A wellbore remote detection high-sensitivity low-noise magnetic sensor

Abstract

The application discloses a kind of well far detection high-sensitivity low-noise magnetic sensor, belong to geophysical exploration technical field.Sensor includes magnetic core and coil assembly, pre-differential amplification module, magnetic flux negative feedback module, temperature compensation module, power supply and filtering module and titanium alloy packaging shell.Magnetic core is permalloy laminated hollow structure, coil assembly includes tightly coupled inductive coil and feedback coil;Pre-amplification module adopts the full differential structure of JFET parallel, realizes low-noise amplification;Magnetic flux negative feedback module expands working frequency band;Temperature compensation module stabilizes sensitivity and operating point;Power supply and filtering module reduce noise interference;Packaging shell realizes electromagnetic shielding, anticorrosion and anti-vibration protection.The application solves the problem of insufficient sensitivity, poor anti-interference and weak adaptability of existing sensor, can effectively capture far-field weak magnetic signal, and is suitable for resource exploration in complex underground environment.

Description

Technical Field

[0001] This invention belongs to the field of geophysical exploration technology of electrical logging technology, specifically involving a high-sensitivity, low-noise magnetic sensor for long-range detection in wells, which is particularly suitable for non-contact, long-distance magnetic signal detection and imaging of underground targets such as oil and gas reservoirs and metal mines. Background Technology

[0002] In the fields of deep-earth resource exploration and downhole engineering, borehole long-range detection technology is a key means of obtaining information on geological bodies around the well and in the far field. By deploying sensors inside the borehole to receive physical field responses such as electromagnetic waves, acoustic waves, or magnetic fields from underground structures, this technology can effectively identify important targets such as hidden structures, faults, and ore bodies near the well. Among them, magnetic detection shows unique advantages in complex geological conditions due to its significant response to magnetic minerals (such as magnetite and iron sulfides) and fluid-bearing fracture zones, and its immunity to high-resistivity layers.

[0003] The downhole working environment places extremely stringent demands on magnetic sensors. Traditional downhole magnetic sensors (such as fluxgate magnetometers and proton magnetometers) mostly employ single-coil or simple magnetic core structures, resulting in low magnetic field coupling efficiency and limited sensitivity. They are primarily suitable for measuring weak changes in the geomagnetic field near the wellbore (<10 meters) and struggle to effectively capture weak magnetic signals generated by weak magnetic targets in the far field. Furthermore, the confined space, high temperature, and high pressure in downhole environments, coupled with strong interference from drill string vibration, mud flow, and diurnal geomagnetic variations, significantly hinder the reliability, miniaturization, and anti-interference capabilities of traditional sensors, leading to low signal-to-noise ratios and limiting their long-range detection capabilities.

[0004] As exploration targets increasingly shift towards deeper layers (>5000 meters), small-scale concealed ore bodies, and complex structural systems, higher demands are placed on the performance of magnetic sensors. Existing technologies are ill-suited to the confined and highly vibrating environments of underground drilling. Therefore, developing a high-performance underground magnetic sensor that combines high sensitivity, wide bandwidth response, excellent anti-interference performance, and a compact structure has become an urgent technological requirement for overcoming the bottleneck of deep weak magnetic signal detection and achieving effective long-range underground exploration. Summary of the Invention

[0005] The purpose of this invention is to provide a high-sensitivity, low-noise magnetic sensor for long-range well detection, which solves the problems of insufficient sensitivity, limited operating bandwidth, and insufficient detection capability of far-field weak magnetic signals of existing magnetic sensors under conditions of high temperature, high pressure, strong vibration, and strong environmental interference. This satisfies the comprehensive requirements of long-range well detection applications for high sensitivity, wide bandwidth, and high reliability.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A high-sensitivity, low-noise magnetic sensor for long-range well detection includes:

[0008] The magnetic core and coil assembly, wherein the magnetic core is a laminated hollow structure magnetic core, and the coil assembly includes an induction coil and a feedback coil wound on the magnetic core;

[0009] A pre-differential amplifier module is electrically connected to the induction coil. The pre-differential amplifier module includes a differential input stage based on a junction field-effect transistor and a differential amplifier stage based on an operational amplifier that is electrically connected to the differential input stage.

