Downhole corrosion monitoring device, system and method

Abstract

The present application provides a downhole corrosion monitoring device, system and method. The device includes: a resistance probe assembly, the resistance probe assembly includes at least one resistance probe; the resistance probe includes a test piece and a reference piece arranged in parallel; an insulating material is filled between the test piece and the reference piece to form a gap-free bonding structure, and the test piece is located outside the reference piece; one end of the test piece and the reference piece are extended and connected to form an integrated structure, the other end of the test piece is connected to a first measurement terminal, and the other end of the reference piece is connected to a second measurement terminal. The scheme of the present application uses a resistance probe with a parallel bonding structure, so that the monitoring result of the resistance probe is more accurate, which can improve the accuracy of the monitoring result of the downhole corrosion monitoring device.

Description

Technical Field

[0001] The present application relates to the technical field of oil production engineering, and in particular to a downhole corrosion monitoring device, system and method. Background Art

[0002] As oilfield development gradually enters the middle and late stages, the comprehensive water content continues to rise. Adopting new technologies such as CCUS and polymer flooding to improve recovery has become the most important measure to increase production. However, the implementation of these measures will cause corrosion of the oil pipes downhole, and the corrosion situation needs to be monitored.

[0003] At present, in some downhole oil pipe corrosion monitoring solutions, the monitoring device is easily disturbed by the downhole oil pollution during the detection process, causing distortion of the monitoring results and leading to inaccurate monitoring results. Summary of the invention

[0004] The present application provides a downhole corrosion monitoring device, system and method, which are used to improve the accuracy of downhole corrosion monitoring results.

[0005] In a first aspect, the present application provides a downhole corrosion monitoring device, which includes a resistance probe assembly, the resistance probe assembly includes at least one resistance probe; the resistance probe includes a test piece and a reference piece arranged in parallel; an insulating material is filled between the test piece and the reference piece to form a gap-free fitting structure, and the test piece is located outside the reference piece; one end of the test piece and the reference piece are extended and connected to form an integrated structure, the other end of the test piece is connected to a first measurement terminal, and the other end of the reference piece is connected to a second measurement terminal.

[0006] In one possible implementation, a resistance probe assembly includes: a component body, and a first resistance probe and a second resistance probe located in the component body; the first resistance probe and the second resistance probe are used for corrosion monitoring inside and outside the oil pipe, respectively; the component body has a first surface and a second surface facing each other; the first surface is provided with a first opening to expose a test piece of the first resistance probe through the first opening; the second surface is provided with a second opening to expose a test piece of the second resistance probe through the second opening; wherein the first surface protrudes from the main surface of the component body, and the main surface of the component body is provided with a sealing structure whose outline surrounds the area of ​​the second surface; the sealing structure matches the oil pipe opening on the side wall of the oil pipe.

[0007] In a possible implementation, the resistance probe assembly further includes: a first conductivity probe and a second conductivity probe located in the assembly body; the first conductivity probe and the second conductivity probe are respectively used for conductivity monitoring inside and outside the oil pipe; a first through hole is also opened on the first surface to expose the electrode of the first conductivity probe through the first through hole; and a second through hole is also opened on the second surface to expose the electrode of the second conductivity probe through the second opening.

[0008] In a possible implementation, the downhole corrosion monitoring device also includes: a circuit sealing assembly and a cable; the circuit sealing assembly includes a shell, a PCB circuit board and a wire located in the shell; one end of the shell of the circuit sealing assembly is used to be sealed and connected to the component body of the resistance probe assembly through a thread and a first sealing structure; one end of the cable is electrically connected to the PCB circuit board, and the other end of the cable extends outward through an outlet at the other end of the shell of the circuit sealing assembly, and the outlet and the cable are sealed by a second sealing structure; an aviation plug is provided at one end of the component body of the resistance probe assembly, and the PCB circuit board has an aviation plug interface corresponding to the aviation plug. When the component body of the resistance probe assembly is connected to the circuit sealing assembly, the PCB circuit board is electrically connected to the resistance probe assembly through the aviation plug interface and the aviation plug.

[0009] In a possible implementation, a PCB circuit board is integrated with a single-chip microcomputer, a bidirectional constant current source circuit and a multi-channel A / D converter; when the PCB circuit board is electrically connected to the resistance probe assembly, the bidirectional constant current source circuit is electrically connected to the first measurement terminal of the first resistance probe and the second measurement terminal of the second resistance probe, and is used to provide a forward driving current and a reverse driving current to the resistance probes to generate a differential voltage between the test piece and the reference piece; the input end of the multi-channel A / D converter is electrically connected to the first measurement terminal and the second measurement terminal, the output end of the multi-channel A / D converter is connected to the single-chip microcomputer, and the multi-channel A / D converter is used to sample the differential voltage between the test piece and the reference piece; the single-chip microcomputer is electrically connected to the multi-channel A / D converter, and is used to obtain the resistance ratio of the test piece and the reference piece according to the differential voltage between the reference piece and the test piece, and calculate the corrosion rate data inside and outside the oil pipe and the remaining thickness data of the test piece according to the resistance ratio.

[0010] In a possible implementation, the bidirectional constant current source circuit includes: a current source circuit, a first NMOS tube, a second NMOS tube, a third NMOS tube, and a fourth NMOS tube; one end of the first NMOS tube and the second NMOS tube are connected to the output end of the current source circuit, and the other end of the first NMOS tube is connected to one end of the third NMOS tube as the first output end of the bidirectional constant current source circuit; the other end of the third NMOS tube is grounded; the other end of the second NMOS tube is connected to one end of the fourth NMOS tube as the second output end of the bidirectional constant current source circuit; the other end of the fourth NMOS tube is grounded; the control ends of the first NMOS tube, the second NMOS tube, the third NMOS tube and the fourth NMOS tube are connected to a single-chip microcomputer; the single-chip microcomputer is used to control the first NMOS tube and the fourth NMOS tube to be turned on, or to control the second NMOS tube and the third NMOS tube to be turned on, so as to output a forward drive current or a reverse drive current.

[0011] In one possible implementation, the current source circuit includes: a first operational amplifier, a transistor and a current sampling module; the second end of the transistor receives an excitation power supply signal, the third end of the transistor is connected to one end of a first NMOS transistor and a second NMOS transistor as the output end of the current source circuit, and the first end of the transistor is connected to the output end of the first operational amplifier; the current sampling module is used to sample the current output current of the current source circuit and output the sampled current; the first operational amplifier receives a reference signal and is connected to the current sampling module, and is used to output a drive signal to the first end of the transistor according to the output current of the current source circuit and the reference signal to perform feedback regulation.

[0012] In a possible implementation, the current sampling module includes: a second operational amplifier and a sampling resistor; one end of the sampling resistor is connected to the second end of the transistor and the second operational amplifier, and the other end of the sampling resistor is connected to one end of the first NMOS tube, one end of the second NMOS tube, and the second operational amplifier; the output end of the second operational amplifier is connected to the first operational amplifier for outputting the sampling current.

[0013] In a possible implementation, the PCB circuit board also includes a conductivity acquisition circuit; the conductivity acquisition circuit is connected to the first conductivity probe and the second conductivity probe, and is used to output the power division ratio of the first conductivity probe and the voltage division ratio of the second conductivity probe; the single-chip computer is connected to the conductivity acquisition circuit, and is also used to obtain the impedance values ​​of the first conductivity probe and the second conductivity probe according to the voltage division ratio of the first conductivity probe and the voltage division ratio of the second conductivity probe, and output the conductivity data inside and outside the oil pipe according to the impedance value.

[0014] In a possible implementation, the conductivity acquisition circuit includes: an analog switch, a pulse signal generator, a first voltage follower, a second voltage follower, a first voltage divider resistor, and a second voltage divider resistor; the input end of the analog switch is respectively connected to the first conductivity probe and the second conductivity probe, and the analog switch is used to output the signals output by the first conductivity probe and the second conductivity probe in a time-sharing manner; the pulse signal generator is used to provide a pulse modulation signal; one end of the first voltage divider resistor is connected to the pulse signal generator and the input end of the first voltage follower; the other end of the first voltage divider resistor is connected to the output end of the analog switch, one end of the second voltage divider resistor, and the input end of the second voltage follower, and the other end of the second voltage divider resistor is grounded; the output end of the first voltage follower is used to output a first follower signal corresponding to the pulse modulation signal; the output end of the second voltage follower is used to output a second follower signal corresponding to the voltage signal collected by the first conductivity probe or the second conductivity probe; the first follower signal and the second follower signal are used to calculate the conductivity inside or outside the oil pipe.

[0015] In a possible implementation, the first measuring terminal includes a first port and a second port, and the second measuring terminal includes a third port and a fourth port; the first port of the first resistance probe is electrically connected to the third port of the second resistance probe; the multi-channel A / D converter includes: multiple ADC acquisition circuits, the multiple ADC acquisition circuits include an ADC acquisition circuit corresponding to the second port of the first resistance probe, an ADC acquisition circuit corresponding to the connection port of the first resistance probe, an ADC acquisition circuit corresponding to the fourth port of the first resistance probe and the second port of the second resistance probe, an ADC acquisition circuit corresponding to the fourth port of the second resistance probe, an ADC acquisition circuit corresponding to the connection port of the second resistance probe, an ADC acquisition circuit corresponding to the first conductivity probe, and an ADC acquisition circuit corresponding to the second conductivity probe.

[0016] In one possible implementation, the ADC acquisition circuit includes a filtering circuit, a first zener diode, and a second zener diode; the input end of the filtering circuit is connected to the port corresponding to the ADC acquisition circuit, and the filtering circuit is used to filter the signal at the port; the cathode of the first zener diode receives a constant voltage signal, the anode of the second zener diode is grounded, and the output end of the filtering circuit is connected to the anode of the first zener diode and the cathode of the second zener diode, so as to output the filtered signal after voltage limiting; the output ends of multiple ADC acquisition circuits are connected to the corresponding ports of the single-chip microcomputer to input the differential voltage between the reference piece and the test piece of the first resistance probe, the differential voltage between the reference piece and the test piece of the second resistance probe, the voltage divider ratio of the first conductivity probe, and the voltage divider ratio of the second conductivity probe to the single-chip microcomputer.

