Directional drilling pipe surface coating damage feature analysis method based on data inversion

Abstract

The present application relates to the technical field of circuit load state monitoring, and discloses a directional drilling pipeline surface coating damage feature analysis method based on data inversion, comprising: injecting a double-frequency composite excitation signal into a transmission loop of a pipeline; locking a current phase, collecting a magnetic flux gradient vector, and performing orthogonal decomposition; performing a hetero-frequency difference operation to construct a loop frequency spectrum attenuation index, generate a decoupling coefficient to strip the interference of medium distribution parameters, and reconstruct an equivalent complex impedance curve of a load insulation layer; the present application eliminates impedance distortion caused by medium heterogeneity through hetero-frequency response differences, solves the misjudgment problem caused by the medium isomorphism assumption of traditional detection, and realizes accurate identification of transmission load leakage impedance abnormalities.

Description

Technical Field

[0001] This invention belongs to the field of circuit load condition monitoring technology, and particularly relates to a method for analyzing the surface coating damage characteristics of directional drilling pipelines based on data inversion. Background Technology

[0002] Currently, in energy transmission and urban pipeline construction, horizontal directional drilling technology has become a key process for long-distance pipeline construction due to its ability to cross rivers, highways, and complex geological environments without excavation. In order to prevent the corrosion of metal pipelines by the underground electrochemical environment, a polymer anti-corrosion coating is usually applied to the outer surface of the pipeline, and a cathodic protection system is used in conjunction with it. At present, for the evaluation of the integrity of the anti-corrosion coating of such concealed projects, the industry generally adopts the ground electromagnetic detection method. By applying an alternating current of a specific frequency to the target pipeline, the electromagnetic field component generated by the current in the pipe is measured on the ground surface, and the insulation performance of the coating is inferred from the attenuation gradient of the signal amplitude during transmission. This detection method based on signal amplitude characteristics can provide effective damage location information in conventional pipeline sections with shallow burial depth and relatively homogeneous soil medium.

[0003] When applied to deep, long-distance directional drilling crossings, this technology is limited by the complex underground physical environment. Directional drilling trajectories typically traverse geological layers with electrical differences. Besides hardware limitations, quantitative evaluation based on measured data and inverse algorithms also restrict detection accuracy. For example, Chinese invention patent CN108663408B discloses a method for determining the damage rate of the anti-corrosion layer in directional drilling of steel oil and gas pipelines. This method quantifies the damage degree by arranging test points on both sides of the directional drill and using algebraic calculations based on the on / off potential shift and current change. However, engineering practice has shown that the evaluation logic based on overall quasi-static electrical parameters has technical flaws, especially considering the limitations of deep-buried directional drilling trajectories traversing geological layers with electrical differences. The entry of high-resistivity sand into low-resistivity riverbed silt causes a spatial abrupt change in soil resistivity, resulting in nonlinear distortion of the pipe-to-soil potential and current redistribution. This causes the calculation formula to lose its physical uniqueness under complex working conditions. For example, when a high-resistivity dry sand layer enters a low-resistivity riverbed silt layer or aquifer, the spatial abrupt change in soil resistivity in such a heterogeneous conductive medium will cause nonlinear distortion of the primary electromagnetic field. Since most existing detection and inversion methods are based on the assumption of a uniform half-space model and mainly rely on single amplitude or potential difference information, the system has difficulty distinguishing from the physical mechanism whether the abnormal response observed on the surface is due to leakage current at the coating damage point or background field fluctuations caused by the increased conductivity of the environmental medium.

[0004] Therefore, the technical problem to be solved by this invention is how to construct an analysis method that can effectively remove the interference of heterogeneous strata environment and achieve accurate decoupling and quantification of the damage characteristics of deep-buried pipeline coatings without relying on an ideal reference section. Summary of the Invention

[0005] This invention provides a method for analyzing the surface coating damage characteristics of directional drilling pipelines based on data inversion, comprising the following steps:

[0006] A closed current transmission loop is configured, consisting of a metal conductor in the pipeline to be measured and the earth medium. A dual-frequency composite excitation signal containing a low-frequency fundamental wave and a high-frequency carrier wave is synchronously injected into the closed current transmission loop. The dual-frequency composite excitation signal is used to establish a controlled electromagnetic energy distribution field in the non-uniform medium space along the pipeline axis.

[0007] Along the extension path of the lossy transmission conductor, the loop space magnetic flux gradient vector data that is time-domain synchronized and phase-locked with the dual-frequency composite excitation signal is acquired in real time, and the loop space magnetic flux gradient vector data is decomposed into in-phase components and quadrature components on the complex plane.

[0008] Perform hetero-frequency differential operation based on source-load response correlation. This operation constructs a loop spectrum attenuation index that characterizes the spatial difference in conductivity of the local return medium based on the nonlinear ratio between the amplitude of the high-frequency carrier response and the amplitude of the low-frequency fundamental wave response at the same measurement point.

[0009] The load-medium decoupling correction coefficient is generated using the loop spectral attenuation index, and this coefficient is used to perform an environmental background stripping operation on the loop spatial flux gradient vector data to filter out non-faulty impedance drift caused by abrupt changes in the distributed parameters of the return medium on the transmission path.

[0010] Based on the target signal after environmental background stripping, the equivalent complex impedance distribution curve of the transmission load insulation layer is reconstructed, and the leakage impedance anomaly characteristics of the transmission load insulation layer are identified according to the difference in amplitude-frequency response of the equivalent complex impedance distribution curve under different frequency excitations.

