A method and device for accurately positioning the fishing depth of a radioactive instrument falling into a well

Abstract

The application discloses a kind of fallen well radioactive instrument fishing depth accurate positioning method and device, by first obtaining the rough depth information of instrument distance ground wellhead of fallen well, then fishing tool is hard connected to the tail end of drill pipe, fishing tool is sequentially lowered into well with drill pipe, until the interval between the top end of fallen well instrument reaches predetermined interval, finally small diameter magnetic positioning gamma logging instrument is lowered through the inner hole of drill pipe, by recording measurement depth, magnetic positioning signal and gamma signal determine the accurate interval of fishing tool to radioactive instrument, since the deformation of drill pipe, fishing tool lowered into well is very small, the length error generated is also very small, the interval between fishing tool and fallen well instrument is very small, the measurement depth error generated when small diameter magnetic positioning gamma logging instrument detects in this interval can be ignored, the accurate distance of fallen well instrument and wellhead is the sum of the two, method is simple, operation is simple, positioning precision is high, without complex calculation, can be read on site.

Description

Technical Field

[0001] This invention relates to the field of petroleum engineering technology, and in particular to a method and apparatus for accurately locating the depth of a fallen radioactive instrument. Background Technology

[0002] During open-hole logging, if a radioactive instrument falls into the well for some reason, and because the instrument contains a radioactive source, all possible measures must be taken to retrieve it from the well.

[0003] To retrieve the instrument, a retrieval tool must be lowered into the well. This tool is rigidly connected to the drill pipe and lowered into the well. Once the tool reaches the top of the instrument (the "fish head"), it secures the "fish head," and then the drill pipe is pulled up, bringing the instrument (the "fish") out. During the lowering process, the tool often encounters obstruction due to well conditions. Without knowing the exact depth of the instrument, the cause of this obstruction is impossible to determine, as the tool encountering the instrument can also cause drilling obstruction. Therefore, the exact depth of the instrument must be known before lowering the tool.

[0004] However, when retrieving radioactive instruments that have fallen into the well, because these instruments contain radioactive sources, it is strictly forbidden for the retrieval tools to come into contact with the radioactive source to prevent damage to the radioactive source and subsequent accidents. Therefore, it is essential to accurately control the precise distance between the retrieval tools and the radioactive instruments in the well, especially the precise distance from the radioactive source.

[0005] The depth measured by the logging instrument, which is hundreds or even thousands of meters underground, before the drill pipe and retrieval tool are lowered, using a large-diameter instrument (89mm-92mm in diameter), represents the distance from the point where the logging instrument encounters resistance to the wellhead. Due to the elasticity of the logging cable and errors in the logging depth measurement system, this depth information is not absolute. As the retrieval tool is lowered with the drill pipe, the elasticity of the drill pipe inside the well differs significantly from that of the cable, leading to errors in determining whether the retrieval tool has reached the top of the instrument.

[0006] Therefore, when large-diameter instruments encounter obstacles during the detection process, the surface staff are unsure whether the problem stems from the wellbore or from the obstruction caused by the deployed instruments, making it difficult to determine the depth of the deployed instruments. Due to the wellbore diameter limitation, large-diameter instruments may run parallel to deployed instruments within the well and become entangled, leading to secondary accidents such as the large-diameter instruments getting stuck. Because it is impossible for large-diameter instruments to pass smoothly next to deployed radioactive instruments, the specific depth of the radioactive source of deployed radioactive instruments cannot be detected.

[0007] Therefore, solving the above-mentioned technical problems is one of the key tasks for those skilled in the art. Summary of the Invention

[0008] The purpose of this invention is to provide a method and apparatus for accurately locating the depth of a fallen radioactive instrument, which can accurately determine the precise data of the distance between the retrieval tool and the fallen radioactive instrument, thereby improving retrieval efficiency and success rate.