[0010] The magnetic flux negative feedback module includes a feedback drive electrically connected to the differential output terminal of the differential amplifier stage and a feedback network connected in series with the feedback coil. The differential output is converted into a feedback current through the feedback network and injected into the feedback coil, so that the feedback coil generates a feedback magnetic flux in the magnetic core that is opposite to the direction of the external magnetic field, thus forming a magnetic flux negative feedback closed loop.

[0011] A temperature compensation module is used to adjust the bias parameters of the pre-differential amplifier module and / or the feedback parameters of the feedback network based on the detected temperature information.

[0012] The power supply and filtering module, including an isolated power supply unit and a filtering unit, is used to provide low-noise power to each module.

[0013] As a further technical solution of the present invention: the laminated hollow magnetic core is formed by stacking multiple layers of soft magnetic alloy sheets, and an insulating layer is provided between adjacent laminates. The soft magnetic alloy is permalloy 1J85.

[0014] As a further technical solution of the present invention: the feedback coil is wound on the outside of the induction coil and tightly coupled to the induction coil, and both the induction coil and the feedback coil are segmented wound using high-temperature resistant copper core enameled wire.

[0015] As a further technical solution of the present invention: the differential input stage includes at least one pair of junction field-effect transistor differential pairs, and multiple junction field-effect transistors are connected in parallel in the differential input stage to reduce input reference noise.

[0016] As a further technical solution of the present invention: the temperature compensation module includes a temperature detection unit, an analog-to-digital converter (ADC), a control unit, and a digital-to-analog converter (DAC). The control unit outputs an adjustment amount according to the temperature detection result, which is then converted by the DAC to adjust the bias parameter and / or the feedback parameter.

[0017] As a further technical solution of the present invention: the magnetic sensor is disposed in a metal encapsulation shell, the metal encapsulation shell is made of titanium alloy material, the inner wall is provided with an electromagnetic shielding layer, the outer layer is coated with a polytetrafluoroethylene anti-corrosion coating, and the interior is filled with high-temperature resistant insulating potting compound.

[0018] As a further technical solution of the present invention: the metal encapsulation shell is a segmented and detachable structure with API standard threaded interfaces at both ends, and a shock-absorbing buffer layer is provided between the magnetic core-coil assembly and the circuit module.

[0019] As a further technical solution of the present invention: the filtering unit includes a π-type filter network disposed on the output side of the isolated power supply unit and a low-noise linear voltage regulator unit. The π-type filter network is used to suppress switching ripple, and the low-noise linear voltage regulator unit is used for secondary voltage regulation.

[0020] As a further technical solution of the present invention: the diameter of the magnetic sensor is ≤5cm, the weight is ≤5.5kg, the length of the magnetic core is 0.85-0.95m, the side length of the cross section is 0.01-0.02m, the diameter of the copper core of the induction coil is 0.2-0.3mm, and the number of turns is ≤46000.

[0021] A design method for a high-sensitivity, low-noise magnetic sensor for long-range well detection includes the following steps:

[0022] (1) Under the constraints of diameter ≤ 5cm and weight ≤ 5.5kg, determine the length, cross-sectional dimensions and number of laminations of the stacked hollow magnetic core. The magnetic core is made of Permalloy 1J85 thin sheets and an insulating layer is provided between adjacent laminations.

[0023] (2) Design the wire diameter, number of turns and winding method of the induction coil and the feedback coil according to the magnetic core parameters, so that the feedback coil is wound on the outside of the induction coil and achieves tight coupling;

[0024] (3) Design a preamplifier differential amplifier circuit, adopting a two-stage structure of junction field-effect transistor differential input stage and operational amplifier differential amplification stage, and optimize the input reference noise by connecting multiple junction field-effect transistors in parallel;

[0025] (4) Design a magnetic flux negative feedback circuit, and convert the output of the differential amplifier stage into a feedback current through the feedback network to inject into the feedback coil to form a reverse feedback magnetic flux;

[0026] (5) Design a temperature compensation circuit to adjust the preamplifier bias parameters and / or feedback network parameters through temperature detection, ADC sampling, control unit operation and DAC output;

[0027] (6) Design an isolation power supply and filtering circuit. Use an isolation power supply unit combined with a π-type filter network and a low-noise linear voltage regulator unit to achieve analog / digital power supply isolation.

