A lost fish head detection device and method for pull and drop construction

Abstract

The application relates to the technical field of downhole operation of oil exploitation, in particular to a lost fish head detection device and method for taking and replacing a casing, the method comprising the following steps: by collecting the magnetic variable of a downhole probe at each sampling depth, a potential interference section is first determined; then, by combining the magnetic field gradient distribution and the horizontal magnetic field direction characteristics, the magnetic field change balance degree and the direction consistency are calculated, the stratum lithology and external interference are effectively removed, and the real lost fish head section is accurately locked; finally, the horizontal distance is calculated by using the magnetic field vector weighted summation, and the fish collecting strategy is output. The application aims to improve the accuracy of fish head positioning and the fish collecting success rate.

Description

Technical Field

[0001] This application relates to the field of downhole operations technology in oil extraction, specifically to a lost fish head detection device and method for casing replacement operations. Background Technology

[0002] During oil extraction, as wells operate for longer periods, downhole casing can become damaged due to corrosion, wear, and formation stress, interfering with normal well production. Repairing the damaged casing requires casing replacement, where the damaged section is removed and replaced with a new one, thus restoring wellbore integrity and production. However, during casing replacement, due to severe corrosion, thread fatigue failure, or improper operation, the casing head may detach and fall into the wellbore, resulting in its loss.

[0003] Passive geomagnetic detection technology uses the geomagnetic field as an excitation source. When a ferromagnetic casing falls into the well, it is magnetized under the influence of the geomagnetic field. When the passive geomagnetic detection equipment approaches the fish head position, the magnetic field strength will be significantly higher than the background geomagnetic field. Thus, the fish head position can be accurately located based on the magnetic field changes, providing technical support for fish retrieval methods.

[0004] In traditional passive geomagnetic detection technology, the horizontal distance between the passive geomagnetic detection device and the lost fish head is determined based on the detected magnetic field strength and a set model, thus pinpointing the location of the lost fish head. However, traditional model detection assumes that the geomagnetic field is uniformly distributed within the well casing. In reality, there may be iron-containing minerals or interfering substances within the well casing. Relying on traditional empirical models for locating the lost fish head leads to positioning errors, making accurate location of the lost fish head impossible. Summary of the Invention

[0005] In view of the above, it is necessary to provide a device and method for detecting lost fish heads during replacement operations to solve the above problems.

[0006] The first aspect of this application provides a method for detecting a lost fish head during a replacement sleeve operation, the method comprising:

[0007] Obtain the magnetic variables measured by the upper and lower probes at each sampling depth inside the wellbore using a passive geomagnetic detection device;

[0008] Analyze the degree of change in magnetic variables between the upper and lower probes at each sampling depth to identify potential fish head interference segments;

[0009] Based on the distribution of magnetic field gradient changes in a single potential fish head interference segment, characteristic values ​​are obtained. Combining the dispersion of the characteristic values ​​of a single potential fish head interference segment with the distribution of magnetic variables, the degree of uniformity of magnetic field variation in a single potential fish head interference segment is obtained.

[0010] Based on the variation characteristics of the horizontal magnetic field direction of adjacent sampling depths of a single potential fish head interference segment, the directional consistency of a single potential fish head interference segment is obtained.

[0011] By comprehensively considering the uniformity of magnetic field changes and the consistency of direction of individual potential fish head interference segments, the screening value of individual potential fish head interference segments is determined to identify the actual lost fish head segments; based on the magnetic field direction vector measured at each sampling depth in the actual lost fish head segments and the background magnetic field vector, the fish head magnetic field vector is determined; the fish head magnetic field vector is weighted and summed using the distance between the center of the actual lost fish head segments and each sampling depth to obtain the calibrated magnetic field and calculate the horizontal distance.

[0012] Based on the obtained horizontal distance, output the fish-catching strategy.

[0013] Preferably, determining the potential fish head interference segment specifically involves:

[0014] For each sampling depth, calculate the first-order difference value of the magnetic variable intensity between the lower and upper probes of the detection device; perform curve fitting on the first-order difference values ​​obtained for all sampling depths, and extract each effective zero-crossing point of the fitted curve; take each effective zero-crossing point as the center, obtain the depth range corresponding to the N nearest sampling depths, and form a potential fish head interference segment; where N is a preset value.

[0015] Preferably, the condition for extracting each effective zero-crossing point of the fitted curve is: the absolute value of the difference between the first-order difference values ​​corresponding to the two depth sampling points closest to the zero-crossing point of the fitted curve is greater than a preset amplitude dead zone threshold.

[0016] Preferably, obtaining the feature characterization value specifically involves:

[0017] The sequence of all magnetic variables in a single potential fish head interference segment is denoted as the magnetic variable sequence. The ratio of the absolute value of the difference between adjacent elements in the magnetic variable sequence to the absolute value of the difference between the corresponding depth values ​​of adjacent elements is calculated to obtain the feature characterization value.

