Oil well casing stress distribution detection device and detection method based on magnetic mechanical coupling effect

Abstract

The application provides a kind of oil well casing stress distribution detection device and detection method based on magnetic mechanical coupling effect, belongs to oil well casing stress distribution detection field.To solve the problem that the existing casing damage detection method can only detect after damage occurs, cannot evaluate stress state, and cannot directly measure.The application includes a controller, an azimuth instrument, a centralizer, a multi-arm caliper, a support slip and a magnetic stress measuring component, a stress distribution model is constructed based on the magnetic mechanical effect principle of ferromagnetic material, then the magnetic circuit of the magnetic stress measuring component is optimized, the attitude is compensated through wall attachment design and azimuth instrument to ensure the reproducibility of the magnetic circuit, and the stable extraction and anti-interference processing of the downhole magnetic mechanical signal are realized.The application is suitable for oil and gas well casing stress measurement, casing damage early warning, wellbore integrity evaluation during oilfield development, and can also be used for geothermal well, underground gas storage and CCUS injection-production well casing safety monitoring.

Description

Technical Field

[0001] This invention relates to the field of oil well casing stress distribution detection technology, and more specifically, to an oil well casing stress distribution detection device and method based on magnetomechanical coupling effect. Background Technology

[0002] Oil well casing is the core load-bearing unit of the oil and gas wellbore structure, and its function is to support the wellbore, isolate the formation, and ensure the long-term stable operation of the wellbore. However, with the increase in the years of oilfield development and the increasing complexity of production conditions, the casing must withstand various mechanical forces from formation side pressure, temperature gradient changes, alternating oil, gas and water injection and production, and non-uniform loads on the wellbore over a long period of time.

[0003] Against this backdrop, oil well casings frequently experience various forms of damage during their service life, including compression, tension, bending, buckling, corrosion, and fatigue, leading to varying degrees of casing deformation or damage. This is particularly true in scenarios such as heavy oil thermal recovery, carbon dioxide injection, fracturing and expansion, and high water-cut extraction in the later stages of waterflooding, where the pressure and temperature dynamics of the wellbore change drastically, resulting in more frequent casing failures. Therefore, monitoring casing stress changes and predicting casing damage trends have become prominent bottleneck issues in oilfield development.

[0004] Direct causes of casing damage include: 1. Local buckling due to uneven stress between the formation and the casing; 2. Cyclic fatigue caused by alternating injection and production; 3. Abnormal pore pressure around the wellbore causing sudden changes in radial load; 4. Casing bending caused by wellbore shearing and formation slip zones. These phenomena are all essentially closely related to changes in the stress distribution inside the casing. Therefore, accurate understanding of the stress distribution in the early stages of damage allows for prediction and prevention.

[0005] Currently, domestic and international casing damage detection technologies are mainly divided into three categories: 1. Geometric morphology detection: Multi-arm caliper can only detect internal deformation and diameter reduction of the casing; ultrasonic imaging logging can only identify macroscopic defects such as casing misalignment and cracks. These methods can only perform "post-incident detection" after damage occurs and cannot provide early warning. 2. Electromagnetic detection: Electromagnetic flaw detectors mainly detect casing wall thinning and corrosion defects; magnetic flux leakage detection is sensitive to penetrating damage, but cannot assess stress state. 3. In-situ stress prediction: Cross-dipole acoustic logging inverts in-situ stress through formation anisotropy; long-spacing acoustic logging indirectly estimates formation pressure distribution; however, none of these methods solve the problem of directly measuring the stress of the casing itself. Summary of the Invention

[0006] The technical problem to be solved by this invention is:

[0007] To address the problem that existing casing damage detection methods can only detect damage after it occurs, cannot assess stress state, and cannot perform direct measurements.

[0008] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0009] This invention provides an oil well casing stress distribution detection device based on magnetomechanical coupling effect, comprising a controller, an azimuth instrument, a centralizer, a multi-arm caliper, support slips, and a magnetic stress measuring component sequentially sleeved on a central rod.

[0010] The controller is used to receive signals transmitted by the orientation instrument and stress sensor, and then to detect the stress distribution of the oil well casing through the built-in algorithm, and output the detection results to the remote terminal.

