A magnetic field tensor gradient-based detection system and positioning method for detecting a broken casing

Abstract

The present application belongs to the field of magnetic positioning detection, and discloses a broken casing detection system and positioning method based on magnetic field tensor gradient, wherein the system comprises three fluxgate sensors vertically arranged along a vertical survey line in a downhole magnetic casing and a host computer located on the ground; the vertical survey line is arranged on the axis of the magnetic casing, wherein: the three fluxgate sensors form a measurement array, which is used for continuously measuring downward along the borehole at the broken position of the magnetic casing to obtain three-component magnetic field data of the broken casing; the host computer is used for receiving data from the three fluxgate sensors, performing data processing and analysis to generate a magnetic anomaly response curve, so as to observe and determine the position and characteristics of the broken casing. The broken casing detection system and positioning method have intuitive distance positioning and positioning functions, high positioning efficiency, and are more widely applicable.

Description

Technical Field

[0001] This invention relates to the field of magnetic positioning detection, and relates to, but is not limited to, a faulty sleeve detection system and positioning method based on magnetic field tensor gradient. Background Technology

[0002] During long-term production, factors such as water injection and extraction, cementing material quality, wellbore structure, and casing materials can all lead to casing damage, including misalignment, deformation, and rupture. These severe damages to oil and water well casings are commonly referred to as casing damage in oil and gas wells. Among these, stress concentration caused by crustal movement and wellbore instability due to shale creep caused by injected water intrusion can generate enormous lateral shear forces on the casing wall, causing it to fracture and displace—a condition known as misalignment.

[0003] Currently, there are numerous methods available both domestically and internationally for detecting casing damage, but all of them have significant drawbacks:

[0004] Acoustic imaging logging technology mainly includes downhole acoustic television, ultrasonic imaging logging, and transverse pole shear wave imaging logging technology. Downhole television, developed abroad in the early 1960s, was the first downhole imaging device applied to typical oil wells. Since then, the technology has been continuously improved, and today all oil companies offer ultrasonic imaging measurement. Its measurement principle is the ultrasonic pulse reflection method. The instrument emits high-frequency ultrasonic waves inside the casing, and the transducer receives most of the reflected ultrasonic waves from the inner wall of the casing, thus detecting the current condition of the casing wall. Based on the detection, clear images of the casing can be obtained, making it widely applicable. However, the detection range of ultrasonic imaging logging is only the inner wall of the casing and cannot obtain information about the outer surface of the casing.

[0005] Electromagnetic logging technology: Its measurements are based on the geomagnetic induction theory of the casing, primarily using magnetic logging tools and electromagnetic induction testing. It utilizes the relationship between the induced electromotive force detected by the instrument and the electromagnetic characteristics and position of the casing string. In the casing section, changes in the position of the casing string and the electromagnetic testing instrument alter the induced electromotive force received by the instrument, thus detecting damage to the casing string. However, its measurement accuracy is relatively limited, the results are not intuitive, and the inversion process has multiple possible interpretations.

[0006] Borehole logging technology using caliper-type instruments involves direct contact between the instrument's measuring arms and the inner wall of the casing. The changes in the well diameter within the casing are detected by recording the instrument's movement along the casing's surface. Currently, the most commonly used caliper-type instruments domestically and internationally are eight-arm and forty-arm tubing caliper gauges. These caliper-type casing damage detection instruments differ only in their external structure; their internal structure and operating methods are essentially the same. Generally, the more measuring arms, the higher the accuracy. However, with a large number of measuring arms, it is easy for sand scraping or jamming to occur within the casing, and the instrument may have difficulty passing through areas of severe casing deformation.

[0007] Downhole optical imaging logging technology is an imaging logging technology that uses area array sensors to directly acquire downhole video images. It has now developed to the stage of downhole television systems capable of real-time transmission of high-definition color video. Among these, the Videolog visualization casing damage detection device developed by Xi'an Petroleum University in China eliminates the need for dedicated logging cables and logging trucks during measurement, enabling localized logging operations. However, its detection results are significantly affected by well fluid.

[0008] The methods described above are mostly used to detect damage to the inner surface of the casing, and some can detect casing breakage. However, these methods are insufficient for determining the location of the broken casing in terms of orientation and distance detection. Therefore, it is necessary to study a magnetic positioning detection system to detect the location of the broken casing.