[0018] Preferably, the degree of uniformity in the magnetic field variation of a single potential fish head interference segment is specifically as follows:

[0019] Calculate the difference between the maximum and mean values ​​of the magnetic variable sequence corresponding to a single potential fish head interference segment; obtain the degree of dispersion of all feature characterization values ​​obtained for a single potential fish head interference segment; positively fuse the negative correlation mapping result of the dispersion with the difference to obtain the degree of magnetic field variation balance of a single potential fish head interference segment.

[0020] Preferably, the directional consistency of obtaining a single potential fish head interference segment specifically involves:

[0021] For a single potential fish head interference segment, obtain the cosine similarity between the magnetic field direction vectors of adjacent elements in the magnetic variable sequence, and use the mean of the cosine similarity between all adjacent elements as the direction consistency.

[0022] Preferably, the directional consistency of obtaining a single potential fish head interference segment specifically involves:

[0023] For a single potential fish head interference segment, obtain the magnitude of the difference vector between the magnetic field direction vectors of adjacent elements in the magnetic variable sequence, and use the negative correlation mapping result after summing the magnitudes obtained between all adjacent elements as the direction consistency.

[0024] Preferably, the screening value of a single potential fish head interference segment is specifically the product of the normalized value of the magnetic field variation balance and the directional consistency.

[0025] Preferably, the actual lost fish head segment is the potential fish head interference segment with the largest screening value.

[0026] Preferably, the background magnetic field vector is obtained by averaging the magnetic field vectors in the non-potential fish head interference segment.

[0027] Preferably, the fish head magnetic field vector is obtained by the difference vector between the magnetic field direction vector of each depth value in the actual lost fish head segment and the background magnetic field vector.

[0028] Preferably, the calculation of the horizontal distance specifically involves multiplying the negative correlation mapping result of the magnitude of the calibrated magnetic field vector with a preset empirical coefficient for fish head positioning to obtain the horizontal distance.

[0029] Preferably, the output fish-catching strategy is as follows:

[0030] If the calculated horizontal distance is within the preset fish-catching range, an enlarging milling head with an effective inner diameter covering the horizontal distance is used in conjunction with a bell mouth to enlarge the diameter for fish catching; if the calculated horizontal distance is not within the enlarged diameter for fish catching, a translational well position technique is used to re-drill.

[0031] Secondly, embodiments of this application also provide a lost fish head detection device for replacement and repair work, including a memory, a processor, and a computer program stored in the memory and running on the processor, wherein the processor executes the computer program to implement the steps of any of the methods described above.

[0032] This application has at least the following beneficial effects:

[0033] This application first obtains the magnetic variables of the upper and lower probes at various sampling depths within the wellbore, and analyzes the degree of change between them to determine potential fish-head interference sections. This step can effectively identify areas where abnormal fluctuations in the magnetic field occur, thus defining the initial investigation scope for subsequent interference elimination and precise location.

[0034] Based on this, this application obtains characteristic values ​​by analyzing the distribution of magnetic field gradient changes in potential interference sections, and calculates the degree of magnetic field gradient uniformity by combining the degree of dispersion of its distribution and the distribution of magnetic variables. Since the magnetic field generated by the fish head and the magnetic field generated by the strata magnetic rock layer have fundamentally different gradient patterns, this index can effectively remove the background interference from the strata magnetic rock layer and improve the signal-to-noise ratio of the signal.

[0035] Furthermore, this application obtains directional consistency based on the variation characteristics of the horizontal magnetic field direction at adjacent sampling depths of potential interference segments. Utilizing the different directional distribution characteristics of interfering objects (such as stray magnetic fields in the wellbore) and the actual fish head magnetic field, this step can further accurately identify external non-target interference factors, thereby achieving accurate locking and coarse positioning of the actual lost fish head segment.

[0036] Finally, this application determines the magnetic field vector of the fish head based on the magnetic field direction vector within the actual lost fish head segment and the background magnetic field vector, and calculates the horizontal distance by weighted summation of the distances from each sampling depth to the center. This weighted algorithm based on the characteristics of the actual magnetic field distribution greatly corrects the errors caused by a single model, ultimately significantly improving the positioning accuracy of lost fish heads and the success rate of fish retrieval operations. Attached Figure Description

[0037] Figure 1 This is a flowchart illustrating the steps of a method for detecting a lost fish head during a replacement sleeve operation, as provided in one embodiment of this application. Detailed Implementation

[0038] In the description of the embodiments in this application, the words "exemplary," "or," and "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design scheme described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design schemes. Specifically, the use of the words "exemplary," "or," and "for example" is intended to present the relevant concepts in a specific manner.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this application's specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0040] It should also be noted that the terms "first" and "second" in this application and its accompanying drawings are used to distinguish similar objects, rather than to describe a specific order or sequence. The methods disclosed in the embodiments of this application or the methods shown in the flowcharts include one or more steps for implementing the method. Without departing from the scope of protection of this application, the execution order of multiple steps can be interchanged, and some steps can also be deleted.

[0041] The following description, in conjunction with the accompanying drawings, details a specific scheme for a lost fish head detection device and method provided in this application for replacement and resizing construction.

