Near-bit electromagnetic wave receiving structure based on modular magnetic core antenna array

Abstract

The invention discloses a near-bit electromagnetic wave receiving structure based on a modular magnetic core antenna array, and belongs to the technical field of coal mine drilling measurement while drilling. Comprising a drill collar, a modular antenna unit and a signal processing circuit, an annular mounting groove is formed in the outer wall of the drill collar, and the multiple modular antenna units are distributed in the annular mounting groove in a circular array mode to jointly form a distributed receiving antenna array; and the signal processing circuit is arranged in the drill collar, is connected with the distributed receiving antenna array through a main interface, and is used for carrying out amplification, synthesis and noise suppression processing on array signals, so that the received signal-to-noise ratio is improved. The antenna is decomposed into a plurality of independent modular antenna units which are distributed in the annular mounting groove of the drill collar in a circular array mode, distributed array receiving is achieved, the units can be rapidly replaced, assembling is convenient, signal sensitivity is high, and the antenna is suitable for drilling of complex coal seams.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coal mine downhole measurement while drilling equipment, and particularly relates to a near-bit electromagnetic wave receiving structure based on a modularized magnetic core antenna array. BACKGROUND

[0002] In coal mining and coalbed methane development engineering, the measurement while drilling (MWD) system is one of the key technologies for realizing real-time formation evaluation and drilling guidance. Among them, the near-bit electromagnetic wave receiving assembly, as an important part of the MWD system, is used to receive electromagnetic signals emitted near the drill bit, so as to obtain key parameters such as coalbed resistivity, dip angle, and azimuth angle. The accurate acquisition of these parameters directly affects the optimization of the drilling trajectory, the accuracy of coal seam identification and gas content evaluation, and especially in complex geological conditions, it can effectively prevent the risk of gas outburst and roof collapse. However, the traditional near-bit electromagnetic wave receiving assembly mostly adopts a monolithic antenna design, which exposes a series of technical problems under the extreme conditions of the coal mine drilling environment.

[0003] Firstly, the coal mine drilling process involves a high-temperature, high-pressure, and strong corrosion environment. The traditional monolithic antenna needs to be wound or embedded on the outer wall of the drill collar as a whole, which leads to a complex structure and makes it difficult to achieve good sealing and insulation. Once local damage occurs, the entire antenna array is disabled, and maintenance requires stopping drilling and disassembling the drill collar, causing significant time and economic losses, and may cause safety hazards in coal mines.

[0004] Secondly, the traditional antenna usually uses a single magnetic core and a single coil winding, which is susceptible to skin effect and proximity effect when receiving high-frequency electromagnetic waves (typical frequency range of 1-10 MHz), resulting in increased signal attenuation and enhanced noise interference. The magnetic core material is mostly ordinary silicon steel or ferrite, with low initial magnetic permeability (μ i <1000), limited saturation magnetic flux density (B s <1.0T), and easy saturation under direct current bias (such as coalbed magnetic mineral interference), which further reduces the receiving sensitivity. In addition, the installation of the monolithic antenna depends on the precise machining during the manufacturing stage of the drill collar, and the annular space matching degree is poor, which is prone to mechanical stress concentration, affecting the durability of the antenna, especially in the vibration environment of thin coal seams and fault zones in coal mines.

[0005] Furthermore, the dynamic environment of coal mine drilling sites amplifies these problems. During drill collar rotation and axial vibration, the antenna must withstand centrifugal force and impact loads. Traditional designs lack modularity, making transportation and on-site assembly inconvenient. High precision is required for the mounting slot; deviations exceeding 0.5mm can lead to uneven gaps between the antenna and drill collar, introducing parasitic capacitance and electromagnetic leakage. In terms of signal processing, traditional systems only support single-channel reception, unable to utilize array effects for beamforming and noise suppression. The received signal-to-noise ratio (SNR) is typically below 10dB, limiting its application in complex coal seams (such as soft coal seams with high gas content). Summary of the Invention

[0006] In view of this, the purpose of this invention is to solve the above-mentioned problems and provide a near-drill bit electromagnetic wave receiving structure based on a modular magnetic core antenna array. This component achieves distributed array reception by decomposing the antenna into multiple independent modular antenna elements and distributing them in a circular array within the annular mounting slot of the drill collar.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A near-drill bit electromagnetic wave receiving structure based on a modular magnetic core antenna array includes a drill collar, modular antenna units, and a signal processing circuit; the outer wall of the drill collar is provided with an annular mounting groove, and multiple modular antenna units are distributed in a circular array within the annular mounting groove to jointly form a distributed receiving antenna array; The signal processing circuit is located inside the drill collar and is connected to the distributed receiving antenna array through a main interface. It is used to amplify, synthesize, and suppress noise in the array signal, thereby improving the received signal-to-noise ratio.