[0011] Preferably, in the step of constructing the loop spectrum attenuation index, which characterizes the spatial difference in conductivity of the local return medium, the calculation of the loop spectrum attenuation index follows the following mathematical relationship: Where α is the loop spectral attenuation exponent. The amplitude of the vertical magnetic flux component of the high-frequency carrier at the measuring point is collected by the sensor. The amplitude of the vertical magnetic flux component of the low-frequency fundamental wave at the measuring point is collected by the sensor. The preset frequency value of the high-frequency carrier. is the preset low-frequency fundamental frequency value, and k is the preset loop correction constant based on the burial depth of the transmission conductor and the average conductivity of the return medium.

[0012] Preferably, the step of decomposing the loop space magnetic flux gradient vector data into in-phase and orthogonal components on the complex plane includes: locking the loop injection current phase of the dual-frequency composite excitation signal as the reference phase in real time; projecting the collected total loop space magnetic flux gradient vector onto a coordinate axis parallel to the reference phase to extract the active field component generated by the conduction current of the lossy transmission conductor; projecting the collected total loop space magnetic flux gradient vector onto a coordinate axis perpendicular to the reference phase to extract the reactive field component generated by the induced current of the adjacent parallel charged conductor or the stray current of the ground grid; in the subsequent differential frequency operation, configuring the logic processing unit to retain only the active field component as valid input data and filtering out the reactive field component to suppress mutual inductance coupling interference.

[0013] Preferably, the step of identifying abnormal leakage impedance characteristics of the transmission load insulation layer includes: for suspected leakage impedance sections where the equivalent complex impedance distribution curve shows anomalies, triggering an excitation source to apply a transient pulse current micro-perturbation with a preset gradient; monitoring the transient response characteristics of the circuit grounding point potential over time; if the transient response characteristics conform to nonlinear resistive polarization behavior, then determining that there is a low-impedance short-circuit path with exposed metal conductor substrate in the section; if the transient response characteristics conform to linear RC behavior and are dominated by capacitance, then determining that there are dielectric aging characteristics in the section where the dielectric constant of the insulation layer changes but the substrate is not exposed.

[0014] Preferably, the step of performing the environmental background stripping operation further includes: comparing the loop spectrum attenuation index with a preset reference dielectric response threshold; when the fluctuation amplitude of the loop spectrum attenuation index exceeds the reference dielectric response threshold, determining that the current measurement point is in the region of sudden change in the electrical parameters of the return dielectric; triggering adaptive compensation logic, calling the load-dielectric decoupling correction coefficient to perform weighted compensation on the magnetic flux amplitude of the measurement point, so that the attenuation gradient of the compensated magnetic flux along the axial direction of the transmission conductor is only related to the leakage conductivity per unit length of the insulation layer.

[0015] Preferably, the step of configuring a closed current transmission loop consisting of the metal conductor of the drilling pipe to be measured and the earth medium, and synchronously injecting a dual-frequency composite excitation signal containing a low-frequency fundamental wave and a high-frequency carrier wave into the closed current transmission loop includes: generating the dual-frequency composite excitation signal using a power transmitter with constant current regulation function; forming a closed current transmission loop through a feed point arranged at the beginning of the transmission conductor and a loop return point arranged at the end of the transmission conductor; monitoring the output impedance of the closed current transmission loop in real time, and adjusting the output voltage of the power transmitter in a closed loop according to the dynamic fluctuation of the output impedance to lock the effective value of the injected loop current constant.

[0016] Preferably, the steps for reconstructing the equivalent complex impedance distribution curve of the transmission load insulation layer include: establishing an equivalent circuit model of the transmission line distributed parameters that includes the longitudinal impedance of the transmission conductor, the transverse admittance of the insulation layer, and the characteristic impedance of the return medium; substituting the magnetic flux gradient data after the environmental background stripping operation as input parameters into the equivalent circuit model of the transmission line distributed parameters; using an iterative algorithm to solve for the real and imaginary parts of the transverse admittance of the insulation layer; defining the reciprocal of the transverse admittance of the insulation layer as the equivalent complex impedance, and plotting its distribution curve along the transmission conductor path.

[0017] Preferably, the steps of using an iterative algorithm to solve for the real and imaginary parts of the transverse admittance of the insulating layer include: setting an initial value for the transverse admittance of the insulating layer; simulating and calculating the theoretical magnetic flux distribution along the loop based on the initial value; calculating the residual functional between the theoretical magnetic flux distribution and the measured magnetic flux distribution; and correcting the value of the transverse admittance of the insulating layer using the Gauss-Newton method until the residual functional converges to a preset error range.

[0018] Preferably, before the step of acquiring loop space magnetic flux gradient vector data that is time-domain synchronized and phase-locked with the dual-frequency composite excitation signal in real time along the extension path of the lossy transmission conductor, the method further includes: acquiring three-dimensional spatial trajectory data of the transmission conductor using a high-precision inertial navigation unit or gyroscope; calculating the actual burial depth and orientation deviation angle of the transmission conductor at each measuring point based on the three-dimensional spatial trajectory data; and performing geometric normalization correction on the acquired original magnetic flux data using the actual burial depth and orientation deviation angle to remove the geometric error introduced by non-perpendicular projection measurement from the original magnetic flux data.

[0019] Preferably, after the step of identifying the abnormal leakage impedance characteristics of the transmission load insulation layer, the method further includes: generating a digital report of circuit health status containing the coordinates of the abnormal point, the equivalent leakage area, and the maintenance priority based on the identified leakage impedance location and impedance type; mapping the digital report of circuit health status to the power distribution network topology model of the transmission system to generate a visualized panoramic map of the insulation layer status.

