A low-frequency magnetic coupling downhole casing inner and outer wireless communication device and method of use

Abstract

The application discloses a low-frequency magnetic coupling downhole casing inner-outer wireless communication device and a use method, and belongs to the technical field of casing inner-outer communication. A variable-diameter centralizer is fixed to the outside of the casing, and a rubber plug is fixed to the inside of the casing; an annular columnar space is formed between the outer rubber plug body and the inner rubber plug body; a high-temperature-resistant sealed cabin is arranged in the inner rubber plug body; a magnetic core is arranged in a coil, and an integrated circuit board is connected with the coil through a wire; a sealing ring set is arranged on the outside of the outer rubber plug body and is in interference fit with the inner wall of the casing; an upper rubber plug cover is connected with the outer rubber plug body and the inner rubber plug body through screws, and a lower rubber plug cover is connected with the outer rubber plug body and the inner rubber plug body through screws; a main control sealed cabin, a driving push rod, a transmission flange, a transmission top rod and a stiffness self-adaptive driving cabin are sequentially connected, the driving push rod is freely slidable in the axial direction, and the stiffness self-adaptive driving cabin is coaxially fixed to the outer wall of the central body. The application greatly reduces the eddy current loss in the metal medium and can stably realize the wireless communication between the inside and the outside of the casing.

Description

Technical Field

[0001] This invention relates to the field of communication technology for oil pipelines, and in particular to a low-frequency magnetic coupling wireless communication device for downhole casing and its usage method. Background Technology

[0002] In the field of oil and gas exploration and development, the casing string system, as the core carrier for oil and gas transportation, is crucial for ensuring production safety and improving transportation efficiency through real-time monitoring of its operational status and interaction of internal and external commands. Monitoring of the casing annulus status and control of downhole tools in oil and gas wells both rely on stable and reliable communication links between the casing and the surrounding environment. This enables the uploading of data from the well and inside the casing to the surface and outside the casing, as well as the downlink transmission of surface control commands. This is the core support for building an intelligent oil and gas transportation system and a wellbore integrity management system.

[0003] Currently, the main technical solutions for communication inside and outside pipelines are wired communication and wireless communication. However, each solution has unavoidable technical bottlenecks in practical applications and cannot fully meet the needs of complex pipeline working conditions.

[0004] Wireless communication technologies, which do not require the laying of physical lines, have been widely explored in pipeline communication scenarios, mainly including microwave communication, electric field coupling, conventional magnetic coupling, and underwater acoustic communication. Microwave communication, as a line-of-sight transmission technology, can serve as a backup link when fiber optic lines are interrupted. However, it is subject to frequency approval restrictions, and signal transmission relies on unobstructed paths. In urban complexes and complex terrains, channel planning needs to be coordinated. Furthermore, it is susceptible to atmospheric conditions and electromagnetic interference, resulting in insufficient stability. Electric field coupling technology forms a closed-loop signal transmission through the transmitter, the formation medium, and the receiver. However, the composition of the formation medium in wells and around pipelines is complex, with some components having high conductivity, leading to severe signal attenuation. It is also difficult to ensure close contact between the transmitter and the medium, resulting in highly unstable transmission efficiency.

[0005] Conventional magnetic coupling technology, based on the principle of electromagnetic induction, uses a coil to generate a magnetic field for signal coupling and transmission. It offers advantages such as small size, ease of installation, and non-invasiveness, and has been tested for application in oil well pipeline signal transmission. However, existing magnetic coupling technologies mostly use medium- or high-frequency signals. Limited by coil structure and operating conditions, the generated magnetic field strength is relatively weak. Under conditions of metal pipe shielding, complex geological environments, and strong electromagnetic interference, the signal attenuates rapidly and has poor penetration, failing to meet the communication requirements of deep wells, long-distance pipelines, or enclosed annulus spaces. Some improved solutions, such as semi-annular couplers, can reduce insertion loss, but their frequency range is limited, performance degrades significantly at low frequencies, and they lack adaptability to pipeline structures, making it difficult to balance transmission stability and ease of installation. Underwater acoustic communication is mainly used in underwater pipeline scenarios, enabling real-time monitoring of data such as casing annulus pressure. However, it suffers from difficulties in implementation, complex equipment composition, and significant susceptibility to underwater medium disturbances, limiting its application scope.

[0006] Furthermore, the operation of oil pipelines places special demands on communication equipment, requiring it to be explosion-proof, corrosion-resistant, and resistant to extreme temperatures and pressures. While existing communication technologies meet these safety standards, they often struggle to balance transmission distance, speed, and stability. For instance, the underground and pipeline perimeters are explosive hazardous areas, further limiting the power and magnetic field strength of conventional high-frequency magnetic coupling coils.

[0007] In summary, existing communication technologies for oil pipelines generally suffer from drawbacks such as the conflict between non-invasiveness and transmission stability, poor adaptability to complex environments, high installation and maintenance costs, and severe signal attenuation. These limitations fail to fully meet the high-precision, long-distance, and long-term stable communication requirements of various scenarios, including long-distance pipelines, deep well shafts, and underwater enclosed annulus environments. Therefore, developing a pipeline communication technology with strong penetration capabilities, low signal attenuation, non-invasive installation, and adaptability to complex operating conditions has become a pressing technical challenge in the intelligent development of the oil and gas industry. Extremely low frequency magnetic coupling technology, with its potential advantages in penetrating metal shielding, resisting electromagnetic interference, and reducing medium attenuation, provides a feasible path to overcome these technical bottlenecks. Summary of the Invention

[0008] The purpose of this invention is to provide a low-frequency magnetically coupled wireless communication device for inside and outside the casing and its usage method.

[0009] A low-frequency magnetically coupled downhole casing internal and external wireless communication device includes: casing, variable diameter centralizer, and rubber plug; wherein, the variable diameter centralizer is fixed on the outside of the casing, and the rubber plug is disposed on the inside of the casing.