[0028] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0029] (1) By combining model reference adaptive control with online parameter identification, the problem of performance degradation of traditional fixed parameter controllers under varying operating conditions is overcome, and dynamic self-tuning of controller parameters is realized, which significantly improves the response speed and control accuracy of primary frequency regulation of pumped storage units.

[0030] (2) An adaptive compensation mechanism based on the estimation of upper and lower bounds of disturbance was designed, which can offset the influence of uncertain factors such as new energy fluctuations and water head changes in real time without the need for prior information of disturbance, thereby enhancing the robustness and frequency stability of the system under strong disturbance scenarios.

[0031] (3) The parameter adaptive optimization model comprehensively considers multi-dimensional frequency modulation performance indicators to ensure that the controller achieves the optimal balance between frequency suppression, response speed and action smoothness. Attached Figure Description

[0032] Figure 1 This is a structural diagram of the stacked magnetic core of an inductive magnetometer provided in an embodiment of the present invention;

[0033] Figure 2 A schematic diagram of the circuit principle provided for an embodiment of the present invention;

[0034] Figure 3 A circuit functional block diagram provided for embodiments of the present invention;

[0035] Figure 4 A schematic diagram of the mechanical structure of the magnetic sensor provided in an embodiment of the present invention;

[0036] Figure 5 This is a schematic diagram of the preset position of the circuit board of the magnetic sensor provided in an embodiment of the present invention. Detailed Implementation

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] like Figures 1-5 As shown, a high-sensitivity, low-noise magnetic sensor for long-range well detection includes a magnetic core assembly, a coil assembly, a power supply and filtering module, a low-noise preamplifier circuit, a magnetic flux negative feedback circuit, a temperature compensation module, and a packaging shell. The structure and parameters of each part are as follows:

[0039] The magnetic core is made of high-permeability permalloy (1J85) laminations. The magnetic core adopts a lamination hollow magnetic core structure, and high-temperature resistant insulating coating is applied between adjacent laminations to reduce eddy current loss. While ensuring magnetic field coupling efficiency, it effectively reduces eddy current loss and overall weight of the magnetic core, and improves the sensitivity and engineering applicability of the magnetic sensor under well application conditions.

[0040] The coil is wound with high-temperature resistant copper core enameled wire and adopts a segmented winding structure to reduce distributed capacitance;

[0041] The power supply and filtering module includes an isolated power supply unit and a filtering unit. The isolated power supply unit isolates the downhole power supply bus from the sensor's analog front-end power supply. It can use an isolated DC-DC power supply module or an isolation transformer rectification and regulation structure to output at least one isolated DC voltage. The filtering unit is located on the output side of the isolated power supply unit and includes a π-type filter network (capacitor-inductor / ferrite bead-capacitor) and a subsequent low-noise linear regulator unit. This unit performs secondary filtering and voltage regulation on the isolated output power supply to suppress switching ripple and conducted interference. Furthermore, the power supply and filtering module supplies power to the analog preamplifier / magnetic flux negative feedback circuit and the temperature compensation control circuit separately, or uses a branched π-type filter under the same isolated power supply to achieve analog / digital power supply isolation, thereby reducing digital switching noise coupling to the weak magnetic signal channel.