[0020] Compared with existing technologies, the present invention's method for analyzing the surface coating damage characteristics of directional drilling pipelines based on multi-source measured data inversion has the following advantages:

[0021] 1. In the analysis of surface coating damage characteristics of directional drilling pipelines, the physical difference between the capacitive impedance of the anti-corrosion coating material and the resistive impedance of the soil medium in the frequency domain response is utilized. By synchronously acquiring the magnetic field gradient vector under multi-frequency excitation, the phase shift characteristics of the signal as a function of frequency are extracted. This mechanism constructs the frequency domain orthogonal identification logic of the medium properties in the inversion model, enabling the system to fundamentally separate the resistivity fluctuations caused by heterogeneous strata, such as riverbeds and wetland boundaries, from the leakage current response caused by coating damage at the physical level based on the nonlinear jump of the phase shift slope. This eliminates the technical drawback of existing technologies that cannot distinguish between geological abrupt changes and coating damage due to simple amplitude comparison, and ensures the physical uniqueness of the damage judgment conclusion under blind testing conditions lacking geological background reference values.

[0022] 2. Trajectory Geometric Adaptive Correction Based on Magnetic Field Zero-Point Drift: This invention extracts the transverse magnetic field component perpendicular to the pipeline axis in real time and identifies the physical zero-point trajectory of this component. It establishes a dynamic correction mechanism for spatial geometric parameters in the inversion model. Utilizing the inherent symmetry of the magnetic field vector around the cylindrical conductor, when the measured zero point does not coincide with the preset axis, it automatically calculates the trajectory geometric drift and corrects the distance parameters between the virtual current source node and the ground measuring point. This enables the inversion algorithm to automatically adapt to the actual pipeline position deviation caused by drill bit yaw or insufficient accuracy of as-built drawings, avoids false impedance anomalies caused by source-field geometric mapping errors, and ensures the authenticity of boundary conditions in the inversion calculation of deeply buried pipelines.

[0023] 3. Suppression of Proximity Electromagnetic Interference Based on Synchronous Vector Projection: This invention introduces a phase reference signal synchronized with the excitation current, projecting the measured magnetic field gradient vector on the ground surface onto the in-phase coordinate axis and the orthogonal coordinate axis in the complex plane. This achieves vector decomposition of the target signal and environmental stray signals. Utilizing the phase-locked characteristics of the leakage current of the target pipeline and its phase non-correlation with the induced current of adjacent parallel pipelines or urban stray currents, mutual inductance coupling interference in the orthogonal components is directly filtered out through vector projection. This signal purification mechanism based on the phase-sensitive detection principle enables the detection system to extract the effective field component that characterizes only the insulation state of the target pipeline from the high-noise background, even in environments with dense urban high-voltage cables or electrified railways and strong electromagnetic interference. Attached Figure Description

[0024] Figure 1 This is an overall flowchart of the method for analyzing the surface coating damage characteristics of directional drilling pipelines using dual-frequency composite excitation and multi-source data inversion according to the present invention;

[0025] Figure 2 This is a data interaction timing diagram of the background stripping and adaptive compensation logic for the loop spectrum attenuation index execution environment of the present invention. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0027] It should be noted that all directional and positional terms used in this invention, such as: up, down, left, right, front, back, vertical, horizontal, inner, outer, top, bottom, transverse, longitudinal, center, etc., are only used to explain the relative positional relationship and connection between components in a specific state (as shown in the accompanying drawings). They are only for the convenience of describing this invention and do not require that this invention be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention. In addition, the descriptions of "first," "second," etc., in this invention are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0028] In the description of this invention, unless otherwise explicitly specified and limited, the terms installation, connection, and linking should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal connection of two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0029] In the description of this specification, references to the terms "an embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example, and the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0030] A method for analyzing surface coating damage characteristics of directional drilling pipelines based on data inversion includes the following steps:

[0031] A closed current transmission loop is configured, consisting of a metal conductor in the pipeline to be measured and the earth medium. A dual-frequency composite excitation signal containing a low-frequency fundamental wave and a high-frequency carrier wave is synchronously injected into the closed current transmission loop. The dual-frequency composite excitation signal is used to establish a controlled electromagnetic energy distribution field in the non-uniform medium space along the pipeline axis.

[0032] Along the extension path of the lossy transmission conductor, the loop space magnetic flux gradient vector data that is time-domain synchronized and phase-locked with the dual-frequency composite excitation signal is acquired in real time, and the loop space magnetic flux gradient vector data is decomposed into in-phase components and quadrature components on the complex plane.

[0033] Perform hetero-frequency differential operation based on source-load response correlation. This operation constructs a loop spectrum attenuation index that characterizes the spatial difference in conductivity of the local return medium based on the nonlinear ratio between the amplitude of the high-frequency carrier response and the amplitude of the low-frequency fundamental wave response at the same measurement point.

[0034] The load-medium decoupling correction coefficient is generated by using the loop spectrum attenuation index, and then used to perform environmental background stripping operation on the loop spatial flux gradient vector data to filter out non-fault impedance drift caused by abrupt changes in the distributed parameters of the return medium on the transmission path.

[0035] Based on the target signal after environmental background stripping, the equivalent complex impedance distribution curve of the transmission load insulation layer is reconstructed, and the leakage impedance anomaly characteristics of the transmission load insulation layer are identified according to the difference in amplitude-frequency response of the equivalent complex impedance distribution curve under different frequency excitations.

[0036] Preferably, in the step of constructing the loop spectrum attenuation index, which characterizes the spatial difference in conductivity of the local return medium, the calculation of the loop spectrum attenuation index follows the following mathematical relationship: Where α is the loop spectral attenuation exponent. The amplitude of the vertical magnetic flux component of the high-frequency carrier at the measuring point is collected by the sensor. The amplitude of the vertical magnetic flux component of the low-frequency fundamental wave at the measuring point is collected by the sensor. The preset frequency value of the high-frequency carrier. is the preset low-frequency fundamental frequency value, and k is the preset loop correction constant based on the burial depth of the transmission conductor and the average conductivity of the return medium.