[0009] To address the aforementioned technical problems, embodiments of the present invention provide a method for accurately locating the depth of a fallen radioactive instrument, comprising:

[0010] S1, obtain the approximate depth information of the well-diving instrument from the wellhead on the ground, and obtain the top depth and the tail depth of the well-diving instrument based on the approximate depth information;

[0011] S2, after the retrieval tool is rigidly connected to the end of the drill pipe, the retrieval tool is lowered into the well along with the drill pipe until the distance between it and the top of the well-diving instrument reaches the predetermined distance;

[0012] S3, a small-diameter magnetic positioning gamma logging instrument is lowered through the inner hole of the drill pipe, and the measurement depth, magnetic positioning signal and gamma signal are recorded simultaneously. After the small-diameter magnetic positioning gamma logging instrument leaves the retrieval tool, it is lowered further through the radioactive instrument. Based on the measurement depth, the magnetic positioning signal of the retrieval tool port, the magnetic positioning signal of the top of the well-falling instrument, and the radioactive ray signal of the location of the radioactive source on the well-falling instrument, the precise distance between the retrieval tool port and the top of the well-falling instrument and the radioactive source carried by the well-falling instrument is determined.

[0013] The following is included after S3:

[0014] S4, the small-diameter magnetic positioning gamma logging instrument is lifted and a lifting measurement is performed. Based on the measurement depth, the magnetic positioning signal and gamma signal detected by the small-diameter magnetic positioning gamma logging instrument, the precise distance between the port of the retrieval tool and the top of the well-dropping instrument, and the radioactive source carried by the well-dropping instrument, is determined.

[0015] The distance between the retrieval tool and the top of the well-falling instrument is 20m-30m.

[0016] The diameter of the small-diameter magnetic positioning gamma logging instrument is 26mm-38mm.

[0017] Wherein, S1 includes:

[0018] Based on theoretical estimations or by deploying logging instruments, approximate depth information of the distance between the logging instrument and the wellhead can be obtained.

[0019] In addition, embodiments of this application also provide a device for precisely locating the depth of a fallen radioactive instrument, comprising:

[0020] The coarse depth information acquisition unit is used to obtain coarse depth information of the well-drilling instrument from the wellhead based on theoretical estimation or by using a logging instrument, and to obtain the top depth and tail depth of the well-drilling instrument based on the coarse depth information.

[0021] The retrieval tool lowering unit is used to rigidly connect the retrieval tool to the end of the drill pipe, and then lower the retrieval tool into the well along with the drill pipe until the distance between it and the top of the well-diving instrument reaches a predetermined distance.

[0022] A precise positioning unit is used to lower a small-diameter magnetic positioning gamma logging instrument through the inner hole of the drill pipe, and simultaneously record the measurement depth, magnetic positioning signal, and gamma signal. After the small-diameter magnetic positioning gamma logging instrument leaves the retrieval tool, it continues to be lowered past the radioactive instrument. Based on the measurement depth, the magnetic positioning signal at the port of the retrieval tool, the magnetic positioning signal at the top of the well-falling instrument, and the radioactive ray signal at the location of the radioactive source on the well-falling instrument, the precise distance between the port of the retrieval tool and the top of the well-falling instrument, and the radioactive source carried by the well-falling instrument are determined.

[0023] It also includes a lifting unit associated with the precise positioning unit, used to lift the small-diameter magnetic positioning gamma logging instrument and perform lifting measurement. By recording the measurement depth, the magnetic positioning signal and gamma signal detected by the small-diameter magnetic positioning gamma logging instrument, the precise distance between the retrieval tool port and the top of the well-falling instrument, and the radioactive source carried by the well-falling instrument are determined again.

[0024] It also includes a parameter setting unit associated with the retrieval tool lowering unit, used to set the distance between the retrieval tool and the top of the well-diving instrument.

[0025] The method and apparatus for accurately locating the depth of a fallen radioactive instrument provided in this invention have the following advantages compared with the prior art:

[0026] The described method and apparatus for precise positioning of the retrieval depth of a radioactive instrument in a well involves first obtaining approximate depth information of the retrieval instrument from the wellhead. Then, a retrieval tool is rigidly connected to the end of the drill pipe, and the tool is sequentially lowered into the well along with the drill pipe until a predetermined distance is reached between it and the top of the retrieval instrument. Finally, a small-diameter magnetic positioning gamma logging instrument is lowered through the inner hole of the drill pipe. The precise position of the radioactive instrument is determined by recording the measured depth, magnetic positioning signal, and gamma signal. Because the deformation of the drill pipe and retrieval tool inside the well is minimal, the resulting length error is also small. The distance between the retrieval tool and the retrieval instrument is very small, and the measurement depth error generated by the small-diameter magnetic positioning gamma logging instrument within this distance is negligible. The sum of these two measurements gives the precise distance between the retrieval instrument and the wellhead. The method is simple, easy to operate, and has high positioning accuracy, requiring no complex calculations and allowing for on-site readings. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 A flowchart illustrating the steps of an embodiment of the method for accurately locating the depth of a fallen radioactive instrument in an embodiment of the present invention;

[0029] Figure 2 A flowchart illustrating the steps of another embodiment of the method for accurately locating the depth of a fallen radioactive instrument in accordance with the present invention.

