Staggered sleeve detection system based on magnetic field tensor gradient and positioning method

Abstract

The invention belongs to the field of magnetic positioning detection, and discloses a staggered casing detection system and positioning method based on magnetic field tensor gradient, and the system comprises three fluxgate sensors which are vertically arranged along a vertical measuring line in an underground magnetic casing, and a host located on the ground; the vertical measuring line is arranged on the axis of the magnetic casing pipe, and the three fluxgate sensors form a measuring array and are used for moving downwards along a drill hole at the dislocation position of the magnetic casing pipe for continuous measurement to obtain three-component data of a magnetic field of the dislocation casing pipe; and the host is used for receiving the data from the three fluxgate sensors and carrying out data processing and analysis to generate a magnetic anomaly response curve so as to observe and determine the position and the characteristics of the broken sleeve. The broken sleeve detection system and the positioning method have visual distance and positioning functions and are high in positioning efficiency and wider in application scene.

Description

Technical Field

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

[0002] During the long-term production of oil and water wells, objective factors such as water injection and production of oil and water wells, quality of cementing materials, main structure of wellbore, and casing materials will cause the casing of oil and water wells to be damaged by faults, deformation, and rupture. These serious damages to the casing of oil and water wells are usually called casing damage of oil and gas wells. Among them, the concentration of ground stress caused by crustal movement and the instability of the well wall caused by the creep of mud shale caused by the intrusion of injected water will generate huge lateral shear force on the casing wall, causing the casing to break and dislocate, which is called fault.

[0003] At present, there are many methods for casing damage detection at home and abroad, but they all have obvious defects:

[0004] Acoustic imaging logging technology: mainly includes downhole acoustic television, ultrasonic imaging logging, transverse pole shear wave imaging logging technology, etc. The downhole television developed abroad in the early 1960s was the first downhole imaging equipment used in typical oil wells. Since then, the technology has been continuously improved. Today, all oil companies provide ultrasonic imaging measurement. The measurement principle is the ultrasonic pulse reflection method. The instrument emits high-frequency ultrasonic waves in the casing, and the transducer receives most of the reflections of the ultrasonic waves on the inner wall of the pipe wall, thereby detecting the current status of the pipe wall. According to the detection situation, clear casing image data can be obtained, which has a very wide range of uses. However, the detection range of ultrasonic imaging logging is only the inner wall of the casing, and the situation of the outer surface of the casing cannot be obtained.

[0005] Electromagnetic logging technology: Its measurement is based on the geomagnetic induction theory of casing, mainly including magnetic logging instruments and electromagnetic induction flaw detection. It uses the relationship between the induced electromotive force detected by the instrument and the electromagnetic characteristics and position of the pipe string. In the casing section, due to the change in the position of the pipe string and the electromagnetic flaw detection test instrument, the induced electromotive force received by the instrument changes accordingly, thereby detecting the damage of the casing string. However, its measurement accuracy is relatively limited, the measurement results are not intuitive, and the inversion has multiple solutions.

[0006] Wellbore caliper logging technology: through the direct contact between the contact measuring arm of the instrument and the inner wall of the casing, the changes in the wellbore diameter in the pipe are detected according to the recorded movement trajectory of the logging instrument on the inner wall of the casing. At present, the wellbore caliper instruments commonly used at home and abroad are eight-arm and forty-arm through-tubing calipers. Except for the different external structures, the internal structures and operation methods of these wellbore casing damage detection instruments are basically the same. Generally, the more measuring arms there are, the more accurate the accuracy is. However, when there are too many measuring arms, it is easy to scrape sand or get stuck in the casing, and it is difficult for the instrument to pass through places where the casing is severely deformed.

[0007] Downhole optical imaging logging technology: It is an imaging logging technology that uses array sensors to directly obtain downhole video images. It has now developed into a downhole television system that can transmit color high-definition video in real time. Among them, the Videolog visual casing damage detection device developed by Xi'an Shiyou University in China no longer requires dedicated logging cables and logging vehicles during measurement, and can realize localized logging construction. However, its detection results are greatly affected by the well fluid.