[0037] Preferably, the step of decomposing the loop space magnetic flux gradient vector data into in-phase and orthogonal components on the complex plane includes: locking the loop injection current phase of the dual-frequency composite excitation signal as the reference phase in real time; projecting the collected total loop space magnetic flux gradient vector onto a coordinate axis parallel to the reference phase to extract the active field component generated by the conduction current of the lossy transmission conductor; projecting the collected total loop space magnetic flux gradient vector onto a coordinate axis perpendicular to the reference phase to extract the reactive field component generated by the induced current of the adjacent parallel charged conductor or the stray current of the ground grid; in the subsequent differential frequency operation, configuring the logic processing unit to retain only the active field component as valid input data and filtering out the reactive field component to suppress mutual inductance coupling interference.

[0038] Preferably, the step of identifying abnormal leakage impedance characteristics of the transmission load insulation layer includes: for suspected leakage impedance sections where the equivalent complex impedance distribution curve shows anomalies, triggering an excitation source to apply a transient pulse current micro-perturbation with a preset gradient; monitoring the transient response characteristics of the circuit grounding point potential over time; if the transient response characteristics conform to nonlinear resistive polarization behavior, then determining that there is a low-impedance short-circuit path with exposed metal conductor substrate in the section; if the transient response characteristics conform to linear RC behavior and are dominated by capacitance, then determining that there are dielectric aging characteristics in the section where the dielectric constant of the insulation layer changes but the substrate is not exposed.

[0039] Preferably, the step of performing the environmental background stripping operation further includes: comparing the loop spectrum attenuation index with a preset reference dielectric response threshold; when the fluctuation amplitude of the loop spectrum attenuation index exceeds the reference dielectric response threshold, determining that the current measurement point is in the region of sudden change in the electrical parameters of the return dielectric; triggering adaptive compensation logic, calling the load-dielectric decoupling correction coefficient to perform weighted compensation on the magnetic flux amplitude of the measurement point, so that the attenuation gradient of the compensated magnetic flux along the axial direction of the transmission conductor is only related to the leakage conductivity per unit length of the insulation layer.

[0040] Preferably, the step of configuring a closed current transmission loop consisting of the metal conductor of the drilling pipe to be measured and the earth medium, and synchronously injecting a dual-frequency composite excitation signal containing a low-frequency fundamental wave and a high-frequency carrier wave into the closed current transmission loop includes: generating the dual-frequency composite excitation signal using a power transmitter with constant current regulation function; forming a closed current transmission loop through a feed point arranged at the beginning of the transmission conductor and a loop return point arranged at the end of the transmission conductor; monitoring the output impedance of the closed current transmission loop in real time, and adjusting the output voltage of the power transmitter in a closed loop according to the dynamic fluctuation of the output impedance to lock the effective value of the injected loop current constant.

[0041] Preferably, the steps for reconstructing the equivalent complex impedance distribution curve of the transmission load insulation layer include: establishing an equivalent circuit model of the transmission line distributed parameters that includes the longitudinal impedance of the transmission conductor, the transverse admittance of the insulation layer, and the characteristic impedance of the return medium; substituting the magnetic flux gradient data after the environmental background stripping operation as input parameters into the equivalent circuit model of the transmission line distributed parameters; using an iterative algorithm to solve for the real and imaginary parts of the transverse admittance of the insulation layer; defining the reciprocal of the transverse admittance of the insulation layer as the equivalent complex impedance, and plotting its distribution curve along the transmission conductor path.

[0042] Preferably, the steps of using an iterative algorithm to solve for the real and imaginary parts of the transverse admittance of the insulating layer include: setting an initial value for the transverse admittance of the insulating layer; simulating and calculating the theoretical magnetic flux distribution along the loop based on the initial value; calculating the residual functional between the theoretical magnetic flux distribution and the measured magnetic flux distribution; and correcting the value of the transverse admittance of the insulating layer using the Gauss-Newton method until the residual functional converges to a preset error range.

[0043] Preferably, before the step of acquiring loop space magnetic flux gradient vector data that is time-domain synchronized and phase-locked with the dual-frequency composite excitation signal in real time along the extension path of the lossy transmission conductor, the method further includes: acquiring three-dimensional spatial trajectory data of the transmission conductor using a high-precision inertial navigation unit or gyroscope; calculating the actual burial depth and orientation deviation angle of the transmission conductor at each measuring point based on the three-dimensional spatial trajectory data; and performing geometric normalization correction on the acquired original magnetic flux data using the actual burial depth and orientation deviation angle to remove the geometric error introduced by non-perpendicular projection measurement from the original magnetic flux data.

[0044] Preferably, after the step of identifying the abnormal leakage impedance characteristics of the transmission load insulation layer, the method further includes: generating a digital report of circuit health status containing the coordinates of the abnormal point, the equivalent leakage area, and the maintenance priority based on the identified leakage impedance location and impedance type; mapping the digital report of circuit health status to the power distribution network topology model of the transmission system to generate a visualized panoramic map of the insulation layer status.

