An induction logging system and method based on an equivalent counter-flux array

Abstract

This invention relates to the field of petroleum exploration technology, specifically disclosing an induction logging system and method based on an equivalent antimagnetic flux array. The method includes a transmitting module and a receiving module. The equivalent antimagnetic flux probe device adopts a modular, compartmentalized structure, consisting of multiple independent equivalent antimagnetic flux detection units axially coaxially cascaded and spliced ​​together. An electromagnetic shielding compartment is provided between adjacent equivalent antimagnetic flux detection units. Each equivalent antimagnetic flux detection unit is a three-coil equivalent antimagnetic flux module consisting of a transmitting coil, a receiving coil, and a compensation coil. By employing an array-type, splicable equivalent antimagnetic flux probe device combined with multi-frequency differential detection, the decoupling advantages of equivalent antimagnetic flux are retained, while the layering capability of multi-frequency detection is introduced. This achieves a balance between vertical resolution and radial detection depth, significantly improving the information acquisition capability of the instrument without increasing the well diameter requirement, and enabling "one probe to multiple depths and one measurement to multiple layers" detection capabilities.

Description

Technical Field

[0001] This invention relates to the field of petroleum exploration technology, specifically to an induction logging system and method based on an equivalent anti-magnetic flux array. Background Technology

[0002] With the increasing demand for mineral resources in human society, induction logging, as a rapidly developing electrical exploration technology, has become increasingly widespread and important in the field of geological prospecting. Induction logging is a geophysical logging method based on the principle of electromagnetic induction to study the conductivity of rock formations, belonging to the branch of electrical logging. Its basic working process involves a transmitting coil emitting an alternating current to generate an alternating magnetic field. This alternating magnetic field excites formation eddies, and the secondary field generated by these eddies induces an electromotive force (EMF) in the receiving coil. This induced EMF is the useful signal we need, and the formation conductivity can be inverted from the acquired useful signal. Based on domestic and international research and applications, induction logging, as an important tool in the fields of resource exploration and energy exploration, has received widespread attention from numerous researchers.

[0003] While induction logging offers significant advantages in exploration, it also has certain limitations. The common coil structure in induction logging is a dual-coil structure, where strong mutual inductive coupling between the transmitting and receiving coils can submerge the secondary field signal. While devices that separate the transmitter and receiver are typically used to eliminate the induced electromotive force in the receiving coil, this is not a complete solution. Traditional methods also involve observing the transient response and transmitted current waveform throughout the entire process, then using numerical calculations to remove the primary field from the measured total field to obtain the subsurface secondary field. However, theoretical calculations inevitably deviate from reality, and conventional induction logging instruments, limited by their dual-coil design, have a relatively large vertical detection range, making it impossible to achieve precise stratigraphic layering. Therefore, addressing the problems of traditional methods and researching effective decoupling methods to improve the system's signal-to-noise ratio and detection accuracy is crucial for induction logging research. Summary of the Invention

[0004] The purpose of this invention is to provide an induction logging system and method based on an equivalent anti-magnetic flux array to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] An induction logging system based on an equivalent anti-magnetic flux array includes:

[0007] The transmitting module includes a program control circuit, a power amplifier circuit, a tuning circuit, and an equivalent reverse magnetic flux probe device;

[0008] The receiving module includes a current acquisition circuit, a low-noise differential amplifier circuit, a data acquisition card, and a host computer;

[0009] The equivalent antimagnetic flux probe device adopts a compartmentalized modular structure, which is composed of multiple independent equivalent antimagnetic flux detection units cascaded coaxially, and an electromagnetic shielding compartment is set between adjacent equivalent antimagnetic flux detection units.

[0010] Each of the aforementioned equivalent reverse magnetic flux detection units is a three-coil equivalent reverse magnetic flux module consisting of a "transmitting coil - receiving coil - compensation coil";

[0011] The program control circuit is connected to the power amplifier circuit, the output terminal of the power amplifier circuit is connected to the input terminal of the transmitting coil and the compensation coil, and the transmitting coil is connected to the current acquisition circuit.