[0017] In a possible implementation, the cable includes: a power line and a communication line; one end of the power line is electrically connected to the PCB circuit board, and the other end of the power line is used to connect to the wellhead power supply; one end of the communication line is electrically connected to the PCB circuit board, and the other end of the communication line is used to connect to the ground control cabinet, and the communication line is used to transmit the corrosion rate data inside and outside the oil pipe and the remaining thickness data of the test piece to the ground control cabinet.

[0018] In one possible implementation, the PCB circuit board also includes a communication interface; the communication interface is connected to the single-chip microcomputer and the communication line, and is used to transmit the corrosion rate, the remaining thickness of the test piece, and the conductivity data to the transceiver in the ground control cabinet via a cable.

[0019] In a possible implementation, the device also includes: a DC step-down converter and a linear regulated power supply; the DC step-down converter is used to connect one end of the power line to step down the power provided by the wellhead power supply; the linear regulated power supply is connected to the DC step-down converter to stabilize the stepped-down voltage and provide it to the PCB circuit board.

[0020] In a possible implementation, the PCB circuit board also includes a temperature sensor; the output end of the temperature sensor is connected to the single-chip microcomputer for monitoring the temperature and transmitting the temperature data to the single-chip microcomputer.

[0021] In the second aspect, the present application provides a downhole corrosion monitoring system, including a ground control cabinet and at least one downhole corrosion monitoring device; at least one downhole corrosion monitoring device is installed on the side wall of the oil pipe underground and connected to the ground control cabinet via a cable, for sending corrosion rate, remaining thickness of the test piece, conductivity and temperature data to the ground control cabinet.

[0022] In a possible implementation, the downhole corrosion monitoring device is installed to the side wall of the oil pipe by means of a clamp and fasteners fixed to the side wall of the oil pipe.

[0023] In a possible implementation, there are multiple downhole corrosion monitoring devices, and the multiple downhole corrosion monitoring devices are installed on the side walls of the oil pipe at different well depths.

[0024] In a third aspect, the present application provides a method for downhole corrosion monitoring, the method comprising: obtaining the differential voltage between a test piece and a reference piece of a resistance probe at multiple moments; obtaining the resistance ratio of the test piece and the reference piece at multiple moments based on the differential voltage at multiple moments; calculating the remaining thickness of the test piece at multiple moments based on the resistance ratio at multiple moments; and obtaining the corrosion rate by performing differential calculation based on the remaining thickness of the test piece at multiple moments.

[0025] The downhole corrosion monitoring device, system and method of the present application are as follows: the test piece and the reference piece of the resistance probe in the resistance probe assembly are filled with insulating material, and are designed as a gapless flat plate structure; one end of the test piece and the reference piece are extended and connected, and the other ends of the test piece and the reference piece are respectively connected to the measuring terminals; the resistance probe assembly includes two resistance probes and two conductivity probes for simultaneous monitoring inside and outside the oil pipe; the two resistance probes and the two conductivity probes are respectively connected to the PCB circuit board in the downhole corrosion monitoring device of this embodiment, and the PCB circuit board is provided with a power supply circuit, an acquisition circuit and a single-chip microcomputer, which are used to collect and process the signal of the resistance probe assembly, and finally obtain the monitoring data of the downhole corrosion monitoring device to reflect the corrosion situation inside and outside the oil pipe in the oil well. The device of this embodiment realizes accurate monitoring of oil pipe corrosion by designing a resistance probe probe assembly structure with a gapless flat plate structure and a precise circuit assembly, and powers the precise circuit assembly through a cable and transmits the monitoring data to the ground control cabinet on the well; the monitoring results are accurate, and the monitoring data can be transmitted in real time. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0027] Figure 1 This is a schematic diagram of the structure of the resistance probe of the downhole corrosion monitoring device of the present application;

[0028] Figure 2 This is a schematic diagram of the structure of the resistance probe assembly in the downhole corrosion monitoring device of the present application;

[0029] Figure 3 A schematic diagram of the structure of the resistance probe assembly of this application Figure 1 ;

[0030] Figure 4 A schematic diagram of the structure of the resistance probe assembly of this application Figure 2 ;

[0031] Figure 5 This is a schematic diagram of the structure of the underground corrosion monitoring device of the present application;

[0032] Figure 6 This is a schematic diagram of the connection between the downhole corrosion monitoring device and the oil pipe of this application;

[0033] Figure 7 This is a schematic diagram of the bidirectional constant current source circuit structure of the present application;

[0034] Figure 8 This is a schematic diagram of the structure of the conductivity collection circuit of this application;

[0035] Fig. 9 This is a port diagram of the resistance probe of this application;

[0036] Fig.10 This is a schematic diagram of the structure of the ADC acquisition circuit of this application;

[0037] Fig.11 This is a curve showing the change of corrosion allowance of the test piece of the resistance probe of the present application over time;

[0038] Fig.12 This is a curve showing the change of corrosion rate of the resistance probe test piece over time for this application;

[0039] Fig.13 The conductivity change curve over time for this application;

[0040] Fig.14 This is a schematic diagram of the structure of the underground corrosion monitoring system of this application;

[0041] Fig.15 This is a schematic diagram of the process of the underground corrosion monitoring method of this application.

[0042] The above drawings have shown clear embodiments of the present application, which will be described in more detail later. These drawings and text descriptions are not intended to limit the scope of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments.

[0043] Description of reference numerals:

[0044] 1: Downhole corrosion monitoring device; 10: Resistance probe assembly; 20: Circuit sealing assembly; 30: Cable; 40: Oil pipe;

[0045] 100: component body; 110: first resistance probe; 120: second resistance probe;

[0046] 111: test piece; 112: reference piece; 113: first measurement terminal; 114: second measurement terminal; 1131: first port; 1132: second port; 1141: third port; 1142: fourth port; 115: first resistance probe connection port; 116: second resistance probe connection port;

[0047] 130: first conductivity probe; 140: second conductivity probe; 150: aerial plug;

[0048] 200: circuit sealing component housing; 210: PCB circuit board; 220: wire; 230: first sealing structure;

[0049] 240: second sealing structure;

[0050] 300: current source circuit; 310: first NMOS transistor; 320: second NMOS transistor; 330: third NMOS transistor; 340: fourth NMOS transistor;

[0051] 301: first operational amplifier; 302: triode; 303: current sampling module;

[0052] 3031: second operational amplifier; 3032: sampling resistor;

[0053] 400: analog switch; 410: pulse signal generator; 420: first voltage follower; 430: second voltage follower; 440: first voltage divider resistor; 450: second voltage divider resistor;

[0054] 401: clamp; 402: fastener; 403: wellhead power supply; 404: ground control cabinet; 405: oil casing;

[0055] 500: filter circuit; 510: first voltage-stabilizing diode; 520: second voltage-stabilizing diode. DETAILED DESCRIPTION

[0056] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present application. Instead, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0057] It should be noted that the brief description of the terms in this application is only for the convenience of understanding the embodiments described below, and is not intended to limit the embodiments of the present application. Unless otherwise specified, these terms should be understood according to their common and usual meanings. The terms "including" and "having" in the specification and claims and the above-mentioned drawings in this application and any variation thereof are intended to cover but not exclude inclusion. For example, a product or device containing a series of components is not necessarily limited to those components clearly listed, but may include other components that are not clearly listed or inherent to these products or devices. The term "module" used in this application refers to any known or later developed hardware, software, firmware, artificial intelligence, fuzzy logic or a combination of hardware and / or software code that can perform functions related to the element.

[0058] As oilfield development gradually enters the middle and late stages, the comprehensive water content continues to rise. Adopting new technologies such as CCUS and polymer flooding to improve recovery has become the most important measure to increase production. However, the implementation of these measures will cause corrosion of the oil pipes downhole, and the corrosion situation needs to be monitored.

[0059] At present, in some downhole oil pipe corrosion monitoring solutions, the monitoring process is easily disturbed by the complex downhole environment, resulting in inaccurate corrosion monitoring results. Therefore, the current problem that needs to be solved is how to improve the accuracy of corrosion monitoring results.

[0060] The technical content provided by this application is intended to solve the above-mentioned technical problems of related technologies. In the downhole corrosion monitoring device, system and method of this application, the test piece and the reference piece of the resistance probe in the resistance probe assembly are filled with insulating material, and are designed as a gapless flat plate structure; one end of the test piece and the reference piece are extended and connected, and the other ends of the test piece and the reference piece are respectively connected to the measurement terminals; the resistance probe assembly includes two resistance probes and two conductivity probes for simultaneous monitoring inside and outside the oil pipe; the two resistance probes and the two conductivity probes are respectively connected to the PCB circuit board in the downhole corrosion monitoring device of this embodiment, and the PCB circuit board is provided with a power supply circuit, an acquisition circuit and a single-chip microcomputer, which are used to collect and process the signals of the resistance probe assembly, and finally obtain the monitoring data of the downhole corrosion monitoring device to reflect the corrosion conditions inside and outside the oil pipe in the oil well. The scheme of this application, by designing a resistance probe probe assembly structure with a gapless flat plate structure and a precise circuit assembly, and powering the precise circuit assembly through a cable and transmitting the monitoring data to the ground control cabinet on the well; accurate monitoring of oil pipe corrosion is achieved, the monitoring results are accurate, and the monitoring data can be transmitted in real time.