[0011] The orientation instrument includes a triaxial magnetometer and a gyroscope sensor, used to calculate the instrument's attitude and magnetic circuit direction;

[0012] The stabilizer is used to control the instrument's posture, ensuring that the magnetic sensor is always perpendicular to the sleeve wall.

[0013] The multi-arm caliper is a 16-arm caliper used to measure well diameter deformation;

[0014] The support clip adopts a three-point or four-point radial support structure, so that the magnetic stress measuring component is in close contact with the inner wall of the sleeve;

[0015] The magnetic stress measurement component includes a stress sensor and an electrode plate, which are used to apply an excitation magnetic field to the bushing and collect magnetic response signals related to the bushing stress, forming a closed magnetic circuit to improve the consistency of magnetic field strength and direction, reduce noise interference, and reduce the impact of magnetic saturation on measurement stability under high temperature conditions.

[0016] A detection method for the oil well casing stress distribution detection device based on magnetomechanical coupling effect as described in claim 1 includes the following steps:

[0017] S100. Based on the magnetomechanical effect principle of ferromagnetic materials, a coupling model between the magnetic response and stress of the bushing is constructed.

[0018] S200. Optimize the magnetic circuit of the magnetic stress measurement component;

[0019] S300, through wall-attached design and orientation instrument for attitude compensation, ensures magnetic circuit reproducibility;

[0020] S400 enables stable extraction and anti-interference processing of downhole magnetomechanical signals to obtain casing stress estimates.

[0021] Further, in step S100, the following are included:

[0022] When a ferromagnetic material is subjected to external stress, its internal magnetic domain structure rearranges, resulting in a change in magnetic permeability:

[0023] Δμ=f(σ)ΔM=g(σ)

[0024] In the formula, Δμ is the change in permeability; σ is the stress; ΔM is the change in magnetization; f(σ) is the effect of stress on the change in permeability Δμ; g(σ) is the effect of stress on the change in magnetization ΔM.

[0025] Within the elastic region, the permeability μ and the stress σ approximately satisfy a linear relationship:

[0026] Δμ=k·Δσ

[0027] In the formula, k is the magnetomechanical coupling coefficient of the material, which is determined through ground calibration;

[0028] When the casing is subjected to external non-uniform loads, its magnetic property changes are captured in real time by sensors, and the stress distribution can be inferred. Furthermore, the downhole magnetic signal can be stably extracted and resisted by interference, achieving stable, low-noise, and reproducible measurements.

[0029] Furthermore, in step S200, the magnetic circuit of the magnetic stress measuring component is optimized to ensure that the magnetic circuit satisfies the following:

[0030]

[0031] In the formula, The magnetic flux passing through the magnetic circuit; This refers to the number of turns of the excitation coil; For excitation current; The equivalent magnetic reluctance of the sensor core and plates; The equivalent magnetic reluctance is the air gap or the bonding gap. This is the equivalent magnetic reluctance of the bushing section.

[0032] Furthermore, in step S300, to reduce magnetoresistive uncertainty, the stress sensor direction is always perpendicular to the sleeve wall surface:

[0033]

[0034] In the formula, The equivalent air gap thickness between the sensor electrode plate and the inner wall of the sleeve; Permeability of free space; The effective magnetic flux area of ​​the air gap;

[0035] When performing attitude compensation using an orientation instrument, the magnetic response is compensated according to the orientation as follows:

[0036]

[0037] In the formula, The measurement signal after attitude compensation; The original measurement signal; It is the angle between the direction of the sensor's magnetic poles and the normal to the inner wall of the sleeve.

[0038] Further, in step S400, the following is included:

[0039] S410, frequency domain optimization and skin depth matching, the skin depth δ is designed as follows:

[0040]

[0041] In the formula, The depth of the electromagnetic field within the casing; The angular frequency of the excitation signal; The magnetic permeability of the bushing material; The electrical conductivity of the bushing material;

[0042] When δ≈ sleeve wall thickness × 30%, the magnetic field distribution is most sensitive to stress changes;

[0043] S420, dual-channel synchronous acquisition, and phase information enhancement.