[0012] The output terminal of the receiving coil is connected to the low-noise differential amplifier circuit, the output terminal of the low-noise differential amplifier circuit is connected to the data acquisition card, and the data acquisition card is communicatively connected to the host computer.

[0013] As a further embodiment of the present invention, the electromagnetic shielding compartment is made of permalloy and is used to block axial magnetic circuit crosstalk between adjacent detection units.

[0014] As a further embodiment of the present invention, in each of the equivalent antimagnetic flux detection units, the transmitting coil and the compensation coil have the same number of turns, opposite winding directions, are equidistant from and coaxially coincident with the receiving coil.

[0015] As a further embodiment of the present invention, the receiving module further includes a digital phase-locked amplifier unit, the output terminal of the low-noise differential amplifier circuit is connected to the digital phase-locked amplifier unit, the output terminal of the digital phase-locked amplifier unit is connected to the data acquisition card, and the digital phase-locked amplifier unit uses the transmit current reference signal acquired by the current acquisition circuit to perform coherent demodulation.

[0016] This invention also provides an induction logging method based on an equivalent anti-magnetic flux array, comprising the following steps:

[0017] The host computer sends control parameters to the program control circuit to configure the working status of the transmitting and receiving modules.

[0018] The program control circuit generates a drive signal according to the control parameters. After being amplified by the power amplifier circuit, the drive signal drives the transmitting coil and compensation coil of the equivalent reverse magnetic flux detection unit to generate an alternating magnetic field.

[0019] The receiving coil generates the original induced signal, while the current acquisition circuit acquires the operating current of the transmitting coil and converts it into a reference signal;

[0020] The original induction signal, after being conditioned by a low-noise differential amplifier circuit, is synchronously acquired by the data acquisition card and transmitted to the host computer along with the reference signal.

[0021] The host computer analyzes and processes the collected signals to reconstruct the geological information.

[0022] As a further embodiment of the present invention, the original induced signal is conditioned by a low-noise differential amplifier circuit and then enters a digital lock-in amplifier unit. The reference signal is used for coherent demodulation to extract the secondary field component with the same frequency as the transmission frequency.

[0023] As a further embodiment of the present invention, the method further includes: independently controlling the transmission frequency and current amplitude of multiple cascaded equivalent antimagnetic flux detection units through the program control circuit, so as to synchronously acquire the formation response at different radial depths.

[0024] Compared with the prior art, the beneficial effects of the present invention are: by using an array-type splicable equivalent back flux probe device combined with multi-frequency differential detection, the decoupling advantage of equivalent back flux is retained, and the layering capability of multi-frequency detection is introduced, achieving a balance between longitudinal resolution and radial detection depth. This allows the instrument to significantly improve its information acquisition capability without increasing the well diameter requirement, and it has the detection capability of "one probe to multiple depths and one measurement to multiple layers". Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention.

[0026] Figure 1 This is a system structure block diagram of an induction logging system based on an equivalent anti-magnetic flux array, provided as an embodiment of the present invention.

[0027] Figure 2 A flowchart of an induction logging method based on an equivalent antimagnetic flux array provided in an embodiment of the present invention.

[0028] Figure 3 This is a block diagram illustrating the processing architecture combining adaptive multi-frequency differential amplification and digital phase-locked amplification provided in an embodiment of the present invention.

[0029] Figure 4 The simulation diagram shows the effect of the equivalent anti-magnetic flux coil system provided in the embodiment of the present invention.

[0030] Figure 5 This is a comparison chart showing the impact of different numbers of anomalies on the received signal, provided in an embodiment of the present invention. Detailed Implementation

[0031] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0032] In this embodiment of the invention, an induction logging system based on an equivalent anti-magnetic flux array includes:

[0033] The transmitting module includes a program control circuit, a power amplifier circuit, a tuning circuit, and an equivalent reverse magnetic flux probe device;

[0034] The receiving module includes a current acquisition circuit, a low-noise differential amplifier circuit, a data acquisition card, and a host computer;

[0035] The equivalent antimagnetic flux probe device adopts a compartmentalized modular structure, which is composed of multiple independent equivalent antimagnetic flux detection units cascaded coaxially, and an electromagnetic shielding compartment is set between adjacent equivalent antimagnetic flux detection units.