[0030] Figure 3 This is a schematic diagram of one embodiment of the device for precisely positioning the depth of a radioactive instrument retrieved from a well, as provided in this invention. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Please refer to Figure 1-3 , Figure 1 A flowchart illustrating the steps of an embodiment of the method for accurately locating the depth of a fallen radioactive instrument in an embodiment of the present invention; Figure 2A flowchart illustrating the steps of another embodiment of the method for accurately locating the depth of a fallen radioactive instrument in accordance with the present invention. Figure 3 This is a schematic diagram of one embodiment of the device for precisely positioning the depth of a radioactive instrument retrieved from a well, as provided in this invention.

[0033] In one specific embodiment, the method for accurately locating the retrieval depth of a fallen radioactive instrument includes:

[0034] S1, obtain the approximate depth information of the well-diving instrument from the wellhead on the ground, and obtain the top depth and the tail depth of the well-diving instrument based on the approximate depth information;

[0035] S2, after the retrieval tool is rigidly connected to the end of the drill pipe, the retrieval tool is lowered into the well along with the drill pipe until the distance between it and the top of the well-diving instrument reaches the predetermined distance;

[0036] S3, a small-diameter magnetic positioning gamma logging instrument is lowered through the inner hole of the drill pipe, and the measurement depth, magnetic positioning signal and gamma signal are recorded simultaneously. After the small-diameter magnetic positioning gamma logging instrument leaves the retrieval tool, it is lowered further through the radioactive instrument. Based on the measurement depth, the magnetic positioning signal of the retrieval tool port, the magnetic positioning signal of the top of the well-falling instrument, and the radioactive ray signal of the location of the radioactive source on the well-falling instrument, the precise distance between the retrieval tool port and the top of the well-falling instrument and the radioactive source carried by the well-falling instrument is determined.

[0037] First, obtain a rough depth information of the wellhead from the drop-down instrument. Then, after rigidly connecting the retrieval tool to the drill pipe end, lower the retrieval tool into the well along with the drill pipe until the distance between it and the top of the drop-down instrument reaches a predetermined distance. Finally, lower a small-diameter magnetic positioning gamma logging instrument through the inner hole of the drill pipe. By recording the measured depth, magnetic positioning signal, and gamma signal, the precise position of the radioactive instrument is determined. Because the deformation of the drill pipe and retrieval tool inside the well is very small, the resulting length error is also very small. The distance between the retrieval tool and the drop-down instrument is very small, and the measurement depth error generated by the small-diameter magnetic positioning gamma logging instrument within this distance is negligible. The sum of the two is the precise distance between the drop-down instrument and the wellhead. The method is simple, easy to operate, and has high positioning accuracy. No complex calculations are required, and on-site readings can be taken.

[0038] Since the above scheme only detects and locates the signal of the downhole instrument obtained during the lowering and measurement process of the small-diameter magnetic positioning gamma logging instrument, but errors may exist, in one embodiment, in order to eliminate possible errors, after S3, the following is also included:

[0039] S4, the small-diameter magnetic positioning gamma logging instrument is lifted and a lifting measurement is performed. Based on the measurement depth, the magnetic positioning signal and gamma signal detected by the small-diameter magnetic positioning gamma logging instrument, the precise distance between the port of the retrieval tool and the top of the well-dropping instrument, and the radioactive source carried by the well-dropping instrument, is determined.

[0040] By raising the small-diameter magnetic positioning gamma logging instrument again and performing a measurement, the results of the lowering and raising measurements can be compared, eliminating potential errors that may occur during the lowering process and thus improving positioning accuracy.