[0042] Currently, fish head retrieval during casing replacement mainly employs direct milling with a casing milling head. For wells with surface casing, limited by the inner diameter of the surface casing (e.g., a 339.7mm casing has an inner diameter of 320mm), a maximum Φ315mm bell-mouth casing milling head can be used for fish head retrieval. For wells without surface casing, an enlarged-diameter fish head retrieval technique can be used, employing a larger-sized casing milling head (e.g., Φ1270mm). However, in most wells where fish heads are lost, the casing offset distance often exceeds the effective retrieval range of the casing milling head, resulting in a low success rate for existing techniques (statistically only about 55%). During construction, repeated attempts with different tools and paths are often necessary, leading to significant uncertainty, severely slowing down the construction progress, and potentially causing secondary damage to the wellbore.

[0043] Basic procedures for replacing the casing and detecting lost fish heads:

[0044] Method 1: Tracing and Directly Collecting Fish

[0045] Wellbore preparation and tracing: In wells without access channels for casing replacement, the drill string connected to a "triangular tracing pen tip" is first lowered (usually used with drill collars to provide sufficient weight). The pump is started to circulate drilling fluid at a high flow rate, and the drill is slowly driven downward using the hydraulic jet effect of the pen tip nozzle, while cleaning the bottom of the well.

[0046] Analyzing the casing indicator: After every 5 meters of drilling, pause the drilling and slowly rotate the drill string while maintaining circulation. Ground operators should closely monitor the rotary table torque changes. If regular, periodic torque changes are felt (i.e., "three-stage resistance"), it indicates that the guide groove of the drill tip is contacting and scraping the casing wall; this is a casing indicator, proving that the fish head is directly below or not far to the side.

[0047] Tracer fishing: Once the casing indication is confirmed, the circulation continues and the pen-tip string is slowly deepened, allowing it to descend approximately 20 meters along the casing wall as a "tracer reference pipe" for subsequent operations. Subsequently, the tracer string is lowered into the well, and fishing tools such as Kennametal flared end mills are lowered. Guided by the tracer string, precise milling is performed to retrieve the fish.

[0048] Method 2: Magnetic Detection and Decision-Making for Fish Harvesting

[0049] Drilling Obstacle Avoidance: Continue drilling downwards for at least 150 meters using a Φ118mm PDC drill bit. The main purpose of this step is to avoid magnetic interference from shallow formation pipelines, upper casing, surface casing, etc., creating a clean background environment for accurate magnetic detection.

[0050] Precise magnetic surveying: A high-precision passive geomagnetic surveying device is lowered into the well to conduct measurements from bottom to top in the target well section. This technology can accurately determine the azimuth of the downhole magnetic object (i.e., the casing) and its horizontal distance from the current wellbore.

[0051] Decision-making and implementation: If the offset is within the range for fish enlargement and retrieval: directly use an enlargement milling head with an effective inner diameter covering the horizontal distance, along with a bell-shaped opening, to enlarge the diameter and retrieve the fish. If the offset is too large: then the "well position shifting" technique must be used, i.e., shifting the well position to ensure that the wellhead is directly above the fish landing area below, drilling a new well vertically from the ground to the fish head position determined by magnetic detection, and then enlarging the diameter and retrieving the fish.

[0052] Please see Figure 1 The diagram illustrates a flowchart of a method for detecting a lost fish head during a replacement sleeve operation, according to an embodiment of this application. The method includes the following steps:

[0053] The first step: Obtain the magnetic variables measured by the upper and lower probes at each sampling depth inside the wellbore using a passive geomagnetic detection device.

[0054] During casing replacement operations, if an operational error occurs causing the fish head to fall into the wellbore, the wellbore enlargement effect can lead to collapse or creep in formations such as shale and rock salt, resulting in a significant increase in wellbore diameter, potentially reaching several times the casing diameter. The uncertain location of the fallen fish head may cause the horizontal distance between it and the casing to exceed the retrieval range of the casing milling head, making effective positioning and retrieval difficult, thus affecting construction efficiency and operational progress.

[0055] Therefore, in cases where the fish head falls outside the effective fish-collecting range of the casing, a passive geomagnetic detection device is needed to locate the lost fish head. While continuing drilling downwards with a Φ118mm PDC drill bit (target depth ≥ 150 meters), a set of coaxial dual-probe array passive geomagnetic detection devices is used for synchronous detection. This device includes an upper probe (Z¹) and a lower probe (Z²), with a fixed axial distance of 0.8 meters between the two probes, covering the drilling section below the drill bit. The passive geomagnetic detection device is lowered from the casing tail end downwards, probing at 30cm intervals, i.e., the sampling depth interval is 30cm. At each sampling depth, the magnetic variables (including the strength and direction of the magnetic field) of the upper and lower probes are obtained. Furthermore, the sampling depth value is the depth value of the midpoint of the passive geomagnetic detection device (which can be considered as a vertical rod). Based on the distance between the upper and lower probes and the midpoint value, the magnetic variables corresponding to the depth values ​​of the upper and lower probes at each sampling depth are obtained.

