Downhole corrosion monitoring device, system and method

Abstract

A downhole corrosion monitoring device (1), system and method. The device comprises a resistance probe assembly (10), the resistance probe assembly (10) comprising at least one resistance probe (110). The resistance probe (110) comprises a test coupon (111) and a reference coupon (112) arranged in parallel, wherein an insulating material is filled between the test coupon (111) and the reference coupon (112) to form a gapless bonded structure; the test coupon (111) is located outside the reference coupon (112); one end of the test coupon (111) and one end of the reference coupon (112) extend and are connected to form an integrated structure; and the other end of the test coupon (111) is connected to a first measurement terminal (113), and the other end of the reference coupon (112) is connected to a second measurement terminal (114). The use of the resistance probe (110) having a parallel bonded structure makes the monitoring results of the resistance probe (110) more accurate, thereby improving the accuracy of the monitoring results of the downhole corrosion monitoring device (1).

Description

Downhole corrosion monitoring device, system and method

[0001] The present application claims priority from the Chinese patent application No. 202411376404.0 filed on September 30, 2024, and entitled "Downhole corrosion monitoring device, system and method", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of oil production engineering, in particular to a downhole corrosion monitoring device, system and method. BACKGROUND

[0003] With the development of oil fields gradually entering the middle and later period, the comprehensive water cut is rising. Using new technologies such as carbon capture, utilization and storage (CCUS) and polymer flooding to improve recovery has become the most important measure to increase production. However, in the process of implementing these measures, corrosion of the downhole tubing will occur, and the corrosion condition needs to be monitored.

[0004] At present, in some downhole tubing corrosion monitoring schemes, the monitoring device is easily disturbed by the downhole oil stains during the detection process, causing the monitoring result to be distorted and leading to inaccurate monitoring results. SUMMARY

[0005] The present application provides a downhole corrosion monitoring device, system and method to improve the accuracy of downhole corrosion monitoring results.

[0006] In a first aspect, the present application provides a downhole corrosion monitoring device, which comprises a resistance probe assembly, the resistance probe assembly comprising at least one resistance probe; the resistance probe comprising a test piece and a reference piece arranged in parallel; the test piece and the reference piece are filled with insulating material to form a gapless fitting structure, and the test piece is located outside the reference piece; one end of the test piece and the reference piece is extended and connected as 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.

[0007] In a possible implementation, 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 respectively used for corrosion monitoring inside and outside the oil pipe; the assembly 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 a body surface of the assembly body, and the body surface of the assembly body is provided with a sealing structure surrounding a region of the second surface; the sealing structure is matched with the oil pipe opening on the oil pipe sidewall.

[0008] In a possible implementation, the resistance probe assembly further comprises: 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; the first surface is further provided with a first through hole to expose an electrode of the first conductivity probe through the first through hole; and the second surface is further provided with a second through hole to expose an electrode of the second conductivity probe through the second opening.

[0009] In a possible implementation, the downhole corrosion monitoring device further comprises: a circuit sealing assembly and a cable; the circuit sealing assembly comprises 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 for sealing connection with the assembly body of the resistance probe assembly through threads and a first sealing structure; one end of the cable is electrically connected with the PCB circuit board, and the other end of the cable extends outward through a wire outlet at the other end of the shell of the circuit sealing assembly, and the wire outlet and the cable are sealed through a second sealing structure; one end of the assembly body of the resistance probe assembly is provided with a jack, and the PCB circuit board has a jack interface corresponding to the jack; when the assembly body of the resistance probe assembly is connected with the circuit sealing assembly, the PCB circuit board is electrically connected with the resistance probe assembly through the jack interface and the jack.

[0010] In a possible implementation, 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 with the resistance probe assembly, the bidirectional constant current source circuit is electrically connected with the first measurement terminal of the first resistance probe and the second measurement terminal of the second resistance probe, for providing 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; an input end of the multi-channel A / D converter is electrically connected to the first measurement terminal and the second measurement terminal, an 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 a resistance ratio of the test piece and the reference piece according to the differential voltage between the test piece and the reference piece, and calculate corrosion rate data inside and outside the oil pipe and residual thickness data of the test piece according to the resistance ratio.

[0011] In a possible implementation, 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 an output end of the current source circuit, the other end of the first NMOS tube is connected to one end of the third NMOS tube as a 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 a second output end of the bidirectional constant current source circuit; the other end of the fourth NMOS tube is grounded; 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; and the single-chip microcomputer is used to control the first NMOS tube and the fourth NMOS tube to be turned on, or control the second NMOS tube and the third NMOS tube to be turned on, to output a forward driving current or a reverse driving current.

[0012] In a possible implementation, the current source circuit comprises: a first operational amplifier, a triode, and a current sampling module; a second end of the triode receives an excitation power supply signal, a third end of the triode is connected to one end of the first NMOS tube and the second NMOS tube as an output end of the current source circuit, and a first end of the triode is connected to an output end of the first operational amplifier; the current sampling module is used to sample a current output by the current source circuit and output a sampling current; the first operational amplifier receives a reference signal and is connected to the current sampling module, and is used to output a driving signal to the first end of the triode according to the output current of the current source circuit and the reference signal, to perform feedback adjustment.

[0013] In a possible implementation, the current sampling module comprises: a second operational amplifier and a sampling resistor; one end of the sampling resistor is connected with the second end of the transistor and the second operational amplifier, and the other end of the sampling resistor is connected with one end of the first NMOS tube, one end of the second NMOS tube and the second operational amplifier; and the output end of the second operational amplifier is connected with the first operational amplifier, and is configured to output the sampling current.

[0014] In a possible implementation, the PCB circuit board further comprises an electrical conductivity acquisition circuit; the electrical conductivity acquisition circuit is connected to the first electrical conductivity probe and the second electrical conductivity probe, and is configured to output the voltage division ratio of the first electrical conductivity probe and the voltage division ratio of the second electrical conductivity probe; the single-chip microcomputer is connected to the electrical conductivity acquisition circuit, and is further configured to obtain impedance values of the first electrical conductivity probe and the second electrical conductivity probe according to the voltage division ratio of the first electrical conductivity probe and the voltage division ratio of the second electrical conductivity probe, and output electrical conductivity data inside and outside the oil pipe according to the impedance values.

[0015] In a possible implementation, the electrical conductivity acquisition circuit comprises: an analog switch, a pulse signal generator, a first voltage follower, a second voltage follower, a first voltage dividing resistor and a second voltage dividing resistor; input ends of the analog switch are connected to the first electrical conductivity probe and the second electrical conductivity probe respectively, and the analog switch is configured to output signals output by the first electrical conductivity probe and the second electrical conductivity probe in time division mode; the pulse signal generator is configured to provide a pulse modulation signal; one end of the first voltage dividing resistor is connected to the pulse signal generator and an input end of the first voltage follower; the other end of the first voltage dividing resistor is connected to an output end of the analog switch, one end of the second voltage dividing resistor and an input end of the second voltage follower, and the other end of the second voltage dividing resistor is grounded; an output end of the first voltage follower is configured to output a first follow-up signal corresponding to the pulse modulation signal; and an output end of the second voltage follower is configured to output a second follow-up signal corresponding to a voltage signal collected by the first electrical conductivity probe or the second electrical conductivity probe; the first follow-up signal and the second follow-up signal are used to calculate the electrical conductivity of the inside of the oil pipe or the outside of the oil pipe.

[0016] In a possible implementation, the first measurement terminal comprises a first port and a second port, and the second measurement terminal comprises a third port and a fourth port; the first port of the first resistance probe and the third port of the second resistance probe are electrically connected; the multi-channel A / D converter comprises: a plurality of ADC acquisition circuits, including 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 electrical conductivity probe and an ADC acquisition circuit corresponding to the second electrical conductivity probe.