[0061] The technical solutions of the present application and the technical solutions of the present application are described in detail with specific embodiments below. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. In the description of the present application, unless otherwise clearly specified and limited, each term should be understood in a broad sense in the art. The embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0062] Embodiment 1

[0063] Figure 1 This is a schematic diagram of the structure of the resistance probe of the downhole corrosion monitoring device of the present application; Figure 1 As shown, the resistance probe includes a test piece 111 and a reference piece 112 arranged in parallel; an insulating material is filled between the test piece 111 and the reference piece 112 to form a gap-free bonding structure, and the test piece 111 is located outside the reference piece 112;

[0064] One end of the test piece 111 and the reference piece 112 are extended and connected to form an integral structure, the other end of the test piece 111 is connected to the first measurement terminal 113 , and the other end of the reference piece 112 is connected to the second measurement terminal 114 .

[0065] Specifically, the downhole corrosion monitoring device 1 includes a resistance probe assembly 10; the resistance probe assembly 10 is used to monitor the corrosion situation in the oil well, and the resistance probe assembly 10 includes at least one resistance probe; the test piece 111 and the reference piece 112 of the resistance probe are filled with insulating material to form a gapless parallel fitting structure; the resistance probe is designed with a gapless fitting structure to prevent the fluid in the oil well from penetrating into the inside of the resistance probe and affecting the monitoring result; in addition, the parallel fitting structure between the test piece 111 and the reference piece 112 can also prevent the temperature inconsistency between the test piece 111 and the reference piece 112 due to the existence of a gap, avoid the influence of temperature on the probe resistance, and further improve the accuracy of the measurement result. In one example, a 0.1mm mica sheet is filled between the test piece 111 and the reference piece 112. In practical applications, by testing the small resistance increment of the test piece 111 in the resistance probe, the corrosion thinning amount of the test piece 111 is calculated, and the corrosion situation at the oil well can be obtained. The resistance probe is suitable for corrosion monitoring of oil, water, and gas multiphase systems, and its type is not limited in this example. Even in the high temperature and high pressure environment underground, the resolution of the resistance probe can reach 1 / 5000 of the life of the sensitive element. The shortest measurement interval of the resistance probe can be up to 1h / time. The resistance probe made of the same material as the oil pipe is used on the inner and outer walls of the underground oil pipe for synchronous online corrosion monitoring, which helps to grasp the average corrosion rate of the underground equipment in a timely manner. The test piece 111 and one end of the reference piece 112 are extended and connected, the other end of the test piece 111 is connected to the first measurement terminal 113, and the other end of the reference piece 112 is connected to the second measurement terminal 114 for subsequent corrosion data monitoring. The test piece and the reference piece of the resistance probe in this example are set as a parallel gapless fitting structure, which ensures that the temperature of the test piece and the reference piece is consistent, eliminates the error of the monitoring result caused by the influence of temperature on the resistance value, and improves the accuracy of the monitoring result.

[0066] Figure 2 This is a schematic diagram of the structure of the resistance probe assembly in the downhole corrosion monitoring device of the present application. Figure 3 A schematic diagram of the structure of the resistance probe assembly of this application Figure 1 ; Figure 4 A schematic diagram of the structure of the resistance probe assembly of this application Figure 2 ;

[0067] like Figures 2 to 4 As shown, the resistance probe assembly 10 includes: an assembly body 100; a first resistance probe 110, a second resistance probe 120, a first conductivity probe 130, a second conductivity probe 140, and an air plug 150. The first resistance probe 110 and the second resistance probe 120 each include a test piece 111, a reference piece 112, a first measurement terminal 113, and a second measurement terminal 114.

[0068] The resistance probe assembly 10 includes: an assembly body 100, and a first resistance probe 110 and a second resistance probe 120 located in the assembly body 100; the first resistance probe 110 and the second resistance probe 120 are used for corrosion monitoring inside and outside the oil pipe respectively;

[0069] The component body 100 has a first surface and a second surface facing each other; the first surface is provided with a first opening to expose the test piece 111 of the first resistance probe 110 through the first opening; the second surface is provided with a second opening to expose the test piece 111 of the second resistance probe 120 through the second opening;

[0070] The first surface protrudes from the main surface of the component body 100 , and the main surface of the component body 100 is provided with a sealing structure whose outline surrounds the area of ​​the second surface; the sealing structure matches the oil pipe opening on the side wall of the oil pipe.

[0071] Specifically, the resistance probe assembly 10 includes an assembly body 100 and a first resistance probe 110 and a second resistance probe 120 in the assembly body 100; wherein the first resistance probe 110 is used to monitor the corrosion condition inside the oil pipe, and the second resistance probe 120 is used to monitor the corrosion condition outside the oil pipe.

[0072] In one example, there is an opening on the oil pipe that matches the probe assembly. The first resistance probe 110 is squeezed into the slot opened on the oil pipe and then fixed to the side surface of the oil pipe with the probe mounting fastener 402 for O-ring sealing. The first resistance probe 110 is squeezed into the inside of the oil pipe for monitoring the corrosion inside the oil pipe. Specifically, the first resistance probe 110 in the oil pipe does not exceed the plane of the inner wall of the oil pipe and has no effect on the movement of the sucker rod in the oil pipe. The height dimension of the downhole corrosion monitoring device outside the oil pipe is kept within 20 mm as a whole, meeting the dimensional requirements of the limited annular space, and can avoid the problem of failure caused by excessive friction and wear during the process of the device going down the well. The second resistance probe 120 is in the space between the oil pipe and the oil casing 405 during installation, and mainly monitors the corrosion rate outside the oil pipe. The technical indicators of the downhole corrosion monitoring device in this example can reach: conductivity indicators: conductivity test frequency: 1kHz~10Hz, square wave excitation amplitude: 10 mV~1000 mV; conductivity test range: 0.1 mS.cm-1 ~ 100 mS.cm-1; resistance probe indicators: corrosion thinning sensitivity: 10 nm, resolution: 1 / 5000, pressure resistance: 40 MPa, temperature resistance: 125℃, communication baud rate: 1200 BPS, transmission distance: 3000 meters. In this example, the two resistance probes of the resistance probe assembly can realize the monitoring of the corrosion conditions inside and outside the oil pipe, making the monitoring results more accurate.

[0073] Specifically, the downhole corrosion monitoring device can monitor the downhole corrosion rate and the conductivity of the downhole environment. Accordingly, based on any example, the resistance probe assembly 10 further includes: a first conductivity probe 130 and a second conductivity probe 140 located in the assembly body 100; the first conductivity probe 130 and the second conductivity probe 140 are used for conductivity monitoring inside and outside the oil pipe, respectively;

[0074] The first surface is also provided with a first through hole to expose the platinum wire electrode of the first conductivity probe 130 through the first through hole; the second surface is also provided with a second through hole to expose the platinum wire electrode of the second conductivity probe 140 through the second opening.

[0075] In one example, the platinum wire electrode of the first conductivity probe 130 in the resistance probe assembly 10, the second conductivity probe 140, the first resistance probe 110 and the second resistance probe 120 are integrally cast with polyetheretherketone or polytetrafluoroethylene. A first through hole is also provided on the first surface of the resistance probe assembly 10, and the first conductivity probe 130 monitors the conductivity in the oil pipe by squeezing into the slot opened on the oil pipe through the first through hole in the same way and sealing with an O-ring. The second conductivity probe 140 is provided between the outer wall of the oil pipe and the oil jacket 405 through the second through hole provided on the second surface of the resistance probe assembly 10, and is used to monitor the conductivity of the outer wall of the oil pipe. In this example, the conductivity probe is installed in the resistance probe assembly to realize the conductivity monitoring in the environment inside and outside the downhole oil pipe, thereby improving the accuracy of the monitoring results.

[0076] Furthermore, the downhole corrosion monitoring device includes other test units in addition to the resistance probe assembly 10. Accordingly, as an example, Figure 5 This is a schematic diagram of the structure of the underground corrosion monitoring device of this application, such as Figure 5 As shown, the downhole corrosion monitoring device further includes: a circuit sealing assembly 20 and a cable 30; the circuit sealing assembly 20 includes a housing 200 and a PCB circuit board 210 and a wire 220 located inside the housing;

[0077] One end of the circuit sealing assembly housing 200 is used to be sealed and connected to the assembly body 100 of the resistance probe assembly 10 through threads and a first sealing structure 230;

[0078] One end of the cable 30 is electrically connected to the PCB circuit 210, and the other end of the cable 30 extends outward through the outlet at the other end of the housing of the circuit sealing assembly 20, and the outlet and the cable 30 are sealed by a second sealing structure 240;

[0079] An aviation plug 150 is provided at one end of the component body 100 of the resistance probe assembly 10, and the PCB circuit board 210 has an aviation plug 150 interface corresponding to the aviation plug 150. When the component body 100 of the resistance probe assembly 10 is connected to the circuit sealing assembly 20, the PCB circuit board 210 is electrically connected to the resistance probe assembly 10 through the aviation plug interface and the aviation plug 150.

[0080] In this example, the metal shell of the circuit sealing component 20 is sealed and connected to the resistance probe component 10 through threads and a first sealing structure 230, and the other end of the circuit sealing component housing 200 is sealed and connected to the cable 30 through a second sealing structure 240. The port of the resistance probe component 10 is provided with a nine-core aviation plug, and the nine-core aviation plug is electrically connected to the PCB circuit board 210 through the wire 220 inside the circuit sealing component 20. The resistance probe component 10 is connected to the aviation plug 150 pin by high-temperature wire welding, and is integrally cast and molded using polyetheretherketone or polytetrafluoroethylene.

[0081] Figure 6 This is a schematic diagram of the connection between the downhole corrosion monitoring device and the oil pipe in this application; Figure 6 As shown, the downhole corrosion monitoring device 1 is fixed to the outside of the oil pipe 40 by means of a clamp 401 and a fastener 402. This ensures that the downhole corrosion monitoring device 1 can be firmly fixed to the oil pipe 40.