[0045] Example 1: In an industrial application scenario involving the integrity analysis of the anti-corrosion coating of a directional drilling pipeline traversing a heterogeneous geological interface, the tested object is a 1.5 km long buried steel pipeline traversing the interface between a dry sand layer and a highly conductive silt layer in a riverbed. The physical challenge in this case lies in the change in conductivity of the return medium at the interface. to The abrupt changes in environmental parameters, such as step-like abrupt shifts, produce signal attenuation artifacts of up to 40% in traditional single-frequency amplitude detection, making it impossible to distinguish whether the signal anomaly originates from changes in the formation medium or physical damage to the coating material. The system is configured with a closed current transmission loop consisting of the metal conductor of the drill pipe to be measured and the earth medium, and a power transmitter with constant current regulation function is used to synchronously inject a low-frequency fundamental wave into the closed current transmission loop. (Set to 4Hz) and high-frequency carrier The dual-frequency composite excitation signal (set to 128Hz) is used. The power transmitter signal modulation unit uses an FPGA controller to drive the H-bridge inverter topology. When a micro-perturbation command is triggered, the FPGA maintains the dual-frequency fundamental wave. and Direct digital synthesis (DDS) maintains the same timing. Pulse width modulation (PWM) technology is used to superimpose a unipolar pulse with a width of less than 5ms at the zero-crossing point of the output current. Since the pulse spectrum energy is concentrated in the frequency band above 1kHz, the duration is much shorter than the integration time constant of the receiver's phase-locked loop (PLL), which is usually set to the level of 100ms. Micro-disturbance operation does not change the phase tracking state of the dual-frequency excitation signal.

[0046] Without interrupting the steady-state measurement loop, transient impedance feature extraction of suspected damage points is completed. A measurement array is deployed on the ground along the pipeline axis to collect loop spatial magnetic flux gradient vector data that is time-domain synchronized and phase-locked with the dual-frequency composite excitation signal in real time. Before performing differential frequency calculation, the data preprocessing module performs sensor attitude geometry normalization. The measurement array integrates a triaxial accelerometer and a magnetometer to output probe Euler angle data in real time, including roll angle Ф, pitch angle θ, and yaw angle ψ. The logic processing unit constructs a rotation matrix R to project and transform the magnetic flux gradient vector in the geocentric coordinate system to the pipe body coordinate system perpendicular to the pipeline axis, and performs sliding window outlier analysis on the raw data. When the abrupt change rate of the orthogonal component amplitude at a measurement point exceeds three times the standard deviation of 3σ of the mean of the five adjacent measurement points, and there is no corresponding change in the in-phase component, the data point is determined to be affected by unrelated interference sources such as high-voltage transmission lines. Cubic spline interpolation is used for reconstruction to ensure that the input inversion model dataset contains only the injected current excitation field component. For each measurement point, the logic processing unit performs differential frequency operation based on source-load response correlation. Based on the nonlinear ratio between the high-frequency carrier response amplitude and the low-frequency fundamental response amplitude at the same measurement point, a loop spectrum attenuation index α characterizing the spatial difference in conductivity of the local return medium is constructed. The calculation of the loop spectrum attenuation index α follows a mathematical relationship: ,in, The amplitude of the vertical magnetic flux component of the high-frequency carrier at the measuring point is collected by the sensor. denoted as the amplitude of the vertical magnetic flux component of the low-frequency fundamental wave at the measurement point acquired by the sensor, and k is a loop correction constant preset based on the burial depth of the transmission conductor and the average conductivity of the return medium.

[0047] Under this operational mechanism, although the conductivity of dry sand and silt differs greatly, both exhibit dispersion-insensitive resistive response characteristics in the 4Hz to 128Hz frequency band. This causes their corresponding α values ​​to fluctuate near a stable baseline close to zero when crossing geological interfaces. Based on this, the logic processing unit identifies that the significant signal fluctuations in this area originate solely from abrupt changes in the distributed parameters of the environmental medium. It then generates a load-medium decoupling correction coefficient and performs an environmental background stripping operation on the loop space magnetic flux gradient vector data, filtering out non-faulty impedance drift caused by the step change in the conductivity of the return medium. Conversely, at pipeline mileage 850 meters, although the original magnetic flux amplitude changes, the calculated... The α value showed a negative jump. The physical root cause of this phenomenon is that the anti-corrosion coating at this location is aged and damaged. Its equivalent impedance characteristics changed from the original pure capacitive dominance to a resistive-capacitive composite characteristic, resulting in a nonlinear deviation in the attenuation rate of high and low frequency responses. Based on the target signal after environmental background stripping, the system reconstructed the equivalent complex impedance distribution curve of the transmission load insulation layer. According to the difference in amplitude-frequency response of the equivalent complex impedance distribution curve under different frequency excitations, this analysis method shielded the background interference of geological changes, identified and locked the abnormal leakage impedance characteristics of the transmission load insulation layer at 850 meters, and output the material physical property analysis results including the coordinates of the abnormal point and the equivalent leakage area.

[0048] Example 2: This example verifies the effectiveness and stability of the method for analyzing the surface coating damage characteristics of directional drilling pipelines based on the heterodyne differential inversion mechanism. The test platform was built in a controlled multiphase medium simulation tank with dimensions of 50 meters (length), 2 meters (width), and 2 meters (height). The simulation tank was filled with a sand-soil mixture with adjustable conductivity, and a stratigraphic abrupt change region with a clear physical interface was constructed by partitions. To simulate the electromagnetic environment of a real industrial site, Gaussian white noise with a signal-to-noise ratio of 20 dB was forcibly injected into the test circuit, and a power frequency interference harmonic with a frequency of 50 Hz and an amplitude 10 times that of the effective signal was superimposed. The experiment established a comparative sequence containing three different test conditions: control group one using a single low-frequency (4 Hz) excitation, control group two using a single high-frequency (128 Hz) excitation, and the test group using the dual-frequency composite excitation (4 Hz and 128 Hz) of this invention. In the geological abrupt change region where the conductivity jumps from 0.005 S / m to 0.05 S / m, the magnetic flux gradient amplitude data collected by both control groups 1 and 2 showed a downward trend, with signal attenuation rates reaching 38.5% and 41.2%, respectively. Under conventional amplitude judgment logic, this large signal drop was incorrectly identified as an abnormal leakage current caused by corrosion layer damage, resulting in false positives. In the experimental group, differential frequency operation based on source-load response correlation was performed. Although the original high-frequency and low-frequency response amplitudes were also modulated by changes in formation conductivity, the loop spectrum attenuation index α calculated by the logic processing unit remained within the baseline range of 0.02 to 0.05 in this region. Dry sand and moist soil mainly exhibited linear resistive load characteristics in the frequency band from 4 Hz to 128 Hz, and their attenuation effect on signals of different frequencies was in the same direction. The differential processing performed mathematically cancels out the common-mode interference caused by the medium parameter σ, confirming the ability of the α exponent to strip away geological background noise.