[0056] It should be further noted that the passive geomagnetic detection device integrates a triaxial magnetometer. At each sampling depth, the triaxial magnetometer directly acquires the magnetic field intensity components along the mutually orthogonal X, Y, and Z axes. This constitutes the three-dimensional magnetic field vector corresponding to that depth value. .

[0057] The second step is to analyze the degree of change in magnetic variables between the upper and lower probes at each sampling depth to identify potential fish head interference segments.

[0058] In traditional passive geomagnetic detection, the maximum geomagnetic variable within the detection range is obtained. It is determined that the depth of the passive geomagnetic detection device and the lost fish head are at a relatively horizontal position. The maximum geomagnetic variable is then substituted into the empirical model, which is to multiply the maximum geomagnetic variable by the empirical coefficient for fish head positioning (which indicates the distance under unit magnetic variable, in m / uT). This gives the distance between the lost fish head and the detector.

[0059] Traditional detection models assume a uniform geomagnetic distribution. However, in practice, interference from magnetic rock layers or iron-containing residues within the well can disrupt the geomagnetic distribution. The measured geomagnetic variables thus include the superposition of external magnetic rock layers or interfering objects with the geomagnetic field created by the lost fish head. Directly measuring distance based on these geomagnetic variables would result in significant locational deviations, impacting the efficiency of fish detection and retrieval.

[0060] During passive geomagnetic detection, changes in the geomagnetic field are received by a highly sensitive magnetic sensor. When iron-containing magnetic materials such as lost fish heads enter the detection range, they will interfere with the distribution of the geomagnetic field and form a local abnormal magnetic field. The passive geomagnetic detection equipment can locate the lost fish heads by capturing the changes in the abnormal magnetic field.

[0061] Within the Earth's magnetic field, magnetic variables typically point from the North (N) pole to the South (S) pole. Since the Earth's radius is much larger than the depth of an oil well, the Earth's magnetic field distribution within the wellbore is uniform under undisturbed conditions. When the fish head falls into the wellbore, it becomes magnetized by the Earth's magnetic field, essentially acting as a magnetic dipole. When the detector enters its sensing range, the measured magnetic variable is the vector superposition of the ambient background magnetic field and the induced magnetic field generated by the fish head. As the relative position of the detector and the fish head changes, the amplitude and direction of the induced magnetic field undergo nonlinear distortion, causing a sudden change in the amplitude of the total magnetic field and a deflection in its vector direction, forming a identifiable local magnetic anomaly distribution.

[0062] During geomagnetic exploration, the first-order difference of the magnetic variable intensity of the upper and lower probes corresponding to a single sampling depth is obtained. This represents the first-order difference value of the passive geomagnetic detection device at the h-th sampling depth, specifically the difference in magnetic variable intensity between the lower and upper probes.

[0063] Furthermore, by traversing all sampling depths, a first-order geomagnetic difference sequence can be obtained. When the detector passes the fish head (magnetic dipole), the total magnetic field amplitude will exhibit a peak (or trough). At the exact center of the peak / trough, the rate of change of the magnetic field is 0. Therefore, the first-order geomagnetic differential sequence of the upper and lower probes will inevitably change from positive to negative (or from negative to positive) when passing the exact center of the fish head, which is the zero-crossing point. Based on this, the least squares method is used to perform nonlinear fitting on the first-order geomagnetic differential sequence to extract each zero-crossing point on the curve. This zero-crossing point represents the position where the magnetic field amplitude reaches its peak, corresponding to the vertical depth of the fish head. Then, with this zero-crossing point as the center, the N sampling depths closest to this center are extracted to form the potential fish head interference segment; in this embodiment, N is taken as 8, and the implementer can determine it according to the actual situation; thus, the set of all potential fish head interference segments can be obtained.

[0064] It should be further explained that before finding the zero-crossing point, the first-order geomagnetic difference sequence is first filtered by moving average to eliminate high-frequency noise spikes; secondly, an amplitude dead zone threshold is set, which in this embodiment is set to 3 times the standard deviation of the fluctuation of the background normal magnetic field difference value. Only when the absolute value of the difference between the first-order difference values ​​corresponding to the two depth sampling points closest to the zero-crossing point of the difference fitting curve is greater than the amplitude dead zone threshold, the zero-crossing point will be determined as a valid zero-crossing point, thereby directly filtering out the noise zero-crossing points that oscillate frequently within a small amplitude near the zero axis.

[0065] Among them, the potential fish head interference segment may be the depth range where the lost fish head is located, or the interference segment formed by the magnetic rock layer of the strata. Further location of the lost fish head needs to be determined based on the distribution of geomagnetism.

[0066] The third step is to obtain characteristic values ​​based on the distribution of magnetic field gradient changes in a single potential fish head interference segment. By combining the dispersion of the characteristic values ​​of a single potential fish head interference segment with the distribution of magnetic variables, the degree of uniformity of magnetic field variation in a single potential fish head interference segment is obtained.