[0009] Magnetic detection technology originated during World War II. To counter the threat of submarines in naval warfare, Western countries conducted research on magnetic detection theory and developed the first fluxgate sensor. In 1975, Wynn et al. in the United States proposed the magnetic gradient tensor localization method, using a measurement array composed of superconducting magnetic gradiometers to detect the magnetic gradient tensor and the three components of the magnetic field for localization inversion of magnetic targets. Subsequently, various localization algorithms were proposed based on this method. Marius Birsan proposed a magnetic localization method based on a recursive Bayesian estimation problem. This method uses data collected by a magnetic gradiometer to estimate the trajectory and magnetic moment components of the target magnetic dipole source, which can be solved using a sequential Monte Carlo method called "particle filtering." The effectiveness of this method was verified using data collected by a car on a straight or curved track using altimeters, showing that compared to traditional methods using direct gradient tensor inversion, this method has better noise resistance, but the calculation process is more complex.

[0010] Based on the current state of research on magnetic positioning both domestically and internationally, most positioning methods suffer from the following problems to varying degrees: the influence of the geomagnetic field and background noise, non-unique solutions, significant measurement system errors, and complex structures and algorithms. Currently, the main research direction for magnetic target detection is magnetic anomaly detection technology based on magnetic field tensor gradients. In magnetic target positioning and detection, traditional magnetic induction intensity information is typically obtained directly using magnetic sensors, while the tensor information of magnetic anomalies is obtained by constructing a magnetic gradient tensor system using multiple fluxgate sensors, such as common cross-shaped, two-point double-cross, tetrahedral, and hexahedral magnetic gradient tensor measurement arrays. Summary of the Invention

[0011] In view of this, embodiments of the present invention provide a fault sleeve detection system and positioning method based on magnetic field tensor gradient, which at least solves the problems of large errors in orientation and distance detection, and complex structure and algorithm of existing measurement systems.

[0012] The specific technical solutions of this invention are as follows:

[0013] In a first aspect, embodiments of the present invention provide a faulty casing detection system based on magnetic field tensor gradient, comprising three fluxgate sensors arranged vertically along a vertical measuring line in a downhole magnetic casing, and a main unit located on the ground; the vertical measuring line is deployed on the axis of the magnetic casing, wherein:

[0014] The three fluxgate sensors form a measurement array, which is used to continuously measure along the borehole at the misalignment position of the magnetic sleeve to obtain the three-component magnetic field data of the misaligned sleeve.

[0015] The host is used to receive data from the three fluxgate sensors, process and analyze the data to generate magnetic anomaly response curves, and observe and determine the position and characteristics of the misaligned bushing.

[0016] Furthermore, a coordinate system is established with the top center of the magnetic sleeve as the origin, the x-axis pointing due north, the y-axis pointing due east, and the z-axis pointing vertically downwards as positive; at the same time, the area pointed to by the tensor synthesis of the x-component and y-component of the magnetic field is used to divide the inside of the well into four quadrants and eight regions. By moving the measurement array at different depths, the magnetic field values ​​at different locations are measured, and the information of the three tensors of magnetic field Bxz, Byz, and Bzz is obtained through analysis.

[0017] Furthermore, the spacing between adjacent fluxgate sensors among the three fluxgate sensors is the same.

[0018] In a second aspect, embodiments of the present invention provide a method for locating a misaligned sleeve, applied to the misaligned sleeve detection system based on the magnetic field tensor gradient described in the first aspect, the method comprising:

[0019] The region is located using the curve shape of the acquired three-component magnetic field data and the relative magnitude of outliers in the horizontal components Hax and Hay. The changes in the tensor composition of the x and y components of the magnetic field are used to determine two possible orientations of the misaligned sleeve relative to the vertical survey line. The relative orientation between the vertical survey line and the misaligned sleeve is determined by combining the regional and relative positioning results. After determining the relative orientation, the offset distance of the misaligned sleeve relative to the original magnetic sleeve is obtained using an empirical distance formula. This empirical distance formula is a relationship between the curve feature points and the distance obtained by fitting the Bxz, Byz, and Bzz tensor curves of the corresponding orientation.

[0020] Furthermore, the method of locating the region using the curve shape of the acquired three-component magnetic field data and the relative magnitude of outliers in the horizontal components Hax and Hay includes: observing the positive and negative signs of the extreme points of the Hax and Hay curves by changing the direction of the vertical measuring line relative to the magnetic sleeve; determining the quadrant in which the misaligned sleeve is located based on the positive and negative signs of the extreme points of the Hax and Hay curves; and determining the specific region of the misaligned sleeve within that quadrant by comparing the relative magnitude of the outliers in the Hax and Hay curves.