[0008] The above methods are mostly used to detect the damage of the inner surface of the casing, and some can detect the misalignment of the casing. However, these methods are relatively insufficient in terms of azimuth and distance detection, that is, determining the position of the misaligned casing. Therefore, it is necessary to study the magnetic positioning detection system to detect the position of the misaligned casing.

[0009] Magnetic detection technology originated in World War II. In order to cope with the threat of submarines in naval battles, 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 positioning method, and used the magnetic gradient tensor and three components of the magnetic field detected by the measurement array composed of superconducting magnetic gradiometers to perform positioning inversion of magnetic targets. Since then, a variety of positioning algorithms have been proposed. Marius Birsan proposed a magnetic positioning method based on the recursive Bayesian estimation problem. This method uses the data collected by the magnetic gradiometer to estimate the trajectory and magnetic moment components of the target magnetic dipole source, which can be solved by the sequential Monte Carlo method called "particle filtering". The effectiveness of this method was verified by using data collected by the car on a straight or curved track using altitude timing, indicating that compared with the traditional method of direct inversion using the gradient tensor, this method has better noise resistance, but the calculation process is more complicated.

[0010] According to the current status of magnetic positioning research at home and abroad, most positioning methods have the following problems to a greater or lesser extent: the influence of the geomagnetic field and background noise, non-unique solutions, large influence of measurement system errors, complex structures and algorithms, etc. At present, the main research direction of magnetic target detection is magnetic anomaly detection technology based on magnetic field tensor gradient. In magnetic target positioning detection, magnetic sensors are usually used to directly obtain traditional magnetic induction intensity information, while the tensor information of magnetic anomaly targets is obtained by building a magnetic gradient tensor system using multiple fluxgate sensors, such as the common cross, two-point double cross, tetrahedron and hexahedron magnetic gradient tensor measurement arrays. Summary of the invention

[0011] In view of this, an embodiment of the present invention provides a broken casing detection system and positioning method based on magnetic field tensor gradient, which at least solves the problems of large error influence in azimuth and distance detection, and complex structure and algorithm in existing measurement systems.

[0012] The technical solutions of the embodiments of the present invention are as follows:

[0013] In a first aspect, an embodiment of the present invention provides a faulty casing detection system based on magnetic field tensor gradient, comprising three fluxgate sensors vertically arranged along a vertical survey line in a downhole magnetic casing, and a host located on the ground; the vertical survey 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 by moving downward along the borehole at the fault position of the magnetic casing to obtain three-component data of the magnetic field of the fault casing;

[0015] The host is used to receive data from the three fluxgate sensors, perform data processing and analysis to generate a magnetic anomaly response curve, so as to observe and determine the position and characteristics of the faulty casing.

[0016] Furthermore, a coordinate system is established with the top center of the magnetic casing as the origin, with the x-axis pointing to due north, the y-axis pointing to due east, and the z-axis pointing vertically downward 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 wellbore into four quadrants and eight areas, and the magnetic field values ​​at different positions are measured at different depths by moving the measurement array, and the information of the three tensors of the magnetic field Bxz, Byz, and Bzz is obtained by analysis.

[0017] Furthermore, the distances between adjacent fluxgate sensors among the three fluxgate sensors are the same.

[0018] In a second aspect, an embodiment of the present invention provides a method for locating a broken casing, which is applied to the broken casing detection system based on magnetic field tensor gradient described in the first aspect, and the method includes:

[0019] Regional positioning is performed using the curve shape of the acquired three-component magnetic field data and the relative size of the outliers of the horizontal components Hax and Hay; the two possible orientations of the faulted casing relative to the vertical survey line are determined using the changes in the tensor synthesis of the magnetic field x-component and y-component; the relative orientation of the vertical survey line and the faulted casing is determined by combining the regional positioning results and the relative positioning results; after determining the relative orientation, the offset distance of the faulted casing relative to the original magnetic casing is obtained using an empirical distance formula; wherein the empirical distance formula is a corresponding relationship between the curve feature points and the distances obtained by fitting the Bxz, Byz and Bzz tensor curves of the corresponding orientation.