[0049] The experiment included a pre-set physical coating failure point with an equivalent area of ​​1 square centimeter at a distance of 25 meters along the pipeline. The contact impedance at this point was set to exhibit nonlinear RC composite characteristics. Under this condition, the α value monitored by the experimental group rapidly jumped from 0.03 at the baseline to -0.58. This nonlinear abrupt change in data stemmed from the absence of the electrochemical double-layer capacitance effect at the coating failure point, resulting in obstruction of the bypass channel for high-frequency signals and a difference in attenuation rate compared to low-frequency signals. To verify the critical conditions for frequency parameter selection, an out-of-range control group was introduced into the experiment, with the high-frequency carrier frequency... Downgraded to , making the frequency ratio When the frequency ratio is reduced to 2, the measured data shows that under this low frequency ratio condition, the change in α value caused by coating damage is only 0.08, which is submerged in the background noise of the environment. When the frequency ratio range is sufficient to excite the difference in dielectric response of the coating material, effective damage identification can be achieved. Finally, based on the equivalent complex impedance curve after decoupling correction, the system outputs a positioning result with a deviation of less than 0.2 meters from the preset damage location, verifying the feature extraction accuracy of the method in complex electromagnetic and geological environments.

[0050] Example 3: This example details the initialization parameter calibration and core inverse algorithm execution process of a directional drilling pipeline inspection system. Before the system is put into formal testing, the value of the loop correction constant k is determined to compensate for the reference attenuation deviation caused by differences in pipeline burial depth and average soil conductivity. The calibration process is performed on a 50-meter-long reference pipe section with a known intact coating and relatively simple geological structure. The system injects a dual-frequency excitation signal into the loop. The logic processing unit collects magnetic flux data from no less than 20 equally spaced measuring points along the axial direction on the reference pipe section and calculates the unweighted logarithmic amplitude difference between the high and low frequencies at each measuring point. The logic processing unit performs a least-squares fitting operation to minimize the root mean square value of the loop spectral attenuation index α of all measuring points within the reference pipe section. The objective function is used to find the unique k-value that makes the baseline approach zero. This calibrated k-value is locked and written into the system's non-volatile memory as a fixed calculation parameter for subsequent full-line inspections. During continuous inspections, the operation of generating load-medium decoupling correction coefficients follows adaptive filtering logic based on spatial wavelength differences. The logic processing unit establishes a sliding sampling window containing N sampling points, where N is set to a range of 32 to 64, corresponding to a pipe length of approximately 15 to 30 meters. This length is greater than the typical spatial distribution width of a single coating failure point, but less than the spatial scale of lithological changes in the formation medium. For the current measuring point i, the system calculates the arithmetic mean or median of the α values ​​of all measuring points within the sliding window, defining it as the background trend term for the current location. The load-medium decoupling correction factor is the background trend term. The system calculates negative values ​​using a formula. Calculate the net attenuation exponent after decoupling correction. This allows for the filtering out of long-wavelength common-mode interference caused by the slow drift of soil conductivity in the time domain, while retaining only short-wavelength anomalous features caused by abrupt changes in the coating.

[0051] The process of reconstructing the equivalent complex impedance distribution curve of the transmission load insulation layer based on the decoupled corrected net attenuation index relies on the lossy propagation model of the transmission line. The logic processing unit uses preset analytical relationships to convert the dimensionless... The mapping is represented by the physically meaningful transverse leakage conductance G and transverse capacitance C per unit length of the coating. Under low-frequency excitation, signal attenuation is mainly dominated by resistive leakage conductance. The logic processing unit calculates the equivalent insulation resistance of the coating based on the product of the net attenuation of the low-frequency fundamental wave and the characteristic impedance of the pipe. Under high-frequency excitation, signal attenuation is affected by capacitive bypass effect. The logic processing unit analyzes the additional attenuation component of the high-frequency carrier wave relative to the low-frequency fundamental wave and calculates the equivalent dielectric capacitance of the coating. The final analysis results output by the system are a set of values ​​distributed along the pipe axis, expressed in ohms per square meter (Ω). The coating insulation resistivity curve is expressed in farads per square meter (F / m²). The system determines that there is a penetrating coating damage defect at a location when the insulation resistivity curve shows a local minimum value below a preset threshold and the corresponding dielectric permittivity curve shows a nonlinear abrupt change that coincides with its spatial location.

[0052] Example 4: Before the system starts the formal coating damage feature inversion process, a spectral fingerprinting and baseline locking procedure is performed to target the electromagnetic background noise level of the current detection environment. In a silent state before the dual-frequency composite excitation signal is injected into the closed current transmission loop, the measurement array is used to monitor the power frequency harmonics, radio frequency interference, and random fluctuations of the ground electric field in the surface environment for a period of not less than 60 seconds. The power spectral density at each frequency point is calculated and an environmental noise basis model is generated. Then, the logic processing unit automatically sets the minimum signal-to-noise ratio threshold for effective signal extraction and the dynamic gain range of the front-end analog amplifier based on the model. Only when the measured amplitudes of the 4Hz and 128Hz excitation responses are both more than 6dB higher than the dynamic noise basis, does the system confirm that the collected magnetic flux gradient vector data has the physical credibility required for inversion and enter the subsequent differential frequency operation stage.