[0017] In a possible implementation, the ADC acquisition circuit comprises a filter circuit, a first voltage stabilizing diode, and a second voltage stabilizing diode; an input end of the filter circuit is connected to a corresponding port of the ADC acquisition circuit, and the filter circuit is configured to filter a signal at the port; a negative electrode of the first voltage stabilizing diode receives a constant voltage signal, a positive electrode of the second voltage stabilizing diode is grounded, an output end of the filter circuit is connected to the positive electrode of the first voltage stabilizing diode and the negative electrode of the second voltage stabilizing diode, and the filter circuit is configured to output a voltage-limited signal after filtering and voltage limiting; and output ends of the plurality of ADC acquisition circuits are connected to corresponding ports of the single-chip microcomputer, so as to input, to the single-chip microcomputer, a differential voltage between the reference piece and the test piece of the first resistance probe, a differential voltage between the reference piece and the test piece of the second resistance probe, a voltage division ratio of the first conductivity probe, and a voltage division ratio of the second conductivity probe.

[0018] In a possible implementation, the cable comprises: 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 configured to be connected to a 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 configured to be connected to a ground control cabinet; and the communication line is configured to transmit corrosion rate data and residual thickness data of the test piece inside and outside the oil pipe to the ground control cabinet.

[0019] In a possible implementation, the PCB circuit board further comprises a communication interface; the communication interface is connected to the single-chip microcomputer and the communication line, and is configured to transmit the corrosion rate, the residual thickness of the test piece, and the conductivity data to a transceiver in the ground control cabinet through the cable.

[0020] In a possible implementation, the device further comprises: a DC voltage step-down converter and a linear voltage stabilizer; the DC voltage step-down converter is configured to be connected to one end of the power line, and to step down a power supply provided by the wellhead power supply; and the linear voltage stabilizer is connected to the DC voltage step-down converter, and is configured to stabilize the stepped-down voltage and provide the stabilized voltage to the PCB circuit board.

[0021] In a possible implementation, the PCB circuit board further comprises a temperature sensor; an output end of the temperature sensor is connected to the single-chip microcomputer, and the temperature sensor is configured to monitor a temperature and transmit temperature data to the single-chip microcomputer.

[0022] In a second aspect, the present application provides a downhole corrosion monitoring system, comprising a ground control cabinet and at least one downhole corrosion monitoring device; the at least one downhole corrosion monitoring device is installed on a sidewall of a downhole oil pipe and connected to the ground control cabinet through a cable, and is configured to send corrosion rate data, residual thickness data of a test piece, conductivity data, and temperature data to the ground control cabinet.

[0023] In a possible implementation, the downhole corrosion monitoring device is installed on the sidewall of the oil pipe through a clamp fixture and a fastener fixed on the sidewall of the oil pipe. In a possible implementation, the downhole corrosion monitoring device is installed on the sidewall of the oil pipe through a clamp fixture and a fastener fixed on the sidewall of the oil pipe.

[0024] In a possible implementation, the number of downhole corrosion monitoring devices is multiple, and the multiple downhole corrosion monitoring devices are installed at the tubing sidewalls at different well depths.

[0025] In a third aspect, the application provides a downhole corrosion monitoring method, which comprises: obtaining the differential voltage between the test piece and the reference piece of the resistance probe at multiple time points; obtaining the resistance ratio of the test piece and the reference piece at the multiple time points according to the differential voltage at the multiple time points; calculating the residual thickness of the test piece at the multiple time points according to the resistance ratio at the multiple time points; and performing differential calculation to obtain the corrosion rate according to the residual thickness of the test piece at the multiple time points.

[0026] The downhole corrosion monitoring device, system and method of the application, the test piece and the reference piece of the resistance probe in the resistance probe assembly are filled with insulating material and designed as a structure of no-gap flat plate fitting; one end of the test piece and the reference piece is extended and connected, and the other end of the test piece and the reference piece is respectively connected to the measurement terminal; the resistance probe assembly contains two resistance probes and two conductivity probes for simultaneous monitoring inside and outside the tubing; the two resistance probes and the two conductivity probes are respectively connected to the PCB circuit board in the downhole corrosion monitoring device of the embodiment, and the PCB circuit board is provided with a power supply circuit, a collection circuit and a single-chip microcomputer, which are used for collecting and processing the signals of the resistance probe assembly, and finally obtaining the monitoring data of the downhole corrosion monitoring device to reflect the corrosion conditions inside and outside the tubing in the oil well. The device of the embodiment realizes accurate monitoring of the corrosion of the tubing by designing the structure of the resistance probe probe assembly with no-gap flat plate fitting and the precise circuit assembly, and by using the cable to supply power to the precise circuit assembly and transmit the monitoring data to the ground control cabinet on the well; accurate monitoring results are obtained, and the monitoring data can be transmitted in real time. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate one embodiment consistent with the application and, together with the description, serve to explain the principles of the application.

[0028] FIG. 1 is a structural schematic diagram of a resistance probe of the downhole corrosion monitoring device of the application;

[0029] FIG. 2 is a structural schematic diagram of a resistance probe assembly in the downhole corrosion monitoring device of the application;

[0030] FIG. 3 is a partial structural schematic diagram one of the resistance probe assembly of the application;

[0031] FIG. 4 is a partial structural schematic diagram two of the resistance probe assembly of the application;

[0032] FIG. 5 is a structural schematic diagram of the downhole corrosion monitoring device of the application;

[0033] Figure 6 is a schematic diagram of the connection between the downhole corrosion monitoring device and the oil pipe of the present application;

[0034] Figure 7 is a schematic diagram of the structure of the bidirectional constant current source circuit of the present application;

[0035] Figure 8 is a schematic diagram of the structure of the conductivity acquisition circuit of the present application;

[0036] Figure 9 is a schematic diagram of the port of the resistance probe of the present application;

[0037] Figure 10 is a schematic diagram of the structure of the ADC acquisition circuit of the present application;

[0038] Figure 11 is a curve of the corrosion allowance of the test piece of the resistance probe of the present application over time;

[0039] Figure 12 is a curve of the corrosion rate of the test piece of the resistance probe of the present application over time;

[0040] Figure 13 is a curve of the conductivity of the present application over time;

[0041] Figure 14 is a schematic diagram of the structure of the downhole corrosion monitoring system of the present application;

[0042] Figure 15 is a schematic diagram of the flow of the downhole corrosion monitoring method of the present application.

[0043] The specific embodiments of the present application have been shown in the above-mentioned drawings, and will be described in more detail hereinafter. These drawings and written descriptions are not intended to limit the scope of the concept 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.

[0044] Explanation of Reference Signs: 1: downhole corrosion monitoring device; 10: resistance probe assembly; 20: circuit sealing assembly; 30: cable; 40: tubing; 100: assembly main body; 110: first resistance probe; 120: second resistance probe; 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; 130: first conductivity probe; 140: second conductivity probe; 150: navigation plug; 200: circuit sealing assembly housing; 210: PCB circuit board; 220: wire; 230: first sealing structure; 240: second sealing structure; 300: current source circuit; 310: first NMOS tube; 320: second NMOS tube; 330: third NMOS tube; 340: fourth NMOS tube; 301: first operational amplifier; 302: transistor; 303: current sampling module; 3031: second operational amplifier; 3032: sampling resistor; 400: analog switch; 410: pulse signal generator; 420: first voltage follower; 430: second voltage follower; 440: first voltage dividing resistor; 450: second voltage dividing resistor; 401: clamp fixture; 402: fastener; 403: wellhead power supply; 404: surface control cabinet; 405: tubing; 500: filter circuit; 510: first zener diode; 520: second zener diode. DETAILED DESCRIPTION

[0045] The exemplary embodiments will be described in detail herein with reference to the attached drawings. The description of the exemplary embodiments is intended to apply to various alternative embodiments as well. The following description is not intended to be exhaustive or to limit the present application to the precise form disclosed. Various modifications and variations are possible in light of the above teachings. It is envisioned that implementations of the present application can provide advantages over conventional implementations, and / or that the present application can provide the conventional implementations with one or more advantages.

[0046] It should be noted that the brief description of the terms in the present 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 in accordance with their ordinary and general meanings. In the present application, the terms "include" and "have" in the specification and claims and the above-mentioned drawings are intended to cover but not exclusively include, for example, a product or device including a series of components does not have to be limited to those components listed clearly, but can include other components not listed clearly or inherent to these products or devices. The term "module" used in the present application refers to any known or later developed hardware, software, firmware, artificial intelligence, fuzzy logic, or a combination of hardware or / and software code capable of performing functions related to the element.