[0041] This application does not limit the specific measurement process of the small-diameter magnetic positioning gamma logging instrument. It can be limited to a certain area, such as the part passing through the well-falling instrument to the retrieval tool, or it can be from the bottom of the well-falling instrument all the way to the wellhead. However, in order to realize the detection of the entire measurement process, in one embodiment, S4 includes:

[0042] The small-diameter magnetically positioned gamma logging instrument is moved from bottom to top, passing sequentially through the radioactive source of the fall-off instrument, the top of the fall-off instrument, the space between the top of the fall-off instrument and the retrieval tool, and the retrieval tool. It then enters the middle hole of the drill pipe and is finally lifted out of the well. The precise distance between the retrieval tool port and the top of the fall-off instrument, and the radioactive source carried by the fall-off instrument, are determined based on the measured depth generated during the retrieval process, the magnetic positioning signal at the port of the retrieval tool, the magnetic positioning signal at the top of the fall-off instrument, and the radioactive ray signal at the location of the radioactive source on the fall-off instrument.

[0043] The precise distance between the retrieval tool port and the top of the well-falling instrument, and the radioactive source carried by the well-falling instrument, is determined by the measured depth generated throughout the entire retrieval process, the magnetic positioning signal of the retrieval tool port, the magnetic positioning signal of the top of the well-falling instrument, and the radioactive ray signal of the location of the radioactive source on the well-falling instrument.

[0044] This application does not limit the specific depth of the retrieval tool. In one embodiment, the distance between the retrieval tool and the top of the well-diving instrument is 20m-30m.

[0045] First, the approximate depth of the logging instrument is obtained. Then, the retrieval tool is lowered to a certain depth to avoid contact with the instrument. Finally, the two precise depth data are combined by measuring the depth and using the magnetic positioning signal and gamma signal obtained by the small-diameter magnetic positioning gamma logging instrument to achieve precise positioning.

[0046] In this application, the measured depth, magnetic positioning signal and gamma signal can be directly displayed on the screen, and the precise location of the radioactive instrument that has fallen into the well can be achieved based on the specific information. The accurate location of the radioactive instrument that has fallen into the well can be read on-site without the need for corresponding calculations, which improves the positioning efficiency.

[0047] This application does not limit the size of the small-diameter magnetic positioning gamma logging instrument. A suitable size of small-diameter magnetic positioning gamma logging instrument can be selected. Generally, the diameter of the small-diameter magnetic positioning gamma logging instrument is 26mm-38mm.

[0048] This application does not limit how to obtain the approximate depth information of the wellhead from the ground. In one embodiment, S1 includes:

[0049] Based on theoretical estimations or by deploying logging instruments, approximate depth information of the distance between the logging instrument and the wellhead can be obtained.

[0050] In one embodiment of the method for accurately locating the depth of a fallen radioactive instrument in this application, the implementation steps are as follows:

[0051] The first step is the pre-positioning of the "fish": After the radioactive instrument is lowered into the well, the depth distance between the instrument and the wellhead is determined based on theoretical estimation or by using other logging instruments. This gives us the depth of the top of the instrument (referred to as the "fish head" in petroleum engineering) and the depth of the bottom of the instrument (referred to as the "fish tail" in petroleum engineering).

[0052] The second step involves lowering the retrieval tool to 20-30 meters above the "fish head": The retrieval tool is rigidly connected to the end of the drill pipe and lowered into the well sequentially with the drill pipe until it is 20-30 meters from the predetermined "fish head". Drill pipes are deployed one string at a time, with each string consisting of three drill pipes of fixed length. Therefore, lowering the retrieval tool to 20-30 meters from the "fish head" is easily controlled. Furthermore, the exact number of drill pipes and strings lowered at this distance is readily known. During the retrieval process within this 20-30 meter range, and even further lowering it to pull the instrument out of the severely enlarged section, this short distance not only minimizes error but also allows for precise control.

[0053] The third step involves lowering the small-diameter magnetic positioning gamma ray logger: The small-diameter magnetic positioning gamma ray logging instrument is lowered through the inner hole of the drill pipe (referred to as the drill pipe "water eye" in petroleum engineering). While lowering it, measurements and records of the depth, magnetic positioning signal, and gamma signal are recorded. This continues until the small-diameter magnetic positioning gamma ray logger leaves the retrieval tool and continues to be lowered and measured. Measurements are taken until the instrument reaches the top of the radioactive instrument. Because the small-diameter magnetic positioning gamma ray logger has a small diameter (26-38mm), it can continue to be lowered through the annulus between the radioactive instrument and the well wall. Measurements are then taken again after passing the radioactive instrument. By measuring the radioactive rays emitted by the radioactive source, the magnetic positioning signal at the port of the retrieval tool, the magnetic positioning signal at the top of the well-dropping instrument, and the radioactive ray signal at the location of the radioactive source on the well-dropping instrument can be detected using a small-diameter magnetic positioning gamma instrument. This is because in wells hundreds or even thousands of meters deep, the distance from the wellhead to the top of the well-dropping instrument is 20-30 meters, and the entire area is drill pipe. The inner hole of the drill pipe is smooth, allowing the small-diameter instrument to be successfully lowered through the inner hole of the drill pipe (called the drill pipe "water eye" in petroleum engineering), avoiding the obstruction of instrument lowering due to well conditions when there is no drill pipe in the well.

