An underground tubing corrosion monitoring device and method

Abstract

The present invention discloses an underground oil pipe corrosion monitoring device and method. The device includes a delivery head, a fishing neck, a positioning seat, and a corrosion monitoring box connected in sequence from top to bottom. The positioning seat includes a plurality of positioning suction cups capable of fitting with the inner wall of the oil pipe and a driving mechanism for driving the plurality of positioning suction cups to contract or expand synchronously. The plurality of positioning suction cups are evenly distributed in the circumferential direction of the positioning seat. The corrosion monitoring box includes a housing and a coupon assembly disposed in the inner cavity of the housing. The coupon assembly includes a mounting seat and a plurality of corrosion coupons mounted on the mounting seat. A bearing is provided on the mounting seat, the inner ring of the bearing is fixed, and the plurality of corrosion coupons are evenly distributed on the outer ring of the bearing. One end of the housing is a perforated plate. The other end of the housing is connected to the positioning seat, and a through hole is provided at this end of the housing. All the corrosion coupons are located between the perforated plate and the through hole. The present invention does not require opening holes in the coupons, can accelerate the corrosion process of the underground coupons, shorten the corrosion monitoring period, and prevent the occurrence of underground accidents.

Description

Technical Field

[0001] The present invention relates to the field of natural gas exploitation, and in particular to a downhole oil pipe corrosion monitoring device and method. Background Art

[0002] In the production practice of oil and gas fields, oil pipe corrosion has become the main factor for oil pipe failure and even oil well overhaul. The main reason is that H2S, CO2, dissolved oxygen, Cl - The single or interactive effects of various corrosive media such as oil pipes may cause local weight loss of the oil pipe or a large amount of corrosion products to accumulate on the inner wall of the oil pipe, which may reduce the diameter of the oil pipe and disrupt the normal production order of oil and gas; in severe cases, the oil pipe may be corroded and perforated, or the oil pipe may fall into the well, which increases the difficulty of salvage and even leads to the scrapping of the wellbore. In the process of natural gas development, with the increase in the production of acidic gases such as H2S and CO2, the corrosion of the oil pipes in the gas wells has become more serious. These serious consequences caused by the corrosion of the oil pipes have greatly shortened the life of the gas wells, brought great challenges to the development of natural gas and well repair operations, and seriously restricted the safe production of gas fields. Therefore, the anti-corrosion and corrosion monitoring of the oil pipes in the natural gas wells have become the top priority for the efficient production of gas wells.

[0003] At present, the corrosion monitoring technology commonly used on site is mainly the weightlessness method of hanging plates. The traditional downhole hanging plate corrosion monitoring is to drill holes for corrosion hanging plates, install them in the short section of the oil pipe, and put them into the well and pull them out at the same time as the oil pipe. Its main disadvantages are: (1) The hanging plates are fixed by drilling holes, and the hanging holes will damage the metal structure around them, disrupt the flow of the monitoring medium at the hanging plates, and affect the monitoring effect; (2) Other auxiliary tools are required to achieve the installation and removal of corrosion hanging plates, and the monitoring and result analysis of the hanging plate corrosion are greatly limited by the timing of well repair operations; (3) The corrosion monitoring depth is difficult to adjust, and usually only fixed-point monitoring is possible. The monitoring cycle is long and the monitoring efficiency is low. It is impossible to grasp the downhole corrosion law in time, and it is difficult to reasonably predict the failure period of the oil pipe, which often results in huge economic losses caused by premature replacement of the oil pipe or serious downhole accidents caused by late replacement of the oil pipe. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a downhole oil pipe corrosion monitoring device and method. The present invention does not require drilling holes in the hanging plate, and can accelerate the corrosion process of the downhole hanging plate, shorten the corrosion monitoring cycle, and prevent the occurrence of downhole accidents.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows:

[0006] A downhole oil pipe corrosion monitoring device comprises a delivery head, a fishing neck, a positioning seat and a corrosion monitoring box, wherein the delivery head is connected to the fishing neck, the fishing neck is connected to the positioning seat, and the positioning seat is connected to the corrosion monitoring box;

[0007] The positioning seat includes a number of positioning suction cups that can fit against the inner wall of the oil pipe and a driving mechanism for driving the synchronous contraction or expansion of the number of positioning suction cups; the number of positioning suction cups are evenly distributed in the circumferential direction of the driving mechanism;

[0008] The corrosion monitoring box includes a housing and a coupon assembly disposed in the inner cavity of the housing. The coupon assembly includes a mounting seat and a number of corrosion coupons mounted on the mounting seat. A bearing is provided on the mounting seat, the inner ring of the bearing is fixed, and the number of corrosion coupons are evenly distributed on the outer ring of the bearing. Each corrosion coupon is disposed along the radial direction of the bearing;

[0009] One end of the housing is provided as a perforated plate; the other end of the housing is connected to the positioning seat, and a through hole is provided at this end of the housing. All the corrosion coupons are located between the perforated plate and the through hole.