[0010] The rubber stopper includes an upper rubber stopper cap, a sealing ring assembly, screws, an outer rubber stopper body, an inner rubber stopper body, and a lower rubber stopper cap; an annular cylindrical space is formed between the outer rubber stopper body and the inner rubber stopper body; a high-temperature resistant sealing chamber is set inside the inner rubber stopper body; a high-temperature resistant battery pack, an integrated circuit board, a coil, and a magnetic core are set inside the high-temperature resistant sealing chamber, wherein the magnetic core is placed inside the coil, and the integrated circuit board is connected to the coil through wires; the sealing ring assembly is fitted onto the outside of the outer rubber stopper body and is interference-fitted with the inner wall of the sleeve; the upper rubber stopper cap is connected to the outer rubber stopper body and the inner rubber stopper body by screws, and the lower rubber stopper cap is connected to the outer rubber stopper body and the inner rubber stopper body by screws;

[0011] The variable diameter centralizer includes a main control sealed chamber, a drive push rod, a transmission flange, a force transmission push rod, a stiffness adaptive drive chamber, a central arm assembly, a multi-parameter sensing unit, a lower connector, and a central body. The main control sealed chamber, drive push rod, transmission flange, force transmission push rod, and stiffness adaptive drive chamber are connected sequentially, with the drive push rod sliding freely along the axial direction. The stiffness adaptive drive chamber is coaxially fixed to the outer wall of the central body. The central body's outer wall is also circumferentially arranged with central arm assemblies and multi-parameter sensing units. A lower connector is located at one end of the central body.

[0012] Furthermore, the main control sealed chamber is equipped with a ring-shaped low-frequency magnetic receiving coil, a power supply module, a main control circuit module, an electric power activation switch, an electromagnet, a high-temperature resistant reset spring, a magnetic alloy locking pin, and a ring-shaped locking slot; wherein, the main control circuit module is connected to the electromagnet; the electromagnet, the high-temperature resistant reset spring, and the magnetic alloy locking pin are connected in sequence; the ring-shaped locking slot is located at one end of the drive push rod near the main control sealed chamber; the main control circuit module is electrically connected to the multi-parameter sensing unit.

[0013] Furthermore, the centering arm assembly includes a transmission link, an upper hinge link, a centering plate, and a lower hinge link; wherein, the transmission link connects the middle part of the upper hinge link to the transmission flange; one end of the upper hinge link is hinged to the central body, and the other end is connected to one end of the centering plate; the other end of the centering plate is connected to one end of the lower hinge link; the other end of the lower hinge link is hinged to the central body; and the upper hinge link, centering plate, lower hinge link, and central body form a parallelogram, with the stiffness adaptive drive cabin located within the parallelogram.

[0014] Furthermore, the stiffness-adaptive drive cabin is equipped with a magnetorheological variable stiffness unit, a support structure, and a pre-energy-storage disc spring assembly. The magnetorheological variable stiffness unit is connected to the main control circuit module through an excitation coil. One end of the pre-energy-storage disc spring assembly rests against a fixed step of the stiffness-adaptive drive cabin, and the other end rests against one end of the magnetorheological variable stiffness unit through the support structure. The other end of the magnetorheological variable stiffness unit is connected to a force-transmitting push rod.

[0015] Furthermore, the number of magnetorheological stiffness units is the same as the number of the straightening arm assembly.

[0016] Furthermore, the multi-parameter sensing unit includes a wellbore distance sensor, a temperature sensor, a pressure sensor, and a drilling fluid density sensor.

[0017] Furthermore, an annulus is formed between the casing and the oil and gas well.

[0018] Furthermore, both the upper and lower rubber stoppers are equipped with a weak structure with a preset pressure breaking threshold of 3MPa.

[0019] A method for using a low-frequency magnetically coupled wireless communication device for inside and outside a downhole casing includes:

[0020] Step 1: Assemble the rubber stopper, fix the high-temperature resistant battery pack, integrated circuit board, coil, and magnetic core inside the high-temperature resistant sealed chamber, perform sealing and insulation tests on the main control sealed chamber, complete the rubber stopper pressure burst test, and verify whether the preset pressure burst threshold of the upper and lower rubber stopper covers meets the requirements.

[0021] Step 2: Lower the casing into the oil and gas well, fix the variable diameter centralizer to the outer wall of the casing, calibrate the multi-parameter sensing unit, and record the depth of the variable diameter centralizer.

[0022] Step 3: Inject pre-fluid into the casing to clean the inner wall of the casing, and put the rubber plug into the casing through the wellhead dropping device; at this time, the high-temperature resistant sealing chamber is in a low-power dormant state, inject displacement fluid into the casing, drive the rubber plug to descend along the casing at a constant speed, and track the downward position of the rubber plug in real time.

[0023] Step 4: When the rubber plug's downward position is within the range of the variable diameter centralizer, the wellhead monitoring system sends a working command to the rubber plug via a wireless link, activating the integrated circuit board inside the high-temperature resistant sealed chamber, driving the coil to generate a stable alternating magnetic field; the annular low-frequency magnetic receiving coil, under the alternating magnetic field, activates the power activation switch, triggering the main control circuit module to work, the electromagnet is energized to generate a magnetic field, and the magnetic alloy locking pin, which is stuck in the annular locking slot, retracts radially by the attraction of the electromagnet overcoming the elasticity of the high-temperature resistant reset spring, releasing the axial lock of the drive push rod; the pre-stored energy disc spring group releases stored energy, pushing the drive push rod axially through the magnetorheological stiffness unit, causing the centralizer plate to open radially until it contacts the well wall; the multi-parameter sensing unit collects data in real time, and the main control circuit module adjusts the stiffness of the magnetorheological stiffness unit to control the opening degree and support force of the centralizer plate;

[0024] Step 5: Inject displacement fluid to drive the rubber stopper down to the bottom of the casing and achieve rubber stopper setting; then continue to pressurize the casing. When the pressure inside the casing reaches the preset pressure breaking threshold, the weak structure of the upper and lower rubber stopper caps is broken, forming a fluid channel.

[0025] Step 6: Inject cement slurry and subsequent displacement fluid sequentially, and isolate the cement slurry and displacement fluid through a sealing ring assembly; during the displacement operation, the multi-parameter sensing unit will upload the collected data to the wellhead monitoring system in real time for analysis and early warning.