[0082] In this example, a sealing structure is used for connection so that the entire downhole corrosion monitoring device 1 is in a sealed environment, thereby improving the accuracy of the monitoring results and ensuring the stability of the monitoring device in the high temperature and high pressure environment downhole.

[0083] Furthermore, the PCB circuit board 210 is provided with a precise circuit structure to collect data on the underground corrosion situation; accordingly, based on any example, the PCB circuit board 210 is provided with a single chip microcomputer 211, a bidirectional constant current source circuit and a multi-channel A / D converter;

[0084] When the PCB circuit board 210 is electrically connected to the resistance probe assembly 10, the bidirectional constant current source circuit is electrically connected to the first measurement terminal 113 of the first resistance probe 110 and the second measurement terminal 114 of the second resistance probe 120, and is used to provide a forward driving current and a reverse driving current to the resistance probes to generate a differential voltage between the test piece 111 and the reference piece 112;

[0085] The input end of the multi-channel A / D converter is electrically connected to the first measurement terminal 113 and the second measurement terminal 114, the output end of the multi-channel A / D converter is connected to the single-chip microcomputer, and the multi-channel A / D converter is used to sample the differential voltage between the test piece 111 and the reference piece 112;

[0086] The single chip microcomputer is electrically connected to the multi-channel A / D converter, and is used to obtain the resistance ratio of the test piece 111 and the reference piece 112 according to the differential voltage between the reference piece 112 and the test piece 111, and calculate the corrosion rate data inside and outside the oil pipe and the remaining thickness data of the test piece 111 according to the resistance ratio.

[0087] In one example, the PCB circuit board 210 is provided with a single-chip microcomputer, a data storage device, a communication interface, a multi-channel A / D converter, a pulse signal generator 410, a temperature sensor and a linear voltage regulator; the maximum operating temperature of the PCB circuit board 210 is 150°C. Among them, the single-chip microcomputer is respectively connected to the data storage device, the communication interface, the multi-channel A / D converter, the pulse signal generator 410, the temperature sensor and the linear voltage regulator. In this example, the data storage device is a dual-channel data storage device, the storage capacity of each chip is 256KByte, and it is resistant to high temperature of 150°C. The two data storage devices simultaneously store the collected time, corrosion rate, conductivity and other data, and perform dual storage chip backup at the same time, thereby improving the security of the data. The PCB circuit board 210 is provided with an RS485 chip, which is used together with the RS485 transceiver in the control cabinet at the wellhead for command control and measurement data transmission. The communication rate of 1200bps can meet the long-distance communication of 3KM underground. The linear voltage regulator supplies power for all circuits. In one example, a bidirectional constant current source circuit is connected to a first measurement terminal 113 of a first resistance probe 110 and a second measurement terminal 114 of a second resistance probe 120 through a wire 220, providing forward and reverse drive currents for the resistance probes. A multi-channel A / D converter is used to synchronously sample the differential voltages at both ends of a test piece 111 and a reference piece 112 of the resistance probe. The output end of the A / D converter is connected to a single-chip microcomputer 211, and the collected differential voltage is input to the single-chip microcomputer 211. The single-chip microcomputer 211 calculates the resistance ratio according to the value of the differential voltage, and further calculates the corrosion rate and the remaining thickness of the test piece 111 according to the resistance ratio. For example, the structure of the resistance probe is a parallel plate bonding structure. For the probe of this structure, the resistance ratio is:

[0088]

[0089] in, , , are the length, width and thickness of the test piece 111, , , are the length, width and thickness of the reference sheet 112; The resistance of the test piece 111, is the resistance of the reference piece 112. Since the length and width of the reference piece 112 in the resistance probe are equal and will not change during the entire measurement process, and the lengths of the reference piece 112 and the test piece 111 will not change over time, we have:

[0090]

[0091] in, ;

[0092] Then the remaining thickness of the test piece 111 at any time t is:

[0093] The corrosion rate at time t is:

[0094] in, is the corrosion rate, A is a constant, represents the remaining thickness of the test piece 111 at time t, Indicates the resistance ratio at time t. In this example, the corrosion data in the underground environment is received and calculated by designing a precise PCB circuit board, so that the data monitored by the underground corrosion monitoring device is more accurate. The data is subsequently transmitted to the ground system, so that the ground monitoring system can obtain more realistic monitoring data, which is convenient for proposing measures to prevent oil pipe corrosion based on the monitoring results.

[0095] Furthermore, in order to provide a forward and reverse constant current, a bidirectional constant current source circuit is designed; accordingly, as an example, the bidirectional constant current source circuit includes: a current source circuit 300, a first NMOS tube 310, a second NMOS tube 320, a third NMOS tube 330, and a fourth NMOS tube 340;

[0096] One end of the first NMOS transistor 310 and the second NMOS transistor 320 are connected to the output end of the current source circuit 300, and the other end of the first NMOS transistor 310 is connected to one end of the third NMOS transistor 330 as the first output end of the bidirectional constant current source circuit; the other end of the third NMOS transistor 330 is grounded;

[0097] The other end of the second NMOS 320 is connected to one end of the fourth NMOS 340 as the second output end of the bidirectional constant current source circuit; the other end of the fourth MOS tube 340 is grounded;

[0098] The control ends of the first NMOS tube 310, the second NMOS tube 320, the third NMOS tube 330 and the fourth NMOS tube 340 are connected to the single chip microcomputer; the single chip microcomputer is used to control the first NMOS tube 310 and the fourth NMOS tube 340 to be turned on, or to control the second NMOS tube 320 and the third NMOS tube 330 to be turned on, so as to output a forward driving current or a reverse driving current.

[0099] In one example, the bidirectional constant current source circuit includes a current source circuit 300 for outputting a constant current; four identical NMOS tubes for realizing forward and reverse conduction of the circuit. The single chip microcomputer 211 is used to control the forward and reverse conduction of the circuit; when the single chip microcomputer provides a high voltage signal to both ends of the first NMOS tube 310 and the fourth NMOS tube 340, at this time, the first NMOS tube 310 and the fourth NMOS tube 340 are turned on, the second NMOS tube 320 and the third NMOS tube 330 are turned off, and the current output by the current source circuit 300 flows forward; when the single chip microcomputer provides a high voltage signal to both ends of the second NMOS tube 320 and the third NMOS tube 330, at this time, the second NMOS tube 320 and the third NMOS tube 330 are turned on, the first NMOS tube 310 and the fourth NMOS tube 340 are turned off, and the current output by the current source circuit 300 flows in the reverse direction. In this example, four NMOS are used to realize the forward and reverse flow of current, so that the voltage values ​​of the test piece and the reference piece of the resistance probe collected later are more accurate, eliminating the influence of inconsistent temperature on the resistance value of the resistance probe when the current flows unidirectionally, making the measurement result more accurate.

[0100] In order to make the circuit output a constant current, accordingly, as an example, the current source circuit 300 includes: a first operational amplifier 301, a transistor 302 and a current sampling module 303;

[0101] The first end of the transistor 302 receives the voltage signal output by the first operational amplifier 301, the second end of the transistor 302 is connected to one end of the first NMOS transistor 310 and the second NMOS transistor 320 as the output end of the current source circuit 300, and the third end of the transistor 302 is connected to the output end of the first operational amplifier 301;

[0102] The current sampling module 303 is used to sample the current output current of the current source circuit 300 and output the sampled current; the first operational amplifier 301 receives a reference signal and is connected to the current sampling module 303, and is used to output a drive signal to the third end of the transistor 302 according to the output current of the current source circuit 300 and the reference signal to perform feedback regulation.

[0103] Specifically, in order to output a constant current, this example uses a first operational amplifier 301, a transistor 302, and a current sampling module 303 to form a current source circuit 300. First, the first end of the transistor 302 receives the voltage signal output by the first operational amplifier 301, and at the same time, the first operational amplifier 301 receives a reference signal for outputting an accurate constant current according to the reference signal. The second end of the transistor 302 outputs a constant current as the output end of the current source current, and is connected to one end of the first NMOS tube 310 and the second NMOS tube 320 mentioned above, and the third end of the transistor 302 is connected to the output end of the first operational amplifier 301; the current sampling module 303 in the current source circuit 300 is used to sample the current currently output by the current source circuit 300 and output the sampled current. In this example, a constant current is output through the current source circuit, and the constant current is subsequently input into the subsequent voltage acquisition circuit, so that the subsequent acquisition results are more accurate, and the accuracy of the corrosion monitoring results is improved.

[0104] Specifically, the current sampling module 303 is used to sample the voltage across the sampling resistor. Accordingly, as an example, the current sampling module 303 includes: a second operational amplifier 3031 and a sampling resistor 3032;

[0105] One end of the sampling resistor 3032 is connected to the second end of the transistor 302 and the second operational amplifier 3031, and the other end of the sampling resistor 3032 is connected to one end of the first NMOS tube 310, one end of the second NMOS tube 320, and the second operational amplifier 3031; the output end of the second operational amplifier 3031 is connected to the first operational amplifier 301 for outputting the sampling current.

[0106] In one example, one end of the sampling resistor 3032 in the current sampling module 303 is connected to the second end of the aforementioned triode 302 and the second operational amplifier 3031, and the other end of the sampling resistor 3032 is connected to one end of the aforementioned first NMOS tube 310, one end of the second NMOS tube 320, and the second operational amplifier 3031; the output end of the second operational amplifier 3031 is connected to the first operational amplifier 301, and the second operational amplifier 3031 is used to output the sampled current collected by the current sampling module 303. In this example, the sampled current output by the current sampling module is used to perform feedback regulation on the output end of the first operational amplifier to achieve accurate and constant current output, thereby improving the accuracy of subsequent collection results.