[0010] Preferably, the driving mechanism includes a mounting shell, an electric telescopic rod, a first connecting rod and a number of second connecting rods. The mounting shell is connected to the fishing neck. The electric telescopic rod is installed in the inner cavity of the mounting shell. One end of the first connecting rod is connected to the end of the telescopic end of the electric telescopic rod. The other end of the first connecting rod is connected to one end of the number of second connecting rods through a compound hinge. The other ends of the number of second connecting rods pass through the mounting shell. A fixed shaft is installed on the mounting shell. A long hole is provided on the second connecting rod and is sleeved on the fixed shaft through the long hole. The number of second connecting rods are evenly distributed along the circumferential direction of the mounting shell; the end of the second connecting rod extending out of the mounting shell is connected to the positioning suction cup.

[0011] Preferably, a pressure-bearing rod is provided below the second connecting rod, and both ends of the pressure-bearing rod are connected between the inner walls of the mounting shell.

[0012] Preferably, three second connecting rods are provided.

[0013] Preferably, the shape of the perforated plate is hemispherical.

[0014] Preferably, the mounting seat includes a fixed rod coaxial with the housing. One end of the fixed rod is fixed, and the other end of the fixed rod faces the perforated plate and is vertically connected with a horizontal rod at this end. The horizontal rod is fixedly connected to the inner ring of the bearing.

[0015] Preferably, corrosion coupon connection seats are evenly provided on the outer ring of the bearing. Threaded holes for connecting the corrosion coupons are provided on the corrosion coupon connection seats. One end of the corrosion coupon is provided with a threaded section adapted to the threaded hole, and the threaded section is connected to the threaded hole.

[0016] Preferably, 3 - 5 corrosion coupons are provided.

[0017] Preferably, the total area of the through hole is not less than the opening area on the perforated plate.

[0018] The present invention also provides a method for monitoring the corrosion of downhole tubing, which includes the following processes:

[0019] The downhole tubing corrosion monitoring device of the present invention as described above is placed into the tubing by wireline operation;

[0020] When the downhole tubing corrosion monitoring device reaches the preset position, all the positioning suction cups are controlled by the driving device to move towards the inner wall of the tubing until all the positioning suction cups are completely attached to the inner wall of the tubing, so that the downhole tubing corrosion monitoring device is set;

[0021] The fluid medium in the tubing enters the inner cavity of the housing through the porous plate and drives the corrosion coupon to rotate with the bearing. After the fluid medium entering the housing contacts the corrosion coupon, it flows out from the through hole;

[0022] When the contact time between the fluid medium and the corrosion coupon reaches the preset duration, all the positioning suction cups are controlled by the driving device to be detached from the inner wall of the tubing, so that the downhole tubing corrosion monitoring device is released;

[0023] After the downhole tubing corrosion monitoring device is released, the downhole tubing corrosion monitoring device is fished out of the oil well, the corrosion coupon is detected, and the corrosion monitoring of the downhole tubing is realized according to the detection result of the corrosion coupon.

[0024] The present invention has the following beneficial effects:

[0025] In the downhole tubing corrosion monitoring device of the present invention, a positioning seat is provided. The driving device can drive all the positioning suction cups to contract or expand synchronously, and the suction cups can be used to set the entire downhole tubing corrosion monitoring device in place. Moreover, the action timing of the driving device is controllable, so as to achieve the precise placement of the corrosion coupon, and its placement position can be flexibly adjusted according to actual needs, and it is not restricted by the operation timing, making it more flexible to use. One end of the shell in the corrosion monitoring box of the present invention is provided with a perforated plate, and the other end of the shell is connected to the positioning seat. A through hole is provided at this end of the shell. Through the perforated plate and the through hole, the fluid medium in the tubing can form a complete passage in the inner cavity of the shell. Moreover, the perforated plate can block dirt such as solid particles in the well outside the shell, avoiding the influence of impurities and dirt on the accuracy of the monitoring effect. A number of corrosion coupons are evenly distributed on the outer ring of the bearing, and each corrosion coupon is arranged along the radial direction of the bearing. All the corrosion coupons are located between the perforated plate and the through hole. Therefore, the fluid medium in the tubing entering the inner cavity of the shell from the perforated plate impacts the corrosion coupons to a certain extent, and the corrosion coupons move circumferentially around the rolling bearing after being impacted by the fluid medium to accelerate the corrosion process and shorten the monitoring period. In the device of the present invention, the corrosion coupons are not perforated, thus avoiding the problem of damaging their metal structure due to the perforation of the coupons and then affecting the experimental accuracy. It can not only prevent corrosion conditions and prevent accidents, but also reduce the investment cost of anti-corrosion work to a certain extent. Since the corrosion process of the corrosion coupons is greatly affected by the impact degree of the bottomhole fluid medium on them, therefore, by studying the corrosion law of the corrosion coupons, the downhole corrosion situation can be truly reflected. In summary, the present invention does not need to perforate the coupons, can accelerate the corrosion process of the downhole coupons, shorten the corrosion monitoring period, and prevent the occurrence of downhole accidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic structural diagram of a downhole tubing corrosion monitoring device of the present invention when it is set in place;

[0027] Figure 2 is a schematic structural diagram of a downhole tubing corrosion monitoring device of the present invention when it is released;

[0028] Figure 3 is a schematic structural diagram of the coupon assembly of the present invention.