[0036] Each of the aforementioned equivalent reverse magnetic flux detection units is a three-coil equivalent reverse magnetic flux module consisting of a "transmitting coil - receiving coil - compensation coil";

[0037] The program control circuit is connected to the power amplifier circuit, the output terminal of the power amplifier circuit is connected to the input terminal of the transmitting coil and the compensation coil, and the transmitting coil is connected to the current acquisition circuit.

[0038] The output terminal of the receiving coil is connected to the low-noise differential amplifier circuit, the output terminal of the low-noise differential amplifier circuit is connected to the data acquisition card, and the data acquisition card is communicatively connected to the host computer.

[0039] In this embodiment, the transmitting module also includes a transmitting power supply, which supplies power to the full-bridge power amplifier circuit. The power amplifier circuit adopts a highly integrated design. The transmitting module works in a coordinated manner according to the logic of energy supply-parameter control-signal amplification-resonant transmission-coupling cancellation: the transmitting power supply first stabilizes and filters the external power into a stable DC power supply to power the program control circuit, power amplifier circuit, etc. The miniaturized design and overall integration scheme reduce the system volume and lower the wellhead size requirements; the program control circuit generates digital control signals according to preset logging parameters to precisely regulate the highly integrated power amplifier. The circuit's operating state enables real-time adaptation of the transmitted signal parameters; the highly integrated power amplifier circuit amplifies the control signal into a high-power drive signal, driving the arrayed and splicable equivalent anti-magnetic flux detection unit to generate an alternating transmitted magnetic field, which penetrates the strata and excites a secondary induced magnetic field; the compensation coil, arranged coaxially with the transmitting coil, generates a compensation magnetic field with the opposite direction and equal amplitude to the transmitting coil's magnetic field under the control of the program control circuit. Through the principle of equivalent anti-magnetic flux, the direct mutual inductance coupling between the transmitting and receiving coils is canceled, solving the problem of secondary field signal submersion. Furthermore, the miniaturized winding process of the coil further reduces the probe size.

[0040] The receiving module also includes a power isolation circuit. The receiving module works collaboratively according to the logic of signal sensing-acquisition conditioning-isolation transmission-analysis output: the receiving coil senses the combined magnetic field of the transmitting magnetic field and the secondary field of the formation, generating a raw induced signal containing formation information; at the same time, the current acquisition circuit collects the operating current of the transmitting coil in real time and converts it into a filtered reference voltage signal, providing a transmitting end reference for subsequent decoupling processing; the weak signal output by the receiving coil is first pre-conditioned by a low-noise differential amplifier circuit, and then enters a digital phase-locked loop amplifier unit, where coherent demodulation is performed using the transmitting current reference signal to extract the secondary field component with the same frequency as the transmitting frequency; the power isolation circuit provides isolated power to the conditioning circuit, acquisition card and other modules, blocking the power interference path of the transmitting system and ensuring the low-noise performance of the receiving end. Its miniaturized design is suitable for instrument integration requirements.

[0041] The host computer is used to transmit the control parameters that need to be configured to the electronic sub-junction and to receive the collected data. It also controls the start and end of the instrument's operation. The data acquisition card synchronously acquires the transmitted current signal and the conditioned secondary field signal, performs analog-to-digital conversion and buffer verification, and then transmits the data to the host computer. The synchronous acquisition design ensures the consistency of signal time. The host computer analyzes the two digital signals through an inverse algorithm, removes interference, and restores the original secondary field signal containing stratigraphic information. After feature extraction, data analysis, and visualization, the exploration results are output, which not only improves the decoupling effect but also enhances the exploration efficiency and the level of operational intelligence, providing a reliable basis for geological prospecting.

[0042] like Figure 1As shown, the equivalent back magnetic flux probe device adopts an integrated titanium alloy sealed probe design. The front end is the front acquisition chamber, the middle is the array coil system chamber, the rear end is the power transmission chamber, and the end is the communication and power isolation chamber. The middle array coil system chamber is composed of multiple independent equivalent back magnetic flux detection units axially coaxially cascaded together.