[0054] The fourth step is to accurately determine the precise depth and distance from the retrieval tool to the "fallen fish" and the radioactive source: A small-diameter magnetic positioning gamma logging instrument is lowered through the inner hole of the drill pipe (referred to as the drill pipe "water eye" in petroleum engineering). Magnetic positioning and gamma signals, as well as depth information, are measured and recorded simultaneously until the small-diameter instrument leaves the retrieval tool. Measurements continue as the instrument is lowered to the top of the radioactive source. Because the small-diameter magnetic positioning gamma logging instrument has a small diameter (26-38mm), it can continue to be lowered through the annulus between the fallen radioactive source and the well wall. Measurements continue as the instrument is lowered past the radioactive source until the measurement is completed. The radioactive rays emitted by the radioactive source are detected by a small-diameter magnetic positioning gamma ray instrument during the lowering measurement method. This detects the magnetic positioning signals at the retrieval tool's port, the top of the descent instrument, and the radioactive ray signal at the location of the radioactive source on the descent instrument. Then, the instrument is raised for measurement. During this upward movement, the small-diameter magnetic positioning gamma ray instrument moves sequentially from bottom to top, passing the radioactive source area of ​​the descent instrument, the top of the descent instrument, the space between the top of the descent instrument and the retrieval tool, the retrieval tool itself, and finally entering the middle orifice of the drill pipe (referred to as the "water eye" in petroleum engineering). The instrument is then lifted out of the well. By recording the measured depth, the magnetic positioning signal detected by the small-diameter magnetic positioning gamma ray instrument, and the gamma ray signal, the precise distance between the retrieval tool's port and the top of the descent instrument ("fish head"), as well as the precise distance of the radioactive source carried by the descent instrument, can be accurately determined.

[0055] The fifth step involves retrieving the small-diameter magnetically positioned gamma logging instrument for subsequent retrieval. With the precise distance between the retrieval tool's port and the top of the instrument and the location of the radioactive source, the retrieval tool's lowering distance can be accurately controlled for successful retrieval. More importantly, by utilizing the measured distance between the retrieval tool's port and the radioactive source, the tool's port can be controlled to avoid the radioactive source, preventing damage and leakage that could lead to radioactive pollution and environmental accidents.

[0056] Compared with the prior art, this application has the following advantages:

[0057] The technical solution in this application fundamentally solves the problems of depth error caused by well depths of hundreds or even thousands of meters in existing technologies, the problem of large-diameter instruments being unable to be lowered due to well conditions, the difficulty in determining whether the obstruction is caused by well conditions or by the instrument being lowered blocking the detection instrument, the problem of large-diameter instruments potentially getting stuck and causing secondary accidents when they are parallel to the instrument being lowered in the well, and the problem of large-diameter detectors being unable to pass by the instrument being lowered and thus unable to detect the location of the radioactive source.

[0058] In addition, embodiments of this application also provide a device for precisely locating the depth of a fallen radioactive instrument, comprising:

[0059] The coarse depth information acquisition unit 10 is used to obtain coarse depth information of the well-drilling instrument from the wellhead on the ground based on theoretical estimation or by running a logging instrument, and to obtain the top depth and the tail depth of the well-drilling instrument based on the coarse depth information.

[0060] The retrieval tool lowering unit 20 is used to rigidly connect the retrieval tool to the end of the drill pipe, and then lower the retrieval tool into the well along with the drill pipe until the distance between it and the top of the well-diving instrument reaches a predetermined distance.