[0044] Detection signal amplitude and phase information :

[0045]

[0046] In the formula, The signal amplitude; The complex voltage signal received by the sensor; The signal phase angle;

[0047] S430: Construct a temperature compensation model and incorporate a built-in temperature sensor for real-time calibration.

[0048]

[0049] In the formula, To be at temperature Relative permeability at the following values; Reference temperature Relative permeability at the following values; This is the temperature coefficient of magnetic permeability as a function of temperature; The current temperature; For reference temperature;

[0050] S440, real-time compensation for air gap and bonding error, estimation of air gap d and correction of magnetic response:

[0051]

[0052] In the formula, This represents the signal amplitude after air gap compensation. The original signal amplitude; This is the air gap sensitivity coefficient; This is the equivalent air gap thickness;

[0053] The S450, adaptive filtering, and 24-bit high-precision sampling, along with digital lock-in amplification, second- and third-order Butterworth filters, and a 24-bit ADC, improve the signal-to-noise ratio (SNR).

[0054] S460, operating condition consistency control, including constant current excitation and magnetic saturation suppression.

[0055] The constant current power supply module guarantees:

[0056]

[0057] In the formula, Input current to the excitation coil; This represents the peak value of the excitation current. The frequency of the excitation signal; For time;

[0058] S470, Feature fusion inversion, using a multi-feature fusion model:

[0059] ,

[0060] In the formula, The estimated value of the casing stress obtained from the inversion; To solve for the stress parameters of the variables; This represents the actual measured characteristic vector of the magnetic response; This is the parameter set for the forward model; The original signal amplitude; The phase angle of the first harmonic signal; The amplitude of the third harmonic; is the L2 norm; argmin is the parameter value that minimizes the objective function; This is a magneto-stress forward model.

[0061] Compared with the prior art, the beneficial effects of the present invention are:

[0062] 1. To achieve direct, in-situ, and quantitative measurement of casing stress.

[0063] This invention achieves direct detection of the stress state of oil well steel casing through magnetomechanical coupling effect, without relying on indirect parameters such as geometric deformation and corrosion loss. It can quantitatively measure the axial stress, circumferential stress, local stress concentration and asymmetric loading of the casing under actual downhole stress conditions, breaking through the technical bottleneck of traditional logging methods that make it difficult to directly obtain stress data.

[0064] 2. It can identify stress anomalies that are "invisible but dangerous," enabling early warning of casing losses.

[0065] Traditional wellbore measurement, ultrasonic imaging, and electromagnetic flaw detection can only identify deformation or defects after casing damage has occurred. However, this invention can identify abnormally high-stress sections before macroscopic deformation of the casing, provide early warning of dangerous locations where "potential casing damage is about to occur," reveal stress trends, provide a basis for preventive intervention in oilfields, and ultimately achieve a technological leap from passive detection to proactive prediction.

[0066] 3. The measurement results are intuitive and have good repeatability, making them suitable for engineering applications.

[0067] The stress logging curve of this invention can continuously reflect the stress distribution characteristics of the entire casing, and has repeatability, high stability, strong resistance to downhole interference, and compatibility with various surface instruments. In field applications, it can effectively avoid the influence of well fluid, electromagnetic noise, and temperature changes, and the measurement results are intuitive and reliable.

[0068] 4. A comprehensive stress inversion and interpretation system has been established, improving the accuracy of interpretation.

[0069] This invention constructs a static database of "magnetic response-stress" for casing materials. By combining finite element calculations and experimental verification, it enables quantitative inversion of casing stress values, automatic identification of abnormal stress zones, evaluation of single-well integrity, and prediction of casing damage risks across a block. The interpretation results are scientific and reliable, and can generate visualized stress distribution maps and risk analysis reports.

[0070] 5. Wide range of applications; can be used for integrity monitoring of various types of well casing projects.

[0071] This invention is not only applicable to stress detection of oil and gas well casings, but can also be extended to geothermal wells, wellbore in goaf areas of salt cavern gas storage facilities, CO2–EOR and CCUS (carbon dioxide sequestration and displacement) injection and production wells, various pressure circulation wellbores, and high-temperature and high-pressure wellbore safety monitoring, which can meet the multi-scenario needs of wellbore integrity management.