[0026] Step 7: Once the displacement fluid reaches the designed position and all the cement slurry has been displaced into the annulus, stop the injection operation, close the wellhead valve, and the wellhead monitoring system records the entire process data.

[0027] A test system for a low-frequency magnetically coupled wireless communication device for inside and outside a downhole casing is disclosed. End caps are installed at both ends of the casing. A coil passes through the end caps and is connected to an oscilloscope and a power amplifier module, respectively. The power amplifier module is connected to a microcontroller and a laboratory power supply, respectively. A ring-shaped low-frequency magnetic receiving coil is connected to the oscilloscope. Both the coil and the ring-shaped low-frequency magnetic receiving coil are placed in a support base, and the ring-shaped low-frequency magnetic receiving coil is at the same horizontal height as the coil. A teslameter is used to measure the magnetic field strength generated by the coil, and the axis of the coil is perpendicular to the axis of the casing.

[0028] The beneficial effects of this invention are as follows:

[0029] 1. This invention employs ultra-low frequency magnetic coupling technology, which significantly reduces eddy current losses in metallic media and enables stable wireless communication between the inside and outside of the bushing. It solves the core problem of insufficient penetration capability of conventional medium and high frequency magnetic coupling technology, providing a non-invasive and highly reliable communication link between the inside and outside of the bushing.

[0030] 2. This invention miniaturizes and integrates the transmitting unit inside the cementing plug. Without changing the core functions of the plug, such as scraping the wall, sealing, bearing pressure, and isolating fluid, the communication device is simultaneously inserted into the well during the cementing operation, eliminating the need for additional insertion procedures and significantly reducing operating costs and construction complexity. At the same time, it requires no modification to conventional cementing tools such as casing and centralizers, and can be directly adapted to existing cementing operation procedures, making it highly applicable to engineering projects.

[0031] 3. The operation method of the present invention covers the entire process of pre-cementing preparation, casing running, rubber plug placement, centralizer control, displacement operation, and waiting for solidification monitoring. It clarifies the working sequence, operation specifications, and control logic of the equipment in each stage, and can realize real-time monitoring, closed-loop control, and abnormal early warning of the cementing process. It effectively improves cementing displacement efficiency, reduces the risk of cementing accidents, ensures cementing quality, and promotes the development of cementing technology towards intelligence. Attached Figure Description

[0032] Figure 1 This is an overall structural diagram of the low-frequency magnetic coupling downhole casing internal and external wireless communication device of the present invention;

[0033] Figure 2 This is a structural diagram of the variable diameter centralizer;

[0034] Figure 3 A partial cross-sectional view of the main control sealed compartment;

[0035] Figure 4 This is a partial cross-sectional view of the stiffness-adaptive drive cabin.

[0036] Figure 5 This is a schematic diagram of the system connection of the integrated circuit board within the sleeve;

[0037] Figure 6 This is a cross-sectional view of the rubber stopper;

[0038] Figure 7 This is a schematic diagram of the usage method of the low-frequency magnetic coupling downhole casing internal and external wireless communication device of the present invention;

[0039] Figure 8 This is a schematic diagram of the indoor testing system;

[0040] Figure 9 This is a graph showing the relationship between excitation frequency and maximum propagation distance. Detailed Implementation

[0041] This invention proposes a low-frequency magnetically coupled wireless communication device for inside and outside the casing of a well and its usage method. The invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0042] Figure 1 The diagram shows the overall structure of the low-frequency magnetic coupling downhole casing internal and external wireless communication device of the present invention, which includes: casing 1, high-temperature resistant battery pack 2, variable diameter centralizer 3, and rubber plug 4; wherein, the variable diameter centralizer 3 is fixed on the outside of casing 1, and the rubber plug 4 is disposed on the inside of casing 1; an annulus 5 is formed between casing 1 and oil and gas well 6.

[0043] Figure 2 This is an overall structural diagram of the variable diameter centralizer. The variable diameter centralizer 3 includes a main control sealing chamber 301, a drive push rod 302, a transmission flange 303, a force transmission push rod 304, a stiffness adaptive drive chamber 305, a centralizing arm assembly 306, a multi-parameter sensing unit 307, a lower connector 308, and a central body 309. The main control sealing chamber 301, drive push rod 302, transmission flange 303, force transmission push rod 304, and stiffness adaptive drive chamber 305 are connected sequentially. The drive push rod 302 slides freely along the axial direction. The stiffness adaptive drive chamber 305 is coaxially fixed to the outer wall of the central body 309. The central body 309 also has the centralizing arm assembly 306 and the multi-parameter sensing unit 307 evenly arranged circumferentially on its outer wall. A lower connector 308 is located at one end of the central body 309. The multi-parameter sensing unit 307 includes a wellbore distance sensor, a temperature sensor, a pressure sensor, and a drilling fluid density sensor.

[0044] The straightening arm assembly 306 includes a transmission link 3061, an upper hinge link 3062, a straightening plate 3063, and a lower hinge link 3064. The transmission link 3061 connects the middle part of the upper hinge link 3062 to the transmission flange 303. One end of the upper hinge link 3062 is hinged to the central body 309, and the other end is connected to one end of the straightening plate 3063. The other end of the straightening plate 3063 is connected to one end of the lower hinge link 3064. The other end of the lower hinge link 3064 is hinged to the central body 309. The upper hinge link 3062, the straightening plate 3063, the lower hinge link 3064, and the central body 309 form a parallelogram, and the stiffness adaptive drive cabin 305 is located within the parallelogram. This structure ensures that the 3063 centralizing plate always moves radially and remains parallel to the well wall during the opening or closing process, maximizing the contact area and avoiding well wall scratches and insufficient centralizing force caused by point contact.