[0042] like Figure 2 As shown, the pre-amplifier differential amplifier circuit adopts a two-stage structure of "JFET differential input stage - operational amplifier fully differential amplification stage": the differential output terminals S+ and S- of the induction coil are respectively connected to the differential input terminals of the pre-amplifier differential amplifier circuit to form a low-noise differential acquisition of the measured weak magnetic signal; the output terminals of the operational amplifier respectively form high-side output V oH With low-end output V oL The magnetic flux negative feedback circuit includes a feedback resistor network R. fb (T) and the feedback coil terminals F+ and F-, where V oH / V oL via R fb (T) A feedback current is provided to the feedback coil, causing the feedback coil to generate a feedback magnetic flux in the magnetic core that is opposite in direction to the external measured magnetic field, thereby forming a magnetic flux negative feedback closed loop and extending the operating frequency band. The temperature compensation module includes an NTC thermistor, an RC filter network (capacitor C and resistor R), an analog-to-digital converter (ADC), a digital-to-analog converter (DAC), and a temperature control module. The ADC samples temperature-related nodes, and the temperature control module generates a control quantity based on the sampled temperature, which is output by the DAC to adjust the bias voltage V of the preamplifier differential amplifier circuit. B (T) and / or feedback resistor network R fb (T) is used to compensate for temperature drift and stabilize sensitivity and operating point.

[0043] The outer casing is made of titanium alloy, with an electromagnetic shielding layer on the inner wall and a polytetrafluoroethylene anti-corrosion coating on the outer layer. The interior is filled with high-temperature resistant insulating potting compound to achieve electromagnetic shielding, corrosion protection, and shock resistance.

[0044] The present invention also discloses a design method for the magnetic sensor, as follows:

[0045] (I) Implementation Design of Core Structure and Dimensional Parameters

[0046] The design of the weight and size of a magnetic sensor is a key aspect of improving its engineering applicability. In one embodiment of the present invention, the magnetic sensor has a diameter of no more than 5 cm and a weight of less than 5.5 kg, thereby achieving synergistic optimization of the magnetic sensor's performance, compactness, and portability.

[0047] Magnetic materials experience energy loss in alternating magnetic fields, generally referred to as magnetic loss, which mainly includes three types: hysteresis loss, eddy current loss, and residual loss. Eddy current loss in a magnetic core is directly proportional to the frequency and amplitude of the magnetic field and the thickness of the core, and inversely proportional to the resistivity of the core material. Therefore, to reduce hysteresis loss, magnetic materials with low coercivity and low saturation magnetic induction intensity should be selected when designing the core of an induction magnetometer.

[0048] This invention uses permalloy material to make the sensor magnetic core because it has the lowest hysteresis loss, and compared with amorphous alloy magnetic materials, permalloy has a lower material cost and a simpler processing technology.

[0049] Table 1: Comparison of physical parameters and magnetic properties of different magnetic core materials;

[0050]

[0051] The magnetic core of an inductive magnetometer operates in a changing geomagnetic field. According to the law of electromagnetic induction, eddy currents are induced inside the magnetic core. When these eddy currents flow through the magnetic material, they are lost due to resistance, resulting in a waste of magnetic field energy.

[0052] Due to its low resistivity, permalloy exhibits higher eddy current losses compared to magnetic materials such as ferrite. To overcome this drawback, permalloy magnetic cores are typically manufactured by bonding and stacking thin sheets of magnetic material, with an insulating coating applied between adjacent sheets. This significantly increases the resistance of the eddy current path, hindering the formation and flow of eddy currents, reducing energy waste, and improving instrument sensitivity.

[0053] Magnetic cores generate eddy current losses in alternating magnetic fields, and these losses are related to the resistivity of the core material, its geometry, and the rate of change of the magnetic field. To reduce eddy current losses, this invention employs a laminated hollow magnetic core structure with an insulating layer between adjacent laminations, thereby effectively blocking eddy current loops.

[0054] According to the principle of electromagnetic induction and combined with the analysis of the magnetic core structure parameters, the relationship between the eddy current loss of the magnetic core and the number of laminated layers is shown in formula (1). It can be seen from formula (1) that as the number of laminated layers n increases, the eddy current loss of the magnetic core decreases significantly according to the 1 / n² law.

[0055]

[0056] K is a proportionality coefficient related to the magnetic core material parameters, geometric dimensions and the amplitude of the external magnetic field,

[0057] n is the number of laminated layers of the magnetic core.