[0072] 6. Fills a gap in the industry and has significant economic and safety value.

[0073] This invention represents a technological breakthrough in the direct measurement of oil well casing stress, both domestically and internationally, filling a long-standing gap in the industry's lack of stress detection methods. By identifying casing damage trends in advance, it can reduce well workover costs, decrease wellbore accident rates, improve oilfield production efficiency and development safety, and promote long-term stable production and green development of oilfields, demonstrating significant socio-economic benefits and broad industrial value. Attached Figure Description

[0074] Figure 1This is a structural diagram of the oil well casing stress distribution detection device based on magnetomechanical coupling effect in an embodiment of the present invention;

[0075] Figure 2 The figures shown are finite element analysis model diagrams in the embodiments of the present invention, wherein (a) is a finite element analysis model diagram of line distributed load, and (b) is a finite element analysis model diagram of cylindrical action;

[0076] Figure 3 This is a stress curve diagram distributed along the well wall in an embodiment of the present invention. Detailed Implementation

[0077] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0078] Specific Implementation Plan 1: Combining Figure 1 As shown, this invention provides a device for detecting stress distribution in oil well casing based on magnetomechanical coupling effect, including a controller, an orientation instrument, a centralizer, a multi-arm caliper, support slips, and a magnetic stress measuring component.

[0079] The controller is used to receive signals transmitted by the orientation instrument and stress sensor, and then to detect the stress distribution of the oil well casing through the built-in algorithm, and output the detection results to the remote terminal; it also includes a wireless power supply for providing power to other devices, with a built-in constant current and voltage stabilizing module and a communication rate of 1Mbps–2Mbps.

[0080] The orientation instrument includes a triaxial magnetometer and a gyroscope sensor, used to calculate the instrument's attitude and magnetic circuit direction, with an error ≤2°;

[0081] The stabilizer is used to control the instrument's posture, ensuring that the stress sensor is always perpendicular to the sleeve wall, effectively reducing the "air gap d" and thus reducing magnetic reluctance uncertainty.

[0082] The multi-arm caliper is a 16-arm caliper used to measure wellbore deformation and provide geometric verification for stress anomalies; the measuring range is ±25mm and the resolution is 0.1mm.

[0083] The supporting clip uses a three- or four-point radial support structure to provide a contact force of 120N–150N, so that the magnetic stress measuring component of the present invention is tightly attached to the inner wall of the sleeve.

[0084] The magnetic stress measurement component includes an AMS-V type stress sensor and an AMSP-IV pole plate system. The component features a closed magnetic circuit structure to improve the consistency of magnetic field strength and direction. Two pole plates are respectively positioned on both sides of the stress sensor, close to the inner wall of the casing under the support of the clamps. This allows magnetic flux to enter the casing from one pole plate, be conducted through the casing wall, and return to the other pole plate, forming a closed magnetic circuit of "pole plate-casing-pole plate." Unlike traditional open magnetic circuits, this allows the magnetic flux to be concentrated mainly within the casing wall, increasing magnetic sensitivity by 1-2 orders of magnitude. Furthermore, the stress sensor employs a dual-coil structure with one excitation coil and one detection coil, improving signal separation and suppressing excitation noise crosstalk. The detection coil is located inside the stress sensor and uses a differential winding structure to reduce common-mode interference and downhole vibration noise. The pole plates are made of a high-permeability μ, low-hysteresis-loss material, maintaining linearity in the 0-10Oe excitation range and avoiding magnetic saturation caused by high downhole temperatures.

[0085] The excitation frequency is 0.5kHz–5kHz, the magnetic field strength is 0Oe–10Oe, the pole gap is 0.8mm–1.5mm, and the sampling rate is 5kS / s.

[0086] Specific Implementation Plan Two: Combining Figure 1 As shown, this invention provides a method for detecting stress distribution in oil well casing based on magnetomechanical coupling effect, comprising the following steps:

[0087] S100. Based on the magnetomechanical effect principle of ferromagnetic materials, a coupling model between the magnetic response and stress of the bushing is constructed.