[0021] Furthermore, determining the quadrant of the misaligned bushing based on the sign of the extreme points of the Hax and Hay curves includes: determining the misaligned bushing in the first quadrant when both extreme points of the Hax and Hay curves are positive; determining the misaligned bushing in the second quadrant when the extreme point of the Hax curve is negative and the extreme point of the Hay curve is positive; determining the misaligned bushing in the third quadrant when both extreme points of the Hax and Hay curves are negative; and determining the misaligned bushing in the fourth quadrant when the extreme point of the Hax curve is positive and the extreme point of the Hay curve is negative.

[0022] The beneficial effects of the technical solutions provided in this application include at least the following:

[0023] Intuitive distance and location determination capabilities: The faulty casing detection system based on magnetic field tensor gradient acquires response curves of multiple magnetic tensors (such as Bxz, Byz, and Bzz), enabling a more intuitive analysis of the distance and positional changes of the faulty casing. In contrast, the well transient electromagnetic method relies on the extraction and analysis of transient electromagnetic data. Although it can locate the azimuth and depth of the casing head, the processing of its response curves is more complex.

[0024] High positioning efficiency: The faulty casing detection system based on magnetic field tensor gradient can invert the magnetic anomaly curve in a short time by observing the curve shape and tensor changes of the three magnetic field components, thus quickly completing the orientation and distance determination of the faulty casing location. In contrast, the transient electromagnetic method for wellbore drilling requires multiple steps such as coordinate transformation, three-dimensional electromagnetic field forward modeling, and pure anomaly extraction, making the processing flow relatively more complex and time-consuming.

[0025] Wider applicability: The fault casing detection system based on magnetic field tensor gradient detects fault casings based on magnetic anomalies, eliminating the need for ground-based transmitting wireframes. This makes it particularly suitable for detecting magnetic targets in complex geological environments. In contrast, the ground-based transient electromagnetic method relies on the deployment of ground-based wireframes, limiting its application in certain specific scenarios. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0027] Figure 1 A schematic diagram of the architecture of a fault sleeve detection system based on magnetic field tensor gradient provided in an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of partitioning and magnetic field tensor synthesis provided in an embodiment of the present invention;

[0029] Figure 3 A flowchart illustrating a method for locating a misaligned sleeve according to an embodiment of the present invention;

[0030] Figure 4 This is a composite image of the magnetic field tensor of the sleeve with different horizontal orientations provided in an embodiment of the present invention;

[0031] Figure 5 The following is a schematic diagram of magnetic anomaly response curves in different quadrants provided for embodiments of the present invention: where a) is the magnetic anomaly response curve of the misaligned bushing located in the first quadrant; b) is the magnetic anomaly response curve of the misaligned bushing located in the second quadrant; c) is the magnetic anomaly response curve of the misaligned bushing located in the third quadrant; and d) is the response curve of the misaligned bushing located in the fourth quadrant.

[0032] Figure 6 The three-tensor response curves varying with distance provided for embodiments of the present invention are as follows: part a) is the curve of Bxz varying with distance, part b) is the curve of Byz varying with distance, and part c) is the curve of Bzz varying with distance. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] In the following description, references are made to “some embodiments,” which describe a subset of all possible embodiments. However, it is understood that “some embodiments” may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict.

[0035] It should be noted that the terms "first, second, and third" used in the embodiments of the present invention are only used to distinguish similar objects and do not represent a specific ordering of objects. It is understood that "first, second, and third" can be interchanged in a specific order or sequence where permitted, so that the embodiments of the present invention described herein can be implemented in an order other than that illustrated or described herein.

[0036] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which these embodiments of the invention pertain. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0037] In magnetic exploration, a survey line is a straight line that follows a path on the surface or underground to measure the magnetic field. The direction of the survey line relative to the cylindrical model refers to the spatial orientation between the survey line and the underground target (such as a casing). The survey line referred to in this embodiment of the invention is a vertical survey line.

[0038] Magnetic field declination: Declination is the horizontal angular difference between the Earth's magnetic field northward direction and the geographic northward direction. In the Northern Hemisphere, the Earth's magnetic field typically declinates westward, while in the Southern Hemisphere it declinates eastward. In magnetic exploration, declination affects magnetic field measurements because it alters the orientation of the magnetic field tensor relative to the geographic coordinate system.

[0039] Inclination of the magnetic field: The inclination is the angle between the geomagnetic field tensor and the horizontal plane. Near the equator, the inclination is close to 0°, while near the poles it is close to 90°. The inclination affects the vertical distribution of the magnetic field tensor, thus affecting magnetic measurement data.