[0043] The transmission frequency and current amplitude of the equivalent reverse magnetic flux detection unit can be independently controlled by the program control circuit. Through multi-frequency differential mode, it can achieve layered detection at different radial depths. 2 to 6 units can be spliced ​​according to logging requirements to adapt to exploration needs of different well depths and different vertical resolutions.

[0044] By using an array-type splicable equivalent anti-magnetic flux probe device, the primary field can be effectively filtered out. By using multi-frequency differential technology to simultaneously transmit signals of different frequencies to multiple equivalent anti-magnetic flux units, the receiving system can simultaneously acquire the formation response at multiple radial depths. Combined with differential processing, common-mode interference can be further suppressed and signal purity can be improved.

[0045] In a preferred embodiment of the present invention, the electromagnetic shielding compartment is made of permalloy and is used to block axial magnetic circuit crosstalk between adjacent detection units.

[0046] In this embodiment, a permalloy electromagnetic shielding compartment is introduced between the equivalent antimagnetic flux detection units. This compartment not only provides structural support, but more importantly, it utilizes the high initial permeability of the permalloy to capture the overflowing axial stray magnetic lines of force when multiple frequency currents are excited simultaneously during the logging process. The permalloy compartment guides these lines to the outer shell for closure, blocking the axial electromagnetic crosstalk between adjacent units. This effectively solves the secondary field inversion error caused by the mutual inductance coefficient between cascaded units.

[0047] In a preferred embodiment of the present invention, in each of the equivalent antimagnetic flux detection units, the transmitting coil and the compensation coil have the same number of turns, opposite winding directions, are equidistant from and coaxially coincident with the receiving coil.

[0048] In this embodiment, the amplitude and phase of the current in the compensation coil are adjusted through hardware design and program control circuitry to ensure that the magnetic field generated by the compensation coil and the magnetic field of the transmitting coil satisfy the equal-value antimagnetic flux condition of "opposite direction and equal amplitude". The control relationship that the hardware design needs to satisfy is: n R =n T S R =S T n R S R n represents the number of turns and area of ​​the receiving coil. T S TThe number of turns and area of ​​the transmitting coil are specified, and the transmitting and receiving coils are wound in opposite directions, placed at opposite ends of the receiving coil and equidistant from it. The program control circuit adjusts the current amplitude and phase of the compensation coil to ensure that the current flowing to the transmitting and compensation coils is equal in magnitude and direction. This physically eliminates primary field interference.

[0049] In a preferred embodiment of the present invention, the receiving module further includes a digital phase-locked amplifier unit. The output terminal of the low-noise differential amplifier circuit is connected to the digital phase-locked amplifier unit, and the output terminal of the digital phase-locked amplifier unit is connected to the data acquisition card. The digital phase-locked amplifier unit uses the transmit current reference signal acquired by the current acquisition circuit to perform coherent demodulation.

[0050] In this embodiment, the receiving section introduces a processing architecture that combines adaptive multi-frequency differential amplification and digital phase-locked amplification. The weak signal output by the receiving coil is first pre-conditioned by a low-noise differential amplifier circuit, and then enters the digital phase-locked amplification unit. Coherent demodulation is performed using the transmit current reference signal to extract the secondary field component with the same frequency as the transmit frequency. The output signal is then connected to the data acquisition card and then input to the host computer for recording of the secondary field signal.

[0051] The working process of this invention is as follows: Based on the detection target and geological conditions, a suitable equivalent reverse magnetic flux detection unit is selected; the transmitting power supply, program control circuit, power amplifier circuit, and tuning circuit of the transmitting module are connected in sequence, and the transmitting coil and compensation coil are connected to the output terminal of the tuning circuit; the output terminal of the receiving coil of the receiving system is connected to the input terminal of the low-noise differential amplifier circuit, the current acquisition circuit is connected to the power supply circuit of the transmitting coil and connected to the low-noise differential amplifier circuit, the power isolation circuit is connected to the power supply terminal of the low-noise differential amplifier circuit and the data acquisition card respectively, and the output terminal of the data acquisition card is connected to the host computer for communication.