[0008] Furthermore, the modular antenna unit includes a unit housing, a magnetic core fixed inside the unit housing, and a coil wound on the magnetic core; the unit housing encapsulates the magnetic core and the coil integrally through an injection molding process to form a sealed structure.

[0009] Furthermore, the coil is made of multiple strands of enameled wire wound together, the multiple strands of enameled wire being Litz wire, the coil being evenly distributed around the circumference of the magnetic core, the magnetic core being axially parallel to the drill collar axis, used to sense axial and radial electromagnetic wave components, and the multi-strand structure reducing resistance loss caused by high-frequency skin effect and proximity effect.

[0010] Furthermore, the radial inner and outer surfaces of the unit housing are concentric arc surfaces, with the radius of curvature matching the outer diameter of the drill collar and the depth of the annular mounting groove. The unit housing is made of high-strength, wear-resistant, and corrosion-resistant insulating material.

[0011] Furthermore, the modular antenna unit is detachably fixed in the annular mounting groove by means of snap-fit, dovetail groove or bolt.

[0012] Furthermore, the modular antenna units are electrically interconnected through flexible contacts, miniature waterproof connectors, or internal wiring.

[0013] Furthermore, a protective cover plate is provided at the radial opening of the annular mounting groove. The protective cover plate is made of high-strength insulating material and is fixed to cover the opening of the annular mounting groove by buckles or bolts. The inner surface of the protective cover plate is flush with the outer surface of the drill collar to form a continuous annular surface.

[0014] Furthermore, the magnetic core is a magnetic powder core or an amorphous / nanocrystalline magnetic core with high initial permeability and high saturation magnetic flux density. The magnetic core is fixed at the center of the unit shell. The circumferential cross-section of the magnetic core is circular or rectangular and is tightly coupled to the coil. The magnetic core is suitable for receiving high-frequency electromagnetic waves of 1~10MHz and has anti-DC bias saturation characteristics.

[0015] Furthermore, the magnetic core is an iron-silicon-aluminum magnetic powder core with an initial permeability greater than 4000 and a saturation magnetic flux density greater than 1.0T. The magnetic core is fixed to the bottom of the inner cavity of the unit shell by epoxy adhesive. The coil is wound in multiple layers with uniform distribution to optimize magnetic field concentration and reduce magnetic leakage.

[0016] Furthermore, the coil has 5 to 10 strands of enameled wire, each strand with a diameter of 0.1 to 0.3 mm, and the coil has 30 to 60 turns. The terminals at both ends of the coil are embedded in the insulating ports of the unit housing and connected to the electrical interconnection points of adjacent units for transmitting induced voltage signals to the signal processing circuit.

[0017] Furthermore, the number of distributed receiving antenna arrays is 4 to 16, the modular antenna elements are arranged at equal intervals along the circumference of the annular mounting slot, and the signal processing circuit includes a preamplifier, an analog-to-digital converter, and a digital beamforming module. The signal processing circuit acquires multi-channel signals from the distributed receiving antenna array through a main interface and performs phase alignment synthesis to achieve directional electromagnetic wave reception and formation parameter measurement.

[0018] The beneficial effects of this invention are as follows: This invention, through its modular magnetic core antenna array design, significantly solves the technical bottleneck of traditional monolithic antennas in drilling environments, achieving multiple advantages such as convenient installation, signal optimization, and improved durability.

[0019] 1. In terms of system architecture, the distributed array is assembled from multiple independent units in a circular array, facilitating on-site adaptation to different drill collar specifications and avoiding dependence on overall machining precision. Traditional antenna installation requires specialized equipment; this invention only requires manual insertion into the annular groove, reducing assembly time to less than 30 minutes and lowering labor costs by 20%. The integrated synthesis function of the signal processing circuit utilizes array coherence to suppress noise, improving receiving sensitivity by 1.5 times, making it suitable for low signal-to-noise ratio formations.

[0020] 2. The innovative structure of the modular antenna unit is a core highlight. The concentric arc surface design of the unit's outer shell precisely matches the gap between the drill collar and the well wall, ensuring uniform electromagnetic field distribution and avoiding parasitic interference. The magnetic core uses high μ... i High B s Materials, such as iron-silicon-aluminum magnetic powder cores, achieve an induction efficiency exceeding 80% at 1MHz high frequencies, exhibit strong resistance to DC bias, and a 30% improvement in saturation threshold, effectively addressing drilling fluid magnetic interference. The array can be expanded in number to improve azimuth resolution. The coils are wound with multiple strands of Litz wire, with skin depth optimized to 0.05mm, reducing proximity effect losses to below 5%. Compared to single-strand coils, the Q value increases by 25%, and signal fidelity is significantly improved.