[0107] Combining the above three examples, Figure 7 Schematic diagram of the structure of the bidirectional constant current source circuit of the present application; Figure 7As shown, the bidirectional constant current source circuit includes: a current source circuit 300, a first NMOS tube 310, a second NMOS tube 320, a third NMOS tube 330, and a fourth NMOS tube 340; wherein the current source circuit 300 includes: a first operational amplifier 301, a triode 302 and a current sampling module 303; the current sampling module 303 also includes: a second operational amplifier 3031 and a sampling resistor 3032;

[0108] First, the first operational amplifier 301 receives a reference signal, and the first operational amplifier 301 outputs a voltage signal to the first end of the triode 302 to be received, the third end of the triode 302 is connected to one end of the sampling resistor 3032, and the second end of the triode 302 receives an excitation power supply signal; the other end of the sampling resistor 3032 is connected to one end of the first NMOS tube 310, one end of the second NMOS tube 320, and the second operational amplifier 3031; the output end of the second operational amplifier 3031 is connected to the first operational amplifier 301 for outputting a sampling current;

[0109] One end of the first NMOS transistor 310 and the second NMOS transistor 320 are connected to the output end of the current source circuit 300, and the other end of the first NMOS transistor 310 is connected to one end of the third NMOS transistor 330 as the first output end of the bidirectional constant current source circuit; the other end of the third NMOS transistor 330 is grounded;

[0110] The other end of the second NMOS 320 is connected to one end of the fourth NMOS 340 as the second output end of the bidirectional constant current source circuit; the other end of the fourth NMOS 340 is grounded;

[0111] The control ends of the first NMOS tube 310, the second NMOS tube 320, the third NMOS tube 330 and the fourth NMOS tube 340 are connected to the single chip microcomputer; the single chip microcomputer is used to control the first NMOS tube 310 and the fourth NMOS tube 340 to be turned on, or to control the second NMOS tube 320 and the third NMOS tube 330 to be turned on, so as to output a forward driving current or a reverse driving current.

[0112] Specifically, the conductivity probe in the resistance probe assembly 10 is used to collect the conductivity in the environment inside and outside the downhole oil pipe. Accordingly, as an example, the PCB circuit board 210 also includes: a conductivity collection circuit;

[0113] The conductivity acquisition circuit is connected to the first conductivity probe 130 and the second conductivity probe 140, and is used to output the divided voltage ratio of the first conductivity probe 130 and the divided voltage ratio of the second conductivity probe 140;

[0114] The single chip microcomputer is connected to the conductivity acquisition circuit, and is also used to obtain the impedance values ​​of the first conductivity probe 130 and the second conductivity probe 140 according to the voltage division ratio of the first conductivity probe 130 and the voltage division ratio of the second conductivity probe 140, and output the conductivity data inside and outside the oil pipe according to the impedance value.

[0115] In one example, the first conductivity probe 130 and the second conductivity probe 140 are respectively connected to a conductivity acquisition circuit, and the conductivity acquisition circuit outputs the collected voltage division ratio of the first conductivity probe 130 and the second conductivity probe 140; subsequently, the conductivity acquisition circuit is connected to a single-chip microcomputer, and the voltage division ratio of the first conductivity probe 130 and the voltage division ratio of the second conductivity probe 140 collected by the conductivity acquisition circuit are input into the single-chip microcomputer, and the single-chip microcomputer calculates the corresponding impedance value according to the voltage division ratio of the first conductivity probe 130 and the voltage division ratio of the second conductivity probe 140, and calculates the conductivity data inside and outside the oil pipe according to the impedance value.

[0116] The conductivity probe in this example is a platinum wire electrode. When conducting a conductivity test, the environmental conductivity between the platinum wire electrode and the resistance probe test piece 111 is tested. One end of the platinum wire electrode is connected to the conductivity acquisition circuit to collect the voltage of one end of the platinum wire electrode, i.e., the conductivity probe, and the test piece 111 of the resistance probe at the other end is grounded. When the area of ​​the test piece 111 of the resistance probe is A, and the distance between the platinum wire electrode and the test piece 111 is L, the resistivity is expressed as:

[0117]

[0118] in, represents the electrode coefficient, Indicates the environmental impedance when measured at 500Hz;

[0119]

[0120] The conductivity formula is expressed as:

[0121]

[0122] in, represents the conductivity, Represents resistivity.

[0123] In this example, by connecting the conductivity probe to the conductivity collection circuit, the conductivity inside and outside the oil pipe is collected. The conductivity value can reflect the concentration of carbon dioxide in the downhole environment, which helps the surface workers to judge the concentration of carbon dioxide in the well according to the conductivity value, and then judge the corrosion situation and take corresponding measures, thereby improving the accuracy of corrosion monitoring results.

[0124] In order to accurately collect the environmental conductivity, a conductivity collection circuit is designed; Figure 8 Schematic diagram of the conductivity collection circuit of the present application; Figure 8 As shown, the conductivity acquisition circuit includes: an analog switch 400, a pulse signal generator 410, a first voltage follower 420, a second voltage follower 430, a first voltage-dividing resistor 440, and a second voltage-dividing resistor 450;

[0125] The input end of the analog switch 400 is connected to the first conductivity probe 130 and the second conductivity probe 140 respectively, and the analog switch 400 is used to output the signals output by the first conductivity probe 130 and the second conductivity probe 140 in a time-sharing manner; the pulse signal generator 410 is used to provide a pulse modulation signal;

[0126] One end of the first voltage-dividing resistor 440 is connected to the pulse signal generator 410 and the input end of the first voltage follower 420; the other end of the first voltage-dividing resistor 440 is connected to the output end of the analog switch 400, one end of the second voltage-dividing resistor 450, and the input end of the second voltage follower 430, and the other end of the second voltage-dividing resistor 450 is grounded;

[0127] The output end of the first voltage follower 420 is used to output a first follower signal corresponding to the pulse modulation signal; the output end of the second voltage follower 430 is used to output a second follower signal corresponding to the voltage signal collected by the first conductivity probe 130 or the second conductivity probe 140; the first follower signal and the second follower signal are used to calculate the conductivity inside or outside the oil pipe.

[0128] In one example, the conductivity acquisition circuit includes an analog switch 400, which is used to select the conductivity measurement inside or outside the oil pipe in time-sharing mode; when the analog switch 400 is connected to the first conductivity probe 130, the value of the environmental conductivity inside the oil pipe is tested; when the switch is connected to the second conductivity probe 140, the value of the conductivity in the environment outside the oil pipe is tested; the analog switch 400 can realize the time-sharing measurement of conductivity. One end of the first voltage-dividing resistor 440 in the conductivity acquisition circuit is connected to the pulse signal generator 410 and the input end of the first voltage follower 420; wherein the pulse signal generator 410 is used to provide a pulse modulation signal; the first voltage follower 420 is used to output a first follower signal corresponding to the pulse modulation signal, and the first voltage follower signal reflects the actual value of the pulse modulation signal. The other end of the first voltage-dividing resistor 440 is connected to one end of the second voltage-dividing resistor 450 and the input end of the second voltage follower 430 in the circuit; the other end of the second voltage-dividing resistor 450 is grounded. The second voltage follower 430 outputs a second voltage follower signal corresponding to the voltage signal of the first conductivity probe 130 or the second conductivity probe 140. The first follower signal and the second voltage follower signal reflect the voltage value of the pulse modulator and the voltage values ​​of the two conductivity probes. The voltage division ratio of the two voltages can be calculated based on the follower signal, and then the impedance value of the environment can be calculated. The environmental conductivity value can be calculated based on the calculation formula of the environmental conductivity.

[0129] In this example, the voltage value collected by the conductivity acquisition circuit is processed by a voltage follower to obtain an output follow-up signal before being transmitted to the single-chip microcomputer for conductivity calculation. When implemented in combination with the above example, the output end of the voltage follower is connected to the input end of the single-chip microcomputer to receive the follow-up signal for calculating the conductivity value. At this time, the received signal is a voltage follower signal, and the voltage follower signal represents the voltage signal. In this example, the voltage corresponding to the pulse modulation signal and the voltage value of the second voltage follower are collected by the first voltage follower and the second voltage follower to calculate the voltage divider ratio, and the value of the environmental conductivity inside or outside the oil pipe is calculated according to the voltage divider ratio, so that the collection result is more accurate and the accuracy of the monitoring result is improved.

[0130] The voltage signal obtained above needs to be collected by the collection circuit to obtain the final corrosion monitoring data. Accordingly, in combination with any of the above examples, Fig. 9 This is a schematic diagram of the port of the resistance probe of this application; Fig. 9As shown, the first measuring terminal 113 includes a first port 1131 and a second port 1132, and the second measuring terminal 114 includes a third port 1141 and a fourth port 1142; the fourth port 1142 of the first resistance probe 110 is electrically connected to the second port 1132 of the second resistance probe 120; the multi-channel A / D converter includes: a plurality of ADC acquisition circuits; the plurality of ADC acquisition circuits include an ADC acquisition circuit corresponding to the first port 1131 of the first resistance probe 110, an ADC acquisition circuit corresponding to the first resistance probe connection port 115 of the first resistance probe 110, an ADC acquisition circuit corresponding to the third port 1141 of the first resistance probe 110 and the first port 1131 of the second resistance probe 120, an ADC acquisition circuit corresponding to the third port 1141 of the second resistance probe 120, an ADC acquisition circuit corresponding to the second resistance probe connection port 116, an ADC acquisition circuit corresponding to the first conductivity probe 130, and an ADC acquisition circuit corresponding to the second conductivity probe 140.