[0045] Figure 3This is a partial cross-sectional view of the main control sealed chamber. The main control sealed chamber 301 contains a ring-shaped low-frequency magnetic receiving coil 3011, a power module 3012, a main control circuit module 3013, a power activation switch 3014, an electromagnet 3015, a high-temperature resistant return spring 3016, a magnetic alloy locking pin 3017, and a ring-shaped locking slot 3018. The main control circuit module 3013 is connected to the electromagnet 3015. The electromagnet 3015, high-temperature resistant return spring 3016, and magnetic alloy locking pin 3017 are connected in sequence. The ring-shaped locking slot 3018 is located at one end of the drive push rod 302 near the main control sealed chamber 301. The main control circuit module 3013 is electrically connected to the multi-parameter sensing unit 307.

[0046] Figure 4 This is a partial cross-sectional view of the stiffness-adaptive drive cabin. The stiffness-adaptive drive cabin 305 contains a magnetorheological variable stiffness unit 3051, a support structure 3052, and a pre-energy-storing disc spring assembly 3053. The magnetorheological variable stiffness unit 3051 is connected to the main control circuit module 3013 via an excitation coil. One end of the pre-energy-storing disc spring assembly 3053 rests against a fixed step in the stiffness-adaptive drive cabin 305, and the other end rests against one end of the magnetorheological variable stiffness unit 3051 via the support structure 3052. The other end of the magnetorheological variable stiffness unit 3051 is connected to a force-transmitting push rod 304. The number of magnetorheological variable stiffness units 3051 is the same as the number of straightening arm assemblies 306.

[0047] Figure 5 This is a schematic diagram of the integrated circuit board system connection within the sleeve. The integrated circuit board 405 includes a microcontroller, a DDS signal generator, a power amplifier module, and an impedance matching module. The microcontroller is an industrial-grade, low-power, high-temperature resistant microcontroller, electrically connected to the DDS signal generator via an SPI communication interface. It outputs control signals to adjust the output frequency, amplitude, and phase of the DDS signal generator, completing the channel encoding of control commands for external devices. The output of the DDS signal generator is electrically connected to the input of the power amplifier module, generating a very low-frequency sine wave baseband signal carrying control commands under the control of the microcontroller. The power amplifier module amplifies the low-frequency sine wave signal, with continuously adjustable output power, and outputs a large current to meet the driving requirements. The signal drives the coil 407 to generate an alternating magnetic field that meets the requirements of penetration and control. The input terminal of the impedance matching module is electrically connected to the output terminal of the power amplifier module, and the output terminal is electrically connected to the coil 407. This is used to achieve conjugate matching between the power amplifier module and the coil 407 to maximize the magnetic field radiation efficiency. The coil 407 is wound with insulated high-permeability enameled wire, and a high-permeability magnetic core is built into the center of the coil. The coil 407 is fixed to the inner wall of the high-temperature resistant sealed chamber 406, and its axis is perpendicular to the axis of the sleeve 1 to ensure that the magnetic field energy is concentrated and radiated to the tube wall of the sleeve 1.

[0048] Figure 6 This is a cross-sectional view of the rubber stopper. The rubber stopper 4 includes an upper rubber stopper cap 401, a sealing ring assembly 402, a screw 403, an outer rubber stopper body 404, an inner rubber stopper body 409, and a lower rubber stopper cap 410; an annular cylindrical space 411 is formed between the outer rubber stopper body 404 and the inner rubber stopper body 409; a high-temperature resistant sealing chamber 406 is disposed within the inner rubber stopper body 409; a high-temperature resistant battery pack 2, an integrated circuit board 405, a coil 407, and a magnetic core 408 are disposed within the high-temperature resistant sealing chamber 406, wherein the magnetic core 408 is placed inside the coil 407. The integrated circuit board 405 is connected to the coil 407 via wires; the sealing ring assembly 402 is fitted onto the outside of the outer rubber plug body 404 and is interference-fitted with the inner wall of the sleeve 1; the upper rubber plug cover 401 is connected to the outer rubber plug body 404 and the inner rubber plug body 409 via screws 403, and the lower rubber plug cover 410 is connected to the outer rubber plug body 404 and the inner rubber plug body 409 via screws 403; both the upper rubber plug cover 401 and the lower rubber plug cover 410 are provided with a weak structure with a preset pressure breaking threshold of 3MPa.

[0049] Figure 7 This is a schematic diagram illustrating the usage method of the low-frequency magnetic coupling downhole casing internal and external wireless communication device of the present invention. First, the hardware assembly and performance testing of the device are completed: the overall assembly of the rubber plug 4 is completed, and the internally installed high-temperature resistant battery pack 2, integrated circuit board 405, coil 407, and magnetic core 408 are fixed inside the high-temperature resistant sealed chamber 406. Static sealing and insulation performance tests of the chamber are completed to ensure the sealing reliability and electrical insulation of the chamber under high-temperature and high-pressure conditions downhole. Subsequently, the rubber plug 4 is powered on and tested on the ground to comprehensively verify whether the signal transmission function, command encoding function, and power consumption indicators meet the design standards, ensuring the stability and reliability of the core communication function. Simultaneously, the pre-assembly and functional debugging of the variable diameter centralizer 3 are completed. A pressure-bearing burst test is performed on the rubber plug 4. The downhole pressurization conditions are simulated using a ground hydraulic pressurization device to verify the burst pressure threshold of the weak structures of the upper rubber plug cover 401 and the lower rubber plug cover 410, ensuring that they meet the design requirements and avoiding abnormal conditions such as premature bursting or failure to burst during downhole operations.

[0050] The threaded connection and torque verification of each casing 1 were completed, and the threading torque was strictly controlled according to the casing thread specifications to ensure the connection sealing and structural strength. The connected casing 1 was then smoothly lowered into the oil and gas well 6, and the lowering speed of casing 1 was precisely controlled to avoid violent collisions between casing 1 and the well wall, preventing casing 1 deformation, thread damage, or well wall collapse. When casing 1 was lowered to the designed position, the pre-assembled variable diameter centralizer 3 was fixed to the corresponding designed position on the outer wall of casing 1. The multi-parameter sensing unit 307 on the variable diameter centralizer 3 was calibrated and its initial state set was completed, and the installation depth of the variable diameter centralizer 3 was accurately recorded. For multi-stage centralizer operation scenarios, the centralizers of each stage were installed sequentially according to the designed spacing to ensure that the cascaded communication distance between adjacent centralizers was within the effective communication range. After installation, the pre-conduction test of the cascaded communication link was completed to ensure smooth communication of the multi-stage cascaded network. After casing 1 is fully lowered to the designed depth, casing 1 is suspended and fixed. The centering of casing 1 is adjusted by the wellhead equipment to ensure that the annulus 5 gap between casing 1 and the well wall is uniform, providing a stable working foundation for subsequent cementing and displacement operations and centralizer support.