[0052] The transmitting module's power supply is activated, providing a stable, regulated, and filtered DC power supply to all modules, including the program control circuit and power amplifier circuit. Preset logging parameters, including the transmission signal frequency, amplitude, transmission duration, and tuning circuit resonance parameters, are sent from the host computer to the program control circuit. The program control circuit then performs initial calibration of the highly integrated power amplifier circuit's operating status and the tuning circuit's resonant frequency. Simultaneously, the receiving system parameters are configured, setting the data acquisition card's sampling rate, the low-noise differential amplifier circuit's amplification factor, and filtering parameters to ensure each module is in a suitable operating state, thus completing the overall system initialization.

[0053] After system initialization, the program control circuit drives the power amplifier circuit to output a high-power drive signal. After optimization by the tuning circuit, the signal drives the transmitting coil of the equivalent anti-magnetic flux detection unit to generate an alternating transmitting magnetic field. This magnetic field penetrates the strata and excites a secondary induced magnetic field. At the same time, the compensation coil generates a compensation magnetic field with the opposite direction and equal amplitude to the magnetic field of the transmitting coil under the control of the program control circuit. The direct mutual inductance coupling between the transmitting and receiving coils is canceled through the principle of equivalent anti-magnetic flux.

[0054] The receiving coil induces a combined magnetic field with the secondary field of the formation, generating a raw induced signal containing formation information. Simultaneously, the current acquisition circuit acquires the operating current of the transmitting coil and converts it into a reference voltage signal; for example... Figure 3 As shown, the weak signal output from the receiving coil is first pre-conditioned by a low-noise differential amplifier circuit, and then enters a digital lock-in amplifier unit. Coherent demodulation is performed using the transmitted current reference signal to extract the secondary field component with the same frequency as the transmission frequency. A power isolation circuit continuously blocks power interference from the transmitting system, ensuring stable operation of the receiver. The data acquisition card synchronously acquires the conditioned secondary field signal and the reference current signal, performs analog-to-digital conversion and buffer verification, and then transmits them to the host computer. The host computer analyzes and processes the two digital signals using an inverse kinematics algorithm, removing interference and restoring the original secondary field signal containing stratigraphic information. After feature extraction, data analysis, and visualization, the exploration results are output, achieving high-precision geological exploration with a small instrument.

[0055] like Figure 2 As shown, this embodiment of the invention also provides an induction logging method based on an equivalent anti-magnetic flux array, comprising the following steps:

[0056] The host computer sends control parameters to the program control circuit to configure the working status of the transmitting and receiving modules.

[0057] The program control circuit generates a drive signal according to the control parameters. After being amplified by the power amplifier circuit, the drive signal drives the transmitting coil and compensation coil of the equivalent reverse magnetic flux detection unit to generate an alternating magnetic field.

[0058] The receiving coil generates the original induced signal, while the current acquisition circuit acquires the operating current of the transmitting coil and converts it into a reference signal;

[0059] The original induction signal, after being conditioned by a low-noise differential amplifier circuit, is synchronously acquired by the data acquisition card and transmitted to the host computer along with the reference signal.

[0060] The host computer analyzes and processes the collected signals to reconstruct the geological information.

[0061] In this embodiment, the program control circuit receives instructions from the host computer, parses the control parameters therein, generates corresponding control instructions, and then outputs the corresponding drive signal to the power amplifier circuit. This drive signal is input to the transmitting coil and the compensation coil. Since two parallel, coaxial coils with opposite winding directions are used as the transmitting source (dual-coil source), and the secondary field is received in the middle plane of the dual-coil source, the primary field flux is always zero because the receiving surface is the plane of equal reverse magnetic flux of the upper and lower coils.

[0062] The output terminal of the transmitting coil is connected to the input terminal of the current acquisition circuit. The current acquisition circuit records the transmitted current. It can be proven that the sum of the integrals of the measured induced voltages received by the receiving coil is equal to the vector sum of the primary and secondary fields, that is:

[0063] ;

[0064] Where V(t) is the actual induced voltage signal received by the receiving coil. It is a pure secondary field signal. This is a single field signal.