[0029] In the drawings, 1. delivery head, 2. fishing neck, 3. positioning seat, 4. corrosion monitoring box; 3-1. electric telescopic rod, 3-2. first connecting rod, 3-3. second connecting rod, 3-5. positioning suction cup, 3-6. compound hinge, 3-7. pressure-bearing rod, 4-1. shell, 4-2. through hole, 4-3. fixed rod, 4-5. perforated plate; 4-4-1. corrosion coupon, 4-4-2. bearing rotating shaft, 4-4-3. rolling bearing. DETAILED DESCRIPTION OF THE INVENTION

[0030] The embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

[0031] Based on the above deficiencies of the traditional coupon weight loss method, the present invention designs a device and method for monitoring the corrosion of downhole tubing using a rotating coupon. The downhole tubing corrosion monitoring device of the present invention does not require drilling holes in the coupon, and the corrosion coupon can be fixed only through the coupon assembly, ensuring the accuracy of the monitoring data; nor does it require a dedicated driving force, and the circumferential rotation of the corrosion coupon can be realized only by the impact of the bottom-hole fluid, thereby accelerating the corrosion process and shortening the monitoring period. Using this device, not only can the corrosion degree of the downhole tubing be monitored and the corrosion law be grasped, but also the corrosion condition can be prevented and accidents can be avoided, and to a certain extent, it can guide the safe and efficient production of gas wells.

[0032] The structure of the downhole tubing corrosion monitoring device of the present invention is specifically introduced as follows:

[0033] Referring to Figures 1 - 3 , the downhole tubing corrosion monitoring device of the present invention sequentially includes a delivery head 1, a fishing neck 2, a positioning seat 3, and a corrosion monitoring box 4 connected in sequence from top to bottom; the positioning seat 3 includes a plurality of positioning suction cups 3-5 capable of fitting with the inner wall of the tubing and a driving mechanism for driving the plurality of positioning suction cups 3-5 to contract synchronously ( Figure 2 The situation shown is the contracted situation) or expand ( Figure 1 The situation shown is the expanded situation); the plurality of positioning suction cups 3-5 are evenly distributed in the circumferential direction of the driving mechanism; the corrosion monitoring box 4 includes a housing 4-1 and a coupon assembly disposed in the inner cavity of the housing 4-1. The coupon assembly includes a mounting seat and a plurality of corrosion coupons 4-4-1 mounted on the mounting seat. A bearing is provided on the mounting seat, the inner ring of the bearing is fixed, and the plurality of corrosion coupons 4-4-1 are evenly distributed on the outer ring of the bearing. Each corrosion coupon 4-4-1 is arranged along the radial direction of the bearing; one end of the housing 4-1 is provided with a perforated plate 4-5; the other end of the housing 4-1 is connected to the positioning seat 3, and a through hole 4-2 is provided at this end of the housing 4-1. All the corrosion coupons 4-4-1 are located between the perforated plate 4-5 and the through hole. In this way, when the fluid medium in the tubing flows from bottom to top, when it flows in from the perforated plate 4-5 and out from the through hole 4-2, the corrosion coupons 4-4-1 and the bearing are located on the flow path of the fluid medium, so that the corrosion coupons 4-4-1 can be driven to rotate around the bearing.

[0034] As a preferred embodiment of the present invention, referring to Figure 1 and Figure 2, the driving mechanism includes a mounting shell, an electric telescopic rod 3-1, a first connecting rod 3-2 and several second connecting rods 3-3. The mounting shell is connected to the fishing neck 2. The electric telescopic rod 3-1 is installed in the inner cavity of the mounting shell. One end of the first connecting rod 3-2 is connected to the end of the telescopic end of the electric telescopic rod 3-1. The other end of the first connecting rod 3-2 is connected to one end of several second connecting rods 3-3 through a composite hinge 3-6. The other ends of several second connecting rods 3-3 pass through the mounting shell. A fixed shaft is installed on the mounting shell. A long hole is formed in the second connecting rod 3-3 and the second connecting rod 3-3 is sleeved on the fixed shaft through the long hole. Several second connecting rods 3-3 are evenly distributed along the circumferential direction of the mounting shell; One end of the second connecting rod 3-3 extending out of the mounting shell is connected to the positioning suction cup 3-5. As Figures 2 to 1 shown in the process, after the electric telescopic rod 3-1 extends, the outer ends of the second connecting rods 3-3 can be extended to the outside of the mounting shell. At this time, all the positioning suction cups 3-5 move synchronously outward in the radial direction, so that the positioning suction cups 3-5 are tightly attached to the inner wall of the oil pipe, realizing the setting of the whole device. Further, the extension amount of the electric telescopic rod 3-1 can also control the tightness of the positioning suction cup 3-5 against the inner wall of the oil pipe, so as to realize the stable setting of the downhole oil pipe corrosion monitoring device of the present invention; When it is necessary to release the setting, the electric telescopic rod 3-1 contracts (refer to Figure 2 ), at this time, all the positioning suction cups 3-5 move synchronously inward in the radial direction, so that the positioning suction cups 3-5 are disengaged from the inner wall of the oil pipe, realizing the release of the downhole oil pipe corrosion monitoring device of the present invention. The device has flexible operation and can realize remote manual operation.