[0051] According to the cementing design, the designed amount of pre-fluid is injected into casing 1 to complete the cleaning of the inner wall of casing 1 and the wellbore pretreatment, removing oil stains, debris and loose mud cake in the wellbore, providing a clean working interface for the subsequent descent of rubber plug 4 and cement slurry replacement; after the pre-fluid injection is completed, the rubber plug 4, which has been successfully tested on the ground, is smoothly put into casing 1 through the wellhead deployment device. The sealing ring group 402 of rubber plug 4 forms an interference seal with the inner wall of casing 1, ensuring that rubber plug 4 descends smoothly along the inner wall of casing 1 under fluid pressure without leakage or jamming; after rubber plug 4 is deployed, its built-in transmitting unit (including high-temperature battery pack 2, integrated circuit board 405, coil 407, and magnetic core 408) switches to a low-power sleep state, retaining only the wake-up monitoring function, minimizing the battery energy consumption of high-temperature battery pack 2 and extending the downhole working time. Displacement fluid is continuously injected into casing 1, and the fluid pressure drives the rubber plug 4 to descend at a constant speed along casing 1. During the operation, the downward position of the rubber plug 4 is calculated in real time by tracking the changes in wellhead pump pressure and the volume of injected fluid, so as to achieve precise control of the trajectory of the rubber plug 4 throughout the entire process.

[0052] When the downward position of the rubber plug 4 is within the range of the target variable diameter centralizer 3, the wellhead monitoring system sends a working command to the transmitter of the rubber plug 4 via a wireless link, waking up the transmitter unit to start full-function operation. The microcontroller of the transmitter unit completes the channel encoding of the control command according to the preset control logic or the command issued in real time from the wellhead, and outputs the control signal to the DDS signal generator to generate an extremely low frequency sine wave signal carrying the control command. After being amplified by the power amplifier module, it drives the coil 407 to generate a stable alternating magnetic field. The alternating magnetic field acts perpendicularly on the wall of the metallic casing 1. According to the principle of electromagnetic induction, induced eddy currents are generated inside the casing, causing some magnetic field energy loss. This embodiment adopts... Using extremely low frequency signals can significantly reduce the skin effect of metallic media, control eddy current losses within a manageable range, and ensure that the effective penetration depth of the extremely low frequency magnetic field is greater than the wall thickness of the metallic casing 1. The remaining magnetic field energy can successfully penetrate the wall of casing 1 and radiate stably into the annulus 5 outside casing 1. The annular low-frequency magnetic receiving coil 3011 of the variable diameter centralizer 3 at the corresponding position picks up the extremely low frequency magnetic field signal penetrating the casing, converts the magnetic signal into a weak electrical signal, and converts it into electrical energy to activate the electrical energy activation switch 3014, triggering the main control circuit module 3013 to work. The electromagnet 3015 is energized to generate a magnetic field, the magnetic alloy locking pin 3017 retracts, and the drive rod 302 is unlocked. The pre-stored energy disc spring assembly 3053 releases stored energy, and through the magnetorheological stiffness unit 3051, it pushes the drive rod 302 to move axially, causing the centralizer plate 3063 to open radially until it contacts the well wall, completing the initial centralization. The multi-parameter sensing unit 307 collects parameters such as well wall distance, temperature and pressure, and density in real time. The main control system independently adjusts the stiffness of each circumferential magnetorheological stiffness unit 3051 according to the well diameter and eccentricity, controlling the opening degree and support force of the centralizing plate 3063. When the well diameter is too large in a certain direction, the excitation current of the magnetorheological stiffness unit 3051 on that side is reduced, decreasing the magnetic field strength and stiffness. The elastic force of the pre-stored disc spring assembly 3053 can more easily push the drive push rod 302 to continue axial movement, causing the centralizing plate 3063 on that side to further open outwards until it tightly fits the well wall, compensating for the gap of the large well diameter and ensuring sufficient centralizing force. When the well diameter is too large in a certain direction... When the centralizing plate 3063 is squeezed by the well wall, it drives the drive push rod 302 to move axially in the opposite direction. At this time, the excitation current of the magnetorheological stiffness unit 3051 on that side is increased, the magnetic field strength is increased, and the stiffness of the magnetorheological stiffness unit 3051 is greatly improved, forming a very strong reverse support force to resist the squeezing of the well wall, prevent the centralizing plate 3063 from being over-closed, and avoid the casing from being eccentric to that side. For elliptical wellbores, stepped variable diameter wellbores, well wall diameter reduction or expansion, the stiffness of the six circumferential magnetorheological stiffness units 3051 is independently adjusted so that the opening degree and support force of each centralizing plate 3063 are completely matched with the well diameter in the corresponding direction, and finally the casing is accurately centered in any well diameter and any wellbore shape.

[0053] Meanwhile, the multi-parameter sensing unit 307 collects the opening data of the support arm in real time, and the temperature and pressure sensors collect the annular temperature and pressure parameters in real time. All collected data is preprocessed and encapsulated into data frames, which are then transmitted to the upper-level centralizer terminal through the cascaded communication unit. In the case of multi-stage centralizer operation, the rubber plug launcher continues to descend with the displacement fluid and arrives at the corresponding position of each stage of centralizer in sequence, completing the sequential activation and action control of each stage of centralizer. The equipment status data and annular sensing parameters collected by each stage of centralizer are transmitted upwards step by step through a chain cascaded network in a multi-hop relay manner, and finally uploaded to the wellhead monitoring system through the wellhead relay unit, so that the operator can keep track of the working status and annular operating parameters of each downhole centralizer in real time.