[0021] 3. Enhanced connection and fixing mechanisms improve reliability and maintainability. Multi-mode fixing via snap-fit / dovetail / bolts ensures a vibration-induced detachment rate of <1%. Flexible contacts and miniature waterproof connectors (IP68 rating) achieve low-impedance interconnection (<0.1Ω), with signal attenuation <3dB. Internal wiring is centralized to a single main interface for easy integration with MWD tools. A protective cover seals the slots, preventing mud intrusion, and providing overall IP69K waterproofing. Compared to traditional soldered connections, this design allows for single-unit replacement without overall disassembly, increasing maintenance efficiency by 5 times and reducing drilling downtime losses.

[0022] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a schematic diagram of the near-drill bit electromagnetic wave receiving structure based on a modular magnetic core antenna array in this invention.

[0024] Figure 2 for Figure 1 Sectional view of AA.

[0025] Figure 3 This is a schematic diagram of the modular antenna unit in this invention.

[0026] Reference numerals: 1-Drill collar; 2-Annular mounting groove; 3-Modular antenna unit; 4-Protective cover; 31-Unit housing; 32-Magnetic core; 33-Coil. Detailed Implementation

[0027] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0028] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0029] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0030] Example 1 like Figures 1-3 As shown, a near-drill bit electromagnetic wave receiving structure based on a modular magnetic core antenna array is presented, including a drill collar 1, with an annular mounting groove 2 on the outer wall of the drill collar 1; multiple modular antenna units 3 are distributed in a circular array within the annular mounting groove 2, together forming a distributed receiving antenna array; a signal processing circuit is provided inside the drill collar 1, which is connected to the distributed receiving antenna array through a main interface, and is used to amplify, synthesize and suppress noise in the array signal, thereby improving the received signal-to-noise ratio.

[0031] Each modular antenna unit 3 includes a unit housing 31, a magnetic core 32 fixed inside the unit housing 31, and a coil 33 wound on the magnetic core 32. The unit housing 31 encapsulates the magnetic core 32 and the coil 33 integrally through injection molding to form a sealed structure. The radial inner surface of the unit housing 31 is in close contact with the outer wall of the drill collar 1 and embedded in the bottom of the annular mounting groove 2, while the radial outer surface faces the well wall to match the annular space. The coil 33 is made of multiple strands of enameled wire wound together. The multiple strands of enameled wire are Litz wire. The coil 33 is evenly distributed around the circumference of the magnetic core 32. The axial direction of the magnetic core 32 is parallel to the axis of the drill collar 1. It is used to sense axial and radial electromagnetic wave components and to reduce resistance loss caused by high-frequency skin effect and proximity effect through the multi-strand structure. The magnetic core 32 is an iron-silicon-aluminum magnetic powder core with an initial permeability greater than 4000 and a saturation magnetic flux density greater than 1.0T. The magnetic core 32 is fixed to the bottom of the inner cavity of the unit housing 31 with epoxy adhesive. The coil 33 is wound in multiple layers with uniform distribution to optimize magnetic field concentration and reduce magnetic leakage. The coil 33 has 5 to 10 strands of enameled wire, each with a diameter of 0.1 to 0.3 mm. The coil 33 has 30 to 60 turns. Terminals are led out from both ends of the coil 33 and embedded in the insulating port of the unit housing 31. They are connected to the electrical interconnection point of the adjacent unit and are used to transmit the induced voltage signal to the signal processing circuit.

[0032] Modular antenna units 3 are detachably fixed within the annular mounting groove 2 using a dovetail groove design. The dovetail groove structure allows the unit housing 31 to wedge into the side wall groove of the annular mounting groove 2, forming a fixed position and vibration-resistant connection. The modular antenna units 3 are electrically interconnected via elastic contacts located at the end faces of adjacent unit housings 31 for low-impedance signal transmission. A protective cover 4, made of high-strength insulating material, is provided at the radial opening of the annular mounting groove 2. The cover 4 is bolted to cover the opening of the annular mounting groove 2. The inner surface of the cover 4 is flush with the outer surface of the drill collar 1, forming a continuous annular surface for sealing against coal dust intrusion and maintaining hydrodynamic balance. The distributed receiving antenna array consists of eight units. The modular antenna units 3 are arranged at equal intervals along the circumference of the annular mounting groove 2. The signal processing circuit includes a preamplifier, an analog-to-digital converter, and a digital beamforming module. The signal processing circuit acquires multi-channel signals from the distributed receiving antenna array through a main interface, performs phase-aligned synthesis, and achieves directional electromagnetic wave reception and coal seam parameter measurement.

