bed is buried outside the oil and gas well casing and cement layer through these holes. Then, the anode cable is connected through the inside of the oil and gas well casing to the anode terminal of the corresponding forced current cathodic protection power supply equipment on the surface; during construction, holes are drilled from the inner wall outwards in the inner wall of the oil and gas well casing in different geological layers downhole, and test pieces are buried outside the oil and gas well casing and cement layer through these holes. Then, the zero-position cable is connected through the inside of the oil and gas well casing to the zero-position terminal of the corresponding forced current cathodic protection power supply equipment on the surface.

2. The method for segmented forced current cathodic protection of the outer wall of an oil and gas well casing according to claim 1, characterized in that, The test piece has the same material and protective measures as the casing of oil and gas wells.

3. A method for segmented forced current cathodic protection of the outer wall of an oil and gas well casing according to any one of claims 1 to 2, characterized in that, After construction was completed, insulating and anti-corrosion materials were used to seal the gaps at the edges of the holes.

4. The method for segmented forced current cathodic protection of the outer wall of an oil and gas well casing according to claim 3, characterized in that, After construction is completed, a trial run is conducted. Based on the feedback of the power-off potential difference and power-on current between the test piece and the reference electrode, it is determined whether the oil and gas well casing section corresponding to the geological layer of the test piece meets the set protection requirements.

5. The method for segmented forced current cathodic protection of the outer wall of an oil and gas well casing according to claim 4, characterized in that, After determining whether the oil and gas well casing section corresponding to the geological layer of the test piece meets the set protection requirements, the protection potential is adjusted to obtain the best protection state for the oil and gas well casing.

6. The method for segmented forced current cathodic protection of the outer wall of an oil and gas well casing according to claim 1, characterized in that, Oil and gas well casing includes one or more of the following: casing for oil and gas production wells, casing for gas injection wells, or casing for water injection wells.

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