[0020] Furthermore, the regional positioning is performed using the curve shape of the acquired three-component magnetic field data and the relative sizes of the outliers of the horizontal components Hax and Hay, including: observing the positive and negative conditions of the extreme points of the Hax curve and the Hay curve by changing the direction of the vertical survey line relative to the magnetic casing; judging the quadrant where the faulty casing is located according to the positive and negative conditions of the extreme points of the Hax curve and the Hay curve; and determining the specific area of ​​the faulty casing in the quadrant by comparing the relative sizes of the outliers of the Hax curve and the Hay curve.

[0021] Furthermore, the quadrant in which the broken casing is located can be determined according to the positive and negative conditions of the extreme points of the Hax curve and the Hay curve, including: when the extreme points of the Hax curve and the Hay curve are both positive, determining that the broken casing is in the first quadrant; when the extreme points of the Hax curve are negative and the extreme points of the Hay curve are positive, determining that the broken casing is in the second quadrant; when the extreme points of the Hax curve and the Hay curve are both negative, determining that the broken casing is in the third quadrant; when the extreme points of the Hax curve are positive and the extreme points of the Hay curve are negative, determining that the broken casing is in the fourth quadrant.

[0022] The beneficial effects brought by the technical solution provided by the embodiment of the present application include at least:

[0023] Intuitive distance determination and positioning function: The faulty casing detection system based on magnetic field tensor gradient can more intuitively analyze the distance and position change of faulty casing by obtaining the response curves of multiple magnetic tensors (such as Bxz, Byz, Bzz). The transient electromagnetic method based on underground wells relies on the extraction and analysis of transient electromagnetic data. Although it can locate the position and depth of the casing head, the processing of its response curve is relatively complicated.

[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 through the curve shape of the three components of the magnetic field and the change of the tensor, that is, it can quickly complete the orientation and distance processing of the faulty casing position. However, the underground transient electromagnetic method requires multiple steps such as coordinate conversion, three-dimensional electromagnetic field forward modeling, and pure anomaly extraction, so the processing flow is relatively more complicated and takes a long time.

[0025] Wider application scenarios: The faulty casing detection system based on magnetic field tensor gradient detects faulty casing based on magnetic anomalies, and does not require the deployment of transmitting wireframes on the ground, which is particularly suitable for the detection of magnetic targets in complex geological environments. However, the underground transient electromagnetic method relies on the deployment of ground wireframes, which limits its use in certain specific scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. 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 work, among which:

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

[0028] Figure 2 A schematic diagram of partitioning and magnetic field tensor synthesis provided by an embodiment of the present invention;

[0029] Figure 3 A schematic diagram of a flow chart of a method for locating a broken casing provided by an embodiment of the present invention;

[0030] Figure 4 A composite diagram of magnetic field tensors of casings with different horizontal azimuth misalignments provided by an embodiment of the present invention;

[0031] Figure 5 Schematic diagram of magnetic anomaly response curves in different quadrants provided by an embodiment of the present invention: a) is a magnetic anomaly response curve of a broken casing in the first quadrant; b) is a magnetic anomaly response curve of a broken casing in the second quadrant; c) is a magnetic anomaly response curve of a broken casing in the third quadrant; d) is a response curve of a broken casing in the fourth quadrant;

[0032] Figure 6 The three tensor response curves that vary with distance provided in the embodiment of the present invention: 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 DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0034] In the following description, reference is made to “some embodiments”, which describe a subset of all possible embodiments, but it will be 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 pointed out that the terms "first\second\third" involved in the embodiments of the present invention are only used to distinguish similar objects and do not represent a specific ordering of the objects. It can be understood that "first\second\third" can be interchanged in a specific order or sequence where permitted, so that the embodiments of the present invention described here can be implemented in an order other than that illustrated or described here.

[0036] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the field to which the embodiments of the present invention belong. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with those in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless specifically defined as here.

[0037] In magnetic exploration, a survey line is a straight line along a path on the surface or underground for measuring magnetic fields. The direction of the survey line relative to the cylindrical model refers to the spatial orientation relationship between the survey line and the underground target (such as casing). The survey line referred to in the embodiment of the present invention is a vertical survey line.

[0038] Declination of magnetic field: Declination is the horizontal angle difference between the north direction of the geomagnetic field and the geographic north direction. In the northern hemisphere, the geomagnetic field usually deflects to the west, while in the southern hemisphere it deflects to the east. In magnetic exploration, declination affects the magnetic field measurement because it changes the direction of the magnetic field tensor relative to the geographic coordinate system.