[0061] The precise positioning unit 30 is used to lower a small-diameter magnetic positioning gamma logging instrument through the inner hole of the drill pipe, and simultaneously record the measurement depth, magnetic positioning signal, and gamma signal. After the small-diameter magnetic positioning gamma logging instrument leaves the retrieval tool, it continues to be lowered past the radioactive instrument. Based on the measurement depth, the magnetic positioning signal at the port of the retrieval tool, the magnetic positioning signal at the top of the well-falling instrument, and the radioactive ray signal at the location of the radioactive source on the well-falling instrument, the precise distance between the port of the retrieval tool and the top of the well-falling instrument, and the radioactive source carried by the well-falling instrument are obtained.

[0062] Since the device for accurately locating the depth of a radioactive instrument retrieved from a well is the same as the device described above for accurately locating the depth of a radioactive instrument retrieved from a well, and has the same beneficial effects, this application does not limit it.

[0063] Furthermore, to avoid positioning errors caused by contact with other objects during the lowering measurement process, in one embodiment, the precise positioning device for the retrieval depth of the radioactive instrument in the well also includes a lifting unit associated with the precise positioning unit. This unit is used to lift the small-diameter magnetic positioning gamma logging instrument and perform lifting measurements. By recording the measurement depth, the magnetic positioning signal detected by the small-diameter magnetic positioning gamma logging instrument, and the gamma signal, the precise distance between the retrieval tool port and the top of the well-dropped instrument, as well as the precise distance of the radioactive source carried by the well-dropped instrument, is determined.

[0064] The small-diameter magnetic positioning gamma logging instrument is lifted up by the lifting unit and measured during the lifting process. The data is then compared with the data collected during the lowering measurement process, thereby achieving a before-and-after comparison, reducing positioning errors, and improving positioning accuracy.

[0065] In this application, it is necessary to first roughly determine the location of the well-dropping instrument, and then lower the retrieval tool. The specific depth of the retrieval tool is not limited. In one embodiment, the well-dropping radioactive instrument retrieval depth precision positioning device also includes a parameter setting unit associated with the retrieval tool lowering unit, which is used to set the distance between the retrieval tool and the top of the well-dropping instrument.

[0066] By setting the distance between the top of the retrieval tool and the well-diving instrument through the parameter setting unit, the retrieval tool can be controlled to be lowered to a specified depth, avoiding the retrieval tool being too far or too close to the well-diving instrument, and achieving a suitable depth.

[0067] This application does not limit the parameter setting method for the parameter setting unit. The parameters can be set in advance or during the process of running drill pipe and fishing tools in the well.

[0068] Furthermore, in one embodiment, the precise positioning device for retrieval depth of the fallen radioactive instrument further includes a pull-back positioning unit associated with the precise positioning unit. This unit moves the small-diameter magnetic positioning gamma logging instrument from bottom to top, sequentially passing through the radioactive source portion of the fallen instrument, the top of the fallen instrument, the space between the top of the fallen instrument and the retrieval tool, the retrieval tool, and then into the middle hole of the drill pipe. Finally, the small-diameter magnetic positioning gamma logging instrument is pulled out of the well. The precise distance between the retrieval tool port and the top of the fallen instrument, and the radioactive source carried by the fallen instrument, is determined based on the measured depth generated during the pull-back process, the magnetic positioning signal generated at the port of the retrieval tool, the magnetic positioning signal at the top of the fallen instrument, and the radioactive ray signal at the location of the radioactive source on the fallen instrument.

[0069] This application does not limit the speed of small-diameter magnetic positioning gamma logging instruments and their lowering and raising. The same moving speed can be used in all stages. The retrieval tool and the part below the retrieval tool can move at a low speed and the part above the retrieval tool can be accelerated, thereby reducing the time of the entire positioning process.

[0070] In summary, the precise positioning method and apparatus for retrieving a radioactive instrument from a well, as provided in this application, first obtains approximate depth information of the instrument's distance from the wellhead. Then, after rigidly connecting the retrieval tool to the drill pipe end, the retrieval tool is sequentially lowered into the well along with the drill pipe until the distance between it and the top of the instrument reaches a predetermined distance. Finally, a small-diameter magnetic positioning gamma logging instrument is lowered through the inner hole of the drill pipe. The precise position of the radioactive instrument is determined by recording the measured depth, magnetic positioning signal, and gamma signal. Because the deformation of the drill pipe and retrieval tool inside the well is minimal, the resulting length error is also small. The distance between the retrieval tool and the instrument is very small, and the measurement depth error generated by the small-diameter magnetic positioning gamma logging instrument within this distance is negligible. The sum of these two measurements gives the precise distance between the instrument and the wellhead. The method is simple, easy to operate, and has high positioning accuracy, requiring no complex calculations and allowing for on-site readings.