[0058] The inductance of the magnetic core increases with the increase of the cross-sectional area, but the weight also increases synchronously. Therefore, the weight constraint is more strict on the limitation of the number of turns of the coil; under the same side length, as the number of turns increases, the weight of the coil increases approximately linearly, the outer diameter increases significantly, the resistance shows a linear upward trend, and the inductance increases with the square relationship of the number of turns, indicating that there is an obvious coupling relationship between the parameters. Based on the above rules, in terms of material selection, permalloy laminated magnetic cores with high magnetic permeability and low loss are preferably used to ensure sensitivity and reduce eddy current loss; in terms of size, the length of the magnetic core is taken as 0.85 - 0.95 m, and the side length of the cross-section of the magnetic core is taken as 0.01 - 0.02 m to balance lightweight and size requirements; in terms of winding, the diameter of the copper core is reasonably selected as 0.2~0.3 mm, which can balance the resistance and weight, and the maximum number of turns should be controlled within 46000 turns under the constraint of a 0.3 mm diameter wire, so as to meet the downhole application constraints of a diameter not exceeding 5 cm and a weight less than 5.5 kg.

[0059] (2) Frequency Band and Sensitivity Characteristics under the Flux Negative Feedback Structure

[0060] To expand the working frequency band of the inductive magnetic sensor and improve the amplitude-phase mutation at the resonance point, the present invention adopts a flux negative feedback closed-loop structure, that is, a feedback flux opposite to the direction of the measured magnetic field is generated by the feedback coil, thereby forming a closed-loop negative feedback.

[0061] The mutual inductance M can be expressed as: , where 0 < k ≤ 1 is the coupling coefficient.

[0062] The sensitivity formula of the flux negative feedback inductive magnetometer is expressed as:

[0063]

[0064] At this time, the amplitude-frequency characteristic and phase-frequency characteristic of the sensor can be expressed as:

[0065]

[0066]

[0067] in, The sensor output voltage is the output variable used in sensitivity calculations. The magnetic flux density of the measured magnetic field is denoted as . It is the angular frequency of the measured magnetic field signal. It is the total number of turns of the induction coil. It is the effective cross-sectional area of ​​the magnetic core. It is the effective permeability of the magnetic core. R is the total amplification factor of the preamplifier circuit. fb It is the feedback resistor, L f It is the feedback coil inductance. It is the inherent inductance of the induction coil, determined by the number of turns and the parameters of the magnetic core. It is the distributed capacitance of the induction coil. It is the DC resistance of the induction coil. It is the mutual inductance between the induction coil and the feedback coil. It is a feedback resistor. This is the amplitude of the amplitude-frequency response (sensitivity modulus), which reflects the ratio of the sensor's "output voltage amplitude / input magnetic field amplitude" at different frequencies. It is the phase angle of the phase frequency characteristic, which represents the phase difference between the output voltage and the input magnetic field.

[0068] By employing a flux negative feedback structure, the operating bandwidth of the inductive magnetometer is no longer constrained by the coil resonance characteristics, resulting in a significantly improved operating bandwidth. Furthermore, the sensor's dynamic range is drastically reduced, and phase abrupt changes are effectively mitigated.

[0069] Key parameters affecting bandwidth and sensitivity include: preamplifier gain G and feedback resistor. and feedback coil inductance :

[0070] (1) The preamplifier does not affect the sensitivity in the flat region near the resonant frequency, but in the low-frequency and high-frequency ranges, the greater the amplification, the greater the sensitivity.

[0071] (2) Both the inductance of the feedback coil and the feedback resistance affect the sensitivity and the bandwidth. The larger the inductance of the feedback coil and the smaller the feedback resistance, the lower the sensitivity and the wider the bandwidth.

[0072] To achieve low-frequency band extension, the cutoff frequency should be adjusted. Lower, that is, increase the preamplifier gain G and increase the feedback coil inductance. Reduce feedback resistance .

[0073] (III) Design of Low-Noise Preamplifier Circuit

[0074] like Figure 2 As shown, the differential output terminals S+ and S- of the induction coil are connected to the differential input stage of the JFET, and the operational amplifier forms a fully differential amplifier, outputting V. oH With V oL V oH / V oL Through the feedback resistor network R fb (T) Feedback current is supplied to the terminals F+ and F- of the feedback coil, and the feedback coil forms a reverse feedback magnetic flux within the magnetic core to form a magnetic flux negative feedback closed loop; the temperature compensation module samples temperature-related nodes through the ADC and controls the temperature and outputs it to the DAC to bias the preamplifier V. B (T) and / or R fb (T) is adjusted to stabilize the operating point and sensitivity.