[0067] During the downward movement of the magnetic detector, it is possible to simultaneously acquire data from the upper probe at a single detection depth. and lower probe The magnetic variable amplitude corresponding to the upper probe is used to sort the detection data within a single potential fish head interference segment by depth (from shallow to deep), resulting in magnetic variable sequence B. For example, at a sampling depth of 1320.3m, the depth value corresponding to the upper probe is 1319.9m, and the depth value corresponding to the lower probe is 1320.7m. At the next sampling depth of 1320.6m, the depth value corresponding to the upper probe is 1320.2m, and the depth value corresponding to the lower probe is 1321m, and so on. Thus, the corresponding magnetic variable sequence B is obtained by sorting according to the depth values.

[0068] During geomagnetic exploration, if a single potential fish-head interference segment is affected by magnetic rock layers, the interference of these layers on the wellbore's magnetic field is related to the distribution of magnetic elements within the rock layers (simply put, it's related to the iron content in the strata near the wellbore). However, the magnetic content within these rock layers is not uniformly distributed and is related to the actual geological and mineral distribution. In contrast, within the potential fish-head interference segment corresponding to the actual lost fish-head, the overall geomagnetic distribution is relatively uniform because the magnetic field strength corresponding to the lost fish-head is related to distance.

[0069] Therefore, based on the single magnetic variable sequence B, a characteristic sequence is obtained. First, the magnetic variable sequence is subjected to first-order difference and the absolute value is taken to characterize the change in magnetic field strength between adjacent elements. At the same time, the ratio of the obtained absolute value of the difference to the absolute value of the depth difference between the corresponding two elements is used to obtain the characteristic value. The purpose is to quantify the gradient of magnetic field change and to measure the uniformity of geomagnetic change.

[0070] This yields the current degree of magnetic field variation equilibrium in a single potential fish head interference segment: In the formula, This indicates the degree of uniformity in the magnetic field variation within the current potential fish-head interference segment. and This represents the maximum and mean values ​​of the magnetic variable sequence within the current potential fish head interference segment. The standard deviation of the obtained characteristic values ​​is given. Since the characteristic values ​​are the ratio of the magnetic field difference to the depth difference for each depth value, and the magnetic fields corresponding to adjacent depth values ​​are subject to slight differences due to the Earth's magnetic field, the characteristic values ​​exhibit some variation and their amplitude is not zero. Consequently, the standard deviation is also a non-zero number. It should be noted that the magnetic field gradient uniformity α is configured as a scalar parameter with the dimension of length (m), which characterizes the spatial equivalent scale at which the magnetic field gradient remains relatively stable within the potential fish-head interference segment. That is, within the potential fish-head interference segment, the "equivalent influence distance" of the magnetic field strength deviation relative to its rate of change fluctuation.

[0071] The fourth step: Based on the variation characteristics of the horizontal magnetic field direction of adjacent sampling depths of a single potential fish head interference segment, the directional consistency of the single potential fish head interference segment is obtained.

[0072] The above analysis focuses on the variation of the magnetic field strength of a single potential fish head interference segment to analyze geomagnetic changes. In actual operation, there may be other interfering objects in the wellbore, such as adjacent well casing, casing string magnetization, drill collars, or fishing tools.

[0073] In practice, the other interfering objects mentioned above will also form a relatively changing magnetic field, which will also interfere with geomagnetic detection. Because the interfering objects have a high iron content, they superimpose with the Earth's magnetic field during the geomagnetic distribution process, making the magnetic field gradient distribution relatively uniform. Therefore, it is difficult to distinguish the influence of the interfering objects by only considering the uniformity of magnetic field changes.

[0074] Compared to other interfering objects, the geometric dimensions of the missing fish head (typically less than 0.16m in diameter) are much smaller than those of long-sized interference sources such as adjacent well casing strings or fishing tools. Long-sized interference sources, due to their longer magnetic dipole moments, generate induced magnetic fields that exhibit significant gradient changes and vector deflections with depth within the detection range, resulting in a noticeable deviation in the direction of the total magnetic field vector at different depth points.

[0075] In contrast, the missing fish head can be considered equivalent to a point magnetic dipole. When the detector maintains a certain horizontal distance from it, within a very small interference segment, the superposition vector of the fish head's induced magnetic field and the background magnetic field tends to point in the same direction at each sampling point. Therefore, by evaluating the directional consistency of the magnetic field vector within the interference segment, the shielding effect of long-sized interference objects can be effectively eliminated.

[0076] Therefore, based on the distribution of magnetic variable directions corresponding to each depth value in the magnetic field variable sequence, the corresponding directional consistency is obtained, specifically:

[0077] Example 1: In the formula, The directional consistency of a single potential fish head interference segment is represented by ; N represents the number of sampling depths in a single potential fish head interference segment; cos() represents the cosine similarity function; and This represents the two-dimensional magnetic field direction vector corresponding to the i-th and (i+1)-th depth values ​​in the magnetic variable sequence. It should be noted that the actual measured magnetic field is a three-dimensional spatial vector. To assess directional similarity, the X-axis and Y-axis components of this three-dimensional magnetic field vector on the horizontal plane are directly extracted to form a two-dimensional magnetic field direction vector for use in the direction consistency calculation. If the magnitude of the horizontal magnetic component vector at a certain depth point is zero, the corresponding values ​​of the two adjacent points in the cosine similarity calculation are directly set to 0 to prevent calculation anomalies where the denominator is zero.