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

[0040] Hax curve and Hay curve usually refer to the projection of the horizontal component of the magnetic field in the x-axis 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 to infer the location, shape and magnetic characteristics of underground magnetic bodies. Hax curve: represents the change of the horizontal component of the magnetic field in the x-axis direction. In magnetic anomaly analysis, the Hax curve can reflect the magnetic characteristics of the magnetic body in the x-axis direction. Hay curve: represents the change of the horizontal component of the magnetic field in the y-axis direction. The Hay curve can also reveal the magnetic characteristics of the magnetic body in the y-axis direction.

[0041] Figure 1A broken casing detection system based on magnetic field tensor gradient is provided in an embodiment of the present invention, such as Figure 1 As shown, it includes three fluxgate sensors vertically arranged along a vertical survey line in a downhole magnetic casing, and a host located on the ground; the vertical survey line is deployed on the axis of the magnetic casing, wherein:

[0042] The three fluxgate sensors form a measurement array, which is used to continuously measure by moving downward along the borehole at the fault position of the magnetic casing to obtain three-component data of the magnetic field of the fault casing;

[0043] The host is used to receive data from the three fluxgate sensors, perform data processing and analysis to generate a magnetic anomaly response curve, so as to observe and determine the position and characteristics of the faulty casing.

[0044] In actual detection of faulty casing, due to the small diameter of the casing and the deep burial depth, it is difficult to obtain obvious abnormal values ​​through magnetic measurement on the ground, and large-area magnetic measurement on the ground cannot be performed. Therefore, it is necessary to conduct magnetic measurement in the well, break through along the upper normal casing, and use an array of three-component fluxgate sensor instruments to measure the three-component data of the magnetic field downward along the well, observe the characteristics of the magnetic anomaly response curve, and determine the position of the faulty casing. In actual field operations, tensor information cannot be obtained directly, and a fluxgate system composed of multiple fluxgates is usually used to obtain tensor data of the magnetic target. Due to space limitations in the well, common cross-shaped, hexahedral and other measurement arrays cannot be used. The embodiment of the present invention uses a measurement array of three three-component fluxgates arranged vertically to be placed in and lifted out of the borehole, such as Figure 1 In the movement direction shown in , continuous measurement is performed by moving downward along the borehole at the fault position to obtain the three-component magnetic field data of the faulty casing.

[0045] In some embodiments, a coordinate system is established with the top center of the magnetic casing as the origin, with the x-axis pointing to due north, the y-axis pointing to due east, and the z-axis pointing vertically downward. 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 wellbore into four quadrants and eight areas. The magnetic field values ​​at different positions are measured at different depths by moving the measurement array, and the information of the three tensors of the 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 which the response numerical accuracy of the three tensors Bxz, Byz, and Bzz is high. The curve shape change law at the interface of the cylindrical casing model can be used to determine the distance of the staggered casing.

[0047] like Figure 2The figure shows a schematic diagram of the partition and magnetic field tensor synthesis. The specific synthesis direction depends on the tensor synthesis of the magnetic field Hax and Hay obtained by the fluxgate measurement. The inside of the wellbore is divided into four quadrants and eight regions, and each region corresponds to a specific rotation position. The first quadrant is divided into region 1 and region 2, the second quadrant is divided into region 3 and region 4, the third quadrant is divided into region 5 and region 6, and the fourth quadrant is divided into region 7 and region 8. In implementation, the direction of the measurement array is arbitrarily set, and then the three-component magnetic field data can be obtained by moving down the well for continuous measurement. Then, the data of the fluxgate array is processed, and the changes in the tensor synthesis of the x component and the y component of the magnetic field are analyzed and processed to determine the approximate direction of the casing. The magnetic field tensor gradient-based misaligned casing detection system provided by the present invention can more intuitively analyze the distance of the misaligned casing and its position change by obtaining the response curves of multiple magnetic tensors (such as Bxz, Byz, Bzz).

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

[0049] Here, in order to ensure the efficiency of the measurement process and the validity of the data, the present invention studies the influence of the change of the fluxgate spacing on the accuracy of the distance determination result. Preferably, in order to achieve high measurement efficiency and obtain good accuracy data, the spacing should be controlled below 0.6 meters.