[0040] Hax and Hay curves typically refer to the projections of the horizontal components of a magnetic field onto the x- and y-axis directions. In magnetic exploration, the geomagnetic field can be decomposed into horizontal components (Hax and Hay) and vertical components (Haz). These components can be used to analyze and interpret magnetic anomaly data, thereby inferring the location, shape, and magnetic characteristics of subsurface magnetic bodies. Hax curve: Represents the variation of the horizontal component of the magnetic field along the x-axis. In magnetic anomaly analysis, the Hax curve reflects the magnetic characteristics of a magnetic body along the x-axis. Hay curve: Represents the variation of the horizontal component of the magnetic field along the y-axis. The Hay curve also reveals the magnetic characteristics of a magnetic body along the y-axis.

[0041] Figure 1An embodiment of the present invention provides a fault sleeve detection system based on magnetic field tensor gradient, such as... Figure 1 As shown, the system includes three fluxgate sensors arranged vertically along a vertical measuring line within a downhole magnetic casing, and a main unit located on the surface; the vertical measuring line is deployed along the axis of the magnetic casing, wherein:

[0042] The three fluxgate sensors form a measurement array, which is used to continuously measure along the borehole at the misalignment position of the magnetic sleeve to obtain the three-component magnetic field data of the misaligned sleeve.

[0043] The host is used to receive data from the three fluxgate sensors, process and analyze the data to generate magnetic anomaly response curves, and observe and determine the position and characteristics of the misaligned bushing.

[0044] In actual casing fault detection, due to the small diameter and deep burial of the casing, it is difficult to obtain obvious anomalies through surface magnetic surveys, making large-area surface magnetic surveys impossible. Therefore, in-well magnetic surveys are necessary. The casing is drilled down along the upper normal casing, and a three-component fluxgate magnetometer array is used to measure the three components of the magnetic field downwards, observing the characteristics of the magnetic anomaly response curve to determine the location of the faulty casing. In actual field operations, tensor information cannot be directly obtained. Typically, a fluxgate magnetometer system composed of multiple fluxgate magnetometers is used to obtain tensor data of the magnetic target. Due to space limitations in the well, common cross-shaped or hexahedral measurement arrays cannot be used. This embodiment of the invention uses a measurement array of three vertically arranged three-component fluxgate magnetometers, inserted and lifted into the borehole. Figure 1 The direction of motion shown is used to continuously measure the magnetic field three-component data of the misaligned casing by moving downwards along the borehole at the fault location.

[0045] In some embodiments, a coordinate system is established with the top center of the magnetic sleeve as the origin, the x-axis pointing due north, the y-axis pointing due east, and the z-axis pointing vertically downwards as positive; at the same time, the area pointed to by the tensor synthesis of the x-component and y-component of the magnetic field is used to divide the inside of the well into four quadrants and eight regions. By moving the measurement array at different depths, the magnetic field values ​​at different locations are measured, and the information of the three tensors of magnetic field Bxz, Byz, and Bzz is obtained by analysis.

[0046] Here, the magnetic field values ​​are measured at different depths. The rate of change of the three components of the magnetic field along the x, y, and z directions in space is the magnetic gradient tensor. There are a total of 9 elements in the magnetic tensor gradient. Among them, the response values ​​of the three tensors Bxz, Byz, and Bzz have high accuracy. The curve shape change law at the interface on the cylindrical sleeve model can be used to determine the distance of the misaligned sleeve.

[0047] like Figure 2The diagram illustrates the partitioning and magnetic field tensor synthesis. The specific synthesis direction depends on the tensor synthesis of the magnetic fields Hax and Hay obtained from fluxgate measurements. The wellbore interior is divided into four quadrants and eight regions, each corresponding to a specific rotational position. The first quadrant is divided into regions 1 and 2, the second quadrant into regions 3 and 4, the third quadrant into regions 5 and 6, and the fourth quadrant into regions 7 and 8. In practice, the direction of the measurement array is arbitrarily set, and continuous measurements are taken along the wellbore to obtain three-component magnetic field data. The data from the fluxgate array is then processed, and the changes in the tensor synthesis of the x and y components of the magnetic field are analyzed to determine the approximate direction of the casing. The faulty casing detection system based on magnetic field tensor gradient provided by this invention obtains the response curves of multiple magnetic tensors (such as Bxz, Byz, and Bzz), enabling a more intuitive analysis of the distance and positional changes of the faulty casing.