[0047] As the oilfield development gradually enters the middle and late stages, the comprehensive water cut continues to rise. The use of new technologies such as CCUS and polymer flooding to improve recovery has become the most important stimulation measure. However, during the implementation of these measures, corrosion of the downhole tubing may occur, and the corrosion condition needs to be monitored.

[0048] Currently, some downhole tubing corrosion monitoring schemes are susceptible to interference from the complex downhole environment during the monitoring process, resulting in inaccurate corrosion monitoring results. Therefore, the problem to be solved at present is how to improve the accuracy of the corrosion monitoring results.

[0049] The technical content provided by the present application aims to solve the above technical problems of the related art. In the downhole corrosion monitoring device, system and method of the present 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 structure of a gapless flat plate fit; one end of the test piece and the reference piece is extended and connected, and the other end of the test piece and the reference piece is respectively connected to a measurement terminal; the resistance probe assembly contains two resistance probes and two conductivity probes for simultaneous monitoring of the inside and outside of the tubing; the two resistance probes and the two conductivity probes are respectively connected to a PCB circuit board in the downhole corrosion monitoring device of the present embodiment, and the PCB circuit board is provided with a power supply circuit, a collection circuit and a single-chip microcomputer, for collecting and processing signals of the resistance probe assembly, and finally obtaining monitoring data of the downhole corrosion monitoring device to reflect the corrosion condition of the inside and outside of the tubing in the oil well. The scheme of the present application designs a resistance probe probe assembly structure of a gapless flat plate fit and a precise circuit assembly, and powers the precise circuit assembly through a cable and transmits the monitoring data to a ground control cabinet on the well; accurate monitoring of the tubing corrosion is achieved, the monitoring result is accurate, and the monitoring data can be transmitted in real time.

[0050] The technical solutions of the present application and the technical solutions of the present application are described in detail below with specific examples. The following specific examples can be combined with each other, and the same or similar concepts or processes may not be described again in some examples. In the description of the present application, unless otherwise explicitly specified and limited, each term should be understood broadly in the art. The embodiments of the present application will be described below with reference to the accompanying drawings.

[0051] Embodiment one

[0052] Figure 1 is a structural schematic diagram of the resistance probe of the downhole corrosion monitoring device of the present application; as shown in Figure 1, the resistance probe includes a test sheet 111 and a reference sheet 112 arranged in parallel; the test sheet 111 and the reference sheet 112 are filled with insulating material to form a gapless fitting structure, and the test sheet 111 is located outside the reference sheet 112;

[0053] One end of the test sheet 111 and the reference sheet 112 is extended and connected as an integral structure, the other end of the test sheet 111 is connected to a first measurement terminal 113, and the other end of the reference sheet 112 is connected to a second measurement terminal 114.

[0054] Specifically, the downhole corrosion monitoring device 1 comprises a resistance probe assembly 10; the resistance probe assembly 10 is used for monitoring the corrosion condition in the oil well, and the resistance probe assembly 10 comprises 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 lamination structure; the resistance probe is designed to have a gapless lamination structure, which can prevent the fluid in the oil well from penetrating into the interior of the resistance probe and affecting the monitoring result; in addition, the parallel lamination 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 the gap, thereby avoiding the influence of temperature on the resistance value of the probe and further improving the accuracy of the measurement result. In one example, 0.1mm mica sheet is filled between the test piece 111 and the reference piece 112. In actual application, the corrosion thinning amount of the test piece 111 can be calculated by testing the small resistance increment of the test piece 111, and thus the corrosion condition at the oil well can be obtained. The resistance probe is suitable for corrosion monitoring of oil, water and gas multiphase systems, and the type is not limited in this example. Even in the high temperature and high pressure environment downhole, the resolution of the resistance probe can reach 1 / 5000 of the service life of the sensitive element. The resistance probe measurement interval can be as short as 1h / time, and the resistance probe made of the same material as the oil pipe is used for synchronous online corrosion monitoring of the inner and outer walls of the oil pipe downhole, which helps to timely grasp the average corrosion rate of the downhole equipment. One end of the test piece 111 and the reference piece 112 is extended and connected, the other end of the test piece 111 is connected with the first measurement terminal 113, and the other end of the reference piece 112 is connected with the second measurement terminal 114, which is used for subsequent corrosion data monitoring. The test piece and the reference piece of the resistance probe in this example are arranged in a parallel gapless lamination structure, which ensures that the temperatures of the test piece and the reference piece are 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.

[0055] Fig. 2 is a structural schematic diagram of the resistance probe assembly in the downhole corrosion monitoring device of the present application, Fig. 3 is a partial structural schematic diagram one of the resistance probe assembly of the present application, and Fig. 4 is a partial structural schematic diagram two of the resistance probe assembly of the present application;

[0056] As shown in Figs. 2 to 4, the resistance probe assembly 10 comprises: an assembly body 100; a first resistance probe 110, a second resistance probe 120, a first electrical conductivity probe 130, a second electrical conductivity probe 140, and a plug 150. The first resistance probe 110 and the second resistance probe 120 each comprise a test piece 111, a reference piece 112, a first measurement terminal 113, and a second measurement terminal 114.

[0057] The resistance probe assembly 10 comprises: 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 respectively used for corrosion monitoring inside and outside the oil pipe;

[0058] The assembly body 100 has a first surface and a second surface opposite to each other; the first surface is provided with a first opening to expose a test piece 111 of the first resistance probe 110 through the first opening; and the second surface is provided with a second opening to expose a test piece 111 of the second resistance probe 120 through the second opening;

[0059] The first surface protrudes from a body surface of the assembly body 100, and the body surface of the assembly body 100 is provided with a sealing structure surrounding a region of the second surface; the sealing structure is matched with an oil pipe opening on the side wall of the oil pipe.

[0060] Specifically, the resistance probe assembly 10 comprises: 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 respectively used for corrosion monitoring inside and outside the oil pipe.

[0061] In one example, there is an opening matched with the probe assembly on the oil pipe, the first resistance probe 110 is fixed on the side surface of the oil pipe by being squeezed into the slot hole on the oil pipe and then being fixed by the probe installation fastener 402 with O-ring sealing, and the first resistance probe 110 is squeezed into the inside of the oil pipe for monitoring the corrosion condition inside the oil pipe. Specifically, the first resistance probe 110 inside the oil pipe does not exceed the inner wall plane of the oil pipe, and does not affect the movement of the sucker rod inside the oil pipe. The height dimension of the downhole corrosion monitoring device outside the oil pipe is kept within 20 mm as a whole, which meets the size requirement of the limited annular space, and can avoid the problem of failure caused by excessive friction and wear during the device is lowered into the well. The second resistance probe 120 is installed in the space between the oil pipe and the oil jacket 405, and is mainly used for monitoring the corrosion rate outside the oil pipe. The downhole corrosion monitoring device in this example can reach the following technical indexes: conductivity index: conductivity test frequency: 1 kHz-10 Hz, square wave excitation amplitude: 10 mV-1000 mV; conductivity test range: 0.1 mS.cm-1-100 mS.cm-1; resistance probe index: corrosion thinning sensitivity: 10 nm, resolution: 1 / 5000, voltage 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 monitor the corrosion conditions inside and outside the oil pipe, so that the monitoring result is more accurate.

[0062] Specifically, the downhole corrosion monitoring device can not only monitor the corrosion rate of the downhole, but also monitor the conductivity of the downhole environment. Accordingly, on the basis of any of the examples, the resistance probe assembly 10 further comprises: 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 respectively used for monitoring the conductivity inside and outside the oil pipe.

[0063] The first surface is also provided with a first through hole for exposing the platinum wire electrode of the first conductivity probe 130; and the second surface is also provided with a second through hole for exposing the platinum wire electrode of the second conductivity probe 140.

[0064] In one example, the platinum wire electrode of the first conductivity probe 130, the second conductivity probe 140 in the resistance probe assembly 10, and the aforementioned first resistance probe 110 and the second resistance probe 120 are integrally casted by polyether ether ketone or polytetrafluoroethylene. The first surface of the resistance probe assembly 10 is also provided with a first through hole, and the first conductivity probe 130 monitors the conductivity inside the oil pipe in the same way by being extruded into the slot hole of the oil pipe and sealed by an O-ring. The second conductivity probe 140 is arranged 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 for monitoring the conductivity of the outer wall of the oil pipe. In this example, the conductivity probe is installed in the resistance probe assembly, which realizes the monitoring of the conductivity in the environment inside and outside the oil pipe in the downhole, and improves the accuracy of the monitoring results.