[0131] In one example, the connection ports on the test piece 111 and the reference piece 112 of the two resistance probes in the resistance probe assembly 10 and the two conductivity probes need to be connected to multiple ADC acquisition circuits of the circuit board respectively; wherein, the corresponding first measurement terminal 113 and the second measurement terminal 114 of each test piece 111 and each reference piece 112 of the resistance probe correspond to two measurement ports, and the positions of each measurement port of the two resistance probes are consistent. The first measurement terminal 113 includes a first port 1131 and a second port 1132, and the second measurement terminal 114 includes a third port 1141 and a fourth port 1142. In practical applications, before connecting the various ports of the resistance probe and the platinum wire electrode of the conductivity probe to the ADC acquisition circuit, the first port 1131 of the first resistance probe 110 and the third port 1141 of the second resistance probe 120 are electrically connected by welding. Accordingly, the multi-channel A / D converter includes multiple ADC acquisition circuits, each ADC acquisition circuit is the same, and each ADC acquisition circuit is connected to the various ports of the resistance probe and the two conductivity probes. Specifically, it includes an ADC acquisition circuit corresponding to the first port 1131 of the first resistance probe 110, an ADC acquisition circuit corresponding to the first resistance probe connection port 115 of the first resistance probe 110, an ADC acquisition circuit corresponding to the third port 1141 of the first resistance probe 110 and the first port 1131 of the second resistance probe 120, an ADC acquisition circuit corresponding to the third port 1141 of the second resistance probe 120, an ADC acquisition circuit corresponding to the second resistance probe connection port 116 of the second resistance probe 120, an ADC acquisition circuit corresponding to the first conductivity probe 130, and an ADC acquisition circuit corresponding to the second conductivity probe 140, which are used to collect voltages of the ports of the resistance probes and the conductivity probes, and subsequently calculate the corrosion rate, the corrosion remaining thickness, and the conductivity value according to the voltage signal. In this example, the accuracy of the monitoring result is improved by accurately collecting the voltage by connecting the resistance probe assembly to multiple identical ADC acquisition circuits.

[0132] The aforementioned multiple ADC acquisition circuits have the same structure. Accordingly, as an example, Fig.10 This is a schematic diagram of the structure of the ADC acquisition circuit of this application; Fig.10 As shown, the ADC acquisition circuit includes a filter circuit 500, a first voltage zener diode 510, and a second voltage zener diode 520;

[0133] The input end of the filter circuit 500 is connected to the port corresponding to the ADC acquisition circuit, and the filter circuit 500 is used to filter the signal at the port;

[0134] The cathode of the first voltage zener diode 510 receives a constant voltage signal, the anode of the second voltage zener diode 520 is grounded, and the output end of the filter circuit 500 is connected to the anode of the first voltage zener diode 510 and the cathode of the second voltage zener diode 520, so as to output the filtered signal after voltage limiting; the output ends of the multiple ADC acquisition circuits are connected to the corresponding ports of the single-chip microcomputer to input the differential voltage between the reference piece 112 and the test piece 111 of the first resistance probe 110, the differential voltage between the reference piece 112 and the test piece 111 of the second resistance probe 120, the voltage divider ratio of the first conductivity probe 130, and the voltage divider ratio of the second conductivity probe 140 to the single-chip microcomputer.

[0135] Specifically, each ADC acquisition circuit includes a filter circuit 500 for filtering the voltage signals of the resistance probe and the conductivity probe; in one example, the filter circuit 500 is composed of a resistor and a capacitor, and the filter circuit 500 can remove noise, protect the circuit, improve the quality of the signal, and make the signal more stable and reliable. The signal passing through the filter circuit 500 is transmitted to the voltage regulator diode, and the circuit includes two voltage regulator diodes, wherein the cathode of the first voltage regulator diode 510 receives the constant voltage signal, and the anode of the second voltage regulator diode 520 is grounded, and the output end of the filter circuit 500 is connected to the anode of the first voltage regulator diode 510 and the cathode of the second voltage regulator diode 520, and is used to output the filtered signal after voltage limiting, so that the voltage signal is limited to the output within the range of 0 and the constant voltage signal. The output end of the ADC acquisition circuit is connected to the microcontroller of the PCB circuit board 210, and the differential voltage between the reference plate 112 and the test plate 111 of the resistance probe and the voltage divider ratio of the conductivity probe collected by the circuit are input into the microcontroller for subsequent calculation of the corrosion rate, corrosion residue and conductivity value.

[0136] In combination with the above examples, this solution shows the curves of the corrosion residue and corrosion rate of the resistance probe test piece over time; Fig.11 This is the curve of the corrosion allowance of the resistance probe test piece changing with time; Fig.11 As shown: It can be seen that the test piece of the resistance probe is corroded in the downhole fluid, and the corrosion allowance decreases linearly with time. Fig.12 This is the curve of the corrosion rate of the resistance probe test piece of this application over time; Fig.12 As shown, it can be seen that the corrosion rate tends to decrease with time. This is because, as the test piece of the resistance probe is in the downhole fluid, as the corrosion products accumulate on the surface of the resistance probe test piece, the corrosion rate of the probe in the simulated fluid is slowed down. This method can be used to evaluate the corrosion status of downhole oil pipes.

[0137] In order to obtain the relationship between the conductivity and the carbon dioxide concentration in the downhole environment, this example experiment obtains the relationship between the carbon dioxide concentration and the conductivity change; keeping other factors in the environment unchanged, using a single variable method, and only testing the change in carbon dioxide concentration, the conductivity value changes with time curve. Fig.13 The conductivity curve of this application over time is as follows; Fig.13 As shown, by introducing carbon dioxide for testing, a conductivity change curve over time is obtained. It can be seen that as the test time increases, the conductivity gradually increases, and the conductivity growth trend slows down at the end of the test. It shows that the conductivity data measured by the conductivity probe in the resistance probe assembly 10 can reflect the trend of changes in the ambient carbon dioxide concentration, and the slowdown in the conductivity growth trend at the end of the experiment is limited by the solubility of carbon dioxide in the fluid. Through the value of conductivity, combined with the curve of conductivity change over time, the concentration of carbon dioxide at the downhole monitoring position can be determined; in this example, the signal of the probe assembly is accurately collected by the ADC acquisition circuit, and the collected results are made more accurate through filtering and voltage limiting processing, thereby improving the accuracy of the monitoring results.

[0138] Specifically, the uphole power supply needs to be transmitted to the downhole corrosion monitoring device 1 through the cable 30 for power supply, and at the same time, the monitoring data of the downhole corrosion monitoring device 1 also needs to be transmitted to the ground control cabinet 404 through the cable 30; accordingly, based on any example, the cable 30 includes: a power line and a communication line;

[0139] One end of the power line is electrically connected to the PCB circuit board 210, and the other end of the power line is used to connect to the wellhead power supply 403; one end of the communication line is electrically connected to the PCB circuit board 210, and the other end of the communication line is used to connect to the ground control cabinet 404, and the communication line is used to transmit the corrosion rate data inside and outside the oil pipe 40 and the remaining thickness data of the test piece 111 to the ground control cabinet 404.

[0140] Specifically, the cable 30 in this example is used to electrically connect the downhole corrosion monitoring device 1 and the wellhead power supply 403; the cable 30 in this example uses a steel cable containing 4 cores, and the 4 cores are two power lines and two communication lines, wherein the communication line is an RS485 communication line. The power line connects the output terminal of the wellhead power supply 403 and the circuit input terminal of the downhole corrosion monitoring device 1 to power the circuit of the downhole corrosion monitoring device 1; the communication line transmits the data monitored by the downhole corrosion monitoring device 1 to the ground control cabinet 404; wherein the monitoring data includes corrosion rate, corrosion residual thickness and conductivity data. The monitoring data in the control cabinet can be transmitted to the database of the server of the online monitoring system, and the monitoring data can be browsed. In this example, the cable is used to power the downhole corrosion monitoring device, and the downhole data is transmitted to the ground control cabinet 404, which can realize real-time data transmission and real-time monitoring of the downhole corrosion condition. The staff on the well can analyze the corrosion condition of the downhole oil pipe in real time to improve the accuracy of the corrosion monitoring results.

[0141] Specifically, a communication interface needs to be set in the circuit board for docking with the transceiver of the well control cabinet to realize the transmission of monitoring data; accordingly, as an example, based on any example, the PCB circuit board 210 also includes a communication interface;

[0142] The communication interface is connected to the single chip microcomputer and the communication line, and is used to transmit the corrosion rate, the remaining thickness of the test piece 111, and the conductivity data to the ground control cabinet 404 through the communication line.

[0143] In one example, the PCB circuit board 210 of the underground corrosion monitoring device 1 is provided with an RS485 chip, and the ground control cabinet 404 on the well includes an RS485 transceiver. The data monitored by the underground corrosion monitoring device 1 is transmitted to the ground control cabinet 404 on the well through the RS485 signal line; one end of the communication interface is connected to the single-chip microcomputer to receive the monitoring data in the single-chip microcomputer, and the other end is connected to the communication line in the cable 30 to transmit the corrosion rate, corrosion residual thickness and conductivity data received from the single-chip microcomputer to the ground control box; in this example, real-time data transmission can be achieved through the cable, and the data received by the ground control cabinet 404 can be transmitted to the online monitoring system for viewing by ground staff. Improve the accuracy of the monitoring results.

[0144] Specifically, the entire downhole corrosion monitoring device 1 needs to be powered by the wellhead power supply 403. Before receiving the power supply, the downhole corrosion monitoring device 1 needs to convert the voltage value transmitted by the wellhead power supply 403 into the voltage value required by the circuit; accordingly, based on any example, the PCB circuit board 210 also includes: a DC buck converter and a linear regulated power supply;

[0145] The DC step-down converter is used to connect one end of the power line to step down the power provided by the wellhead power supply 403; the linear regulated power supply is connected to the DC step-down converter to stabilize the stepped-down voltage and provide it to the PCB circuit board 210.

[0146] In actual applications, the wellhead power supply 403 supplies power to the PCB circuit board 210 of the entire downhole corrosion monitoring device 1. First, the 48V DC power supply provided by the wellhead is stepped down through a DC step-down converter to output a DC 5V voltage; the linear regulated power supply cooperates with the DC voltage converter to output a 3.3V voltage through the linear regulated power supply, and the output regulated power supply can reduce power supply noise and ripple. In this example, a DC step-down converter is used to step down the high voltage provided by the wellhead power supply 403 to obtain the voltage value required by the circuit board. After the voltage is stabilized by the linear regulated power supply, the inaccuracy of the monitoring results caused by the inaccurate collection results caused by the unstable voltage can be reduced, and the accuracy of the monitoring results can be improved.