[0065] The primary induced voltage generated by the transmitting coil on the receiving coil is:

[0066] ;

[0067] Where I is the emission current, µ is the magnetic permeability of the medium, and n R S R n represents the number of turns and area of ​​the receiving coil. T S T Let represent the number of turns and area of ​​the transmitting coil, j be the imaginary unit, ω be the angular frequency of the alternating current, and L be the distance between the transmitting and receiving coils.

[0068] The current measurement circuit is connected to the transmitting coil, and then the data is transmitted to the acquisition card to read the magnitude of the current, thereby determining the magnitude of the primary field signal and the secondary field signal.

[0069] The primary induced voltage generated on the receiving coil by the compensation coil is:

[0070] ;

[0071] The sum of the induced electromotive forces generated in the receiving coil by the transmitting coil and the compensation coil is:

[0072] ;

[0073] The value of is zero, and the coupling effects of the transmitting coil and the compensation coil on the receiving coil cancel each other out, thus realizing the measurement of a pure secondary field.

[0074] Once the coil system and the transmitting current intensity are determined... The value is fixed and can be obtained using the following formula:

[0075] ;

[0076] The expression for formation conductivity in a homogeneous medium is:

[0077] ;

[0078] The weak signal output from the receiving coil is first pre-conditioned by a low-noise adaptive multi-frequency differential amplifier, and then enters a digital phase-locked loop amplifier unit. The transmitting current reference signal is used for coherent demodulation to extract the secondary field component with the same frequency as the transmitting frequency.

[0079] The extracted secondary field component, which has the same frequency as the transmission frequency, is output to the data acquisition card. The acquisition card then transmits the data to the host computer for display and recording of the secondary field signal after the primary field influence has been removed.

[0080] In a preferred embodiment of the present invention, the original induced signal is conditioned by a low-noise differential amplifier circuit and then enters a digital lock-in amplifier unit. The reference signal is used for coherent demodulation to extract the secondary field component with the same frequency as the transmission frequency.

[0081] In this embodiment, the receiving coil captures the combined signal of the secondary field of the formation and the residual transmission magnetic field, which then enters the digital phase-locked amplification unit. The transmission current reference signal is used for coherent demodulation to extract the secondary field component with the same frequency as the transmission frequency. The operating current of the transmitting coil is simultaneously acquired as a reference signal. The extracted secondary field signal and the reference signal are preprocessed, and after differential amplification and filtering conditioning, the two conditioning signals are simultaneously acquired and transmitted to the host computer.

[0082] The host computer analyzes the acquired signals using an inverse kinematics algorithm to reconstruct the original secondary field signal containing stratigraphic information, thus completing the geological exploration.

[0083] The control relationship is as follows: , ;

[0084] Among them, I c I represents the current in the compensation coil. t φ represents the current in the transmitting coil. c φ represents the phase of the magnetic field of the compensation coil. t The phase of the transmitting coil's magnetic field is represented by k, which is the current amplitude matching coefficient (k>0), and π is the phase difference constant. This control is used to cancel the direct mutual inductance coupling between the transmitting and receiving coils, thus preventing the secondary field signal from being submerged.

[0085] In a preferred embodiment of the present invention, the method further includes: independently controlling the transmission frequency and current amplitude of multiple cascaded equivalent antimagnetic flux detection units through the program control circuit, so as to synchronously acquire the formation response at different radial depths.

[0086] In this embodiment, establishing an equivalent reverse magnetic flux decoupling circuit includes:

[0087] Multiple independent equivalent countermagnetic flux detection units are cascaded coaxially, with the transmitting coil and compensation coil arranged coaxially and coplanarly to ensure overlapping magnetic field coverage areas of the two coils for effective cancellation. The simulated primary field distribution at both ends of the receiving coil is as follows: Figure 4 As shown, z=0 represents the position of the receiving coil. The current directions of the coils symmetrically distributed about z=0 are opposite. The final simulation results show that the primary fields at z=0 cancel each other out, resulting in 0, which is consistent with the theoretical analysis. The resonance states of the transmitting coil and the compensation coil are calibrated by the tuning circuit to make the operating frequencies of the two coils consistent with the frequency of the transmitted signal, thereby improving the magnetic field strength and stability. The compensation coil is connected to the output of the program control circuit, which adjusts the current parameters of the compensation coil in real time according to the feedback of the current of the transmitting coil, ensuring that the equivalent reverse magnetic flux condition dynamically adapts to the transmission state.