[0078] When measuring directional consistency, the focus is on assessing whether the magnetic variables point in the same direction. Therefore, this embodiment uses cosine similarity to assess directional consistency. Cosine similarity is a commonly used method for calculating directional consistency. The higher the degree of directional consistency, the larger the cosine similarity value, and the greater the final value of directional consistency.

[0079] Example 2: In the formula, This indicates the directional consistency of a single potential fish head interference segment. This represents the difference vector between the three-dimensional magnetic field direction vectors corresponding to the i-th and (i+1)-th depth values. This is used to calculate the magnitude of the vector. It should be noted that this calculation involves summing the magnitudes of all difference vectors within the potential fish-head interference segment. Therefore, while it's possible that occasionally a single difference vector might have a magnitude of zero, it's impossible for all difference vectors to have zero magnitudes. Thus, there's no need to set parameters to prevent the denominator from being zero. Furthermore, it should be noted that before calculating the difference vector between two magnetic field direction vectors, the magnetic variables must be normalized to obtain the magnetic field direction vector.

[0080] In the current embodiment, the difference vector is used to measure the degree of difference in the direction of the magnetic variable. The difference vector evaluates the deviation between two vectors. The larger the magnitude of the difference vector, the greater the difference between the two vectors, and the smaller the directional consistency.

[0081] The fifth step is to comprehensively consider the uniformity of magnetic field changes and the consistency of direction of a single potential fish head interference segment to determine the screening value of the single potential fish head interference segment and identify the real lost fish head segment; based on the magnetic field direction vector measured at each sampling depth in the real lost fish head segment and the background magnetic field vector, the fish head magnetic field vector is determined; the fish head magnetic field vector is weighted by the distance between the center of the real lost fish head segment and each sampling depth to obtain the calibration magnetic field.

[0082] This involves iterating through all sets of all potentially missing fish head interference segments to obtain the magnetic field variation balance and directional consistency of each interference segment. From this, the selection value for the actual missing fish head segment can be obtained. The specific method for obtaining this value is as follows: In the formula, This represents the current filter value for a single potentially missing fish head interference segment. This indicates the degree of uniformity in the magnetic field variation within a single potential fish-head interference segment. This indicates the directional consistency of a single potential fish head interference segment. Norm() represents the normalization function. In this embodiment, the minimum-maximum normalization method is used for all potential interference segments. Perform normalization processing, Mapping to the [0,1] interval is to eliminate the influence of the absolute magnetic field strength on feature extraction under different operating conditions.

[0083] Based on the current search for lost fish heads within the wellbore, the lost fish head must be at a certain depth. Therefore, this application uses the potential lost fish head interference segment corresponding to the maximum screening value as the actual lost fish head segment. Within the actual lost fish head segment, the magnetic variable corresponding to each depth value includes the magnetic field formed by the lost fish head and the background magnetic field. Therefore, it is necessary to combine the background magnetic field to obtain the magnetic field formed by the lost fish head.

[0084] Therefore, based on the magnetic field at each depth value within the currently lost fish head segment and the background magnetic field, the corresponding fish head magnetic field is obtained, specifically: ,in, This represents the magnetic field vector of the fish head corresponding to the i-th depth value within the actual lost fish head segment; This represents the magnetic field direction vector obtained by the detector at the i-th depth value, i.e., the measured three-dimensional magnetic field vector; The background magnetic field is indicated by the marker. The background magnetic field is obtained as follows: In the detection sequence, after removing all potential fish-head interference segments corresponding to the depth range, a preset number of stable magnetic field segments are obtained, located closest to the currently lost fish-head segment. These stable magnetic field segments are sampling depth segments that do not correspond to potential fish-head interference segments (each segment is 5 meters long in this embodiment). All magnetic field vectors within these stable magnetic field segments are extracted, summed, and averaged to obtain the interference-free background magnetic field. If the data for stable segments within the detection range is insufficient, the average magnetic field value within 10 meters of the detection starting position (usually far from the fish-head and without interference) is directly used as the background magnetic field. In this embodiment, the preset number is 4, which can be adjusted by the implementer according to the actual situation.

[0085] Furthermore, the magnetic field direction vector corresponding to the magnetic field generated by the fish head for each depth value within the currently lost fish head segment is obtained, and the final calibrated magnetic field is obtained by weighted summation based on distance: ,in, This indicates the calibrated magnetic field of the currently missing fish head segment. This indicates the distance weight (the farther the vertical distance from the zero-crossing point, the smaller the weight value). This represents the magnetic field vector of the fish head corresponding to the i-th depth value within the actual lost fish head segment; N represents the number of sampling depths within the actual lost fish head segment.