[0088] When a ferromagnetic material is subjected to external stress, its internal magnetic domain structure rearranges, resulting in a change in magnetic permeability:

[0089] Δμ=f(σ)ΔM=g(σ)

[0090] In the formula, Δμ is the change in permeability; σ is the stress; ΔM is the change in magnetization; f(σ) is the effect of stress on the change in permeability Δμ; and g(σ) is the effect of stress on the change in magnetization ΔM.

[0091] The variation of this magnetic property with stress can be sensitively captured by sensors in the form of electrical signals, enabling quantitative measurement of the corresponding force; within the elastic region, the permeability μ and the stress σ approximately satisfy a linear relationship:

[0092] Δμ=k·Δσ

[0093] In the formula, k is the magnetomechanical coupling coefficient of the material, which is determined through ground calibration;

[0094] When the casing is subjected to external non-uniform loads (such as local compressive stress concentration), its magnetic property changes can be captured in real time by sensors. After processing, the stress distribution can be inverted. Furthermore, the downhole magnetic signal can be stably extracted and resisted interference, achieving stable, low-noise, and reproducible measurements.

[0095] S200. Optimize the magnetic circuit of the magnetic stress measurement component to ensure that the magnetic circuit meets the following requirements:

[0096]

[0097] In the formula, The magnetic flux passing through the magnetic circuit; This refers to the number of turns of the excitation coil; The excitation current (usually an AC sinusoidal current); The equivalent magnetic reluctance of the sensor core and plates; The equivalent magnetic reluctance is the air gap or the bonding gap. The equivalent magnetic reluctance of the casing section varies with stress. change;

[0098] The S300 employs a wall-attached design and orientation instruments for attitude compensation to ensure magnetic circuit reproducibility.

[0099] The 16-arm caliper ensures three or four radial contact points; the centralizer controls the instrument's attitude, ensuring the stress sensor is always perpendicular to the casing wall, effectively reducing the "air gap d" and thus minimizing magnetic reluctance uncertainty.

[0100]

[0101] In the formula, The equivalent air gap thickness between the sensor electrode plate and the inner wall of the sleeve; The permeability of free space (constant 4π × 10⁻) 7 H / m); The effective magnetic flux area of ​​the air gap;

[0102] When performing attitude compensation using orientation instruments, a triaxial accelerometer and a triaxial magnetometer monitor the attitude in real time, enabling the magnetic response to be compensated according to orientation as follows:

[0103]

[0104] In the formula, The measurement signal after attitude compensation; The original measurement signal; The angle between the direction of the sensor's magnetic poles and the normal to the inner wall of the sleeve (obtained by an orientation instrument);

[0105] S400 enables stable extraction and anti-interference processing of downhole magnetomechanical signals, including:

[0106] S410, frequency domain optimization and skin depth matching, selecting an excitation frequency of 0.5kHz–5kHz, based on the conductivity of the steel sleeve. Given magnetic permeability μ, the designed skin depth δ is:

[0107]

[0108] In the formula, The depth of the electromagnetic field within the casing; The angular frequency of the excitation signal ( ), where f represents the frequency of the excitation signal; The magnetic permeability of the bushing material; The electrical conductivity of the bushing material;

[0109] When δ≈ sleeve wall thickness × 30%, the magnetic field distribution is most sensitive to stress changes;

[0110] S420, dual-channel synchronous acquisition and phase information enhancement.

[0111] The detection signal not only acquires the amplitude, but also extracts the phase information. :

[0112]

[0113] In the formula, The signal amplitude (first harmonic amplitude); The complex voltage signal received by the sensor; The signal phase angle;

[0114] Phase is more sensitive to eddy current disturbances and can be used to eliminate well fluid conductivity interference, thereby improving stress inversion stability;

[0115] S430. Construct a temperature compensation model.

[0116] Downhole temperatures can reach 120°C–180°C, significantly affecting magnetic permeability. This invention constructs a linear temperature-compensated model and incorporates a temperature sensor for real-time correction.

[0117]

[0118] In the formula, To be at temperature Relative permeability at the following values; Reference temperature Relative permeability at the following values; This is the temperature coefficient of magnetic permeability as a function of temperature; The current temperature; For reference temperature;

[0119] S440, real-time compensation for air gap and bonding errors.