[0033] During installation at the coal mine drilling site, operators place the drill collar 1 in the underground drilling position and fix it by sequentially embedding multiple modular antenna units 3 into the dovetail grooves of the annular mounting slot 2. The concentric arc surface of the unit shell 31 ensures that the gap between it and the outer wall of the drill collar 1 and the well wall is less than 1mm, achieving uniform array distribution. The electrical contacts automatically align to form an interconnected network, and all signal lines converge to the main interface for connection with the signal processing circuit. The entire assembly process requires no special tools; simply pushing the unit shell 31 manually completes the insertion and fixation. Subsequently, the protective cover 4 is installed and tightened with bolts to close the opening of the annular mounting slot 2, preventing coal dust and gas from interfering with the electromagnetic signals.

[0034] During drilling, the magnetic core 32 senses high-frequency electromagnetic waves near the drill bit, and the coil 33 efficiently transmits the weak induced voltage to the signal processing circuit through the multi-strand structure of Litz wire. The circuit amplifies and synthesizes the multi-channel array signal, suppresses noise and improves the signal-to-noise ratio to more than 20dB, realizing real-time measurement of coal seam resistivity and azimuth angle. When a single modular antenna unit 3 is damaged by coal mine vibration, the protective cover plate 4 can be removed, and only the faulty unit can be replaced without disassembling the entire drill collar 1. The maintenance time is shortened to less than 30 minutes, avoiding drilling stoppage and delay in gas monitoring.

[0035] Example 2 This embodiment, based on Embodiment 1, adds high-temperature and pressure resistance optimization. The unit shell 31 is made of epoxy composite material resistant to 200℃. The modular antenna unit 3 is detachably fixed in the annular mounting groove 2 by bolts. The bolt structure connects the unit shell 31 to the side wall of the drill collar 1 through radial screws, forming a high-strength mechanical lock. The modular antenna units 3 are electrically interconnected through miniature waterproof connectors inserted into the side wall port of the unit shell 31, with a waterproof rating of IP68, ensuring that the signal transmission impedance is less than 0.1Ω in the high-pressure coal seam environment. The magnetic core 32 is made of nanocrystalline alloy with an initial permeability greater than 5000 and a saturation magnetic flux density greater than 1.2T. The magnetic core 32 is fixed to the bottom of the inner cavity of the unit shell 31 with epoxy adhesive. The coil 33 is wound in multiple layers with uniform distribution to further optimize magnetic field concentration and reduce magnetic leakage. The distributed receiving antenna array consists of 12 units. The modular antenna elements 3 are arranged at equal intervals along the circumference of the annular mounting slot 2. The signal processing circuit includes a preamplifier, an analog-to-digital converter, and a digital beamforming module. The signal processing circuit acquires multi-channel signals from the distributed receiving antenna array through the main interface and performs phase alignment synthesis to achieve directional electromagnetic wave reception and coal seam parameter measurement.

[0036] Under high-temperature and high-pressure conditions in coal mines, such as when drilling into deep coal seams (>1000m), when the modular antenna unit 3 is fixed in the annular mounting groove 2, the bolted connection can withstand temperatures above 150℃ and pressures above 100MPa. The epoxy composite material of the unit shell 31 ensures that the insulation breakdown voltage is greater than 10kV. At the same time, the miniature waterproof connector embedded in the port forms a precision seal to prevent gas and high-temperature drilling fluid from entering and causing short circuits. The nanocrystalline alloy structure of the magnetic core 32 improves the anti-saturation capability under DC bias interference by 30%. The multi-strand Litz wire of the coil 33 further reduces high-frequency loss by 15%, and the induction efficiency reaches over 85%. This design forces the array signal to be transmitted to the signal processing circuit through the main interface for digital beamforming, enhancing the azimuth resolution of complex coal seams (such as high-gas soft coal seams) to 0.5°. Operators can perceive the real-time data feedback after array synthesis and adjust the drilling trajectory to avoid the risk of gas outbursts. At the same time, the extended array of 12 units broadens the coverage area and is suitable for thin coal seam fault zones.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A near-drill bit electromagnetic wave receiving structure based on a modular magnetic core antenna array, characterized in that: It includes a drill collar (1), a modular antenna unit (3), and a signal processing circuit (4); the outer wall of the drill collar (1) is provided with an annular mounting groove (2), and multiple modular antenna units (3) are distributed in a circular array in the annular mounting groove (2) to form a distributed receiving antenna array. The signal processing circuit (4) is located inside the drill collar (1) and is connected to the distributed receiving antenna array through a main interface. It is used to amplify, synthesize and suppress noise in the array signal, thereby improving the received signal-to-noise ratio.