[0048] In some embodiments, the spacing between adjacent fluxgate sensors among the three fluxgate sensors is the same.

[0049] To ensure the efficiency of the measurement process and the validity of the data, this invention studies the influence of changes in fluxgate spacing on the accuracy of the distance determination results. Preferably, to achieve high measurement efficiency while obtaining accurate data, the spacing should be controlled below 0.6 meters.

[0050] Figure 3 This is a flowchart illustrating a method for locating a misaligned sleeve according to an embodiment of the present invention, applied to the aforementioned misaligned sleeve detection system based on magnetic field tensor gradient, such as... Figure 3 As shown, the method includes at least the following steps:

[0051] Step S310: Use the curve shape of the acquired three-component magnetic field data and the relative magnitude of outliers in the horizontal components Hax and Hay to locate the region.

[0052] Here, magnetic field data from multiple locations are first collected using the magnetic field tensor gradient-based fault sleeve detection system provided by this invention to reflect the magnetic field characteristics at different locations. Analysis of the processed data curve morphology reveals that the extreme values ​​of the Hax and Hay curves change when the orientation of the vertical survey line relative to the cylindrical sleeve model is altered. Based on this conclusion obtained from forward modeling results, by changing the relative position of the fault sleeve to the vertical survey line (e.g., testing at the center of eight regions), patterns are summarized to achieve a qualitative analysis of the fault sleeve's orientation. This method can orient the fault sleeve within a 45° region around the vertical survey line.

[0053] Step S320: By utilizing the change in the tensor composition of the x and y components of the magnetic field, the two possible orientations of the misaligned sleeve relative to the vertical survey line are determined.

[0054] Here, the characteristic that the tensor of the horizontal component Ha, which is the composite tensor of the x and y components of the magnetic field, has different directions in different azimuths can be used to determine the azimuth of the misaligned casing relative to the original upper casing. The Ha tensor represents the horizontal component of the geomagnetic field, and its direction change reflects the positional change of the misaligned casing relative to the vertical survey line. Using known conditions, including the starting position of the vertical survey line and the declination and inclination of the local magnetic field, the direction of the Ha tensor changes when the declination and azimuth change. Due to the characteristics of the geomagnetic field, the change in the direction of the Ha tensor may correspond to two possible azimuth angles, which usually occurs when the two azimuth angles are symmetrical about magnetic north. Therefore, by measuring and recording the change in the direction of the Ha tensor, the two possible azimuths can be calculated by combining the known local magnetic declination.

[0055] Step S330: Combine the regional positioning results and the relative positioning results to determine the relative orientation of the vertical survey line and the misaligned sleeve.

[0056] Here, the regional positioning result indicates that the specific area where the misaligned casing is located is one of the eight divided areas. Combined with two possible orientations, the relative orientation of the vertical survey line and the misaligned casing is finally determined.

[0057] Step S340: After determining the relative orientation, the offset distance of the misaligned sleeve relative to the original magnetic sleeve is obtained using an empirical distance formula.

[0058] Here, the empirical distance determination formula is the correspondence between the curve feature points and the distance obtained by fitting the Bxz, Byz, and Bzz tensor curves of the corresponding azimuth. After roughly orienting the misaligned casing through steps S310 to 330, distance measurement is performed based on the empirical distance determination formula corresponding to the current azimuth. In actual detection, the vertical measuring line is laid on the same axis as the original casing. By analyzing the magnetic anomaly response curves at different distances between the vertical measuring line and the cylindrical casing model, the relationship between curve changes and distance is obtained, and the offset distance can be calculated. Among them, the response values ​​of the three tensors Bxz, Byz, and Bzz have high accuracy, and the curve shape change law at the interface of the cylinder is shown. By simulating the three tensors at different azimuths, the corresponding correspondence between the Bxz, Byz, and Bzz curve feature points and the distance is obtained. The empirical distance determination formula based on the three tensors is summarized and can be used to determine the distance of the model.

[0059] The determination of the distance of underground fault casing is part of the magnetic anomaly inversion process. There are many conventional magnetic anomaly inversion methods, such as analytical methods, tangent methods, and integral methods. The analytical method, also known as the feature point method, is based on the anomaly formula for regular geological bodies under simple conditions, and solves for the relationship between the coordinates of feature points on the anomaly curve and the position, geometry, and other parameters of the target body.