[0147] In addition to real-time monitoring of the underground corrosion rate, the underground corrosion monitoring device 1 can also monitor the underground temperature. Accordingly, as an example, the PCB circuit board 210 also includes a temperature sensor;

[0148] The output end of the temperature sensor is connected to the microcontroller to monitor the temperature and transmit the temperature data to the microcontroller.

[0149] Specifically, a temperature sensor is provided on the circuit board to monitor the temperature of the underground monitoring environment. In this example, the maximum operating temperature of the circuit board is 150°C. In practical applications, temperature is one of the important factors affecting the corrosion rate; at different temperatures, the activity of the corrosive medium, the chemical reaction rate, and the stability of the corrosion products will change; therefore, monitoring the temperature helps to understand the actual situation of the corrosion environment and provide important parameters for analyzing the causes of corrosion and formulating protective measures. Changes in temperature are often associated with specific types of corrosion. For example, oxidative corrosion may be more likely to occur in high temperature environments, while stress corrosion cracking may be more likely to occur in low temperature environments. In this example, the underground temperature is monitored by a temperature sensor, and the monitoring data includes temperature data, which can fully reflect the corrosion conditions underground and further improve the accuracy of the monitoring results.

[0150] In the downhole corrosion monitoring device of this embodiment, the test piece and the reference piece of the resistance probe in the resistance probe assembly are filled with insulating material, and are designed as a gapless flat plate structure; one end of the test piece and the reference piece are extended and connected, and the other ends of the test piece and the reference piece are respectively connected to the measuring terminals; the resistance probe assembly contains two resistance probes and two conductivity probes for simultaneous monitoring inside and outside the oil pipe; the two resistance probes and the two conductivity probes are respectively connected to the PCB circuit board in the downhole corrosion monitoring device of this embodiment, and the PCB circuit board is provided with a power supply circuit, an acquisition circuit and a single-chip microcomputer, which are used to collect and process the signals of the resistance probe assembly, and finally obtain the monitoring data of the downhole corrosion monitoring device to reflect the corrosion conditions inside and outside the oil pipe in the oil well. The device of this embodiment realizes accurate monitoring of oil pipe corrosion by designing a resistance probe probe assembly structure with a gapless flat plate structure and a precise circuit assembly, and powers the precise circuit assembly through a cable and transmits the monitoring data to the ground control cabinet on the well; the monitoring results are accurate, and the monitoring data can be transmitted in real time.

[0151] Embodiment 2

[0152] Fig.14 Schematic diagram of the structure of the underground corrosion monitoring system of this application; Fig.14 As shown, the downhole corrosion monitoring system includes a ground control cabinet 404 and at least one downhole corrosion monitoring device 1;

[0153] At least one downhole corrosion monitoring device 1 is installed on the side wall of the oil pipe 40 downhole and connected to the ground control cabinet 404 through the cable 30 to send the corrosion rate, the remaining thickness of the test piece 111 and the conductivity data to the ground control cabinet 404.

[0154] In actual application, at least one downhole corrosion monitoring device 1 is installed on the side wall of the oil pipe 40 downhole. The downhole corrosion monitoring device 1 is connected to the ground control cabinet 404 through a cable 30, and the corrosion rate, remaining thickness of the test piece 111, conductivity and temperature data monitored by the downhole corrosion monitoring device 1 are transmitted to the ground control cabinet 404.

[0155] Specifically, the downhole corrosion monitoring device 1 needs to be fixed on the side wall of the oil pipe 40 . Accordingly, as an example, the downhole corrosion monitoring device is installed to the side wall of the oil pipe 40 through a clamp 401 and a fastener 402 fixed on the side wall of the oil pipe 40 .

[0156] Specifically, the downhole corrosion monitoring device 1 is installed on the short section of the oil pipe 40, one end of the downhole corrosion monitoring device 1 is fixed to the outer wall of the oil pipe 40 by a clamp 401, and the probe assembly at the other end of the downhole corrosion monitoring device 1 is fixed to the side wall of the oil pipe 40 by a fastener 402. The height dimension of the downhole corrosion monitoring device 1 outside the oil pipe 40 is kept within 20 mm as a whole, which meets the dimensional requirements of the limited annular space, and can avoid the problem of failure caused by excessive friction and wear during the process of the device being lowered into the well. In this example, the downhole corrosion monitoring device is fixed to the oil pipe using a clamp and fasteners to ensure a close fit between the device and the pipeline, to avoid monitoring errors caused by loose installation of the downhole corrosion monitoring device or damage to the device on the oil pipe.

[0157] Specifically, the downhole corrosion monitoring system has multiple downhole corrosion monitoring devices 1. Accordingly, as an example, the number of downhole corrosion monitoring devices 1 is multiple, and the multiple downhole corrosion monitoring devices 1 are installed on the side wall of the oil pipe 40 at different well depths.

[0158] In the actual monitoring process, downhole corrosion monitoring devices can be installed at different depths of the well to monitor the corrosion conditions at different depths of the well. The downhole corrosion monitoring system in this example can monitor the corrosion conditions at different depths of the well. It can be used in oil wells with a maximum depth of 3000m from the ground, and realizes real-time and accurate monitoring of corrosion monitoring results at different depths.

[0159] The downhole corrosion monitoring system of the present embodiment includes a plurality of downhole corrosion monitoring devices, which are located at different depths of the side wall of the downhole oil pipe, thereby realizing the monitoring of the corrosion conditions in different well depth environments. While realizing real-time and accurate monitoring, it is also possible to monitor the corrosion conditions at different well depths, and transmit the corrosion monitoring data to the control cabinet on the ground in real time; the corrosion monitoring data received by the ground control cabinet can be wirelessly transmitted to the online monitoring system for real-time browsing by the staff.

[0160] Embodiment 3

[0161] Fig.15 The schematic diagram of the process of the underground corrosion monitoring method of this application is as follows: Fig.15 As shown, the method includes:

[0162] Step 101, obtaining the differential voltage between the test piece and the reference piece of the resistance probe at multiple times;

[0163] Step 102: Obtain the resistance ratio of the test piece and the reference piece at multiple moments according to the differential voltage at multiple moments; and calculate the remaining thickness of the test piece at multiple moments according to the resistance ratio at multiple moments;

[0164] Step 103: performing differential calculation according to the remaining thickness of the test piece at multiple times to obtain the corrosion rate.

[0165] In practical applications, combined with the aforementioned implementation methods, the executor of this example method is the single-chip microcomputer of the downhole corrosion monitoring device. The value of the differential voltage obtained in step 101 of the method is the differential voltage value between the reference plate and the test plate of the resistance probe of the parallel plate structure in this scheme; however, there is no limitation on the circuit structure for obtaining the differential voltage between the test plate and the reference plate, and the method for obtaining the differential voltage.

[0166] The underground corrosion monitoring method of this embodiment obtains the differential voltage between the test piece and the reference piece of the resistance probe at multiple different moments, and calculates the resistance ratio according to the differential voltage value, and obtains the remaining thickness of the resistance probe test piece at multiple moments according to the resistance ratio at multiple moments; and then differentiates the remaining thickness of the test piece to obtain the corrosion rate. The method of this example obtains the differential voltage value between the test piece and the reference piece, so that the resistance ratio obtained later is more accurate, and the corrosion remaining thickness and corrosion rate obtained later according to the accurate resistance ratio are more accurate. The method of this example improves the accuracy of the monitoring results.

[0167] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the invention disclosed herein. The present application is intended to cover any modification, use or adaptation of the present application, which follows the general principles of the present application and includes common knowledge or customary techniques in the art that are not disclosed in the present application. The specification and examples are intended to be exemplary only.

[0168] It should be understood that the present application is not limited to the exact construction that has been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof.

[0169] Finally, it should be noted that those skilled in the art will readily conceive of other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variation, use or adaptation of the present invention, which follows the general principles of the present invention and includes common knowledge or conventional techniques in the art not disclosed by the present invention, is not limited to the precise structure described above and shown in the drawings, and may be modified and changed in various ways without departing from the scope thereof.

Claims

1. A downhole corrosion monitoring device, characterized in that: The downhole corrosion monitoring device includes a resistance probe assembly, and the resistance probe assembly includes at least one resistance probe; The resistance probe comprises a test piece and a reference piece arranged in parallel; an insulating material is filled between the test piece and the reference piece to form a gap-free bonding structure, and the test piece is located outside the reference piece; wherein the insulating material is a 0.1 mm mica sheet; One end of the test piece and the reference piece are extended and connected to form an integral structure, the other end of the test piece is connected to a first measurement terminal, and the other end of the reference piece is connected to a second measurement terminal; The resistance probe assembly comprises: an assembly body, and a first resistance probe and a second resistance probe located in the assembly body; the first resistance probe and the second resistance probe are used for corrosion monitoring inside and outside the oil pipe respectively; The component body has a first surface and a second surface facing each other; the first surface is provided with a first opening to expose the test piece of the first resistance probe through the first opening; the second surface is provided with a second opening to expose the test piece of the second resistance probe through the second opening; The first surface protrudes from the main surface of the component body, and the main surface of the component body is provided with a sealing structure whose outline surrounds the area of ​​the second surface; the sealing structure matches the oil pipe opening on the side wall of the oil pipe.

2. The device according to claim 1, characterized in that The resistance probe assembly further includes: a first conductivity probe and a second conductivity probe located in the assembly body; the first conductivity probe and the second conductivity probe are used for conductivity monitoring inside and outside the oil pipe, respectively; The first surface is also provided with a first through hole to expose the electrode of the first conductivity probe through the first through hole; the second surface is also provided with a second through hole to expose the electrode of the second conductivity probe through the second opening.