[0035] As a preferred implementation scheme of the present invention, a pressure-bearing rod 3-7 is arranged below the second connecting rod 3-3, and both ends of the pressure-bearing rod 3-7 are connected to the inner wall of the mounting shell. The use of the pressure-bearing rod 3-7 can improve the stiffness of the opening part of the mounting shell (the opening is a through hole formed in the mounting shell for the second connecting rod 3-3 to pass through), and prevent deformation from occurring and causing the second connecting rod 3-3 to not swing normally.

[0036] As a preferred implementation scheme of the present invention, three second connecting rods 3-3 are provided, and the three second connecting rods 3-3 help to stably fix the whole device in the oil well.

[0037] As a preferred implementation scheme of the present invention, the shape of the porous plate 4-5 is hemispherical. This shape is beneficial to reducing the impact of downhole fluid on the whole device, ensuring that the whole device can be stably set. In addition, it can also ensure that the fluid entering the inner cavity of the shell can evenly scour all the corrosion coupons while ensuring the flow rate, ensuring the detection effect.

[0038] As a preferred embodiment of the present invention, the mounting seat includes a fixing rod 4-3 coaxial with the housing 4-1. One end of the fixing rod 4-3 is fixed, and the other end of the fixing rod 4-3 faces the porous plate 4-5 and is vertically connected with a horizontal rod at this end. The horizontal rod is fixedly connected with the inner ring of the bearing, and this structure can ensure that the corrosion coupon can rotate flexibly around the rotating shaft of the bearing.

[0039] As a preferred embodiment of the present invention, corrosion coupon connection seats are evenly arranged on the outer ring of the bearing. Threaded holes for connecting with the corrosion coupon 4-4-1 are provided on the corrosion coupon connection seats. One end of the corrosion coupon 4-4-1 is provided with a threaded section adapted to the threaded hole, and the threaded section is connected to the threaded hole. This structure makes the disassembly and assembly of the corrosion coupon 4-4-1 very convenient and improves the detection efficiency.

[0040] As a preferred embodiment of the present invention, 3-5 corrosion coupons 4-4-1 are provided. The limitation of this quantity is to ensure that the corrosion coupons 4-4-1 can rotate flexibly around the bearing rotating shaft. Too many or too few are likely to cause rotation dead points, resulting in the corrosion coupons not being able to contact the fluid in the oil well evenly.

[0041] As a preferred embodiment of the present invention, the total area of the through holes 4-2 is not less than the opening area on the porous plate 4-5 to ensure the smooth flow of the fluid in the housing 4-1.

[0042] The present invention also provides a method for monitoring the corrosion of downhole tubing, including the following processes:

[0043] The downhole tubing corrosion monitoring device of the present invention as described above is placed into the tubing by wireline operation;

[0044] When the downhole tubing corrosion monitoring device reaches the preset position, all the positioning suction cups 3-5 are controlled by the driving device to move towards the inner wall of the tubing until all the positioning suction cups 3-5 are completely attached to the inner wall of the tubing (as Figure 1 shown), so that the downhole tubing corrosion monitoring device is set;

[0045] The fluid medium in the tubing enters the inner cavity of the housing 4-1 through the porous plate 4-5 and drives the corrosion coupon 4-4-1 to rotate with the bearing. After the fluid medium entering the housing 4-1 contacts the corrosion coupon 4-4-1, it flows out from the through hole 4-2;

[0046] When the fluid medium contacts the corrosion coupon 4-4-1 for a preset duration, all the positioning suction cups 3-5 are controlled by the driving device to be detached from the inner wall of the tubing, so that the downhole tubing corrosion monitoring device is released (as Figure 2 shown);

[0047] After the downhole tubing corrosion monitoring device is unsealed, the downhole tubing corrosion monitoring device is fished out of the oil well, and the corrosion coupon 4-4-1 is detected. The corrosion monitoring of the downhole tubing is realized according to the detection result of the corrosion coupon 4-4-1.