[0120] This invention dynamically estimates the air gap d based on the adhesion force, wellbore diameter, and instrument attitude, and corrects the magnetic response to ensure that signals from all depth segments return to a unified adhesion reference.

[0121]

[0122] In the formula, This represents the signal amplitude after air gap compensation. The original signal amplitude; This is the air gap sensitivity coefficient (obtained through calibration); This is the equivalent air gap thickness;

[0123] S450, adaptive filtering and 24-bit high-precision sampling

[0124] The main interference frequency bands in the well are 50Hz and 16Hz–32Hz vibration range. This invention uses digital phase-locked amplification technology, second-order and third-order Butterworth filters and 24-bit ADC (analog-to-digital converter, >100dB dynamic range) to improve the signal-to-noise ratio (SNR) by 40dB–60dB.

[0125] S460, operating condition consistency control, including constant current excitation and magnetic saturation suppression.

[0126] The constant current power supply module guarantees:

[0127]

[0128] In the formula, Input current to the excitation coil; This represents the peak value of the excitation current. The frequency of the excitation signal; For time;

[0129] Even if the well temperature rises or the line impedance changes, it will not affect the excitation intensity;

[0130] S470, Feature Fusion Inversion (Amplitude + Phase + Harmonics).

[0131] The final stress inversion is not a simple linear transformation, but rather employs a multi-feature fusion model:

[0132] ,

[0133] In the formula, The actual stress (estimated value) of the casing obtained through inversion; To solve for the stress parameters of the variables; The actual measured magnetic response characteristic vector includes amplitude, phase, and higher harmonics; This is the parameter set for the forward model, including material magnetic properties, temperature parameters, and calibration constants; The amplitude of the first harmonic (the main sensitive characteristic, corresponding to the most significant stress change); The signal phase angle of the first harmonic (sensitive to eddy currents / hysteresis, which can enhance inversion stability); The third harmonic amplitude (used to supplement nonlinear and hysteresis characteristics); is the 2-norm (Euclidean distance), used to measure the error between the actual signal and the theoretical signal; argmin is the parameter value that minimizes the objective function (optimization solution). The magnetic-stress forward model constructed for this invention.

[0134] This invention establishes a static magnetic-stress database for oil well casing, containing over 20 loading methods, such as axial tension, external pressure loading, eccentric compression, bending loading, and non-uniform circumferential load; the database has been validated using finite element analysis.

[0135]

[0136] In the formula, For the sleeve in radius Circumferential or radial stress at the location; The constant for the Lamé solution is determined by the internal and external pressures; The radius of the casing cross-section (between the inner and outer radii);

[0137] Corresponding change in permeability:

[0138] In the formula, This represents the change in the relative permeability of the bushing material; This represents the stress value of the casing under stress. A magnetomechanical coupling function describing the change of magnetic permeability with stress;

[0139] This enables quantitative inversion of stress.

[0140] The other combinations and connections in this implementation scheme are the same as in Specific Implementation Scheme 1.

[0141] Example

[0142] Combination Figure 2 and Figure 3 As shown, this embodiment conducted a graded loading and unloading experiment on a ground loading platform to verify the measurability and stability of the magnetic-stress signal of the present invention. In the figure, the vertical axis represents the digital count value output by the sensor, and the horizontal axis represents the sampling point sequence. The experiment adopted a three-stage progressive loading method, with each stage applying a constant external force and holding it stable for 1–2 seconds before releasing the load.

[0143] from Figure 3 As can be seen from this, the output signal of the magnetic stress sensor of the present invention exhibits the following characteristics:

[0144] (1) The signal exhibits a stable step response with the applied load.

[0145] The curve exhibits a clear jump from low to high levels during loading, with stable plateau regions between each jump segment. Specifically, in the initial stage, the signal stabilizes around 7800 counts; after the first loading, the signal jumps to approximately 8800 counts; after the second loading, it rises to approximately 9300 counts; and finally, during the loading segment, the signal remains between 9600 and 9800 counts, forming a high-level plateau. This "step-plateau" characteristic indicates that the sensor can produce a clearly differentiated magnetic response to different stress levels.