[0060] The full-space forward modeling results of the cylindrical magnetic anomaly show that the variation of the anomaly along the vertical direction can be used to determine the position of the misaligned sleeve head, and the characteristic that the tensor of the horizontal component Ha has different directions in different orientations can be used as a basis for determining the orientation of the misaligned sleeve relative to the original upper sleeve.

[0061] Based on the physical property that casing is a ferromagnetic material, this invention proposes a method for locating misaligned casing by analyzing the magnetic anomaly response characteristics of misaligned casing and using target location technology based on magnetic field tensor gradient, providing technical support for locating misaligned casing in the repair of misaligned wells.

[0062] In some embodiments, step S310 further includes the following steps: by changing the direction of the vertical measuring line relative to the magnetic sleeve, observe the positive and negative signs of the extreme points of the Hax curve and the Hay curve; based on the positive and negative signs of the extreme points of the Hax curve and the Hay curve, the quadrant in which the misaligned sleeve is located can be determined; by comparing the relative magnitudes of the outliers of the Hax curve and the Hay curve, the specific region of the misaligned sleeve within that quadrant can be determined.

[0063] Here, Hax and Hay represent the two components of the horizontal magnetic field, typically east-west (Hax) and north-south (Hay). Extreme points refer to the points on the magnetic measurement curve where the magnetic field changes most significantly; these points help determine the location of the magnetic casing. In practice, the sign of the abnormal extreme points of Hax and Hay is first used to determine the quadrant where the misaligned casing is located, and then the relative magnitude of the outliers in Hax and Hay is used to determine the region where the misaligned casing is located. Combining the sign of the extreme points and the relative magnitude of the outliers allows for more precise location of the casing within the well. This method helps engineers understand the misalignment of the casing and thus take appropriate repair measures.

[0064] In some embodiments, the above-mentioned "determining the quadrant of the misaligned bushing based on the sign of the extreme points of the Hax and Hay curves" is further implemented through the following process: when both the extreme points of the Hax and Hay curves are positive, the misaligned bushing is determined to be in the first quadrant; when the extreme point of the Hax curve is negative and the extreme point of the Hay curve is positive, the misaligned bushing is determined to be in the second quadrant; when both the extreme points of the Hax and Hay curves are negative, the misaligned bushing is determined to be in the third quadrant; and when the extreme point of the Hax curve is positive and the extreme point of the Hay curve is negative, the misaligned bushing is determined to be in the fourth quadrant.

[0065] Here, because the x-axis and y-axis coordinates are positive in the first quadrant, the extreme points of the corresponding Hax and Hay curves will also be positive. In the second quadrant, the x-axis coordinates are negative, while the y-axis coordinates are positive; therefore, the extreme points of the Hax curve will be negative, and the extreme points of the Hay curve will be positive. In the third quadrant, the x-axis and y-axis coordinates are both negative, so the extreme points of the corresponding Hax and Hay curves will also be negative. In the fourth quadrant, the x-axis coordinates are positive, while the y-axis coordinates are negative; therefore, the extreme points of the Hax curve will be positive, and the extreme points of the Hay curve will be negative. Therefore, based on the relationship between the sign of the extreme points and the coordinate quadrant, the location of the misaligned bushing can be effectively determined.

[0066] The above-mentioned faulty sleeve detection system and faulty sleeve positioning method based on magnetic field tensor gradient are described below with reference to a specific embodiment. However, it should be noted that this specific embodiment is only for better illustrating the present invention and does not constitute an improper limitation of the present invention.

[0067] The location of underground misaligned casings mainly involves two steps: determining the relative direction and distance between the misaligned casing and the original casing. Therefore, this embodiment of the invention first uses the magnetic field response curve of a vertical cylindrical model to simulate the magnetic anomaly response of the underground misaligned casing and analyzes the changes in the magnetic anomaly response curve under different conditions. Based on previous research on the magnetic anomaly response curves of cylinders with different parameters, a method for orienting and locating the misaligned casing is designed.

[0068] The vertical variation of the cylindrical magnetic anomaly can be used to determine the position of the misaligned sleeve head, while the characteristic that the tensor of the horizontal component Ha has different directions at different locations can be used as a basis for determining the orientation of the misaligned sleeve relative to the upper original sleeve. After roughly orienting the misaligned sleeve, it needs to be distanced. The main purpose is to obtain the offset distance between the misaligned sleeve and the upper original sleeve. In actual detection, the vertical measuring line is laid on the same axis as the original sleeve. By analyzing the magnetic anomaly response curves at different distances between the vertical measuring line and the cylindrical sleeve model, the relationship between the curve change and the distance can be obtained, and the offset distance can be calculated. Among them, the response values ​​of the three tensors Bxz, Byz, and Bzz have high accuracy, and the curve shape change law at the interface of the cylindrical sleeve model can be used to determine the distance of the model.