[0048] Embodiment 1

[0049] The device for monitoring the corrosion of the downhole tubing in this embodiment is as Figures 1 - 3 shown. The device mainly includes a delivery head 1, a fishing neck 2, a positioning seat 3, and a corrosion monitoring box 4. Among them, the delivery head 1 and the fishing neck 2 are mainly used for the delivery or fishing of the device and are located at the top of the device. The overall height of this part (the total height of the delivery head 1 and the fishing neck 2) H1 = 200 mm; the positioning seat 3 includes an electric telescopic rod 3-1, a first connecting rod 3-2, a second connecting rod 3-3, a positioning suction cup 3-5, a composite hinge 3-6, and a pressure-bearing rod 3-7. The position of the pressure-bearing rod 3-7 is fixed and immovable. The upper end of the positioning seat 3 is connected to the fishing neck 2, and the lower end is connected to the corrosion monitoring box 4. The positioning seat 3 is located in the middle of the downhole tubing corrosion monitoring device; the overall height of this part H2 = 350 mm; the corrosion monitoring box 4 is the main component of this device, including a housing 4-1 and a fixing rod 4-3. A through hole 4-2 is opened at the upper end of the housing 4-1, and the lower bottom surface of the housing 4-1 is a porous plate 4-5. The corrosion monitoring box 4 is located at the bottom of the downhole tubing corrosion monitoring device. The porous plate 4-5 is a hemispherical baffle. On the one hand, it can effectively prevent wellbore dirt from entering the inside of the corrosion monitoring box and adhering to the surface of the coupon, affecting the accuracy of the monitoring effect. On the other hand, it can reduce the resistance of the airflow passing through the device and ensure the stability of the entire device at the bottom of the well. Four corrosion coupons 4-4-1 are provided. The four corrosion coupons 4-4-1 are evenly distributed on the outer ring of the bearing and are arranged along the radial direction of the bearing. The corrosion coupon 4-4-1 is threadedly connected to the connecting seat on the outer ring of the bearing. The upper part of the corrosion monitoring box 4 is provided with a shoulder for hanging the box body. During connection, the shoulder can be embedded in the groove at the bottom of the positioning seat 3 for fixation. The overall height of this part H3 = 300 mm.

[0050] Refer to Figure 1 、 Figure 2, the positioning seat 3 is mainly used to suspend the entire device on the inner wall of the oil pipe, and the length H2 is 350 mm. Among them, the upper part of the first connecting rod 3-2 is welded to the lower end of the electric telescopic rod 3-1. The first connecting rod 3-2 and the second connecting rod 3-3 are connected by a composite hinge 3-6. Both the first connecting rod 3-2 and the second connecting rod 3-3 are made of corrosion-resistant alloy BG15Cr material. In a strong acidic environment (coexistence of H2S and CO2) and high-temperature environment (120 °C), the corrosion rate is only 0.0092 mm / a, and it is hardly damaged by the corrosion environment. The main material of the positioning suction cup 3-5 is rubber with a high-density cross-linked polyethylene film coated on the surface and a magnetic coating coated inside. It has better barrier properties, corrosion resistance and higher tensile strength, and can deform when squeezed. When the electric telescopic rod 3-1 extends, it can push the first connecting rod 3-2 downward. The second connecting rod 3-3 is stressed and pushes the positioning suction cup 3-5 to move towards the inner wall of the oil pipe, and finally fits with the inner wall of the oil pipe to realize the setting of the device. When the electric telescopic rod 3-1 contracts, it can pull the first connecting rod 3-2 upward. The second connecting rod 3-3 is stressed and pulls the positioning suction cup 3-5 to move towards the inside of the device, and the positioning suction cup 3-5 disengages from the inner wall of the oil pipe to realize the release of the device.

[0051] Refer to Figure 1 , Figure 2 , the fixing rod 4-3 is made of corrosion-resistant alloy BG15Cr material and is provided with internal threads for connection within its strength range (≥735 MPa). Refer to Figures 1 - 3 , the width of the rolling bearing is 10 mm, the inner diameter is 5 mm, the outer diameter is 20 mm, the thickness of the outer ring is 5 mm, and 4 connecting seats with a thread hole depth of 2 mm are symmetrically opened on the outer ring for fixing the corrosion coupon 4-4-1. Refer to Figures 1 - 3 , the material of the corrosion coupon 4-4-1 is usually the same as that of the downhole oil pipe, and different materials of the corrosion coupon to be monitored can be selected according to the pipe material of the oil pipe. The applicable corrosion coupon 4-4-1 has a length of 30 mm to 50 mm, a width of 15 mm to 25 mm, and a thickness of 1 mm to 2 mm.

[0052] When the device for monitoring the corrosion of downhole oil pipes in this embodiment is in use, the delivery head, fishing neck, positioning seat and corrosion monitoring box are connected in sequence by pipelines, and the device is placed into the oil pipe by wireline operation. The electric telescopic rod in the positioning seat extends and applies a downward thrust to the first connecting rod. The second connecting rod is stressed and pushes the positioning suction cup to move towards the inner wall of the oil pipe until it completely fits with the inner wall of the oil pipe to complete the setting of the device. After the monitoring is completed, a fishing tool string is lowered into the oil pipe by wireline operation. After encountering resistance, the fishing neck is grabbed and lifted, and the positioning suction cup disengages from the inner wall of the oil pipe to realize the release of the device.

[0053] Using this device for monitoring the corrosion of downhole oil pipes, in vertical wells, it can be set and suspended at any position in the downhole oil pipe; in horizontal wells, it can be suspended at any position above the kick-off point.