[0088] The synthesized signal and reference signal are preprocessed, including: using a low-noise differential amplifier circuit to differentially amplify the synthesized signal output from the receiving coil, with the amplification factor dynamically adjusted to 50~1500 times according to the signal amplitude; simultaneously, a low-pass filter circuit is used to filter out 50Hz power frequency interference and high-frequency noise, with the filter cutoff frequency set to 5~10 times the transmission signal frequency; then, the signal enters the digital phase-locked loop amplifier unit, where coherent demodulation is performed using the transmission current reference signal to extract the secondary field component with the same frequency as the transmission frequency; the amplitude of the reference signal acquired by the current acquisition circuit is calibrated before analog-to-digital conversion to match the amplitude range of the reference signal and the synthesized signal, facilitating subsequent differential decoupling analysis.

[0089] Construction of simulation experiments:

[0090] A simulated well environment of 0.1m×0.1m×1m was constructed in the laboratory and filled with 70-mesh quartz sand to simulate the actual geological layer. Low-resistivity anomalies were preset at a depth of 0.5m in the simulated formation pool, and then the number of low-resistivity anomalies was adjusted to test the measurement effect.

[0091] The equivalent reverse magnetic flux detection unit is fixed to the test frame and placed 0.5m directly above the simulated formation pool; the receiving coil is laid flat on the surface of the simulated formation pool to ensure close contact with the medium;

[0092] The transmitting power supply, program control circuit, highly integrated power amplifier circuit, tuning circuit, and the receiving system's low-noise differential amplifier circuit, lock-in amplifier circuit, power isolation circuit, data acquisition card, and host computer are connected in sequence.

[0093] The two sets of devices are set with the same parameters via the host computer: transmission signal frequency 30kHz, transmission amplitude 6V, transmission duration 60s, and data acquisition card sampling rate 1MHz.

[0094] The device of the present invention is additionally configured with equivalent reverse magnetic flux control parameters and the current amplitude matching coefficient k=1 to ensure that the magnetic field of the compensation coil and the magnetic field of the transmitting coil meet the reverse equivalent condition.

[0095] After the settings are complete, start the system to perform a synchronous detection.

[0096] The acquired transmit current signal and receive voltage signal are transmitted to the host computer for real-time display and storage.

[0097] Keeping the experimental parameters constant, the detection mechanism of the device is moved along the surface of the simulated formation pool in steps of 0.03m to cover the entire simulated formation area; data is collected three times at each detection location, and the signal amplitude, signal-to-noise ratio and anomaly detection results are recorded to avoid random errors from affecting the experimental conclusions.

[0098] Keeping the experimental parameters unchanged, the number of low-resistivity anomalies was increased, and the detection mechanism of the device was moved along the surface of the simulated formation pool in 0.03m increments to cover the entire simulated formation area. Data was collected three times at each detection location, and the signal amplitude, signal-to-noise ratio, and anomaly detection results were recorded to avoid random errors from affecting the experimental conclusions.

[0099] The average data collected by the device at each detection location was processed, and outlier data points exceeding three times the standard deviation were removed. The results of the device for detecting different numbers of anomalies were then obtained.

[0100] The results are as follows Figure 5 As shown, with minute variations in coordinates from -0.15cm to 0.15cm, each curve exhibits continuous and significant signal fluctuations with positional changes, indicating that the system possesses high sensitivity to minute displacements in the measurement location and subtle changes in medium distribution, enabling it to capture fine signal characteristics of the target logging area. With increasing aluminum block quantity, the corresponding curve's signal peak (near coordinate 0) shows a significant increasing trend, indicating a significant positive correlation between the system's measurement signal and the target medium content. This allows for quantitative detection of formation medium content, enhancing the quantitative analysis capabilities of induction logging. The background signal suppression effect is good; the data has already deducted the uncollected signal, and the signal changes in each curve represent effective responses to the target medium, with no significant background interference. This demonstrates that the system's signal processing effectively highlights the effective signal, improving the signal-to-noise ratio and reliability of the logging data.