[0069] First, the orientation analysis of the misaligned bushing:

[0070] When the magnetic field deflection angle and inclination angle are changed respectively, the signs of the extreme values ​​of the Hax and Hay curves remain unchanged. However, when the direction of the vertical survey line relative to the casing model is changed, the extreme values ​​of the Hax and Hay curves change. Therefore, based on this conclusion obtained from the forward modeling results, by changing the relative position of the misaligned casing and the vertical survey line, we can summarize the patterns and achieve a qualitative analysis of the orientation of the misaligned casing.

[0071] In practice, the location of the vertical survey line is often known. Therefore, in this simulation, the location of the vertical survey line is fixed at the origin. In order to obtain a clear magnetic anomaly curve, the distance between the vertical survey line and the cylindrical sleeve model is set to 1 meter.

[0072] When the misaligned casing is located in the first or third quadrant, the extreme points of the Hax and Hay curves have the same sign, and the relative magnitude of the outliers of the Hax and Hay curves can be used to determine the region where the misaligned casing is located. When the misaligned casing is located in the second or fourth quadrant, the extreme points of the Hax and Hay curves have opposite signs, and the relative magnitude of the outliers of the Hax and Hay curves can then be used to determine the region where the misaligned casing is located. Region localization is mainly carried out in two steps: first, the sign of the outliers of the Hax and Hay curves is used to determine the quadrant where the misaligned casing is located; then, the relative magnitude of the outliers of the Hax and Hay curves is used to determine the region where the casing is located. As shown in Table 1, this method can orient the misaligned casing within a 45° area around the vertical survey line.

[0073] Table 1. Location results of the misaligned sleeve area

[0074]

[0075]

[0076] After roughly orienting the misaligned sleeve using the methods described above, the sleeve needs to be distanced. The main purpose is to obtain the offset distance between the misaligned sleeve and the original upper sleeve. In actual detection, the vertical measuring line is laid on the same axis as the original sleeve. By analyzing the magnetic anomaly response curves at different distances between the vertical measuring line and the cylindrical model, the relationship between the curve change and the distance can be obtained, and the offset distance can be calculated. Among them, the response values ​​of the three tensors Bxz, Byz, and Bzz have high accuracy, and the curve shape change law at the interface of the cylinder can be used to determine the distance of the model.

[0077] Based on the analysis of the feature points of each tensor, the empirical distance formula based on the three tensors is summarized as follows:

[0078]

[0079] In the formula, X Bxx X BxyX Bxz These are the eigenvalues ​​of the three tensors; l x l y l z These are the distances in the corresponding spatial directions obtained from the three tensors, respectively.

[0080] Based on the above analysis, it can be seen that determining the offset distance between the misaligned casing and the original upper casing can be achieved using the mathematical relationship between the characteristic points and distances of the three tensor curves Bxz, Byz, and Bzz. The curve shapes and relationships differ depending on the orientation, but when the orientation is constant, the curve shape is stable, and the fitting curve has a relatively small distance estimation error. Therefore, the corresponding relationship between the curve characteristic points and distances can be obtained by simulating the three tensors at different orientations, i.e., the empirical distance estimation formula. After determining the orientation of the anomaly, the approximate offset distance of the misaligned casing can be obtained using the corresponding empirical distance estimation formula.

[0081] The faulty sleeve detection system and faulty sleeve location method based on magnetic field tensor gradient provided by this invention have at least the following advantages:

[0082] Intuitive distance and location determination capabilities: The faulty casing detection system based on magnetic field tensor gradient acquires response curves of multiple magnetic tensors (such as Bxz, Byz, and Bzz), enabling a more intuitive analysis of the distance and positional changes of the faulty casing. In contrast, the well transient electromagnetic method relies on the extraction and analysis of transient electromagnetic data. Although it can locate the azimuth and depth of the casing head, the processing of its response curves is more complex.

[0083] High positioning efficiency: The faulty casing detection system based on magnetic field tensor gradient can invert the magnetic anomaly curve in a short time by observing the curve shape and tensor changes of the three magnetic field components, thus quickly completing the orientation and distance determination of the faulty casing location. In contrast, the transient electromagnetic method for wellbore drilling requires multiple steps such as coordinate transformation, three-dimensional electromagnetic field forward modeling, and pure anomaly extraction, making the processing flow relatively more complex and time-consuming.