[0054] This embodiment also provides a method for monitoring the corrosion of downhole tubing. The method for monitoring the corrosion of downhole tubing is carried out using the device for monitoring the corrosion of downhole tubing in the above embodiment, and includes the following steps:

[0055] (1) Record the data before the corrosion coupon is lowered into the well, including the coupon mass Ao, the total coupon area f, and the coupon density ρ;

[0056] (2) Use wireline operation to lower the device for monitoring the corrosion of downhole tubing into the tubing. When reaching the preset position, the electric telescopic rod in the positioning seat extends and applies a downward thrust to the first connecting rod. The second connecting rod is forced to push the positioning suction cup towards the inner wall of the tubing until it is completely attached to the inner wall of the tubing to complete the setting of the device;

[0057] (3) After the corrosion coupon comes into contact with the fluid medium in the downhole tubing, it rotates circumferentially around the axis of the rolling bearing by itself. The corrosion coupon is corroded and scaled due to the action of the fluid medium;

[0058] (4) After the monitoring is completed, use wireline operation to lower the fishing tool string into the tubing. When encountering resistance, grasp the fishing neck, control the electric telescopic rod to disengage the positioning suction cup from the well wall, so that the device for monitoring the corrosion of downhole tubing is released, and then lift it to fish out the device for monitoring the corrosion of downhole tubing.

[0059] (5) After fishing out the monitoring device from the well, record the monitoring time T and the data of the corrosion coupon after it is lowered into the well, including the coupon mass and the pitting depth;

[0060] (6) Compare the relevant data of the corrosion coupon before and after it is lowered into the well, calculate the average corrosion rate C and the maximum pitting rate E, analyze the corrosion condition of the downhole tubing, and predict the service life of the tubing.

[0061] The formula for calculating the average corrosion rate is:

[0062]

[0063] The formula for calculating the maximum pitting rate is:

[0064]

[0065] Where C is the average corrosion rate, mm / a; Ao is the mass of the corrosion coupon before it is lowered into the well, g; A is the mass of the corrosion coupon after the corrosion monitoring is completed, g; f is the total area of the corrosion coupon, cm 2 ; T is the corrosion monitoring time, h; ρ is the density of the corrosion coupon, kg / m 3 ; E is the maximum pitting rate, mm / a; I is the maximum pitting depth of the corrosion coupon, mm.

[0066] (7) Analyze the corrosion results by referring to the corrosion evaluation indicators of the media in pipelines and containers specified in JB / T 7901-1999 "Full-immersion Test Method for Laboratory Uniform Corrosion of Metallic Materials" and GB / T 23258-2009 "Code for Corrosion Control of Steel Pipelines".

[0067] (8) Compare the corrosion results of the traditional coupon weight-loss method, analyze the corrosion status of downhole tubing, and further distinguish the corrosion types.

[0068] In this embodiment, after being impacted by the fluid medium, the corrosion coupon 4-4-1 makes a circumferential movement around the rolling bearing to accelerate the corrosion process and shorten the monitoring period. Since the corrosion process of the corrosion coupon is greatly affected by the impact degree of the bottom-hole fluid medium on it, therefore, by studying the corrosion law of the corrosion coupon, the downhole corrosion situation can be truly reflected. After the monitoring is completed, use wireline operation to fish out this device from the well, take out the corrosion coupon, carefully clean it, record its weight change, calculate the corrosion rate, and analyze the corrosion type of the downhole tubing according to the corrosion shape on its surface, and further study its corrosion law to provide guidance for the safe production of gas wells.

[0069] Embodiment 2

[0070] In this embodiment, a corrosion coupon with a steel grade of N80, a size of 50 mm × 20 mm × 2 mm is selected, and the above device for monitoring the corrosion of downhole tubing using a rotating coupon is used to complete this corrosion monitoring.

[0071] The main steps of this embodiment are as follows:

[0072] (1) Record the data of the corrosion coupon before it is lowered into the well, including the coupon mass Ao = 18.84 g, the total coupon area f = 22.8 cm 2 , the coupon density ρ = 7.85×10 3 kg / m 3 ;

[0073] (2) Use wireline operation to lower the device for monitoring the corrosion of downhole tubing into the tubing, with a designed depth of 2440 m. When the device for monitoring the corrosion of downhole tubing reaches the preset position, control the electric telescopic rod to set the whole device.

[0074] (3) After the corrosion coupon comes into contact with the fluid medium in the downhole tubing, it rotates circumferentially around the rolling bearing by itself, and the corrosion coupon corrodes and scales due to the action of the fluid medium.

[0075] (4) After the monitoring is completed, use wireline operation to fish out the device for monitoring the corrosion of downhole tubing.

[0076] (5) After fishing out the monitoring device from the well, record the monitoring time T = 720 h and the data of the corrosion coupon after being put into the well, including the coupon mass A = 18.81 g and the maximum pitting depth I = 0.009 mm;

[0077] (6) Calculate the average corrosion rate C and the maximum pitting rate E according to the relevant data of the corrosion coupon before and after being put into the well;

[0078]

[0079] (7) Refer to the corrosion evaluation indexes of the media in pipelines and containers specified in JB / T 7901 - 1999 "Method of Immersion Test for Uniform Corrosion of Metallic Materials in Laboratory" and GB / T 23258 - 2009 "Code for Corrosion Control of Steel Pipelines" to analyze the corrosion results.