3. The device according to claim 2, characterized in that The downhole corrosion monitoring device further includes: a circuit sealing assembly and a cable; the circuit sealing assembly includes a housing and a PCB circuit board and a wire located in the housing; One end of the housing of the circuit sealing assembly is used to be sealed and connected to the assembly body of the resistance probe assembly through threads and a first sealing structure; One end of the cable is electrically connected to the PCB circuit board, and the other end of the cable extends outward through a wire outlet at the other end of the housing of the circuit sealing assembly, and the wire outlet and the cable are sealed by a second sealing structure; An aviation plug is provided at one end of the component body of the resistance probe assembly, and the PCB circuit board has an aviation plug interface corresponding to the aviation plug. When the component body of the resistance probe assembly is connected to the circuit sealing assembly, the PCB circuit board is electrically connected to the resistance probe assembly through the aviation plug interface and the aviation plug.

4. The device according to claim 3, characterized in that The PCB circuit board is integrated with a single-chip microcomputer, a bidirectional constant current source circuit and a multi-channel A / D converter; When the PCB circuit board is electrically connected to the resistance probe assembly, the bidirectional constant current source circuit is electrically connected to the first measurement terminal of the first resistance probe and the second measurement terminal of the second resistance probe, and is used to provide a forward driving current and a reverse driving current to the resistance probe to generate a differential voltage between the test piece and the reference piece; The input end of the multi-channel A / D converter is electrically connected to the first measurement terminal and the second measurement terminal, the output end of the multi-channel A / D converter is connected to the single-chip microcomputer, and the multi-channel A / D converter is used to sample the differential voltage between the test piece and the reference piece; The single chip microcomputer is electrically connected to the multi-channel A / D converter, and is used to obtain the resistance ratio of the test piece and the reference piece according to the differential voltage between the reference piece and the test piece, and calculate the corrosion rate data inside and outside the oil pipe and the remaining thickness data of the test piece according to the resistance ratio.

5. The device according to claim 4, characterized in that The bidirectional constant current source circuit comprises: a current source circuit, a first NMOS tube, a second NMOS tube, a third NMOS tube, and a fourth NMOS tube; One end of the first NMOS tube and the second NMOS tube is connected to the output end of the current source circuit, and the other end of the first NMOS tube is connected to one end of the third NMOS tube as the first output end of the bidirectional constant current source circuit; the other end of the third NMOS tube is grounded; The other end of the second NMOS tube is connected to one end of the fourth NMOS tube as the second output end of the bidirectional constant current source circuit; the other end of the fourth NMOS tube is grounded; The control ends of the first NMOS tube, the second NMOS tube, the third NMOS tube and the fourth NMOS tube are connected to the single-chip microcomputer; the single-chip microcomputer is used to control the first NMOS tube and the fourth NMOS tube to be turned on, or to control the second NMOS tube and the third NMOS tube to be turned on, so as to output a forward driving current or a reverse driving current.

6. The device according to claim 5, characterized in that The current source circuit comprises: a first operational amplifier, a triode and a current sampling module; The second end of the triode receives an excitation power supply signal, the third end of the triode is connected to one end of the first NMOS transistor and the second NMOS transistor as the output end of the current source circuit, and the first end of the triode is connected to the output end of the first operational amplifier; The current sampling module is used to sample the current output current of the current source circuit and output the sampled current; the first operational amplifier receives a reference signal and is connected to the current sampling module, and is used to output a drive signal to the first end of the transistor according to the output current of the current source circuit and the reference signal to perform feedback regulation.

7. The device according to claim 6, characterized in that The current sampling module comprises: a second operational amplifier and a sampling resistor; One end of the sampling resistor is connected to the second end of the transistor and the second operational amplifier, and the other end of the sampling resistor is connected to one end of the first NMOS tube, one end of the second NMOS tube, and the second operational amplifier; the output end of the second operational amplifier is connected to the first operational amplifier for outputting the sampling current.

8. The device according to claim 4, characterized in that The PCB circuit board also includes: a conductivity collection circuit; The conductivity acquisition circuit is connected to the first conductivity probe and the second conductivity probe, and is used to output the power distribution ratio of the first conductivity probe and the voltage distribution ratio of the second conductivity probe; The single chip microcomputer is connected to the conductivity acquisition circuit, and is also used to obtain the impedance values ​​of the first conductivity probe and the second conductivity probe according to the voltage division ratio of the first conductivity probe and the voltage division ratio of the second conductivity probe, and output the conductivity data inside and outside the oil pipe according to the impedance values.

9. The device according to claim 8, characterized in that The conductivity acquisition circuit includes: an analog switch, a pulse signal generator, a first voltage follower, a second voltage follower, a first voltage divider resistor, and a second voltage divider resistor; The input end of the analog switch is connected to the first conductivity probe and the second conductivity probe respectively, and the analog switch is used to output the signals output by the first conductivity probe and the second conductivity probe in a time-sharing manner; the pulse signal generator is used to provide a pulse modulation signal; One end of the first voltage-dividing resistor is connected to the pulse signal generator and the input end of the first voltage follower; the other end of the first voltage-dividing resistor is connected to the output end of the analog switch, one end of the second voltage-dividing resistor, and the input end of the second voltage follower, and the other end of the second voltage-dividing resistor is grounded; The output end of the first voltage follower is used to output a first follower signal corresponding to the pulse modulation signal; the output end of the second voltage follower is used to output a second follower signal corresponding to the voltage signal collected by the first conductivity probe or the second conductivity probe; the first follower signal and the second follower signal are used to calculate the conductivity inside or outside the oil pipe.

10. The device according to claim 4, characterized in that The first measurement terminal includes a first port and a second port, and the second measurement terminal includes a third port and a fourth port; the fourth port of the first resistance probe is electrically connected to the second port of the second resistance probe; The multi-channel A / D converter includes: multiple ADC acquisition circuits; the multiple ADC acquisition circuits include an ADC acquisition circuit corresponding to the first port of the first resistance probe, an ADC acquisition circuit corresponding to the connection port of the first resistance probe, an ADC acquisition circuit corresponding to the third port of the first resistance probe and the first port of the second resistance probe, an ADC acquisition circuit corresponding to the third port of the second resistance probe, an ADC acquisition circuit corresponding to the connection port of the second resistance probe, an ADC acquisition circuit corresponding to the first conductivity probe, and an ADC acquisition circuit corresponding to the second conductivity probe.

11. The device according to claim 10, characterized in that The ADC acquisition circuit includes a filter circuit, a first voltage stabilizing diode, and a second voltage stabilizing diode; The input end of the filter circuit is connected to a port corresponding to the ADC acquisition circuit, and the filter circuit is used to filter the signal at the port; The cathode of the first voltage zener diode receives a constant voltage signal, the anode of the second voltage zener diode is grounded, and the output end of the filter circuit is connected to the anode of the first voltage zener diode and the cathode of the second voltage zener diode, so as to output the filtered signal after voltage limiting; the output ends of the multiple ADC acquisition circuits are connected to the corresponding ports of the single-chip microcomputer to input the differential voltage between the reference piece and the test piece of the first resistance probe, the differential voltage between the reference piece and the test piece of the second resistance probe, the voltage divider ratio of the first conductivity probe, and the voltage divider ratio of the second conductivity probe into the single-chip microcomputer.

12. The device according to claim 4, characterized in that The cable includes: a power line and a communication line; One end of the power cord is electrically connected to the PCB circuit board, and the other end of the power cord is used to connect to the wellhead power supply; one end of the communication line is electrically connected to the PCB circuit board, and the other end of the communication line is used to connect to the ground control cabinet, and the communication line is used to transmit the corrosion rate data inside and outside the oil pipe and the remaining thickness data of the test piece to the ground control cabinet.

13. The device according to claim 12, characterized in that The PCB circuit board also includes a communication interface; The communication interface is connected to the single chip microcomputer and the communication line, and is used to transmit the corrosion rate, the remaining thickness of the test piece, and the conductivity data to the ground control cabinet through the communication line.

14. The device according to claim 13, characterized in that The PCB circuit board also includes: a DC step-down converter and a linear voltage-regulated power supply; The DC step-down converter is used to connect one end of the power line to step down the power provided by the wellhead power supply; the linear regulated power supply is connected to the DC step-down converter to stabilize the stepped-down voltage and provide it to the PCB circuit board.

15. The device according to any one of claims 4 to 14, characterized in that: The PCB circuit board also includes a temperature sensor; The output end of the temperature sensor is connected to the single chip microcomputer for monitoring the temperature and transmitting the temperature data to the single chip microcomputer.

16. A downhole corrosion monitoring system, characterized in that: comprising a ground control cabinet and at least one downhole corrosion monitoring device as claimed in any one of claims 1 to 15; The at least one downhole corrosion monitoring device is installed on the side wall of the oil pipe downhole and is connected to the ground control cabinet through a cable in the downhole corrosion monitoring device to send the corrosion rate, remaining thickness of the test piece, conductivity and temperature data to the ground control cabinet.

17. The system according to claim 16, characterized in that The downhole corrosion monitoring device is mounted to the side wall of the oil pipe by means of a clamp and fasteners fixed to the side wall of the oil pipe.

18. The system according to claim 16, characterized in that There are multiple downhole corrosion monitoring devices, and the multiple downhole corrosion monitoring devices are installed on the side walls of the oil pipe at different well depths.

19. A method for monitoring underground corrosion, characterized in that: Applicable to the downhole corrosion monitoring device according to any one of claims 1 to 15; the method comprises: Obtaining the differential voltage between the test piece and the reference piece of the resistance probe at multiple times; According to the differential voltages at the multiple moments, the resistance ratio of the test piece to the reference piece at the multiple moments is obtained; according to the resistance ratio at the multiple moments, the remaining thickness of the test piece at the multiple moments is calculated; The corrosion rate is obtained by differential calculation according to the remaining thickness of the test piece at the multiple moments.

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