[0086] The distance weights are obtained as follows: First, the absolute difference between the depth of each sampled point within the currently lost fish head segment and the depth of the corresponding zero-crossing point is calculated as the absolute vertical distance. Second, to prevent the calculation from crashing due to a zero absolute vertical distance, a preset constant smaller than the sampling interval (0.1m in this embodiment) is added to this absolute vertical distance. Then, the reciprocal of the sum is taken. Finally, the reciprocals corresponding to all depth points are summed, and each reciprocal is normalized by dividing the sum to obtain the distance weight corresponding to each depth value. This calculation method ensures that the closer the data is to the zero-crossing point (i.e., the exact center of the fish head), the greater its weight in the calibration magnetic field calculation.

[0087] It should be noted that the actual lost fish head segment is an element within the set of potential lost fish head interference segments. As mentioned earlier, a single potential fish head interference segment is divided with the zero-crossing point of the first-order geomagnetic difference sequence fitting curve as the center. Therefore, when calculating the distance weight here, the reference point is the unique zero-crossing point within the current actual lost fish head segment. This zero-crossing point represents the exact center in the vertical depth direction of the fish head, ensuring the physical uniqueness and accuracy of the distance calculation.

[0088] Finally, the calibration magnetic field is imported into the model to obtain the corresponding horizontal distance, specifically... .in, This represents the horizontal distance between the lost fish head and the detector, and the corresponding vertical depth value of the fish head is the depth value corresponding to the zero-crossing point of the differential fitting within the current true lost fish head segment. This represents the empirical coefficient for locating the fish head; in this embodiment, the value range is 0.1~0.5m / uT (preferably 0.3m / uT). This coefficient... The method of obtaining ε is as follows: using a reference object of the same material and size as the lost fish head on the ground, the relationship between the known horizontal distance and the corresponding magnetic induction intensity is measured in advance, and nonlinear fitting is performed to obtain ε; ε is a very small positive number to prevent the denominator from being zero, and in this embodiment, the value is taken as 0.01.

[0089] The sixth step: Based on the obtained horizontal distance, output the fish-catching strategy.

[0090] By calculating the vertical depth and horizontal distance of the fish head, the three-dimensional spatial plane position of the missing fish head is determined. Simultaneously, the calculated calibration magnetic field vector is projected onto the horizontal plane to obtain the horizontal component. and Using the arctangent function The target azimuth angle relative to the wellbore coordinate system is calculated. Therefore, by combining the horizontal distance and the target azimuth angle, positioning information similar to a cylindrical coordinate system is established, enabling precise three-dimensional location of the lost fish head. Finally, a corresponding fish retrieval strategy is set based on the calculated horizontal distance, specifically:

[0091] If the calculated horizontal distance is within the range for expanding the diameter to retrieve the fish: directly use a milling head with an effective inner diameter covering the horizontal distance, along with a bell-shaped opening, to expand the diameter and retrieve the fish. If the calculated horizontal distance is not within the range for expanding the diameter to retrieve the fish: then the "well position shifting" technique must be used, i.e., shifting the well position to ensure the wellhead is directly above the lost fish head, drilling a new well vertically from the ground to the fish head position determined by magnetic detection, and then expanding the diameter to retrieve the fish. The specific fish retrieval method is a well-known technique in the art and will not be described in detail in this application. The range for expanding the diameter to retrieve the fish (horizontal distance) is set to 0.3m in this application.

[0092] Based on the same inventive concept as the above methods, this application also provides a lost fish head detection device for replacement and repair operations, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, it implements the steps of any of the above methods.

[0093] The flowcharts in the accompanying drawings illustrate possible implementations of the method according to embodiments of this application. In some alternative implementations, the functions marked in the blocks may occur in a different order than that shown in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, or they may sometimes be executed in reverse order, depending on the functions involved. In the descriptions corresponding to the flowcharts in the accompanying drawings, the operations or steps corresponding to different blocks may also occur in a different order than disclosed in the description, and sometimes there is no specific order between different operations or steps. For example, two consecutive operations or steps may actually be executed substantially in parallel, or they may sometimes be executed in reverse order, depending on the functions involved. Each block in the flowchart, and combinations of blocks in the flowchart, can be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0094] It will be apparent to those skilled in the art that this application is not limited to the details of the exemplary embodiments described above, and that this application can be implemented in other specific forms without departing from its essential characteristics. Therefore, the embodiments described above should be considered exemplary and non-limiting in all respects; modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions of some technical features, without causing the essence of the corresponding technical solutions to deviate from the scope of the technical solutions in the embodiments of this application, should all be included within the protection scope of this application.