[0080] (8) Compare the corrosion results of the traditional coupon weight loss method, analyze the corrosion condition of the downhole tubing, and further determine the corrosion category.

[0081] The corrosion results of this embodiment are as follows:

[0082] According to the evaluation indexes, when the average corrosion rate is less than 0.025 mm / a and the pitting rate is less than 0.13 mm / a, it is low corrosion. The average corrosion rate of the corrosion coupon in this embodiment is 0.0204 mm / a, and the maximum pitting rate is 0.1299 mm / a, belonging to low corrosion.

[0083] Example 3

[0084] In this embodiment, a corrosion coupon with a steel grade of J55 and dimensions of 40 mm × 25 mm × 1 mm is selected, and the same device as in Example 2 is used to complete the monitoring of this corrosion situation.

[0085] The main steps of this embodiment are as follows:

[0086] (1) Record the data of the corrosion coupon before being put into the well, including the coupon mass Ao = 31.4 g, the total coupon area f = 21.3 cm 2 , and the coupon density ρ = 7.85×10 3 kg / m 3 ;

[0087] (2) Use wireline operation to lower the device for downhole tubing corrosion monitoring into the tubing. The designed depth is 4547 m. When the device for downhole tubing corrosion monitoring reaches the preset position, control the electric telescopic rod to make the whole device seal;

[0088] (3) After the corrosion coupon comes into contact with the fluid medium in the downhole tubing, it rotates circumferentially by itself with the rolling bearing as the rotation center, and the corrosion coupon corrodes and scales due to the action of the fluid medium;

[0089] (4) After the monitoring is completed, use wireline operation to fish out the device for downhole tubing corrosion monitoring.

[0090] (5) After fishing out the monitoring device from the well, record the monitoring time T = 720h and the corrosion coupon data after running into the well, including the coupon mass A = 30.97g and the maximum pitting depth I = 0.015mm.

[0091] (6) Calculate the average corrosion rate C and the maximum pitting rate E according to the relevant data of the corrosion coupons before and after running into the well.

[0092]

[0093] (6) Refer to the corrosion evaluation indexes of pipelines and containers specified in JB / T 7901 - 1999 "Method of Immersion Test for Uniform Corrosion of Metallic Materials in Laboratory" and GB / T 23258 - 2009 "Code for Corrosion Control of Steel Pipelines" to analyze the corrosion results.

[0094] (7) Compare the corrosion results of the traditional coupon weight loss method, analyze the corrosion condition of the downhole tubing, and further distinguish the corrosion category.

[0095] The corrosion results of this embodiment are as follows:

[0096] According to the evaluation indexes, when the average corrosion rate is greater than 0.25mm / a and the pitting rate is greater than 0.38mm / a, it is severe corrosion. The average corrosion rate of the corrosion coupon in this embodiment is 0.3129mm / a, and the maximum pitting rate is 0.4954mm / a, which belongs to severe corrosion, and necessary control measures should be taken.

[0097] The corrosion results of Example 2, Example 3 and the traditional coupon weight loss method are shown in Table 1:

[0098] Table 1

[0099]

[0100] Analysis of the monitoring data in Table 1 shows that within the 720h monitoring period, the average corrosion rate of the N80 coupon is 0.0204mm / a, and the average corrosion rate of the J55 coupon is 0.3129mm / a. The corrosion degree of the two steel grade corrosion coupons by the downhole fluid medium is J55 > N80 in turn. Compared with the traditional method, using the present invention can accelerate the corrosion process, shorten the corrosion monitoring period, is beneficial to understanding the corrosion situation of downhole pipe strings in advance, mastering the corrosion law, and providing certain technical support for the safe production of gas wells.

[0101] In summary, it can be seen that the present invention has the following several characteristics:

[0102] (1) It changes the traditional method of monitoring by driving the coupon to rotate with a motor. Without specially providing a driving force, the coupon can be automatically rotated by the impact of the downhole fluid medium, thus accelerating the corrosion process, shortening the monitoring period, and improving the monitoring accuracy.

[0103] (2) There is no need to drill holes in the coupon. The corrosion monitoring box is fixed by directly fitting the upper shoulder of the box into the groove at the lower part of the positioning seat, avoiding the problem that the metal structure of the coupon is damaged due to drilling holes, which in turn affects the experimental accuracy. It can not only prevent corrosion conditions and prevent accidents, but also reduce the investment cost of anti-corrosion work to a certain extent.

[0104] (3) It can understand the downhole corrosion law as early as possible and reasonably predict the failure period of the oil pipe, effectively avoiding the huge economic losses caused by premature replacement of the oil pipe and serious downhole accidents caused by too late replacement of the oil pipe.