[0065] Further, the downhole corrosion monitoring device further comprises other test units in addition to the resistance probe assembly 10. Accordingly, as an example, FIG. 5 is a structural schematic diagram of the downhole corrosion monitoring device of the present application. As shown in FIG. 5, the downhole corrosion monitoring device further comprises: a circuit sealing assembly 20 and a cable 30; the circuit sealing assembly 20 comprises a housing 200 and a PCB circuit board 210 and a wire 220 located in the housing;

[0066] One end of the circuit sealing assembly housing 200 is used for sealing and connecting with the assembly body 100 of the resistance probe assembly 10 through threads and a first sealing structure 230;

[0067] One end of the cable 30 is electrically connected with the PCB circuit 210, and the other end of the cable 30 extends outwardly through a wire outlet at the other end of the housing of the circuit sealing assembly 20, and the wire outlet and the cable 30 are sealed by a second sealing structure 240;

[0068] One end of the assembly main body 100 of the resistance probe assembly 10 is provided with a jack 150, and the PCB circuit board 210 has a jack 150 interface corresponding to the jack 150. When the assembly main body 100 of the resistance probe assembly 10 is connected with the circuit sealing assembly 20, the PCB circuit board 210 is electrically connected with the resistance probe assembly 10 through the jack interface and the jack 150.

[0069] In this example, the metal shell of the circuit sealing assembly 20 is sealingly connected with the resistance probe assembly 10 through threads and the first sealing structure 230, and the other end of the circuit sealing assembly shell 200 is sealingly connected with the cable 30 through the second sealing structure 240. The port of the resistance probe assembly 10 is provided with a nine-core jack, and the nine-core jack is electrically connected with the PCB circuit board 210 through the wire 220 inside the circuit sealing assembly 20. The resistance probe assembly 10 is connected with the jack 150 pin through high-temperature wire welding, and is integrally casted by polyether ether ketone or polytetrafluoroethylene.

[0070] Figure 6 is a schematic view of the connection between the downhole corrosion monitoring device and the oil pipe of the present application; as shown in Figure 6, the downhole corrosion monitoring device 1 is fixed on the outside of the oil pipe 40 through the clamp 401 and the fastener 402. It is ensured that the downhole corrosion monitoring device 1 can be firmly fixed on the oil pipe 40.

[0071] In this example, the sealing structure is used for connection, so that the entire downhole corrosion monitoring device 1 is in a sealed environment, improving the accuracy of the monitoring results and ensuring the stability of the monitoring device in the high temperature and high pressure environment in the well.

[0072] Further, the PCB circuit board 210 is provided with a precise circuit structure for collecting data on the downhole corrosion; correspondingly, on the basis of 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;

[0073] When the PCB circuit board 210 is electrically connected with the resistance probe assembly 10, the bidirectional constant current source circuit is electrically connected with the first measurement terminal 113 of the first resistance probe 110 and the second measurement terminal 114 of the second resistance probe 120, for providing forward driving current and reverse driving current to the resistance probe, so as to generate a differential voltage between the test piece 111 and the reference piece 112;

[0074] 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, and the output end of the multi-channel A / D converter is connected to the single-chip microcomputer. The multi-channel A / D converter is used for sampling the differential voltage between the test piece 111 and the reference piece 112;

[0075] The single-chip microcomputer is electrically connected with the multi-channel A / D converter, and is used for obtaining the resistance ratio of the test piece 111 and the reference piece 112 according to the differential voltage between the test piece 111 and the reference piece 112, and calculating the corrosion rate data in and outside the oil pipe and the residual thickness data of the test piece 111 according to the resistance ratio.

[0076] In one example, the PCB circuit board 210 is provided with a single-chip microcomputer, a data storage, a communication interface, a multi-channel A / D converter, a pulse signal generator 410, a temperature sensor and a linear voltage stabilizer; the highest working temperature of the PCB circuit board 210 is 150℃. The single-chip microcomputer is connected with the data storage, the communication interface, the multi-channel A / D converter, the pulse signal generator 410, the temperature sensor and the linear voltage stabilizer respectively. In this example, the data storage is a double-channel data storage, the storage capacity of each chip is 256KByte, and the data storage can resist 150℃ high temperature. Two data storages simultaneously store the collected data such as time, corrosion rate and conductivity, and simultaneously perform double storage chip backup, thereby improving the safety of the data. The PCB circuit board 210 is provided with an RS485 chip, which is used together with an RS485 transceiver in a control cabinet at the wellhead for instruction control and measurement data transmission, uses a communication rate of 1200bps, and can meet the remote communication of 3KM underground. The linear voltage stabilizer supplies power to all circuits. In one example, a bidirectional constant current source circuit is 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 through the wire 220, and provides forward and reverse driving current for the resistance probe. The multi-channel A / D converter is used for synchronously sampling the differential voltage between the test piece 111 and the reference piece 112 of the resistance probe. The output end of the A / D converter is connected with the single-chip microcomputer 211, 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 residual thickness of the test piece 111 according to the resistance ratio. In one example, the structure of the resistance probe is a parallel plate structure, and for the probe with this structure, the resistance ratio is:

[0077] L x , w x , d x are the length, width and thickness of the test piece 111, L f , w f , d f are the length, width and thickness of the reference piece 112; R x is the resistance of the test piece 111, and R fThe resistance of the reference sheet 112. Since the length and width of the reference sheet 112 in the resistance probe are equal, they do not change throughout the measurement process, and the length of the reference sheet 112 and the test sheet 111 also does not change over time, so there is:

[0078] wherein,

[0079] The remaining thickness of the test sheet 111 at any time t is:

[0080] The corrosion rate at time t is:

[0081] wherein, is the corrosion rate, A is a constant, represents the remaining thickness of the test sheet 111 at time t, represents the resistance ratio at time t. In this example, by designing a precise PCB circuit board to receive and calculate corrosion data in the downhole environment, the data monitored by the downhole corrosion monitoring device is more accurate, and the subsequent transmission of these data to the ground system can make the ground monitoring system obtain more real monitoring data, which is convenient for subsequent prevention of oil pipe corrosion measures based on the monitoring results.

[0082] Further, in order to provide a constant current in the forward and reverse directions, 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.

[0083] One end of the first NMOS tube 310 and the second NMOS tube 320 is connected to the output end of the current source circuit 300, the other end of the first NMOS tube 310 is connected to one end of the third NMOS tube 330, which is the first output end of the bidirectional constant current source circuit; the other end of the third NMOS tube 330 is grounded.

[0084] The other end of the second NMOS tube 320 is connected to one end of the fourth NMOS tube 340, which is the second output end of the bidirectional constant current source circuit; the other end of the fourth NMOS tube 340 is grounded.

[0085] 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 a single-chip microcomputer; the single-chip microcomputer is used to control the first NMOS tube 310 and the fourth NMOS tube 340 to be conductive, or to control the second NMOS tube 320 and the third NMOS tube 330 to be conductive, so as to output a forward driving current or a reverse driving current.

[0086] In one example, the bidirectional constant current source circuit includes a current source circuit 300 for outputting constant current, four identical NMOS tubes for realizing the forward and reverse conduction of the circuit. A 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, 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 in the forward direction. 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, the second NMOS tube 320 and the third NMOS tube 330 are turned on, the first NMOS tube 310 and the fourth NMOS 340 are turned off, and the current output by the current source circuit 300 flows in the reverse direction. In this example, four NMOS tubes are used to realize the forward and reverse flow of current, making the voltage values of the test piece and the reference piece of the resistance probe collected subsequently more accurate, eliminating the influence of temperature inconsistency on the resistance of the resistance probe when the current flows in one direction, and making the measurement result more accurate.

[0087] In order to make the circuit output 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.

[0088] 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 tube 310 and the second NMOS 320 tube 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.

[0089] The current sampling module 303 is used to sample the current output by the current source circuit 300 and output a sampling 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 driving 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 adjustment.