[0050] Figure 3 A schematic flow chart of a method for locating a broken casing provided by an embodiment of the present invention is applied to the above-mentioned broken casing detection system based on magnetic field tensor gradient, such as Figure 3 As shown, the method comprises at least the following steps:

[0051] Step S310, regional positioning is performed using the curve shape of the acquired three-component magnetic field data and the relative sizes of the abnormal values ​​of the horizontal components Hax and Hay.

[0052] Here, the magnetic field data of multiple positions are first collected by the magnetic field tensor gradient-based misaligned casing detection system provided by the present invention to reflect the magnetic field characteristics of different positions. The shape of the data curve after analysis and processing is found that when the direction of the vertical survey line relative to the cylindrical casing model is changed, the extreme values ​​of the Hax and Hay curves will change. Based on this conclusion obtained from the forward modeling results, by changing the relative position of the misaligned casing and the vertical survey line (for example, testing at the center of eight areas respectively), the rules are summarized to achieve a qualitative analysis of the orientation of the misaligned casing. This method can orient the misaligned casing within a 45° area around the vertical survey line.

[0053] Step S320, using the change of the tensor synthesis of the x-component and y-component of the magnetic field, two possible orientations of the faulted casing relative to the vertical survey line are determined.

[0054] Here, the tensor synthesis of the x-component and y-component of the magnetic field, that is, the tensor of the horizontal component Ha, has different directions in different orientations, which can be used to determine the orientation of the faulty casing relative to the original upper casing. The Ha tensor represents the horizontal component of the geomagnetic field, and its direction change can reflect the position change of the faulty 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, when the declination and orientation change, the direction of the Ha tensor will change. Due to the characteristics of the geomagnetic field, the direction change of the Ha tensor may correspond to two possible azimuths, which usually occurs when the two azimuths are symmetrical about the geomagnetic north. Therefore, by measuring and recording the change in the direction of the Ha tensor, two possible orientations can be calculated in combination with the known local geomagnetic declination.

[0055] Step S330, combining the regional positioning result and the relative positioning result to determine the relative position of the vertical survey line and the faulty casing.

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

[0057] Step S340: After determining the relative orientation, an empirical distance formula is used to obtain an offset distance of the staggered casing relative to the original magnetic casing.

[0058] Here, the empirical distance formula is the corresponding relationship between the characteristic points of the curve and the distance obtained by fitting the Bxz, Byz and Bzz tensor curves of the corresponding orientation. After roughly orienting the misaligned casing through steps S310 to 330, the distance measurement is performed based on the corresponding empirical distance formula under the current orientation. In actual detection, the vertical survey line is arranged on the same axis of the original casing. By analyzing the magnetic anomaly response curves of the vertical survey line and the cylindrical casing model at different distances, the relationship between the curve change and the distance is obtained, and the offset distance can be obtained. Among them, the numerical response accuracy of the three tensors Bxz, Byz and Bzz is high, and the curve morphology changes regularly at the interface on the cylinder. By simulating the three tensors in different orientations, the corresponding Bxz, Byz and Bzz curve characteristic points and distances are obtained, and the empirical distance formula based on the three tensors is summarized, which can be used to distance the model.

[0059] The distance determination of underground faulty casing is part of the magnetic anomaly inversion process. There are many conventional magnetic anomaly inversion methods, such as analytical method, tangent method and integral method. The analytical method is also called the characteristic point method. It is based on the regular geological body anomaly formula under simple conditions to solve the relationship between the characteristic point coordinates on the anomaly curve and the target body position, geometry and other parameters.

[0060] From the full-space forward modeling results of the cylindrical magnetic anomaly, it can be seen that the change of the anomaly along the vertical direction can be used to determine the position of the faulty casing 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 faulty casing relative to the upper original casing.

[0061] According to the physical property that the casing is a ferromagnetic material, the embodiment of the present invention analyzes the magnetic anomaly response characteristics of the faulty casing and proposes a faulty casing positioning method based on the target positioning technology of the magnetic field tensor gradient, thereby providing technical support for the positioning of the faulty casing in the repair of the faulted well.