Claims

1. A method for detecting lost fish heads during replacement and repair work, characterized in that, The method includes the following steps: Obtain the magnetic variables measured by the upper and lower probes at each sampling depth inside the wellbore using a passive geomagnetic detection device; Analyze the degree of change in magnetic variables between the upper and lower probes at each sampling depth to identify potential fish head interference segments; Based on the distribution of magnetic field gradient changes in a single potential fish head interference segment, characteristic values ​​are obtained. Combining the dispersion of the characteristic values ​​of a single potential fish head interference segment with the distribution of magnetic variables, the degree of uniformity of magnetic field variation in a single potential fish head interference segment is obtained. Based on the variation characteristics of the horizontal magnetic field direction of adjacent sampling depths of a single potential fish head interference segment, the directional consistency of a single potential fish head interference segment is obtained; By comprehensively considering the uniformity of magnetic field changes and the consistency of direction of individual potential fish head interference segments, the screening value of individual potential fish head interference segments is determined to identify the actual lost fish head segments; based on the magnetic field direction vector measured at each sampling depth in the actual lost fish head segments and the background magnetic field vector, the fish head magnetic field vector is determined; the fish head magnetic field vector is weighted and summed using the distance between the center of the actual lost fish head segments and each sampling depth to obtain the calibrated magnetic field and calculate the horizontal distance. Based on the obtained horizontal distance, output the fish-catching strategy.

2. The method for detecting a lost fish head during a sleeve replacement operation as described in claim 1, characterized in that, The determination of potential fish head interference segments specifically includes: For each sampling depth, calculate the first-order difference value of the magnetic variable intensity between the lower and upper probes of the detection device; perform curve fitting on the first-order difference values ​​obtained for all sampling depths, and extract each effective zero-crossing point of the fitted curve; take each effective zero-crossing point as the center, obtain the depth range corresponding to the N nearest sampling depths, and form a potential fish head interference segment; where N is a preset value.

3. The method for detecting a lost fish head during a sleeve replacement operation as described in claim 2, characterized in that, The condition for extracting each effective zero-crossing point of the fitted curve is: the absolute value of the difference between the first-order difference values ​​corresponding to the two depth sampling points closest to the zero-crossing point of the fitted curve is greater than the preset amplitude dead zone threshold.

4. The method for detecting a lost fish head during a sleeve replacement operation as described in claim 1, characterized in that, The obtained feature representation value is specifically as follows: The sequence of all magnetic variables in a single potential fish head interference segment is denoted as the magnetic variable sequence. The ratio of the absolute value of the difference between adjacent elements in the magnetic variable sequence to the absolute value of the difference between the corresponding depth values ​​of adjacent elements is calculated to obtain the feature characterization value.

5. A method for detecting a lost fish head during a sleeve replacement operation as described in claim 4, characterized in that, The degree of magnetic field variation balance obtained for a single potential fish head interference segment is specifically as follows: Calculate the difference between the maximum and mean values ​​of the magnetic variable sequence corresponding to a single potential fish head interference segment; obtain the degree of dispersion of all feature characterization values ​​obtained for a single potential fish head interference segment; positively fuse the negative correlation mapping result of the dispersion with the difference to obtain the degree of magnetic field variation balance of a single potential fish head interference segment.

6. The method for detecting a lost fish head during a sleeve replacement operation as described in claim 4, characterized in that, The obtained directional consistency of a single potential fish head interference segment is specifically as follows: For a single potential fish head interference segment, obtain the cosine similarity between the magnetic field direction vectors corresponding to adjacent elements in the magnetic variable sequence, and use the mean of the cosine similarity between all adjacent elements as the direction consistency.

7. A method for detecting a lost fish head during a sleeve replacement operation as described in claim 4, characterized in that, The obtained directional consistency of a single potential fish head interference segment is specifically as follows: For a single potential fish head interference segment, obtain the magnitude of the difference vector between the magnetic field direction vectors corresponding to adjacent elements in the magnetic variable sequence, and use the negative correlation mapping result after summing the magnitudes obtained between all adjacent elements as the direction consistency.

8. A method for detecting a lost fish head during a sleeve replacement operation as described in claim 1, characterized in that, The screening value for a single potential fish head interference segment is specifically the product of the normalized value of the magnetic field variation balance and the directional consistency.

9. A method for detecting a lost fish head during a sleeve replacement operation as described in claim 1, characterized in that, The actual lost fish head segment is specifically the potential fish head interference segment with the largest screening value.

10. A method for detecting a lost fish head during a sleeve replacement operation as described in claim 1, characterized in that, The background magnetic field vector is obtained by averaging the magnetic field vectors in the non-potential fish head interference segment.

11. A method for detecting a lost fish head during a sleeve replacement operation as described in claim 1, characterized in that, The fish head magnetic field vector is obtained by the difference vector between the magnetic field direction vector of each depth value in the actual lost fish head segment and the background magnetic field vector.

12. The method for detecting a lost fish head during a sleeve replacement operation as described in claim 1, characterized in that, The calculation of the horizontal distance specifically involves multiplying the negative correlation mapping result of the magnitude of the calibrated magnetic field vector with a preset empirical coefficient for fish head positioning to obtain the horizontal distance.

13. A method for detecting a lost fish head during a sleeve replacement operation as described in claim 1, characterized in that, The output fish-catching strategy is as follows: If the calculated horizontal distance is within the preset fish-catching range, an enlarged diameter milling head with an effective inner diameter covering the horizontal distance is used in conjunction with a bell mouth to enlarge the diameter for fish catching; if the calculated horizontal distance is not within the enlarged diameter for fish catching, a translational well position technique is used to re-drill.

14. A device for detecting lost fish heads during replacement work, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method as described in any one of claims 1-13.

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