[0146] (2) The platform section is stable and without drift, indicating that the device can work reliably under steady stress.

[0147] Within the platform segment after each loading stage, the short-term fluctuation amplitude of the curve is typically less than ±20 counts, with no obvious random drift or trend drift observed. This indicates that the magnetic circuit remains stable and closed, the wall-attached structure exhibits no significant slippage or loosening, and temperature and power supply noise have no significant impact on the measurement. Therefore, the device of this invention can maintain high stability under steady-state stress conditions downhole, meeting the requirements of engineering applications.

[0148] (3) The unloading process has good reversibility.

[0149] The curve exhibits a step-like drop during unloading, eventually returning to a count level close to the initial 7800, consistent with the output before loading. This demonstrates that the sensor's magnetomechanical response lacks significant hysteresis, the coupling between the sleeve material's magnetic properties and the sensor of this invention is repeatable and reliable, and the "magnetic response-stress" mapping constructed in this invention possesses engineering reversibility and calibrability. Therefore, the reliability of the inversion model can be verified using unloading data.

[0150] (4) High signal-to-noise ratio and strong anti-interference ability

[0151] The complete waveform of the entire curve shows that the signal remains stable throughout the unloaded segment; the noise between each plateau segment is far below the level of stress-induced step noise; and the curve does not exhibit vibration ripples, jitter, or obvious electromagnetic interference stripes.

[0152] This is because the excitation signal uses constant current control, the magnetic detection coil uses a differential structure, and the shielding and filtering design of the acquisition circuit effectively suppresses interference that may occur downhole. This proves that the present invention is very suitable for use in high-noise downhole environments.

[0153] (5) The step amplitude is monotonically related to the applied stress, which proves the engineering applicability of the magnetic-stress coupling law.

[0154] The three step amplitudes (approximately 1000, 500, and 300) correspond one-to-one with the magnitude of the applied external force, and the step directions are monotonically consistent.

[0155] illustrate:

[0156]

[0157] in is the magnetomechanical coupling coefficient.

[0158] The monotonicity and repeatability of this relationship ensure that the present invention can achieve the core function of "quantitatively inverting sleeve stress from magnetic signals".

[0159] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A device for detecting stress distribution in oil well casing based on magnetomechanical coupling effect, characterized in that: This includes a controller, azimuth instrument, centralizer, multi-arm caliper, support slips, and magnetic stress measurement components, all sequentially mounted on the center rod. The controller is used to receive signals transmitted by the orientation instrument and stress sensor, and then to detect the stress distribution of the oil well casing through the built-in algorithm, and output the detection results to the remote terminal. The orientation instrument includes a triaxial magnetometer and a gyroscope sensor, used to calculate the instrument's attitude and magnetic circuit direction; The stabilizer is used to control the instrument's posture, ensuring that the magnetic sensor is always perpendicular to the sleeve wall. The multi-arm caliper is a 16-arm caliper used to measure well diameter deformation; The support clip adopts a three-point or four-point radial support structure, so that the magnetic stress measuring component is in close contact with the inner wall of the sleeve; The magnetic stress measurement component includes a stress sensor and an electrode plate, which are used to apply an excitation magnetic field to the bushing and collect magnetic response signals related to the bushing stress, forming a closed magnetic circuit to improve the consistency of magnetic field strength and direction, reduce noise interference, and reduce the impact of magnetic saturation on measurement stability under high temperature conditions.

2. A detection method for the oil well casing stress distribution detection device based on magnetomechanical coupling effect as described in claim 1, characterized in that, Includes the following steps: S100. Based on the magnetomechanical effect principle of ferromagnetic materials, a coupling model between the magnetic response and stress of the bushing is constructed. S200. Optimize the magnetic circuit of the magnetic stress measurement component; S300, through wall-attached design and orientation instrument for attitude compensation, ensures magnetic circuit reproducibility; S400 enables stable extraction and anti-interference processing of downhole magnetomechanical signals to obtain casing stress estimates.