[0090] Specifically, in order to output constant current, the first operational amplifier 301, the triode 302, and the current sampling module 303 are adopted to form the current source circuit 300. First, the first end of the triode 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 accurate constant current according to the reference signal. The second end of the triode 302 is connected to the first NMOS tube 310 and the second NMOS tube 320, and the third end of the triode 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 output by the current source circuit 300 and output the sampling current. In this example, the constant current output by the current source circuit is input into the subsequent voltage acquisition circuit, so that the subsequent acquisition result is more accurate, and the accuracy of the corrosion monitoring result is improved.

[0091] Specifically, the current sampling module 303 is used to sample the voltage across the sampling resistor. As an example, the current sampling module 303 includes a second operational amplifier 3031 and a sampling resistor 3032.

[0092] One end of the sampling resistor 3032 is connected to the second end of the triode 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.

[0093] In one example, one end of the sampling resistor 3032 in the current sampling module 303 is connected to the second end of the triode 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, and the second operational amplifier 3031 is used to output the sampling current collected by the current sampling module 303. In this example, the sampling current output by the current sampling module is used to feedback adjust the output end of the first operational amplifier, so as to realize accurate constant current output and improve the accuracy of the subsequent acquisition result.

[0094] In combination with the above three examples, FIG. 7 is a structural schematic diagram of the bidirectional constant current source circuit of the present application; as shown in FIG. 7, the bidirectional constant current source circuit comprises: a current source circuit 300, a first NMOS transistor 310, a second NMOS transistor 320, a third NMOS transistor 330, and a fourth NMOS transistor 340; wherein the current source circuit 300 comprises: a first operational amplifier 301, a triode 302, and a current sampling module 303; the current sampling module 303 further comprises: a second operational amplifier 3031 and a sampling resistor 3032;

[0095] Firstly, 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, the third end of the triode 302 is connected with 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 with one end of the first NMOS transistor 310, one end of the second NMOS transistor 320, and the second operational amplifier 3031; the output end of the second operational amplifier 3031 is connected with the first operational amplifier 301, for outputting a sampling current;

[0096] One end of the first NMOS transistor 310 and one end of the second NMOS transistor 320 are connected with the output end of the current source circuit 300, the other end of the first NMOS transistor 310 is connected with 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 transistor 320 is connected with one end of the fourth NMOS transistor 340, as the second output end of the bidirectional constant current source circuit; the other end of the fourth NMOS transistor 340 is grounded;

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

[0099] Specifically, the conductivity probe in the resistance probe assembly 10 is used for collecting the conductivity in the environment inside and outside the downhole oil pipe, and accordingly, as an example, the PCB circuit board 210 further comprises: a conductivity collection circuit;

[0100] The conductivity collection circuit is connected with the first conductivity probe 130 and the second conductivity probe 140, and is used for outputting the voltage division ratio of the first conductivity probe 130 and the voltage division ratio of the second conductivity probe 140;

[0101] The single-chip microcomputer is connected with the conductivity acquisition circuit, and is further used for obtaining impedance values of the first conductivity probe 130 and the second conductivity probe 140 according to a voltage division ratio of the first conductivity probe 130 and a voltage division ratio of the second conductivity probe 140, and outputting conductivity data in and out of the oil pipe according to the impedance values.

[0102] In one example, the first conductivity probe 130 and the second conductivity probe 140 are respectively connected to the conductivity acquisition circuit, and the conductivity acquisition circuit outputs the acquired voltage division ratios of the first conductivity probe 130 and the second conductivity probe 140; subsequently, the conductivity acquisition circuit is connected with the single-chip microcomputer, and the voltage division ratios of the first conductivity probe 130 and the second conductivity probe 140 acquired by the conductivity acquisition circuit are input to the single-chip microcomputer; the single-chip microcomputer calculates corresponding impedance values according to the voltage division ratios of the first conductivity probe 130 and the second conductivity probe 140, and calculates conductivity data in and out of the oil pipe according to the impedance values.

[0103] The conductivity probe in the example is a platinum wire electrode, and when the conductivity is tested, 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, and the voltage at one end of the conductivity probe is acquired; 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 represented as:

[0104] ρ=Z 500 ×γ

[0105] Wherein, γ represents the electrode coefficient, Z 500 represents the environmental impedance when measured at 500 Hz;

[0106] γ=A / L

[0107] The conductivity formula is represented as:

[0108] σ=1 / ρ

[0109] Wherein, σ represents the conductivity, and ρ represents the resistivity.

[0110] In the example, the conductivity probe is connected to the conductivity acquisition circuit, and the conductivity in and out of the oil pipe is acquired; the value of the conductivity can reflect the concentration of carbon dioxide in the downhole environment, which is beneficial for the workers on the well to judge the concentration of carbon dioxide in the downhole according to the value of the conductivity, and to further judge the corrosion condition and take corresponding measures; and the accuracy of the corrosion monitoring result is improved.

[0111] In order to realize accurate collection of the environmental conductivity, a conductivity collection circuit is designed; Fig. 8 is a structural schematic diagram of the conductivity collection circuit of the application; as shown in Fig. 8, the conductivity collection circuit comprises: 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;

[0112] The input ends of the analog switch 400 are connected to the first conductivity probe 130 and the second conductivity probe 140 respectively, and the analog switch 400 is used for outputting signals output by the first conductivity probe 130 and the second conductivity probe 140 in time; the pulse signal generator 410 is used for providing a pulse modulation signal;

[0113] 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;

[0114] The output end of the first voltage follower 420 is used for outputting a first following signal corresponding to the pulse modulation signal; the output end of the second voltage follower 430 is used for outputting a second following signal corresponding to a voltage signal collected by the first conductivity probe 130 or the second conductivity probe 140; the first following signal and the second following signal are used for calculating the conductivity of the inside or the outside of the oil pipe.

[0115] In one example, the conductivity acquisition circuit includes an analog switch 400, which is used to select the conductivity measurement inside or outside the tubing in time; when the analog switch 400 is connected to the first conductivity probe 130, the environmental conductivity value inside the tubing is tested; when the switch is connected to the second conductivity probe 140, the conductivity value in the environment outside the tubing is tested; the analog switch 400 can realize the time-sharing measurement of the conductivity. One end of the first voltage dividing resistor 440 in the conductivity acquisition circuit is connected with 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 following signal corresponding to the pulse modulation signal, and the first voltage following signal reflects the actual value of the pulse modulation signal. The other end of the first voltage dividing resistor 440 is connected with 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 following signal corresponding to the voltage signal of the first conductivity probe 130 or the second conductivity probe 140. The first following signal and the second voltage following signal reflect the voltage value of the pulse modulator and the voltage value of the two conductivity probes, and according to the following signals, the voltage dividing ratio of the two voltages can be inversely calculated, and then the impedance value of the environment is calculated, and the environmental conductivity value can be calculated according to the calculation formula of the environmental conductivity.

[0116] In the example, the voltage value collected by the conductivity acquisition circuit is processed by the voltage follower to obtain the output following signal before being transmitted to the single-chip microcomputer for conductivity calculation; when combined with the foregoing example, the output end of the voltage follower is connected with the input end of the single-chip microcomputer to receive the following signal for calculating the conductivity value. At this time, the received signal is the voltage following signal, and the voltage following signal represents the voltage signal. In the 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 dividing ratio, and the environmental conductivity value inside or outside the tubing is calculated according to the voltage dividing ratio, so that the collection result is more accurate, and the accuracy of the monitoring result is improved.

[0117] The foregoing obtained voltage signal needs to be collected by a collection circuit to obtain the final corrosion monitoring data. Correspondingly, in combination with any of the foregoing examples, FIG. 9 is a schematic diagram of a port of the resistance probe of the present application; as shown in FIG. 9, 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; the fourth port 1142 of the first resistance probe 110 and the second port 1132 of the second resistance probe 120 are electrically connected; the multi-channel A / D converter includes a plurality of ADC collection circuits; the plurality of ADC collection circuits include an ADC collection circuit corresponding to the first port 1131 of the first resistance probe 110, an ADC collection circuit corresponding to the first resistance probe connection port 115 of the first resistance probe 110, an ADC collection 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 collection circuit corresponding to the third port 1141 of the second resistance probe 120, an ADC collection circuit corresponding to the second resistance probe connection port 116, an ADC collection circuit corresponding to the first conductivity probe 130, and an ADC collection circuit corresponding to the second conductivity probe 140.