[0075] This invention proposes a fully differential ultra-low noise preamplifier circuit based on a JFET-op-amp hybrid structure. The circuit employs a high-performance JFET in the input stage to achieve low current noise and high input impedance; in the main amplification stage, it combines a high-performance operational amplifier to form a fully differential dual-terminal topology, thereby significantly improving common-mode rejection and differential output stability while maintaining low voltage noise.

[0076] As a fully differential circuit, it contains two signals simultaneously: a common-mode voltage that sets the operating point and a differential-mode signal to be amplified. Normal operation of the circuit requires stable operation in both modes.

[0077] This invention employs a fully differential preamplifier circuit structure based on junction field-effect transistors and operational amplifiers. To ensure the stability of the circuit in fully differential operating mode, the differential-mode channel and common-mode channel are analyzed separately.

[0078] Analysis results show that introducing a compensation capacitor C into the common-mode channel... F Afterwards, the common-mode loop can form a first-order stable closed loop, thereby effectively avoiding common-mode oscillation and ensuring that the preamplifier circuit operates stably over a wide frequency range.

[0079] Further noise analysis shows that the input reference noise is mainly dominated by the voltage noise of the junction field-effect transistors (JFETs). When multiple JFET devices are connected in parallel, the input reference voltage noise decreases as the number of parallel devices increases, as shown in Equation (5).

[0080]

[0081] Therefore, by reasonably selecting the number of parallel-connected MOSFETs, a trade-off optimization can be achieved between noise performance, input capacitance, and power consumption, thereby obtaining an ultra-low noise preamplifier effect.

[0082] (iv) Design of isolated power supply and filtering circuit

[0083] Due to the presence of switching ripple, long-line conducted interference, and common-mode noise in the downhole power supply environment, this embodiment includes a power supply and filtering module to provide low-noise power to the low-noise pre-differential amplifier module, the flux negative feedback module, and the temperature compensation module. The power supply and filtering module includes an isolated power supply unit and a filtering unit.

[0084] Isolated power supply unit: Used to isolate the external power supply from the analog front-end power supply, reducing ground loop interference and common-mode noise coupling; the isolated power supply unit can output one or more isolated DC voltages to meet the power supply requirements of the preamplifier circuit and feedback drive circuit.

[0085] Filtering unit: Located at the output of the isolated power supply unit, it includes at least one stage of π-type filter network (C in -L / C fb -Cout), where L can be a power inductor, common-mode choke, or ferrite bead; and a low-noise linear regulator (LDO) can be further configured to achieve secondary regulation, thereby reducing the ripple and broadband noise of the isolated power supply.

[0086] Power supply distribution and isolation: The analog front end (JFET differential input stage and op-amp differential amplification stage) and the temperature compensation control circuit (ADC / DAC / control unit) can use independent voltage regulation branches, or use the "branch π-type filter + single-point grounding" method under the same isolated power supply to achieve analog / digital isolated power supply and suppress digital switching noise crosstalk.

[0087] Through the above-mentioned isolated power supply and multi-stage filtering and voltage regulation design, the equivalent input noise introduced by power supply noise can be significantly reduced, thereby improving the detection capability of weak magnetic signals in well remote detection.

[0088] (v) Encapsulation and structural protection design suitable for downhole environments

[0089] The encapsulation shell is made of TC4 titanium alloy, which has high specific strength and can meet the requirements for downhole pressure and vibration resistance; it can maintain stable performance in low-temperature to medium-temperature environments, resisting both low-temperature impact and general high-temperature operating conditions. The potting compound is an epoxy-based high-temperature resistant potting compound to achieve heat conduction and insulation protection.

[0090] The outer casing is designed with a segmented, detachable structure for easy downhole installation and maintenance. A shock-absorbing buffer layer is placed between the magnetic core-coil assembly and the circuit module to reduce vibration transmission. The circuit module is fixed with potting compound. API standard threaded interfaces are installed at both ends of the casing for compatibility with downhole drill pipe and detection instruments. The inner wall is lined with a permalloy shielding layer, and the outer layer is coated with a polytetrafluoroethylene (PTFE) anti-corrosion coating.