[0101] Measurements show that the device of this invention, due to its highly integrated circuit design and miniaturized coil structure, has an overall volume of 0.08m × 0.08m × 0.8m, which can be adapted to a small simulated wellhead with a diameter of 9cm, proving that this invention achieves a balance between small size and high performance.

[0102] Therefore, this invention is able to detect more subtle geological changes and resource distributions, providing strong technical support for geological exploration and resource development.

[0103] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An induction logging system based on an equivalent anti-magnetic flux array, characterized in that, include: The transmitting module includes a program control circuit, a power amplifier circuit, a tuning circuit, and an equivalent reverse magnetic flux probe device; The receiving module includes a current acquisition circuit, a low-noise differential amplifier circuit, a data acquisition card, and a host computer; The equivalent antimagnetic flux probe device adopts a compartmentalized modular structure, which is composed of multiple independent equivalent antimagnetic flux detection units cascaded coaxially, and an electromagnetic shielding compartment is set between adjacent equivalent antimagnetic flux detection units. Each of the aforementioned equivalent reverse magnetic flux detection units is a three-coil equivalent reverse magnetic flux module consisting of a "transmitting coil - receiving coil - compensation coil"; The program control circuit is connected to the power amplifier circuit, the output terminal of the power amplifier circuit is connected to the input terminal of the transmitting coil and the compensation coil, and the transmitting coil is connected to the current acquisition circuit. The output terminal of the receiving coil is connected to the low-noise differential amplifier circuit, the output terminal of the low-noise differential amplifier circuit is connected to the data acquisition card, and the data acquisition card is communicatively connected to the host computer.

2. The induction logging system based on an equivalent anti-magnetic flux array according to claim 1, characterized in that, The electromagnetic shielding compartment is made of permalloy and is used to block axial magnetic circuit crosstalk between adjacent detection units.

3. The induction logging system based on an equivalent anti-magnetic flux array according to claim 1, characterized in that, In each of the equivalent antimagnetic flux detection units, the transmitting coil and the compensating coil have the same number of turns, opposite winding directions, are equidistant from and coaxially coincident with the receiving coil.

4. The induction logging system based on an equivalent anti-magnetic flux array according to claim 1, characterized in that, The receiving module further includes a digital phase-locked amplifier unit. The output of the low-noise differential amplifier circuit is connected to the digital phase-locked amplifier unit, and the output of the digital phase-locked amplifier unit is connected to the data acquisition card. The digital phase-locked amplifier unit uses the transmit current reference signal acquired by the current acquisition circuit to perform coherent demodulation.

5. An induction logging method based on an equivalent anti-magnetic flux array, applied to an induction logging system based on an equivalent anti-magnetic flux array as described in any one of claims 1-4, characterized in that, Includes the following steps: The host computer sends control parameters to the program control circuit to configure the working status of the transmitting and receiving modules. The program control circuit generates a drive signal according to the control parameters. After being amplified by the power amplifier circuit, the drive signal drives the transmitting coil and compensation coil of the equivalent reverse magnetic flux detection unit to generate an alternating magnetic field. The receiving coil generates the original induced signal, while the current acquisition circuit acquires the operating current of the transmitting coil and converts it into a reference signal; The original induction signal, after being conditioned by a low-noise differential amplifier circuit, is synchronously acquired by the data acquisition card and transmitted to the host computer along with the reference signal. The host computer analyzes and processes the collected signals to reconstruct the geological information.

6. The induction logging method based on an equivalent anti-magnetic flux array according to claim 5, characterized in that, The original induced signal is conditioned by a low-noise differential amplifier circuit and then enters a digital lock-in amplifier unit. The reference signal is used for coherent demodulation to extract the secondary field component with the same frequency as the transmission frequency.

7. The induction logging method based on an equivalent anti-magnetic flux array according to claim 5, characterized in that, The method further includes: independently controlling the transmission frequency and current amplitude of multiple cascaded equivalent antimagnetic flux detection units through the program control circuit, so as to synchronously acquire the formation response at different radial depths.

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