[0118] In one example, the connection ports on the test pieces 111 and the reference pieces 112 of the two resistance probes in the resistance probe assembly 10, and the two conductivity probes are respectively connected to a plurality of ADC acquisition circuits of a circuit board; 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 all corresponding and 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 actual application, before the various ports of the resistance probe and the platinum wire electrodes of the conductivity probes are connected to the ADC acquisition circuit, the first port 1131 of the first resistance probe 110 is electrically connected to the third port 1141 of the second resistance probe 120 by welding. Correspondingly, the multi-channel A / D converter includes a plurality of ADC acquisition circuits, each of which is the same, and each of which 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, for collecting the voltage of the ports of the resistance probe and the conductivity probe. Subsequently, the corrosion rate, the corrosion residual thickness, and the value of the conductivity are calculated according to the voltage signal. In this example, by connecting the resistance probe assembly to a plurality of identical ADC acquisition circuits to accurately collect the voltage, the accuracy of the monitoring results is improved.

[0119] The plurality of ADC acquisition circuits are structurally identical, and accordingly, as an example, FIG. 10 is a structural schematic diagram of the ADC acquisition circuit of the present application; as shown in FIG. 10, the ADC acquisition circuit includes a filter circuit 500, a first voltage stabilizing diode 510, and a second voltage stabilizing diode 520;

[0120] 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;

[0121] The negative electrode of the first voltage stabilizing diode 510 receives a constant voltage signal, the positive electrode of the second voltage stabilizing diode 520 is grounded, and the output end of the filter circuit 500 is connected to the positive electrode of the first voltage stabilizing diode 510 and the negative electrode of the second voltage stabilizing diode 520, for limiting and outputting the filtered signal; the output end of the plurality of ADC acquisition circuits is connected to the corresponding port of the single-chip microcomputer, to input the differential voltage between the reference sheet 112 and the test sheet 111 of the first resistance probe 110, the differential voltage between the reference sheet 112 and the test sheet 111 of the second resistance probe 120, the voltage division ratio of the first conductivity probe 130, and the voltage division ratio of the second conductivity probe 140 into the single-chip microcomputer.

[0122] Specifically, each ADC acquisition circuit includes a filter circuit 500 for filtering the voltage signal of the resistance probe and the conductivity probe; in an example, the filter circuit 500 is composed of a resistor and a capacitor, which can remove noise, protect the circuit, and improve the quality of the signal, so that the signal is more stable and reliable. The signal transmitted through the filter circuit 500 is transmitted to the voltage stabilizing diode, and the circuit includes two voltage stabilizing diodes, wherein the negative electrode of the first voltage stabilizing diode 510 receives a constant voltage signal, the positive electrode of the second voltage stabilizing diode 520 is grounded, and the output end of the filter circuit 500 is connected to the positive electrode of the first voltage stabilizing diode 510 and the negative electrode of the second voltage stabilizing diode 520, for limiting and outputting the filtered signal, so that the voltage signal is limited within the range of 0 and the constant voltage signal. The output end of the ADC acquisition circuit is connected to the single-chip microcomputer of the PCB circuit board 210, to input the differential voltage between the reference sheet 112 and the test sheet 111 of the resistance probe and the voltage division ratio of the conductivity probe into the single-chip microcomputer, for subsequent calculation of the corrosion rate, the corrosion residual amount, and the conductivity value.

[0123] In combination with the foregoing example, the present scheme shows the corrosion residual amount and the corrosion rate of the resistance probe test sheet over time; FIG. 11 is a curve of the corrosion residual amount of the resistance probe test sheet over time according to the present application; as shown in FIG. 11, it can be seen that the test sheet of the resistance probe is corroded in the downhole fluid, and the corrosion residual amount decreases linearly over time. FIG. 12 is a curve of the corrosion rate of the resistance probe test sheet over time according to the present application; as shown in FIG. 12, it can be seen that the corrosion rate decreases over time, because the test sheet of the resistance probe is in the downhole fluid, and the corrosion product accumulates on the surface of the test sheet, slowing down the corrosion rate of the probe in the simulated fluid. This method can be used for corrosion state evaluation of the downhole tubing.

[0124] In order to obtain the relationship between the conductivity and the carbon dioxide concentration in the downhole environment, the example test obtains the relationship between the carbon dioxide concentration and the conductivity change; keeping other factors in the environment unchanged, using a single variable method, only testing the change of the carbon dioxide concentration, the value of the conductivity changes over time. Figure 13 is the conductivity change curve over time according to the present application; as shown in Figure 13, the conductivity change curve over time is obtained by testing by passing in carbon dioxide, it can be seen that as the test time is prolonged, 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 change trend of the carbon dioxide concentration in the environment, and the conductivity growth trend slows down at the end of the experiment is limited by the carbon dioxide solubility of the fluid. By the value of the conductivity, combined with the conductivity change curve over time, the concentration of carbon dioxide at the monitoring position in the well can be judged; in this example, the signal of the probe assembly is accurately collected by the ADC acquisition circuit, and the collected results are more accurate through filtering and voltage limiting processing, and the accuracy of the monitoring results is improved.

[0125] Specifically, the power supply on the well needs to be transmitted to the downhole corrosion monitoring device 1 for power supply through the cable 30, 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, on the basis of any example, the cable 30 includes: a power line and a communication line;

[0126] 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 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 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.

[0127] Specifically, the cable 30 in the example is used to electrically connect the downhole corrosion monitoring device 1 and the wellhead power supply 403; the cable 30 in the example adopts a steel cable containing four cores, two of which are power lines and the other two are communication lines, and the communication lines are RS485 communication lines. The power lines connect the output terminals of the wellhead power supply 403 and the circuit input terminals of the downhole corrosion monitoring device 1 to supply power to the circuit of the downhole corrosion monitoring device 1; the communication lines transmit 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 the example, the cable is used to supply power to the downhole corrosion monitoring device and transmit the data in the downhole to the ground control cabinet 404, so that real-time data transmission and real-time monitoring of the corrosion condition in the downhole can be realized. The staff on the well can analyze the corrosion condition of the downhole tubing in real time, and the accuracy of the corrosion monitoring result can be improved.

[0128] Specifically, a communication interface needs to be provided in the circuit board to interface with the transceiver of the control cabinet on the well to realize transmission of the monitoring data; accordingly, as an example, the PCB circuit board 210 further includes a communication interface based on any of the examples;

[0129] The communication interface is connected with the single-chip microcomputer and the communication lines to transmit the corrosion rate, the residual thickness of the test piece 111, and the conductivity data to the ground control cabinet 404 through the communication lines.

[0130] In one example, the PCB circuit board 210 of the downhole corrosion monitoring device 1 is provided with an RS485 chip, the ground control cabinet 404 on the well includes an RS485 transceiver, and the data monitored by the downhole 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 with the single-chip microcomputer to receive the monitoring data in the single-chip microcomputer, and the other end is connected with the communication lines in the cable 30 to transmit the corrosion rate, the corrosion residual thickness and the conductivity data of the received single-chip microcomputer to the control cabinet on the ground; in the example, real-time data transmission can be realized through the cable, and the data received by the ground control cabinet 404 can be transmitted to the online monitoring system for viewing by the staff on the ground. The accuracy of the monitoring result can be improved.

[0131] Specifically, the entire downhole corrosion monitoring device 1 needs to be powered by the wellhead power supply 403, and 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, the PCB circuit board 210 further includes a DC step-down converter and a linear voltage stabilizer based on any of the examples;

[0132] The DC voltage converter is used to connect one end of the power line to reduce the voltage provided by the wellhead power supply 403; the linear voltage regulator is connected with the DC voltage converter, which is used to provide the voltage to the PCB circuit board 210 after the voltage is stabilized.

[0133] In practical applications, the wellhead power supply 403 provides power to the entire downhole corrosion monitoring device 1 PCB circuit board 210. First, the 48V DC power provided by the wellhead is output as 5V DC voltage through the DC voltage converter; the linear voltage regulator cooperates with the DC voltage converter to output 3.3V voltage through the linear voltage regulator. The output of the stabilized power supply can reduce power supply noise and ripple. In this example, the DC voltage converter is used to reduce 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 voltage regulator, the inaccuracy of the monitoring results caused by the inaccuracy of the collected results due to unstable voltage can be reduced, and the accuracy of the monitoring results can be improved.