[0091] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0092] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment have been appropriately combined to form other embodiments that are easy for those skilled in the art to understand.

Claims

1. A high-sensitivity, low-noise magnetic sensor for long-range well detection, characterized in that, include: The magnetic core and coil assembly, wherein the magnetic core is a laminated hollow structure magnetic core, and the coil assembly includes an induction coil and a feedback coil wound on the magnetic core; A pre-differential amplifier module is electrically connected to the induction coil. The pre-differential amplifier module includes a differential input stage based on a junction field-effect transistor and a differential amplifier stage based on an operational amplifier that is electrically connected to the differential input stage. The magnetic flux negative feedback module includes a feedback drive electrically connected to the differential output terminal of the differential amplifier stage and a feedback network connected in series with the feedback coil. The differential output is converted into a feedback current through the feedback network and injected into the feedback coil, so that the feedback coil generates a feedback magnetic flux in the magnetic core that is opposite to the direction of the external magnetic field, thus forming a magnetic flux negative feedback closed loop. A temperature compensation module is used to adjust the bias parameters of the pre-amplifier differential amplifier module and / or the feedback parameters of the feedback network based on the detected temperature information. The power supply and filtering module, including an isolated power supply unit and a filtering unit, is used to provide low-noise power to each module.

2. The high-sensitivity, low-noise magnetic sensor for long-range well detection according to claim 1, characterized in that, The hollow magnetic core is formed by stacking multiple layers of soft magnetic alloy sheets, with an insulating layer between adjacent sheets. The soft magnetic alloy is permalloy 1J85.

3. The high-sensitivity, low-noise magnetic sensor for long-range well detection according to claim 1, characterized in that, The feedback coil is wound around the outside of the induction coil and is tightly coupled to the induction coil. Both the induction coil and the feedback coil are wound in sections using high-temperature resistant copper core enameled wire.

4. The high-sensitivity, low-noise magnetic sensor for long-range well detection according to claim 1, characterized in that, The differential input stage includes at least one pair of junction field-effect transistor differential pairs, and multiple junction field-effect transistors are connected in parallel in the differential input stage to reduce input reference noise.

5. The high-sensitivity, low-noise magnetic sensor for long-range well detection according to claim 1, characterized in that, The temperature compensation module includes a temperature detection unit, an analog-to-digital converter (ADC), a control unit, and a digital-to-analog converter (DAC). The control unit outputs an adjustment amount based on the temperature detection result, which is then converted by the DAC to adjust the bias parameter and / or the feedback parameter.

6. The high-sensitivity, low-noise magnetic sensor for long-range well detection according to claim 1, characterized in that, The magnetic sensor is housed in a metal encapsulation shell made of titanium alloy. The inner wall is provided with an electromagnetic shielding layer, the outer layer is coated with a polytetrafluoroethylene anti-corrosion coating, and the interior is filled with high-temperature resistant insulating potting compound.

7. The high-sensitivity, low-noise magnetic sensor for long-range well detection according to claim 6, characterized in that, The metal encapsulation shell has a segmented and detachable structure with API standard threaded interfaces at both ends, and a shock-absorbing buffer layer is set between the magnetic core-coil assembly and the circuit module.

8. The high-sensitivity, low-noise magnetic sensor for long-range well detection according to claim 1, characterized in that, The filtering unit includes a π-type filter network disposed on the output side of the isolated power supply unit and a low-noise linear voltage regulator unit. The π-type filter network is used to suppress switching ripple, and the low-noise linear voltage regulator unit is used for secondary voltage regulation.

9. The high-sensitivity, low-noise magnetic sensor for long-range well detection according to claim 1, characterized in that, The magnetic sensor has a diameter ≤5cm and a weight ≤5.5kg. The magnetic core has a length of 0.85-0.95m and a cross-sectional side length of 0.01-0.02m. The induction coil has a copper core diameter of 0.2-0.3mm and a number of turns ≤46000.

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