[0071] The above provides a detailed description of the method and apparatus for precise positioning of the retrieval depth of radioactive instruments dropped into wells, as provided by this invention. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the protection scope of the claims of this invention.

Claims

1. A method for accurately locating the depth of a radioactive instrument retrieved from a well, characterized in that, include: S1, obtain the approximate depth information of the well-diving instrument from the wellhead on the ground, and obtain the top depth and the tail depth of the well-diving instrument based on the approximate depth information; S2, after the retrieval tool is rigidly connected to the end of the drill pipe, the retrieval tool is lowered into the well along with the drill pipe until the distance between it and the top of the well-diving instrument reaches the predetermined distance; S3, a small-diameter magnetic positioning gamma logging instrument is lowered through the inner hole of the drill pipe, simultaneously recording the measurement depth, magnetic positioning signal, and gamma signal. This continues until the small-diameter magnetic positioning gamma logging instrument leaves the retrieval tool and is lowered further past the radioactive instrument. The measurement depth, magnetic positioning signal, and gamma signal are obtained, and based on the measurement depth, the magnetic positioning signal at the retrieval tool port, the magnetic positioning signal at the top of the fall-off instrument, and the radioactive ray signal at the location of the radioactive source on the fall-off instrument, the precise distance between the retrieval tool port and the top of the fall-off instrument, and the precise distance of the radioactive source carried by the fall-off instrument, are determined. Following S3, the following steps are also included: S4, the small-diameter magnetic positioning gamma logging instrument is lifted and a lifting measurement is performed. Based on the measured depth, the magnetic positioning signal detected by the small-diameter magnetic positioning gamma logging instrument, and the gamma signal, the precise distance between the retrieval tool port and the top of the well-falling instrument, and the precise distance of the radioactive source carried by the well-falling instrument, are determined. The distance between the retrieval tool and the top of the well-falling instrument is 20m-30m, and the diameter of the small-diameter magnetic positioning gamma logging instrument is 26mm-38mm. S1 includes: Based on theoretical estimations or by deploying logging instruments, approximate depth information of the distance between the logging instrument and the wellhead can be obtained.

2. A device for precisely positioning the depth of a radioactive instrument retrieved from a well, characterized in that, The method for accurately locating the depth of a fallen radioactive instrument as described in claim 1 includes: The coarse depth information acquisition unit is used to obtain coarse depth information of the well-drilling instrument from the wellhead based on theoretical estimation or by using a logging instrument, and to obtain the top depth and tail depth of the well-drilling instrument based on the coarse depth information. The retrieval tool lowering unit is used to rigidly connect the retrieval tool to the end of the drill pipe, and then lower the retrieval tool into the well along with the drill pipe until the distance between it and the top of the well-diving instrument reaches a predetermined distance. A precise positioning unit is used to lower a small-diameter magnetically positioned gamma logging instrument through the inner hole of the drill pipe, simultaneously recording the measured depth, magnetic positioning signal, and gamma signal. This continues until the small-diameter magnetically positioned gamma logging instrument leaves the retrieval tool and then passes through the radioactive instrument. The unit obtains the measured depth, magnetic positioning signal, and gamma signal, and determines the distance between the retrieval tool port and the retrieval instrument based on the measured depth, the magnetic positioning signal at the retrieval tool port, the top magnetic positioning signal of the retrieval instrument, and the radioactive ray signal from the location of the radioactive source on the retrieval instrument. The precise distance between the top of the retrieval tool and the radioactive source carried by the well-falling instrument also includes a lifting unit associated with the precise positioning unit, used to lift the small-diameter magnetic positioning gamma logging instrument and perform lifting measurements. By recording the measurement depth, the magnetic positioning signal and gamma signal detected by the small-diameter magnetic positioning gamma logging instrument, the precise distance between the retrieval tool port and the top of the well-falling instrument and the radioactive source carried by the well-falling instrument is determined again. The precise distance also includes a parameter setting unit associated with the retrieval tool lowering unit, used to set the distance between the retrieval tool and the top of the well-falling instrument.

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