[0053] For the final determination of abnormal leakage impedance characteristics of the transmission load insulation layer, the system does not use a single fixed threshold for binary decision-making. Instead, it runs a dynamic confidence interval evaluation procedure based on statistical significance testing. The logic processing unit calculates the net attenuation index after decoupling correction within the sliding sampling window in real time. The probability density function is used, and a local statistical model containing the expected value μ and standard deviation σ is constructed based on the normal distribution assumption. The response range of the normal coating is defined within the confidence interval of μ ± 3σ. When multiple consecutive sampling points are used... When the numerical value unidirectionally breaks through the lower limit of the confidence interval, and the corresponding equivalent complex impedance imaginary part shows a phase angle shift consistent with the capacitance loss, the system triggers a damage warning and outputs a risk level assessment report for the area, thereby mathematically minimizing the risk of false alarms induced by random micro-disturbances in the formation medium.

[0054] Example 5: This example establishes a standardized pre-deployment calibration and engineering parameter solidification procedure to address the adaptability issue of core inversion parameter settings under different geological backgrounds and testing conditions. Before performing any field testing task, a benchmark test window with a clear spatial dimension is established. Its length is set to be no less than 20 times the pipeline burial depth, and it is located in a pipe section area with known intact coating and relatively simple soil stratification. The system starts a self-test mode, injects a standard intensity dual-frequency excitation signal into the closed current transmission loop, and simultaneously controls the measurement array to perform high-density spatial scanning within the benchmark window. The sampling interval is set to be less than 0.1 times the pipeline burial depth to ensure sufficient capture of the micro-gradient characteristics of the surface magnetic field. The logic processing unit calculates the loop spectrum attenuation index α of all measuring points within the benchmark window in real time and performs statistical distribution tests. When the standard deviation of the α value is less than 0.005, the area is determined to meet the steady-state conditions for parameter calibration.

[0055] Under these steady-state conditions, the system automatically inverts and locks the optimal solution of the loop correction constant k based on the deviation between the measured low-frequency fundamental response amplitude and the theoretical propagation model. This k value directly characterizes the combined influence weight of the average soil conductivity and pipeline burial depth on signal attenuation under the current working conditions. Based on this locked k value, the system automatically generates a load-medium decoupling benchmark model for subsequent full-line detection. To address the slight sensitivity differences that may exist between different batches of sensors, the procedure requires that each fluxgate sensor in the measurement array be calibrated in situ using a standard magnetic source before each deployment, and that the gain correction factor for each channel be calculated and stored. In subsequent data processing, this factor is automatically called to normalize and compensate the original flux gradient vector data. Through this standardized pre-calibration and parameter solidification process, this invention eliminates system errors caused by differences in geological conditions, individual equipment discreteness, and initial environmental uncertainties at the engineering implementation level.

[0056] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit of this application and the scope of protection of this invention, and all of these forms are within the protection scope of this application.

Claims

1. A method for analyzing the surface coating damage characteristics of directional drilling pipelines based on data inversion, characterized in that, Includes the following steps: A closed current transmission loop is configured, consisting of a metal conductor in the pipeline to be measured and the earth medium. A dual-frequency composite excitation signal containing a low-frequency fundamental wave and a high-frequency carrier wave is synchronously injected into the closed current transmission loop. The dual-frequency composite excitation signal is used to establish a controlled electromagnetic energy distribution field in the non-uniform medium space along the pipeline axis. Along the extension path of the lossy transmission conductor, the loop space magnetic flux gradient vector data that is time-domain synchronized and phase-locked with the dual-frequency composite excitation signal is acquired in real time, and the loop space magnetic flux gradient vector data is decomposed into in-phase components and quadrature components on the complex plane. Perform heterodyne differential operation based on source-load response correlation. This operation constructs a loop spectrum attenuation index that characterizes the spatial difference in conductivity of the local return medium based on the nonlinear ratio between the amplitude of the high-frequency carrier response and the amplitude of the low-frequency fundamental wave response at the same measurement point. The load-medium decoupling correction coefficient is generated using the loop spectral attenuation index, and this coefficient is used to perform an environmental background stripping operation on the loop spatial flux gradient vector data to filter out non-faulty impedance drift caused by abrupt changes in the distributed parameters of the return medium on the transmission path. Based on the target signal after environmental background stripping, the equivalent complex impedance distribution curve of the transmission load insulation layer is reconstructed, and the leakage impedance anomaly characteristics of the transmission load insulation layer are identified according to the difference in amplitude-frequency response of the equivalent complex impedance distribution curve under different frequency excitations.

2. The method for analyzing surface coating damage characteristics of directional drilling pipelines based on data inversion according to claim 1, characterized in that, In the step of constructing the loop spectral attenuation index, which characterizes the spatial difference in conductivity of the local return medium, the calculation of the loop spectral attenuation index follows the mathematical relationship: Where α is the loop spectral attenuation exponent. The amplitude of the vertical magnetic flux component of the high-frequency carrier at the measuring point is collected by the sensor. The amplitude of the vertical magnetic flux component of the low-frequency fundamental wave at the measuring point is collected by the sensor. The preset frequency value of the high-frequency carrier. is the preset low-frequency fundamental frequency value, and k is the preset loop correction constant based on the burial depth of the transmission conductor and the average conductivity of the return medium.