[0062] In some embodiments, the above step S310 further includes the following steps: by changing the direction of the vertical survey line relative to the magnetic casing, observing the positive and negative conditions of the extreme points of the Hax curve and the Hay curve; according to the positive and negative conditions of the extreme points of the Hax curve and the Hay curve, the quadrant where the broken casing is located can be determined; by comparing the relative sizes of the abnormal values ​​of the Hax curve and the Hay curve, the specific area of ​​the broken casing in the quadrant is determined.

[0063] Here, Hax and Hay represent the two components of the horizontal magnetic field, usually the east-west direction (Hax) and the north-south direction (Hay). Extreme points refer to the points on the magnetic survey curve where the magnetic field changes most significantly. These points can help determine the location of the magnetic casing. In implementation, the positive and negative conditions of the abnormal extreme points of Hax and Hay are first used to determine the quadrant where the misaligned casing is located, and then the relative size of the abnormal values ​​of Hax and Hay is used to determine the area where the misaligned casing is located. Combining the positive and negative conditions of the extreme points and the relative size of the abnormal values, the specific position of the casing in the well can be more accurately located. This method can help engineers understand the misalignment of the casing and take corresponding repair measures.

[0064] In some embodiments, the above-mentioned "according to the positive and negative conditions of the extreme points of the Hax curve and the Hay curve, the quadrant in which the broken casing is located can be determined" is further implemented by the following process: when the extreme points of the Hax curve and the Hay curve are both positive, the broken casing is determined to be in the first quadrant; when the extreme points of the Hax curve are negative and the extreme points of the Hay curve are positive, the broken casing is determined to be in the second quadrant; when the extreme points of the Hax curve and the Hay curve are both negative, the broken casing is determined to be in the third quadrant; when the extreme points of the Hax curve are positive and the extreme points of the Hay curve are negative, the broken casing is determined to be in the fourth quadrant.

[0065] Here, because in the first quadrant, the coordinate values ​​of the x-axis and the y-axis are both positive, the corresponding extreme points of the Hax and Hay curves will also be positive. In the second quadrant, the coordinate value of the x-axis is negative, and the coordinate value of the y-axis is positive, so the extreme point of the Hax curve will be negative, and the extreme point of the Hay curve will be positive. In the third quadrant, the coordinate values ​​of the x-axis and the y-axis are both negative, so the corresponding extreme points of the Hax and Hay curves will also be negative. In the fourth quadrant, the coordinate value of the x-axis is positive, and the coordinate value of the y-axis is negative, so the extreme point of the Hax curve will be positive, and the extreme point of the Hay curve will be negative. Therefore, based on the relationship between the positive and negative of the extreme point and the coordinate quadrant, the position of the faulted casing can be effectively determined.

[0066] The above-mentioned broken casing detection system and broken casing positioning method based on magnetic field tensor gradient are described below in conjunction with 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 to the present invention.

[0067] The positioning of underground misaligned casing is mainly divided into two steps: determining the relative direction and distance between the misaligned casing and the original casing. Therefore, the embodiment of the present invention first uses the magnetic field response curve of the upright cylinder 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 the previous study of the magnetic anomaly response curve of cylinders with different parameters, a method for orienting and locating the misaligned casing is designed.

[0068] The change of the cylindrical magnetic anomaly along the vertical direction can be used to determine the position of the faulty casing head, and the tensor of the horizontal component Ha has different directions in different directions, which can be used as a basis for determining the position of the faulty casing relative to the upper original casing. After roughly orienting the faulty casing, the faulty casing needs to be distanced. The main purpose is to obtain the offset distance between the faulty casing and the upper original casing. In actual detection, the vertical survey line is arranged on the same axis of the original casing. By analyzing the magnetic anomaly response curve at different distances between the vertical survey line and the cylindrical casing model, the relationship between the curve change and the distance is obtained, and the offset distance can be obtained. Among them, the numerical response accuracy of the three tensors Bxz, Byz and Bzz is high, and the law of curve shape change at the interface of the cylindrical casing model can be used to determine the distance of the model.