3. The method for detecting stress distribution in oil well casing based on magnetomechanical coupling effect according to claim 2, characterized in that: In step S100, the following are included: When a ferromagnetic material is subjected to external stress, its internal magnetic domain structure rearranges, resulting in a change in magnetic permeability: Δμ=f(σ)ΔM=g(σ) In the formula, Δμ is the change in permeability; σ is the stress; ΔM is the change in magnetization; f(σ) is the effect of stress on the change in permeability Δμ; g(σ) is the effect of stress on the change in magnetization ΔM. Within the elastic region, the permeability μ and the stress σ approximately satisfy a linear relationship: Δμ=k·Δσ In the formula, k is the magnetomechanical coupling coefficient of the material, which is determined through ground calibration; When the casing is subjected to external non-uniform loads, its magnetic property changes are captured in real time by sensors, and the stress distribution can be inferred. Furthermore, the downhole magnetic signal can be stably extracted and resisted by interference, achieving stable, low-noise, and reproducible measurements.

4. The method for detecting stress distribution in oil well casing based on magnetomechanical coupling effect according to claim 3, characterized in that: In step S200, the magnetic circuit of the magnetic stress measuring component is optimized to ensure that the magnetic circuit satisfies the following: In the formula, The magnetic flux passing through the magnetic circuit; This refers to the number of turns of the excitation coil; For excitation current; The equivalent magnetic reluctance of the sensor core and plates; The equivalent magnetic reluctance is the air gap or the bonding gap. This is the equivalent magnetic reluctance of the bushing section.

5. The method for detecting stress distribution in oil well casing based on magnetomechanical coupling effect according to claim 4, characterized in that: In step S300, to reduce magnetoresistance uncertainty, the stress sensor direction is always perpendicular to the sleeve wall surface: In the formula, The equivalent air gap thickness between the sensor electrode plate and the inner wall of the sleeve; The vacuum permeability; The effective magnetic flux area of ​​the air gap; When performing attitude compensation using an orientation instrument, the magnetic response is compensated according to the orientation as follows: In the formula, The measurement signal after attitude compensation; The original measurement signal; It is the angle between the direction of the sensor's magnetic poles and the normal to the inner wall of the sleeve.

6. The method for detecting stress distribution in oil well casing based on magnetomechanical coupling effect according to claim 5, characterized in that: In step S400, the following are included: S410, frequency domain optimization and skin depth matching, the skin depth δ is designed as follows: In the formula, The depth of the electromagnetic field within the casing; The angular frequency of the excitation signal; The magnetic permeability of the bushing material; The electrical conductivity of the bushing material; When δ≈ sleeve wall thickness × 30%, the magnetic field distribution is most sensitive to stress changes; S420, dual-channel synchronous acquisition, and phase information enhancement. Detection signal amplitude and phase information : In the formula, The signal amplitude; The complex voltage signal received by the sensor; The signal phase angle; S430: Construct a temperature compensation model and incorporate a built-in temperature sensor for real-time calibration. In the formula, For temperature Relative permeability at the following values; Reference temperature Relative permeability at the following values; This is the temperature coefficient of magnetic permeability as a function of temperature; The current temperature; For reference temperature; S440, real-time compensation for air gap and bonding error, estimation of air gap d and correction of magnetic response: In the formula, This represents the signal amplitude after air gap compensation. The original signal amplitude; This is the air gap sensitivity coefficient; This is the equivalent air gap thickness; The S450, adaptive filtering, and 24-bit high-precision sampling, along with digital lock-in amplification, second- and third-order Butterworth filters, and a 24-bit ADC, improve the signal-to-noise ratio (SNR). S460, operating condition consistency control, including constant current excitation and magnetic saturation suppression. The constant current power supply module guarantees: In the formula, Input current to the excitation coil; This represents the peak value of the excitation current. The frequency of the excitation signal; For time; S470, Feature fusion inversion, using a multi-feature fusion model: ， In the formula, The estimated value of the casing stress obtained from the inversion; To solve for the stress parameters of the variables; This represents the actual measured characteristic vector of the magnetic response; This is the parameter set for the forward model; The original signal amplitude; The phase angle of the first harmonic signal; The amplitude of the third harmonic; is the L2 norm; argmin is the parameter value that minimizes the objective function; This is a magneto-stress forward model.

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