[0084] Wider applicability: The fault casing detection system based on magnetic field tensor gradient detects fault casings based on magnetic anomalies, eliminating the need for ground-based transmitting wireframes. This makes it particularly suitable for detecting magnetic targets in complex geological environments. In contrast, the ground-based transient electromagnetic method relies on the deployment of ground-based wireframes, limiting its application in certain specific scenarios.

[0085] It should be understood that the phrase "one embodiment" or "an embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of the invention. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. It should be understood that in the various embodiments of the invention, the sequence numbers of the above-described processes do not imply a sequential order of execution; the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the invention. The sequence numbers of the above-described embodiments of the invention are merely descriptive and do not represent the superiority or inferiority of the embodiments.

[0086] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0087] In the several embodiments provided by this invention, it should be understood that the disclosed methods can be implemented in other ways. The methods disclosed in the several method embodiments provided by this invention can be arbitrarily combined without conflict to obtain new method embodiments. The features disclosed in the several method embodiments provided by this invention can be arbitrarily combined without conflict to obtain new method embodiments.

[0088] The above description is merely an embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A fault sleeve detection system based on magnetic field tensor gradient, characterized in that, It includes three fluxgate sensors arranged vertically along the vertical measuring line inside the downhole magnetic casing, and a main unit located on the surface; the vertical measuring line is deployed on the axis of the magnetic casing, wherein: The three fluxgate sensors form a measurement array, which is used to continuously measure along the borehole at the misalignment position of the magnetic sleeve to obtain the three-component magnetic field data of the misaligned sleeve. The host is used to receive data from the three fluxgate sensors, perform data processing and analysis to generate magnetic anomaly response curves, so as to observe and determine the position and characteristics of the misaligned bushing. A coordinate system is established with the top center of the magnetic sleeve as the origin, the x-axis pointing due north, the y-axis pointing due east, and the z-axis pointing vertically downwards. At the same time, the area pointed to by the tensor synthesis of the x and y components of the magnetic field divides the inside of the well into four quadrants and eight regions. By moving the measurement array at different depths, the magnetic field values ​​at different locations are measured, and the information of the three tensors of magnetic field Bxz, Byz, and Bzz is obtained through analysis.

2. The system according to claim 1, characterized in that, The spacing between adjacent fluxgate sensors among the three fluxgate sensors is the same.

3. A method for locating a misaligned sleeve, applied to the misaligned sleeve detection system based on the magnetic field tensor gradient as described in claim 1 or 2, characterized in that, include: The region is located by using the curve shape of the acquired three-component magnetic field data and the relative magnitude of outliers in the horizontal components Hax and Hay. By utilizing the tensor composition change of the magnetic field x-component and y-component, two possible orientations of the misaligned sleeve relative to the vertical survey line are determined; Based on the combined regional and relative positioning results, the relative orientation of the vertical survey line and the misaligned sleeve is determined. After determining the relative orientation, the offset distance of the misaligned sleeve relative to the original magnetic sleeve is obtained using an empirical distance formula; wherein, the empirical distance formula is a correspondence between the feature points of the curve and the distance obtained by fitting the Bxz, Byz and Bzz tensor curves of the corresponding orientation.

4. The method according to claim 3, characterized in that, The method of locating regions using the curve shape of the acquired three-component magnetic field data and the relative magnitude of outliers in the horizontal components Hax and Hay includes: By changing the direction of the vertical measuring line relative to the magnetic sleeve, observe the positive and negative extreme points of the Hax and Hay curves. Based on the sign of the extreme points of the Hax and Hay curves, determine the quadrant in which the misaligned bushing is located; By comparing the relative magnitudes of outliers in the Hax and Hay curves, the specific region of the misaligned bushing within that quadrant can be determined.

5. The method according to claim 4, characterized in that, The step of determining the quadrant in which the misaligned bushing is located based on the sign of the extreme points of the Hax and Hay curves includes: When both the extreme points of the Hax curve and the extreme points of the Hay curve are positive, the misaligned sleeve is determined to be in the first quadrant. When the extreme point of the Hax curve is negative and the extreme point of the Hay curve is positive, the misaligned sleeve is determined to be in the second quadrant. When both the extreme points of the Hax curve and the Hay curve are negative, the misaligned bushing is determined to be in the third quadrant. When the extreme point of the Hax curve is positive and the extreme point of the Hay curve is negative, the misaligned sleeve is determined to be in the fourth quadrant.

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