[0069] First, directional analysis of the broken casing:

[0070] When the magnetic field deflection and inclination are changed respectively, the extreme positive and negative values ​​of the Hax curve and the Hay curve will not change, but when the direction of the vertical survey line relative to the casing model is changed, the extreme values ​​of the Hax curve and the Hay curve will change. Therefore, based on this conclusion obtained from the forward modeling results, by changing the relative position of the faulty casing and the vertical survey line, the law is summarized to achieve a qualitative analysis of the orientation of the faulty casing.

[0071] In actual situations, the position of the vertical survey line is often known. Therefore, in this simulation, the position of the vertical survey line is fixed at the origin. In order to obtain an obvious magnetic anomaly curve, the distance between the vertical survey line and the cylindrical casing model is set to 1 meter.

[0072] When the faulty casing is located in the first and third quadrants, the extreme points of the Hax curve and the Hay curve are the same in terms of positive and negative, and the relative size of the abnormal values ​​of the Hax curve and the Hay curve can be used to determine the area where the faulty casing is located; when the faulty casing is in the second and fourth quadrants, the extreme points of the Hax curve and the Hay curve are opposite in terms of positive and negative, and then the relative size of the abnormal values ​​of the Hax curve and the Hay curve can be used to determine the area where the faulty casing is located. Regional positioning is mainly carried out in two steps: first, the quadrant where the faulty casing is located is determined by the positive and negative conditions of the abnormal extreme points of the Hax curve and the Hay curve, and then the area where the casing is located is determined by the relative size of the abnormal values ​​of the Hax and Hay curves. As shown in Table 1, this method can orient the faulty casing in the 45° area around the vertical survey line.

[0073] Table 1 Results of positioning the faulty casing area

[0074]

[0075]

[0076] After roughly orienting the faulty casing by the above method, the casing needs to be distanced. The main purpose is to obtain the offset distance between the faulty casing and the upper original casing. In actual detection, the vertical survey line is arranged on the same axis of the original casing. By analyzing the magnetic anomaly response curve at different distances between the vertical survey line and the cylindrical model, the relationship between the curve change and the distance is obtained, and the offset distance can be obtained. Among them, the numerical response accuracy of the three tensors Bxz, Byz and Bzz is high, and the curve shape change law at the upper interface of the cylinder can be used to determine the distance of the model.

[0077] By analyzing the characteristic points of each tensor, the empirical distance formula based on the three tensors is summarized as follows:

[0078]

[0079] Where, X Bxx , X Bxy, X Bxz are the eigenvalues ​​of the three tensors respectively; l x , l y , l z They are the distances in the corresponding directions of space obtained for the three tensors respectively.

[0080] Based on the above analysis, it can be known that the offset distance between the faulted casing and the original upper casing can be determined by using the certain mathematical relationship between the characteristic points and distances of the three tensor curves Bxz, Byz and Bzz. The curves at different orientations have different shapes and different relationships, but when the orientation is certain, the curve shape is stable and the fitting curve distance error is small. Therefore, the three tensors at different orientations can be simulated to obtain the corresponding relationship between the characteristic points of the curve and the distance, that is, the empirical distance formula. After determining the orientation of the abnormal body, the corresponding empirical distance formula can be used to obtain the approximate offset distance of the faulted casing.

[0081] The broken casing detection system and the broken casing positioning method based on magnetic field tensor gradient provided by the present invention have at least the following advantages:

[0082] Intuitive distance determination and positioning function: The faulty casing detection system based on magnetic field tensor gradient can more intuitively analyze the distance and position change of faulty casing by obtaining the response curves of multiple magnetic tensors (such as Bxz, Byz, Bzz). The transient electromagnetic method based on underground wells relies on the extraction and analysis of transient electromagnetic data. Although it can locate the position and depth of the casing head, the processing of its response curve is relatively complicated.

[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 through the curve shape of the three components of the magnetic field and the change of the tensor, that is, it can quickly complete the orientation and distance processing of the faulty casing position. However, the underground transient electromagnetic method requires multiple steps such as coordinate conversion, three-dimensional electromagnetic field forward modeling, and pure anomaly extraction, so the processing flow is relatively more complicated and takes a long time.