[0054] After all levels of centralizers are activated and complete their actions, displacement fluid is injected into casing 1 to drive rubber plug 4 down to the float collar position at the bottom of casing 1, thus achieving rubber plug 4 setting. At this time, the wellhead pump pressure shows a significant jump, confirming that rubber plug 4 has been set. Subsequently, pressure is continued to be applied into casing 1. When the pressure inside casing 1 reaches the design threshold of 3MPa, the weak structure of the upper rubber plug cap 401 and the lower rubber plug cap 410 of rubber plug 4 is precisely broken through, forming a through fluid channel, thus avoiding obstruction to subsequent cement slurry displacement operations. According to the cementing design, cement slurry and subsequent displacement fluid are injected sequentially into casing 1. The sealing ring assembly 402 of the rubber plug 4 effectively isolates the cement slurry and displacement fluid, preventing mixing of the two phases and ensuring stable cement slurry performance. Throughout the displacement operation, the transmitting unit inside the rubber plug 4 continuously operates, transmitting command signals and a synchronization clock signal according to a preset cycle. The sensing and acquisition units of each stage of the centralizer collect key parameters such as annular temperature, pressure, cement slurry density, and displacement velocity in real time, and upload them to the wellhead monitoring system via a cascaded network. When the displacement fluid reaches the designed position and all the cement slurry has been replaced in the annulus between the casing and the wellbore, the injection operation is stopped, the wellhead valve is closed, and the cementing displacement operation is completed. The wellhead monitoring system records all operation data throughout the process, confirming that all downhole equipment is in normal condition and that the cementing operation has been completed according to design requirements.

[0055] Figure 8This is a schematic diagram of the indoor experimental system. The experimental setup includes: a casing 1 simulating downhole operations, end caps 11, a coil 407, a microcontroller 12, a laboratory power supply 13, a power amplifier module 14, an oscilloscope 7, a ring-shaped low-frequency magnetic receiving coil 3011, a support base 9, a teslameter 10, and several wiring connections. End caps 11 are installed at both ends of the casing 1. The coil 407 passes through the end caps 11 and is connected to the oscilloscope 7 and the power amplifier module 14, respectively. The power amplifier module 14 is connected to the microcontroller 12 and the laboratory power supply 13, respectively. The ring-shaped low-frequency magnetic receiving coil 3011 is connected to the oscilloscope 7. Both the coil 407 and the ring-shaped low-frequency magnetic receiving coil 3011 are placed in the support base 9, and the ring-shaped low-frequency magnetic receiving coil 3011 and the coil 407 are at the same horizontal level. The teslameter 10 is used to measure the magnetic field strength generated by the coil 407, and the axis of the coil 407 is perpendicular to the axis of the casing 1.

[0056] The main purpose of this test system is to test the performance of the low-frequency magnetic coupling device under simulated actual working conditions. During operation, before starting the test, check the performance of each component to ensure it is working properly. Then place the coil 407 in the support base 9, and place the support base 9 inside the sleeve 1. Connect the microcontroller 12 to the power amplifier module 14 and the coil 407. Use insulating tape to wrap the connections between wires and between wires and the coil 407 interface to prevent short circuits from burning out the circuit. Connect the microcontroller 12 to an external power supply, edit the frequency, amplitude, and other information of the transmitted signal, and amplify the transmitted signal through the power amplifier module 14. Turn on the laboratory power supply 13 to supply alternating current to the coil 407. Driven by the amplified transmitted signal, the coil 407 generates an alternating magnetic field, which acts on the wall of the metal sleeve 1. Eddy currents are generated inside the tube wall due to electromagnetic induction, causing some magnetic field energy loss. However, due to the use of an extremely low frequency signal, the skin effect of the eddy currents is weak, and the energy loss is within a controllable range. The remaining extremely low frequency magnetic field component penetrates the tube wall and radiates outward. Turn on the teslameter 10 and use the probe of the teslameter 10 to move and monitor the position of the coil 407 outside the tube. The reading of the teslameter 10 confirms that the magnetic field can penetrate the tube wall. The placement of the coil 407 is changed one by one for testing. The optimal placement of the coil 407 is determined by the reading of the teslameter 10, that is, the axis of the coil 407 is perpendicular to the axis of the sleeve 1. The ring-shaped low-frequency magnetic receiving coil 3011 is then placed in the support base 9, ensuring that it is at the same horizontal level as coil 407, and that their axes are collinear. An oscilloscope 7 is connected to coil 407 and the ring-shaped low-frequency magnetic receiving coil 3011 via wires. The power is then turned on again. The oscilloscope 7, model FNIRSI-1040D, is used to detect the waveform and frequency of the signal emitted by the microcontroller 12, and to compare the waveform and peak value after the signal passes through the power amplification module 14. The dual-channel oscilloscope 7 can display the amplitude, frequency, and other information of the output signal of the microcontroller 12 and the signal received by the ring-shaped low-frequency magnetic receiving coil 3011. Comparing the two confirms that communication is possible. The relative position, angle, and coaxiality of coil 407 and the ring-shaped low-frequency magnetic receiving coil 3011 are adjusted, and the communication reliability under different installation conditions is recorded to optimize the installation process.

[0057] Under the condition that the indoor test system was completed, the alternating magnetic field strength of hollow coils, permalloy cores, and pure iron cores was compared and tested in the near field (the center of the coil in air) and the transition region (the level where the magnetic gain of the solid core cancels out the internal eddy current loss). When coil 407 was placed perpendicular to the pipe axis, the results were as follows: the magnetic field strength of the hollow coil at close range in air was 130 Gs, the strength of the permalloy core was 183 Gs, and the amplification effect was 40.8%; the strength of the pure iron core was 178 Gs, and the amplification effect was 36.9%. The magnetic focusing effect of both types of cores significantly enhanced the magnetic field at the center of the coil.

[0058] The placement method of coil 407 was tested as follows:

[0059] When coil 407 is placed perpendicular to the pipe axis, at a distance of 35mm from the inner wall and 41.2mm from the outer wall, its magnetic field strength is measured axially at the same distance in air. The alternating magnetic field strength of the air-core coil at 35mm is 18.6Gs, and at 41.2mm it is 13.3Gs. When using a permalloy core, the average alternating magnetic field strength at 35mm is 18.7Gs, and at 41.2mm it is 13.3Gs. When using a pure iron core, the average alternating magnetic field strength at 35mm is 18.6Gs, and at 41.2mm it is 13.4Gs.