[0134] In addition to monitoring the corrosion rate in the well in real time, the downhole corrosion monitoring device 1 can also monitor the temperature in the well. Accordingly, as an example, the PCB circuit board 210 also includes a temperature sensor;

[0135] 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.

[0136] Specifically, the temperature sensor is provided on the circuit board to monitor the temperature of the downhole monitoring environment. In this example, the maximum operating temperature of the circuit board is 150℃. In practical applications, temperature is one of the important factors affecting corrosion rate; at different temperatures, the activity of the corrosion medium, the chemical reaction rate, and the stability of the corrosion product will change; therefore, monitoring the temperature helps to understand the actual situation of the corrosion environment, and provides important parameters for analyzing the corrosion causes and developing protection measures. Changes in temperature are often associated with specific corrosion types. For example, oxidation corrosion is more likely to occur in high-temperature environments, while stress corrosion cracking is more likely to occur in low-temperature environments. In this example, the temperature in the well is monitored by the temperature sensor, and the monitoring data includes temperature data, which can fully reflect the corrosion situation in the well and further improve the accuracy of the monitoring results.

[0137] The downhole corrosion monitoring device of the 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 structure of a gapless flat plate fit; one end of the test piece and the reference piece is extended and connected, and the other end of the test piece and the reference piece is respectively connected to a measurement terminal; the resistance probe assembly contains two resistance probes and two conductivity probes for simultaneous monitoring of the inside and outside of 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 the embodiment, and the PCB circuit board is provided with a power supply circuit, a collection circuit and a single-chip microcomputer, for collecting and processing the signals of the resistance probe assembly, and finally obtaining the monitoring data of the downhole corrosion monitoring device to reflect the corrosion conditions of the inside and outside of the oil pipe in the oil well. The device of the embodiment realizes accurate monitoring of the corrosion of the oil pipe by designing the structure of the resistance probe probe assembly with a gapless flat plate fit and a precise circuit assembly, and by supplying power to the precise circuit assembly through the cable and transmitting the monitoring data to the ground control cabinet on the well; accurate monitoring results are obtained, and the monitoring data can be transmitted in real time.

[0138] Embodiment two

[0139] Fig. 14 is a structural schematic diagram of the downhole corrosion monitoring system of the application; as shown in Fig. 14, the downhole corrosion monitoring system comprises a ground control cabinet 404 and at least one downhole corrosion monitoring device 1;

[0140] The at least one downhole corrosion monitoring device 1 is installed on the sidewall of the oil pipe 40 in the well, and is connected to the ground control cabinet 404 through the cable 30, for sending the corrosion rate, the remaining thickness of the test piece 111 and the conductivity data to the ground control cabinet 404.

[0141] In actual application, the at least one downhole corrosion monitoring device 1 is installed on the sidewall of the oil pipe 40 in the well, and the downhole corrosion monitoring device 1 is connected to the ground control cabinet 404 through the cable 30, and transmits the corrosion rate, the remaining thickness of the test piece 111, the conductivity and the temperature data monitored by the downhole corrosion monitoring device 1 to the ground control cabinet 404.

[0142] Specifically, the downhole corrosion monitoring device 1 needs to be fixed on the sidewall of the oil pipe 40, and accordingly, as an example, the downhole corrosion monitoring device is installed on the sidewall of the oil pipe 40 through the clamp fixture 401 and the fastener 402 fixed on the sidewall of the oil pipe 40.

[0143] 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 on the outer wall of the oil pipe 40 through the clamp 401, and the other end of the downhole corrosion monitoring device 1 is fixed on the side wall of the oil pipe 40 through the fastener 402. The height of the downhole corrosion monitoring device 1 outside the oil pipe 40 is kept within 20mm, which meets the size requirement of the limited ring space, and can avoid the problem of failure caused by excessive friction and wear during the device downhole process. In this example, the clamp and the fastener are used to fix the downhole corrosion monitoring device on the oil pipe to ensure the close fit between the device and the pipe and avoid monitoring errors caused by loose installation of the downhole corrosion monitoring device or damage to the oil pipe.

[0144] Specifically, the downhole corrosion monitoring system has multiple downhole corrosion monitoring devices 1, and correspondingly, 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 depths.

[0145] In the actual monitoring process, the downhole corrosion monitoring device can be installed at different depths in the well to monitor the corrosion condition at different depths, and the downhole corrosion monitoring system in this example can monitor the corrosion condition at different depths, and can be applied to an oil well with a maximum distance of 3000m from the ground, realizing real-time and accurate monitoring of corrosion monitoring results at different depths.

[0146] The downhole corrosion monitoring system in this embodiment includes multiple downhole corrosion monitoring devices, which are located at different depths on the side wall of the downhole oil pipe, realizing monitoring of the corrosion condition in different depth environments, and realizing real-time and accurate monitoring, as well as monitoring of the corrosion condition at different depths, and real-time transmission of the corrosion monitoring data to the ground control cabinet; 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.

[0147] Embodiment three

[0148] FIG. 15 is a flowchart of the downhole corrosion monitoring method of the present application, as shown in FIG. 15, the method comprises:

[0149] Step 101, obtaining the differential voltage between the test piece and the reference piece of the resistance probe at multiple times;

[0150] Step 102, obtaining the resistance ratio of the test piece and the reference piece at multiple times according to the differential voltage at multiple times; calculating the residual thickness of the test piece at multiple times according to the resistance ratio at multiple times;

[0151] Step 103: Based on the remaining thickness of the test piece at multiple time points, perform differential calculations to obtain the corrosion rate.

[0152] In practical applications, in conjunction with the aforementioned implementation methods, the execution subject of this example method is the microcontroller of this downhole corrosion monitoring device. The differential voltage value obtained in step 101 of this method is the differential voltage value between the resistance probe reference piece and the test piece in the parallel plate structure of this scheme; however, the circuit structure for obtaining the differential voltage between the test piece and the reference piece, as well as the method of obtaining it, are not limited.

[0153] The downhole corrosion monitoring method in this embodiment acquires the differential voltage between the test piece and the reference piece of a resistance probe at multiple different times, calculates the resistance ratio based on the differential voltage values, and obtains the remaining thickness of the test piece at multiple times based on the resistance ratio. The corrosion rate is then calculated by differentiating the remaining thickness of the test piece. This example method, by acquiring the differential voltage values ​​between the test piece and the reference piece, makes the subsequently obtained resistance ratio more accurate. The remaining corrosion thickness and corrosion rate obtained based on the accurate resistance ratio are therefore more accurate, thus improving the accuracy of the monitoring results.

[0154] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only.

[0155] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope.

[0156] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope.

Claims

1. A downhole corrosion monitoring device, characterized by, The downhole corrosion monitoring device comprises a resistance probe assembly, and the resistance probe assembly comprises at least one resistance probe; The resistance probe comprises a test sheet and a reference sheet arranged in parallel; an insulating material is filled between the test sheet and the reference sheet to form a gapless and close-fitting structure, and the test sheet is located outside the reference sheet; wherein the insulating material is a 0.1mm mica sheet; One end of the test sheet and the reference sheet is connected as an integral structure, the other end of the test sheet is connected to a first measurement terminal, and the other end of the reference sheet is connected to a second measurement terminal; The resistance probe assembly comprises a component main body and first and second resistance probes located in the component main body; the first and second resistance probes are used for corrosion monitoring inside and outside the oil pipe respectively; The component main body has opposite first and second surfaces; the first surface is provided with a first opening to expose the test sheet of the first resistance probe through the first opening; and the second surface is provided with a second opening to expose the test sheet of the second resistance probe through the second opening; Wherein, the first surface protrudes from the main surface of the component main body, and the main surface of the component main body is provided with a sealing structure surrounding the area of the second surface; the sealing structure matches the oil pipe opening on the oil pipe sidewall.