[0084] Wider application scenarios: The faulty casing detection system based on magnetic field tensor gradient detects faulty casing based on magnetic anomalies, and does not require the deployment of transmitting wireframes on the ground, which is particularly suitable for the detection of magnetic targets in complex geological environments. However, the underground transient electromagnetic method relies on the deployment of ground wireframes, which limits its use in certain specific scenarios.

[0085] It should be understood that "one embodiment" or "an embodiment" mentioned throughout the specification means that specific features, structures or characteristics related to the embodiment are included in at least one embodiment of the present invention. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. In addition, these specific features, structures or characteristics can be combined in one or more embodiments in any suitable manner. It should be understood that in various embodiments of the present invention, the size of the serial number of the above-mentioned processes does not mean the 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 embodiment of the present invention. The serial numbers of the above-mentioned embodiments of the present invention are only for description and do not represent the advantages and disadvantages of the embodiments.

[0086] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0087] In the several embodiments provided by the present 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 the present invention can be arbitrarily combined without conflict to obtain new method embodiments. The features disclosed in the several method embodiments provided by the present invention can be arbitrarily combined without conflict to obtain new method embodiments.

[0088] The above is only an embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A faulty casing detection system based on magnetic field tensor gradient, characterized in that: It includes three fluxgate sensors vertically arranged along a vertical survey line in a downhole magnetic casing, and a main engine located on the ground; the vertical survey 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 by moving downward along the borehole at the fault position of the magnetic casing to obtain three-component data of the magnetic field of the fault casing; The host is used to receive data from the three fluxgate sensors, perform data processing and analysis to generate a magnetic anomaly response curve, so as to observe and determine the position and characteristics of the faulty casing.

2. The system according to claim 1, characterized in that A coordinate system is established with the top center of the magnetic casing as the origin, with the x-axis pointing to the north, the y-axis pointing to the east, and the z-axis pointing vertically downward. 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 wellbore into four quadrants and eight areas. The magnetic field values ​​at different positions at different depths are measured by moving the measurement array, and the information of the three tensors of the magnetic field Bxz, Byz, and Bzz is obtained by analysis.

3. The system according to claim 1 or 2, characterized in that: The distances between adjacent fluxgate sensors in the three fluxgate sensors are the same.

4. A method for locating a broken casing, applied to a broken casing detection system based on magnetic field tensor gradient as claimed in any one of claims 1 to 3, characterized in that: include: The curve shape of the acquired three-component magnetic field data and the relative size of the abnormal values ​​of the horizontal components Hax and Hay are used to locate the region; Using the changes in the tensor synthesis of the x-component and y-component of the magnetic field, two possible orientations of the faulted casing relative to the vertical survey line are determined; Combining the regional positioning results and relative positioning results, determine the relative position of the vertical survey line and the faulted casing; After determining the relative orientation, the offset distance of the staggered casing relative to the original magnetic casing is obtained using an empirical distance formula; wherein the empirical distance formula is a corresponding relationship between the characteristic points of the curve and the distance obtained by fitting the Bxz, Byz and Bzz tensor curves of the corresponding orientation.

5. The method according to claim 4, characterized in that The method of performing regional positioning by using the curve shape of the acquired three-component magnetic field data and the relative size of the abnormal values ​​of the horizontal components Hax and Hay includes: By changing the direction of the vertical survey line relative to the magnetic casing, observe the positive and negative extreme points of the Hax curve and the Hay curve; According to the positive and negative conditions of the extreme points of the Hax curve and the Hay curve, the quadrant where the faulty casing is located can be determined; By comparing the relative sizes of the abnormal values ​​of the Hax curve and the Hay curve, the specific area of ​​the faulted casing in the quadrant is determined.

6. The method according to claim 5, characterized in that The quadrant where the broken casing is located can be determined according to the positive and negative conditions of the extreme points of the Hax curve and the Hay curve, including: When the extreme value points of the Hax curve and the Hay curve are both positive, it is determined that the staggered casing is in the first quadrant; When the extreme value point of the Hax curve is negative and the extreme value point of the Hay curve is positive, it is determined that the staggered casing is in the second quadrant; When the extreme value points of the Hax curve and the Hay curve are both negative, it is determined that the faulty casing is in the third quadrant; When the extreme value point of the Hax curve is positive and the extreme value point of the Hay curve is negative, it is determined that the broken casing is in the fourth quadrant.

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