Claims

1. An underground tubing corrosion monitoring device, characterized in that It includes a delivery head (1), a fishing neck (2), a positioning seat (3) and a corrosion monitoring box (4). The delivery head (1) is connected to the fishing neck (2), the fishing neck (2) is connected to the positioning seat (3), and the positioning seat (3) is connected to the corrosion monitoring box (4). The positioning seat (3) includes a number of positioning suction cups (3-5) that can fit against the inner wall of the oil pipe and a driving mechanism for driving the synchronous contraction or expansion of the number of positioning suction cups (3-5); the number of positioning suction cups (3-5) are evenly distributed in the circumferential direction of the driving mechanism; The corrosion monitoring box (4) includes a housing (4-1) and a coupon assembly disposed in the inner cavity of the housing (4-1). The coupon assembly includes a mounting seat and a number of corrosion coupons (4-4-1) mounted on the mounting seat. A bearing is provided on the mounting seat, the inner ring of the bearing is fixed, and the number of corrosion coupons (4-4-1) are evenly distributed on the outer ring of the bearing. Each corrosion coupon (4-4-1) is arranged along the radial direction of the bearing; One end of the housing (4-1) is provided as a perforated plate (4-5); the other end of the housing (4-1) is connected to the positioning seat (3). A through hole (4-2) is provided on the side of the housing (4-1) near the positioning seat (3). All the corrosion coupons (4-4-1) are located between the perforated plate (4-5) and the through hole; Corrosion coupon connecting seats are evenly provided on the outer ring of the bearing. Threaded holes for connecting the corrosion coupons (4-4-1) are provided on the corrosion coupon connecting seats. One end of the corrosion coupon (4-4-1) is provided with a threaded section adapted to the threaded hole, and the threaded section is connected to the threaded hole; The total area of the through hole (4-2) is not less than the opening area of the perforated plate (4-5).

2. The downhole tubing corrosion monitoring device according to claim 1, wherein, The driving mechanism includes a mounting shell, an electric telescopic rod (3-1), a first connecting rod (3-2) and a number of second connecting rods (3-3). The mounting shell is connected to the fishing neck (2). The electric telescopic rod (3-1) is installed in the inner cavity of the mounting shell. One end of the first connecting rod (3-2) is connected to the end of the telescopic end of the electric telescopic rod (3-1). The other end of the first connecting rod (3-2) is connected to one end of the number of second connecting rods (3-3) through a composite hinge (3-6). The other ends of the number of second connecting rods (3-3) pass through the mounting shell. A fixed shaft is installed on the mounting shell. A long hole is provided on the second connecting rod (3-3) and the second connecting rod (3-3) is sleeved on the fixed shaft through the long hole. The number of second connecting rods (3-3) are evenly distributed in the circumferential direction of the mounting shell; the end of the second connecting rod (3-3) extending out of the mounting shell is connected to the positioning suction cup (3-5).

3. The downhole tubing corrosion monitoring device according to claim 2, wherein A pressure-bearing rod (3-7) is provided below the second connecting rod (3-3), and both ends of the pressure-bearing rod (3-7) are connected between the inner walls of the mounting shell.

4. The downhole tubing corrosion monitoring device according to claim 2, characterized in that, Three second connecting rods (3-3) are provided.

5. The downhole tubing corrosion monitoring device according to claim 1, characterized in that The shape of the perforated plate (4-5) is hemispherical.

6. The downhole tubing corrosion monitoring device according to claim 1, wherein, The mounting seat includes a fixed rod (4-3) coaxial with the housing (4-1). One end of the fixed rod (4-3) is fixed. The other end of the fixed rod (4-3) faces the perforated plate (4-5) and a horizontal rod is vertically connected to this end. The horizontal rod is fixedly connected to the inner ring of the bearing.

7. An underground oil pipe corrosion monitoring device according to claim 1, characterized in that, 3-5 corrosion coupons (4-4-1) are provided.

8. A downhole tubing corrosion monitoring method, characterized in that, It includes the following process: The downhole tubing corrosion monitoring device described in any one of claims 1-7 is placed into the tubing by wireline operation; After the downhole tubing corrosion monitoring device reaches the preset position, all the positioning suction cups (3-5) are controlled by the driving device to move towards the inner wall of the tubing until all the positioning suction cups (3-5) are completely attached to the inner wall of the tubing, so that the downhole tubing corrosion monitoring device is set; The fluid medium in the tubing enters the inner cavity of the housing (4-1) through the perforated plate (4-5) and drives the corrosion coupon (4-4-1) to rotate with the bearing. The fluid medium entering the housing (4-1) flows out from the through hole (4-2) after contacting the corrosion coupon (4-4-1); When the fluid medium contacts the corrosion coupon (4-4-1) for a preset duration, all the positioning suction cups (3-5) are controlled by the driving device to be detached from the inner wall of the tubing, so that the downhole tubing corrosion monitoring device is released; After the downhole tubing corrosion monitoring device is released, the downhole tubing corrosion monitoring device is fished out of the oil well, the corrosion coupon (4-4-1) is detected, and the corrosion monitoring of the downhole tubing is realized according to the detection result of the corrosion coupon (4-4-1).

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