[0060] When the pipe and coil 407 are placed coaxially, measurements show that the center of coil 407 is 67mm from the inner wall of the pipe and 73.2mm from the outer wall. Using a permalloy magnetic core, the average alternating magnetic field strength at 67mm is 2.2Gs, and at 73.2mm it is 2Gs. Using a pure iron magnetic core, the average alternating magnetic field strength at 67mm is 1.9Gs, and at 73.2mm it is 1.6Gs. These values ​​are very small, and applying the magnetic core in air has no amplifying effect at this distance. After passing through the metal pipe wall, the attenuation reaches 86.62%, with a value of 0.27Gs, which is far less than 1. Therefore, even with a magnetic core, the value is very small when coil 407 is placed coaxially with the pipe. Thus, the method of placing coil 407 coaxially with the pipe is weaker than the method of placing the toroidal low-frequency magnetic receiving coil 3011 coaxially with the pipe.

[0061] Figure 9This graph shows the relationship between excitation frequency and maximum propagation distance. The magnetic field distribution of the detection coil itself, i.e., the relationship between the coaxial upward frequency and the maximum detectable distance, shows very small differences in the broken line data from the three experiments, indicating good stability and repeatability of the experimental data, and the observed pattern is reliable. It can be seen that as the excitation frequency increases, the maximum propagation distance of the magnetic field (the range of magnetic field strength greater than 1 Gs) exhibits a monotonically decreasing trend. When the frequency increases from 15Hz to 150Hz, the maximum distance decreases from approximately 141mm to approximately 75mm, a decrease of nearly 47%. Therefore, in practical downhole applications, if a longer detection distance is required, a lower excitation frequency should be selected. If resolution or response speed is required, the relationship between frequency and propagation distance must be weighed.

[0062] This invention employs ultra-low frequency magnetic coupling technology, significantly reducing eddy current losses in metallic media and enabling stable wireless communication between the casing and the surrounding environment. The miniaturized transmitting unit is integrated into the cementing plug, allowing the communication device to be deployed into the well simultaneously with cementing operations without altering the plug's core functions of scraping, sealing, pressure bearing, and fluid isolation. This eliminates the need for additional deployment procedures, significantly reducing operating costs and construction complexity. The indoor testing and verification device can comprehensively perform tests on the device's magnetic field penetration capability, communication reliability, environmental adaptability, functional verification, and full-process simulation, enabling precise optimization of device parameters and reliability verification before deployment. This effectively reduces field application risks and ensures a high success rate for field operations.

Claims

1. A low-frequency magnetically coupled wireless communication device for inside and outside a downhole casing, characterized in that, include: Sleeve (1), variable diameter stabilizer (3), rubber plug (4); wherein, the variable diameter stabilizer (3) is fixed on the outside of sleeve (1), and the rubber plug (4) is set on the inside of sleeve (1); The rubber stopper (4) includes an upper rubber stopper cap (401), a sealing ring assembly (402), a screw (403), an outer rubber stopper body (404), an inner rubber stopper body (409), and a lower rubber stopper cap (410); an annular space (411) is formed between the outer rubber stopper body (404) and the inner rubber stopper body (409); a high-temperature resistant sealed chamber (406) is provided inside the inner rubber stopper body (409); a high-temperature resistant battery pack (2), an integrated circuit board (405), a coil (407), and a magnetic core are provided inside the high-temperature resistant sealed chamber (406). (408), wherein the magnetic core (408) is placed inside the coil (407), and the integrated circuit board (405) is connected to the coil (407) through wires; the sealing ring assembly (402) is fitted on the outside of the outer rubber plug body (404) and is interference-fitted with the inner wall of the sleeve (1); the upper rubber plug cover (401) is connected to the outer rubber plug body (404) and the inner rubber plug body (409) through screws (403), and the lower rubber plug cover (410) is connected to the outer rubber plug body (404) and the inner rubber plug body (409) through screws (403); The variable diameter centralizer (3) includes a main control sealed chamber (301), a drive push rod (302), a transmission flange (303), a force transmission push rod (304), a stiffness adaptive drive chamber (305), a centralizing arm assembly (306), a multi-parameter sensing unit (307), a lower connector (308), and a central body (309); wherein, the main control sealed chamber (301), the drive push rod (302), the transmission flange (303), the force transmission push rod (304), and the stiffness adaptive drive chamber (305) are connected in sequence, and the drive push rod (302) slides freely along the axial direction; the stiffness adaptive drive chamber (305) is coaxially fixed to the outer wall of the central body (309); the central body (309) is also evenly arranged with the centralizing arm assembly (306) and the multi-parameter sensing unit (307) in the circumferential direction; and a lower connector (308) is provided at one end of the central body (309).

2. The low-frequency magnetically coupled downhole casing internal and external wireless communication device according to claim 1, characterized in that, The main control sealed chamber (301) is equipped with an annular low-frequency magnetic receiving coil (3011), a power supply module (3012), a main control circuit module (3013), an electric power activation switch (3014), an electromagnet (3015), a high-temperature resistant reset spring (3016), a magnetic alloy locking pin (3017), and an annular locking slot (3018). The main control circuit module (3013) is connected to the electromagnet (3015). The electromagnet (3015), the high-temperature resistant reset spring (3016), and the magnetic alloy locking pin (3017) are connected in sequence. The annular locking slot (3018) is located at one end of the drive push rod (302) near the main control sealed chamber (301). The main control circuit module (3013) is electrically connected to the multi-parameter sensing unit (307).