3. The method for analyzing surface coating damage characteristics of directional drilling pipelines based on data inversion according to claim 1, characterized in that, The steps of decomposing the loop space magnetic flux gradient vector data into in-phase and quadrature components on the complex plane include: locking the loop injection current phase of the dual-frequency composite excitation signal as the reference phase in real time; projecting the acquired total loop space magnetic flux gradient vector onto a coordinate axis parallel to the reference phase to extract the active field component generated by the conduction current of the lossy transmission conductor; projecting the acquired total loop space magnetic flux gradient vector onto a coordinate axis perpendicular to the reference phase to extract the reactive field component generated by the induced current of the adjacent parallel charged conductor or the stray current of the ground grid; in the subsequent differential frequency operation, the logic processing unit is configured to retain only the active field component as valid input data and filter out the reactive field component to suppress mutual inductance coupling interference.

4. The method for analyzing surface coating damage characteristics of directional drilling pipelines based on data inversion according to claim 1, characterized in that, The steps for identifying abnormal leakage impedance characteristics of the transmission load insulation layer include: for suspected leakage impedance sections where the equivalent complex impedance distribution curve shows anomalies, triggering an excitation source to apply a transient pulse current micro-perturbation with a preset gradient; monitoring the transient response characteristics of the circuit grounding point potential over time; if the transient response characteristics conform to nonlinear resistive polarization behavior, it is determined that there is a low-impedance short-circuit path with exposed metallic conductor substrate in this section; if the transient response characteristics conform to linear RC behavior and are dominated by capacitance, it is determined that there are dielectric aging characteristics in this section where the dielectric constant of the insulation layer changes but the substrate is not exposed.

5. The method for analyzing surface coating damage characteristics of directional drilling pipelines based on data inversion according to claim 1, characterized in that, The steps for performing the environmental background stripping operation further include: comparing the loop spectrum attenuation index with a preset reference dielectric response threshold; when the fluctuation amplitude of the loop spectrum attenuation index exceeds the reference dielectric response threshold, determining that the current measurement point is in the region of sudden change in the electrical parameters of the return dielectric; triggering adaptive compensation logic, calling the load-dielectric decoupling correction coefficient to perform weighted compensation on the magnetic flux amplitude of the measurement point, so that the attenuation gradient of the compensated magnetic flux along the axial direction of the transmission conductor is only related to the leakage conductivity per unit length of the insulation layer.

6. The method for analyzing surface coating damage characteristics of directional drilling pipelines based on data inversion according to claim 1, characterized in that, The steps of configuring a closed current transmission loop consisting of a metal conductor of the drilling pipe to be measured and the earth medium, and synchronously injecting a dual-frequency composite excitation signal containing a low-frequency fundamental wave and a high-frequency carrier wave into the closed current transmission loop include: generating the dual-frequency composite excitation signal using a power transmitter with constant current regulation function; forming a closed current transmission loop through a feed point arranged at the beginning of the transmission conductor and a loop return point arranged at the end of the transmission conductor; monitoring the output impedance of the closed current transmission loop in real time, and adjusting the output voltage of the power transmitter in a closed loop according to the dynamic fluctuation of the output impedance to lock the effective value of the injected loop current constant.

7. The method for analyzing surface coating damage characteristics of directional drilling pipelines based on data inversion according to claim 1, characterized in that, The steps for reconstructing the equivalent complex impedance distribution curve of the transmission load insulation layer include: establishing an equivalent circuit model of the transmission line distributed parameters that includes the longitudinal impedance of the transmission conductor, the transverse admittance of the insulation layer, and the characteristic impedance of the return medium; substituting the magnetic flux gradient data after environmental background stripping operation as input parameters into the equivalent circuit model of the transmission line distributed parameters; solving for the real and imaginary parts of the transverse admittance of the insulation layer using an iterative algorithm; defining the reciprocal of the transverse admittance of the insulation layer as the equivalent complex impedance, and plotting its distribution curve along the transmission conductor path.

8. The method for analyzing surface coating damage characteristics of directional drilling pipelines based on data inversion according to claim 7, characterized in that, The steps for solving the real and imaginary parts of the transverse admittance of the insulating layer using an iterative algorithm include: setting an initial value for the transverse admittance of the insulating layer; simulating and calculating the theoretical magnetic flux distribution along the loop based on the initial value; calculating the residual functional between the theoretical magnetic flux distribution and the measured magnetic flux distribution; and correcting the value of the transverse admittance of the insulating layer using the Gauss-Newton method until the residual functional converges to the preset error range.

9. The method for analyzing surface coating damage characteristics of directional drilling pipelines based on data inversion according to claim 1, characterized in that, Before the step of acquiring loop space magnetic flux gradient vector data that is time-domain synchronized and phase-locked with the dual-frequency composite excitation signal in real time along the extension path of the lossy transmission conductor, the method further includes: acquiring three-dimensional spatial trajectory data of the transmission conductor using a high-precision inertial navigation unit or gyroscope; calculating the actual burial depth and orientation deviation angle of the transmission conductor at each measuring point based on the three-dimensional spatial trajectory data; and performing geometric normalization correction on the acquired raw magnetic flux data using the actual burial depth and orientation deviation angle to remove the geometric error introduced by non-perpendicular projection measurement from the raw magnetic flux data.

10. The method for analyzing surface coating damage characteristics of directional drilling pipelines based on data inversion according to claim 1, characterized in that, Following the step of identifying abnormal leakage impedance characteristics of the transmission load insulation layer, the process further includes: generating a digital report of circuit health status based on the identified leakage impedance location and impedance type, which includes the coordinates of the abnormal point, the equivalent leakage area, and the maintenance priority; mapping the digital report of circuit health status to the power distribution network topology model of the transmission system to generate a visualized panoramic map of the insulation layer status.

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