2. The apparatus of claim 1, wherein, The resistance probe assembly further comprises first and second conductivity probes located in the component main body; the first and second conductivity probes 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; and 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 apparatus of claim 1 or 2, wherein, The downhole corrosion monitoring device further comprises a circuit sealing assembly and a cable; the circuit sealing assembly comprises a housing, a PCB circuit board and wires located in the housing; One end of the housing of the circuit sealing assembly is used for sealing connection with the component main body of the resistance probe assembly through threads and a first sealing structure; One end of the cable is electrically connected with 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; the wire outlet and the cable are sealed through a second sealing structure; One end of the component main body of the resistance probe assembly is provided with a navigation plug, and the PCB circuit board has a navigation plug interface corresponding to the navigation plug; when the component main body of the resistance probe assembly is connected with the circuit sealing assembly, the PCB circuit board is electrically connected with the resistance probe assembly through the navigation plug interface and the navigation plug.

4. The apparatus of claim 3, wherein, 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 with the resistance probe assembly, the bidirectional constant current source circuit is electrically connected with the first measurement terminal of the first resistance probe and the second measurement terminal of the second resistance probe, for providing forward driving current and reverse driving current to the resistance probe, to generate a differential voltage between the test sheet and the reference sheet; An input end of the multi-channel A / D converter is electrically connected to the first measurement terminal and the second measurement terminal, and an 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 for sampling the differential voltage between the test sheet and the reference sheet; The single-chip microcomputer is electrically connected with the multi-channel A / D converter, for obtaining a resistance ratio of the test sheet and the reference sheet according to the differential voltage between the test sheet and the reference sheet, and calculating corrosion rate data inside and outside the oil pipe and residual thickness data of the test sheet according to the resistance ratio.

5. The apparatus of claim 4, wherein, 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 an output end of the current source circuit, the other end of the first NMOS tube is connected to one end of the third NMOS tube, as a 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 a second output end of the bidirectional constant current source circuit; the other end of the fourth NMOS tube is grounded. 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 for controlling the first NMOS tube and the fourth NMOS tube to be turned on, or controlling the second NMOS tube and the third NMOS tube to be turned on, to output forward driving current or reverse driving current.

6. The apparatus of claim 5, wherein, The current source circuit comprises a first operational amplifier, a triode and a current sampling module. A second end of the triode receives an excitation power supply signal, a third end of the triode is connected to one end of the first NMOS tube and the second NMOS tube as an output end of the current source circuit, and a first end of the triode is connected to an output end of the first operational amplifier; The current sampling module is used for sampling a current output by the current source circuit, and outputting a sampling current; the first operational amplifier receives a reference signal and is connected to the current sampling module, for outputting a driving signal to the first end of the triode according to the output current of the current source circuit and the reference signal, to perform feedback adjustment.

7. The apparatus of claim 6, wherein, The current sampling module comprises a second operational amplifier and a sampling resistor. One end of the sampling resistor is connected with the second end of the transistor and the second operational amplifier, and the other end of the sampling resistor is connected with 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 with the first operational amplifier, and is used for outputting the sampling current.

8. The device of any one of claims 4-7, wherein, The PCB circuit board further comprises an electric conductivity acquisition circuit; The electric conductivity acquisition circuit is connected to the first electric conductivity probe and the second electric conductivity probe, and is used for outputting a voltage division ratio of the first electric conductivity probe and a voltage division ratio of the second electric conductivity probe; The single-chip microcomputer is connected with the electric conductivity acquisition circuit, and is further used for obtaining impedance values of the first electric conductivity probe and the second electric conductivity probe according to the voltage division ratio of the first electric conductivity probe and the voltage division ratio of the second electric conductivity probe, and outputting electric conductivity data inside and outside the oil pipe according to the impedance values.

9. The apparatus of claim 8, wherein, The electric conductivity acquisition circuit comprises an analog switch, a pulse signal generator, a first voltage follower, a second voltage follower, a first voltage dividing resistor and a second voltage dividing resistor. Input ends of the analog switch are connected to the first electric conductivity probe and the second electric conductivity probe respectively, and the analog switch is used for outputting signals output by the first electric conductivity probe and the second electric conductivity probe in time; the pulse signal generator is used for providing a pulse modulation signal; One end of the first voltage dividing resistor is connected with the pulse signal generator and an input end of the first voltage follower; the other end of the first voltage dividing resistor is connected with an output end of the analog switch, one end of the second voltage dividing resistor, and an input end of the second voltage follower, and the other end of the second voltage dividing resistor is grounded; An output end of the first voltage follower is used for outputting a first follow-up signal corresponding to the pulse modulation signal; an output end of the second voltage follower is used for outputting a second follow-up signal corresponding to a voltage signal collected by the first electric conductivity probe or the second electric conductivity probe; and the first follow-up signal and the second follow-up signal are used for calculating electric conductivity inside or outside the oil pipe.

10. The device of any of claims 4-9, wherein, The first measurement terminal comprises a first port and a second port, and the second measurement terminal comprises a third port and a fourth port; a fourth port of the first resistance probe and a second port of the second resistance probe are electrically connected; The multi-channel A / D converter comprises a plurality of ADC acquisition circuits; the plurality of ADC acquisition circuits comprise 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 electric conductivity probe, and an ADC acquisition circuit corresponding to the second electric conductivity probe.

11. The apparatus of claim 10, wherein, The ADC acquisition circuit comprises a filter circuit, a first voltage stabilizing diode and a second voltage stabilizing diode. An input end of the filter circuit is connected with a port corresponding to an ADC acquisition circuit, and the filter circuit is used for filtering a signal at the port; A negative electrode of the first voltage stabilizing diode receives a constant voltage signal, a positive electrode of the second voltage stabilizing diode is grounded, and an output end of the filter circuit is connected with a positive electrode of the first voltage stabilizing diode and a negative electrode of the second voltage stabilizing diode, used for limiting and outputting a filtered signal; and output ends of the plurality of ADC acquisition circuits are connected to corresponding ports of the single-chip microcomputer, so as to input, to the single-chip microcomputer, a differential voltage between a reference piece and a test piece of the first resistance probe, a differential voltage between a reference piece and a test piece of the second resistance probe, a voltage division ratio of the first conductivity probe, and a voltage division ratio of the second conductivity probe.

12. The device of any one of claims 4-11, wherein, The cable comprises 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 for connecting a 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 for connecting a ground control cabinet, and the communication line is used for transmitting corrosion rate data inside and outside the oil pipe and residual thickness data of the test piece to the ground control cabinet.

13. The apparatus of claim 12, wherein, The PCB circuit board further comprises a communication interface; The communication interface is connected with the single-chip microcomputer and the communication line, and is used for transmitting the corrosion rate, test piece residual thickness, and conductivity data to the ground control cabinet through the communication line.

14. The apparatus of claim 13, wherein, The PCB circuit board further comprises a DC voltage reduction converter and a linear voltage stabilizing power supply; The DC voltage reduction converter is used for connecting one end of the power line to reduce voltage supplied by the wellhead power supply; and the linear voltage stabilizing power supply is connected with the DC voltage reduction converter, and is used for stabilizing the reduced voltage and supplying the stabilized voltage to the PCB circuit board.

15. The device of any one of claims 4-14, wherein, The PCB circuit board further comprises a temperature sensor; An output end of the temperature sensor is connected to the single-chip microcomputer, and is used for monitoring temperature and transmitting temperature data to the single-chip microcomputer.

16. A downhole corrosion monitoring system, characterized by The system comprises 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 a sidewall of an oil pipe in a downhole, and is connected to the ground control cabinet through a cable in the downhole corrosion monitoring device, and is used for transmitting the corrosion rate, test piece residual thickness, conductivity, and temperature data to the ground control cabinet.

17. The system of claim 16, wherein, The downhole corrosion monitoring device is installed on the sidewall of the oil pipe through a clamp fixture and a fastener fixed on the sidewall of the oil pipe.

18. The system of claim 16 or 17, wherein, The number of the downhole corrosion monitoring devices is multiple, and the multiple downhole corrosion monitoring devices are installed on sidewalls of the oil pipe at different well depths.

19. A method of monitoring corrosion downhole, characterized by, The method is applied to the downhole corrosion monitoring device as claimed in any one of claims 1 to 15, and the method comprises: acquiring a differential voltage between a test piece and a reference piece of a resistance probe at multiple time points; obtaining resistance ratios of the test piece and the reference piece at the multiple time points according to the differential voltages at the multiple time points; and calculating residual thicknesses of the test piece at the multiple time points according to the resistance ratios at the multiple time points. According to the residual thickness of the test piece at the plurality of time points, a differential calculation is performed to obtain a corrosion rate.

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