3. The low-frequency magnetically coupled downhole casing internal and external wireless communication device according to claim 2, characterized in that, The straightening arm assembly (306) includes a transmission link (3061), an upper hinge link (3062), a straightening plate (3063), and a lower hinge link (3064); wherein, the transmission link (3061) connects the middle part of the upper hinge link (3062) to the transmission flange (303); one end of the upper hinge link (3062) is hinged to the central body (309), and the other end is connected to one end of the straightening plate (3063); the other end of the straightening plate (3063) is connected to one end of the lower hinge link (3064); the other end of the lower hinge link (3064) is hinged to the central body (309); and the upper hinge link (3062), the straightening plate (3063), the lower hinge link (3064), and the central body (309) form a parallelogram, and the stiffness adaptive drive cabin (305) is located within the parallelogram.

4. The low-frequency magnetically coupled downhole casing internal and external wireless communication device according to claim 3, characterized in that, The stiffness adaptive drive cabin (305) is equipped with a magnetorheological variable stiffness unit (3051), a support structure (3052), and a pre-energy storage disc spring assembly (3053). The magnetorheological variable stiffness unit (3051) is connected to the main control circuit module (3013) through an excitation coil. One end of the pre-energy storage disc spring assembly (3053) rests against a fixed step of the stiffness adaptive drive cabin (305), and the other end rests against one end of the magnetorheological variable stiffness unit (3051) through the support structure (3052). The other end of the magnetorheological variable stiffness unit (3051) is connected to a force transmission rod (304).

5. The low-frequency magnetically coupled downhole casing internal and external wireless communication device according to claim 4, characterized in that, The number of magnetorheological variable stiffness units (3051) is the same as the number of straightening arm assemblies (306).

6. The low-frequency magnetically coupled downhole casing internal and external wireless communication device according to claim 2, characterized in that, The multi-parameter sensing unit (307) includes a wellbore distance sensor, a temperature sensor, a pressure sensor, and a drilling fluid density sensor.

7. The low-frequency magnetically coupled downhole casing internal and external wireless communication device according to claim 1, characterized in that, An annulus (5) is formed between the casing (1) and the oil and gas well (6).

8. The low-frequency magnetically coupled downhole casing internal and external wireless communication device according to claim 1, characterized in that, Both the upper rubber stopper cap (401) and the lower rubber stopper cap (410) are provided with a weak structure with a preset pressure breaking threshold of 3MPa.

9. A method of using the low-frequency magnetically coupled downhole casing internal and external wireless communication device according to any one of claims 1 to 8, characterized in that, include: Step 1: Assemble the rubber plug (4), fix the high-temperature resistant battery pack (2), integrated circuit board (405), coil (407), and magnetic core (408) inside the high-temperature resistant sealed chamber (406), perform sealing and insulation tests on the main control sealed chamber (301), complete the rubber plug pressure burst test, and verify whether the preset pressure burst threshold of the upper rubber plug cover (401) and the lower rubber plug cover (410) meets the requirements; Step 2: Lower the casing (1) into the oil and gas well (6), fix the variable diameter centralizer (3) to the outer wall of the casing (1), calibrate the multi-parameter sensing unit (307), and record the depth of the variable diameter centralizer (3); Step 3: Inject pre-fluid into the casing (1) to clean the inner wall of the casing (1), and put the rubber plug (4) into the casing (1) through the wellhead launching device; at this time, the high temperature resistant sealing chamber (406) is in a low power consumption dormant state, inject displacement fluid into the casing (1), drive the rubber plug (4) to descend at a constant speed along the casing (1), and track the downward position of the rubber plug (4) in real time. Step 4: When the downward position of the rubber plug (4) is within the range of the variable diameter centralizer (3), the wellhead monitoring system sends a working command to the rubber plug (4) via a wireless link, waking up the integrated circuit board (405) in the high-temperature resistant sealing chamber (406), driving the coil (407) to generate a stable alternating magnetic field; the annular low-frequency magnetic receiving coil (3011) activates the power activation switch (3014) under the alternating magnetic field, triggering the main control circuit module (3013) to work, and the electromagnet (3015) is energized to generate a magnetic field, which is engaged in the magnetic alloy locking pin (301) in the annular locking slot (3018). 7) The electromagnet (3015) overcomes the elastic force of the high-temperature return spring (3016) and retracts radially, releasing the axial lock of the drive push rod (302); the pre-stored energy disc spring group (3053) releases stored energy and pushes the drive push rod (302) to move axially through the magnetorheological stiffness unit (3051), causing the centralizing plate (3063) to open radially until it contacts the well wall; the multi-parameter sensing unit (307) collects data in real time, and the main control circuit module (3013) adjusts the stiffness of the magnetorheological stiffness unit (3051) to control the opening degree and support force of the centralizing plate (3063); Step 5: Inject displacement fluid to drive the rubber stopper (4) down to the bottom of the sleeve (1) to achieve the setting of the rubber stopper (4); then continue to pressurize the sleeve (1). When the pressure in the sleeve (1) reaches the preset pressure breaking threshold, the weak structure of the upper rubber stopper cap (401) and the lower rubber stopper cap (410) is broken, forming a fluid channel. Step 6: Inject cement slurry and subsequent displacement fluid in sequence, and isolate the cement slurry and displacement fluid through the sealing ring assembly (402); during the displacement operation, the multi-parameter sensing unit (307) uploads the collected data to the wellhead monitoring system in real time for analysis and early warning; Step 7: When the displacement fluid reaches the designed position, all the cement slurry is replaced in the annulus (5), stop the injection operation, close the wellhead valve, and the wellhead monitoring system records the entire process operation data.

10. A test system for a low-frequency magnetically coupled downhole casing internal and external wireless communication device as described in any one of claims 1 to 8, characterized in that, Both ends of the sleeve (1) are provided with end caps (11). The coil (407) passes through the end caps (11) and is connected to the oscilloscope (7) and the power amplifier module (14) respectively. The power amplifier module (14) is connected to the microcontroller (12) and the laboratory power supply (13) respectively. The ring low-frequency magnetic receiving coil (3011) is connected to the oscilloscope (7). The coil (407) and the ring low-frequency magnetic receiving coil (3011) are both placed in the support base (9), and the ring low-frequency magnetic receiving coil (3011) and the coil (407) are at the same horizontal height. The teslameter (10) is used to measure the magnetic field strength generated by the coil (407), and the axis of the coil (407) is perpendicular to the axis of the sleeve (1).

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