2. The near-drill bit electromagnetic wave receiving structure based on a modular magnetic core antenna array according to claim 1, characterized in that, The modular antenna unit (3) includes a unit housing (31), a magnetic core (32) fixed inside the unit housing (31), and a coil (33) wound on the magnetic core (32); the unit housing (31) encapsulates the magnetic core (32) and the coil (33) in one piece through injection molding to form a sealed structure.

3. The near-drill bit electromagnetic wave receiving structure based on a modular magnetic core antenna array according to claim 2, characterized in that, The coil (33) is made of multiple strands of enameled wire wound together. The multiple strands of enameled wire are Litz wire. The coil (33) is evenly distributed around the magnetic core (32). The magnetic core (32) is axially parallel to the axis of the drill collar (1) and is used to sense axial and radial electromagnetic wave components.

4. The near-drill bit electromagnetic wave receiving structure based on a modular magnetic core antenna array according to claim 2, characterized in that, The radial inner and outer surfaces of the unit housing (31) are concentric arc surfaces, and the radius of curvature matches the outer diameter of the drill collar (1) and the depth of the annular mounting groove (2). The unit housing (31) is made of high-strength, wear-resistant, and corrosion-resistant insulating material.

5. The near-drill bit electromagnetic wave receiving structure based on a modular magnetic core antenna array according to claim 1, characterized in that, The modular antenna unit (3) is detachably fixed in the annular mounting groove (2) by means of snap-fit, dovetail groove or bolt.

6. The near-drill bit electromagnetic wave receiving structure based on a modular magnetic core antenna array according to claim 5, characterized in that, The modular antenna units (3) are electrically interconnected through flexible contacts, miniature waterproof connectors or internal wiring.

7. The near-drill bit electromagnetic wave receiving structure based on a modular magnetic core antenna array according to claim 1, characterized in that, A protective cover plate (5) is provided at the radial opening of the annular mounting groove (2). The protective cover plate (5) is made of high-strength insulating material and is fixed to cover the opening of the annular mounting groove (2) by buckles or bolts. The inner surface of the protective cover plate (5) is flush with the outer surface of the drill collar (1) to form a continuous annular surface.

8. The near-drill bit electromagnetic wave receiving structure based on a modular magnetic core antenna array according to claim 2, characterized in that, The magnetic core (32) is a magnetic powder core or an amorphous / nanocrystalline magnetic core with high initial permeability and high saturation magnetic flux density. The magnetic core (32) is fixed at the center of the unit shell (31). The circumferential cross section of the magnetic core (32) is circular or rectangular and is tightly coupled with the coil (33). The magnetic core (32) is suitable for receiving high-frequency electromagnetic waves of 1-10MHz and has anti-DC bias saturation characteristics.

9. The near-drill bit electromagnetic wave receiving structure based on a modular magnetic core antenna array according to claim 8, characterized in that, The magnetic core (32) is an iron-silicon-aluminum magnetic powder core with an initial permeability greater than 4000 and a saturation magnetic flux density greater than 1.0T. The magnetic core (32) is fixed to the bottom of the inner cavity of the unit shell (31) by epoxy adhesive. The coil (33) is wound in multiple layers with uniform distribution to optimize magnetic field concentration and reduce magnetic leakage.

10. The near-drill bit electromagnetic wave receiving structure based on a modular magnetic core antenna array according to claim 3, characterized in that, The coil (33) has 5 to 10 strands of enameled wire, each strand with a diameter of 0.1 to 0.3 mm. The coil (33) has 30 to 60 turns. The terminals at both ends of the coil (33) are embedded in the insulating port of the unit housing (31) and connected to the electrical interconnection point of the adjacent unit for transmitting induced voltage signals to the signal processing circuit (4).

11. The near-drill bit electromagnetic wave receiving structure based on a modular magnetic core antenna array according to any one of claims 1 to 10, characterized in that, The number of distributed receiving antenna arrays is 4 to 16. The modular antenna units (3) are arranged at equal intervals around the annular mounting slot (2). The signal processing circuit (4) includes a preamplifier, an analog-to-digital converter and a digital beamforming module. The signal processing circuit (4) collects multi-channel signals from the distributed receiving antenna array through the main interface and performs phase alignment synthesis to realize directional electromagnetic wave reception and formation parameter measurement.

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