A density logging tool structure and assembly method

Abstract

This application relates to the field of logging equipment technology, and in particular to a density logging tool structure and assembly method. The structure includes a logging tool shell, comprising a column and a center-of-gravity offset section. The center-of-gravity offset section shifts the center of gravity of the shell towards the well wall and has an internal cavity containing a shielding body. The shielding body has a first mounting hole for installing a radioactive source and a radioactive hole. A radioactive source protection component is located within the radioactive hole. The center-of-gravity offset section has a protective cover plate with a radiation window cover plate opposite to the radioactive hole. The application also includes an assembly method for this structure, including steps such as fixing the shielding body, inserting the protective component, installing the radioactive source, and installing the protective cover plate. This application achieves the technical effect of shifting the center of gravity of the logging tool structure towards the well wall, facilitating contact measurement with the well wall surface, and providing a safe and convenient assembly method that effectively protects the radioactive source.

Description

Technical Field

[0001] This application relates to the field of logging equipment technology, and in particular to a density logging instrument structure and assembly method. Background Technology

[0002] Radioactive density logging tools are key equipment in the field of oil well logging, primarily used to accurately measure formation density parameters through the interaction of radiation emitted from a radioactive source with the formation. As oil and gas exploration and development extend to complex formations and deep reservoirs, the requirements for the accuracy of logging data and the safety of the instruments are becoming increasingly stringent. Traditional density logging tools use a source chamber made of tungsten-nickel-iron alloy to enclose the density source, acquiring data through a direct-push logging method. Tungsten-nickel-iron material is widely used due to its high density and radiation shielding properties, but its non-magnetic properties pose a significant safety hazard in instrument design. During logging operations, the instrument needs to be in close contact with the wellbore to ensure directional radiation emission, resulting in the source chamber and wellbore being subjected to high-intensity friction for extended periods. Currently, the industry practice is to use an openable source chamber structure and mechanical fasteners to load and fix the radioactive source, but this design has revealed serious deficiencies in complex downhole environments.

[0003] The contact method between the source chamber (the component that holds the radioactive source) and the wellbore in existing logging tools has a fundamental flaw. They generally employ a "line contact" design, meaning the instrument is only in contact with the wellbore through a narrow line. This design leads to a high concentration of pressure and a dramatic increase in contact stress (up to 8-10 times that of surface contact). This results in two serious consequences: First, severe wear. The high-density tungsten-nickel-iron alloy source chamber wears rapidly under high-pressure friction, and the resulting metal debris not only contaminates the wellbore but can also cause major accidents such as stuck pipe. Second, inaccurate measurements. The unstable contact method makes the instrument prone to slight vibrations when moving downhole, leading to a significant decrease in the signal quality received by the gamma ray detector (signal-to-noise ratio deterioration of over 15%), directly affecting the accuracy and reliability of formation density data. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this application provides a density logging instrument structure and assembly method. By setting a center of gravity offset part and an arc-shaped contact surface design, the logging instrument is stably attached to the well wall, reducing the gap between the instrument and the well wall, improving the stability and accuracy of the radiation source to the formation and the signal received by the detector, and ensuring the reliability and measurement accuracy of density logging data.

[0005] This application is achieved through the following technical solution:

[0006] A density logging tool structure, comprising:

[0007] The logging instrument housing includes a column and a center of gravity offset part. The center of gravity offset part is located on one side of the column and is used to offset the center of gravity of the logging instrument housing towards the well wall. A receiving cavity is formed inside the center of gravity offset part.

[0008] A shield is installed inside the receiving cavity. The side wall of the shield has a first mounting hole for installing a radiation source and a radiation hole. The radiation hole communicates with the first mounting hole, and a radiation source protection component is installed inside the radiation hole.

[0009] A protective cover plate is installed on the side of the center of gravity offset portion away from the column. The protective cover plate is provided with a ray window cover plate, which is arranged opposite to the ray hole.

[0010] The side of the center of gravity offset portion away from the column is provided as an arc-shaped contact surface, which can form a surface contact with the well wall, and the surface of the protective cover plate is located on the same arc surface as the arc-shaped contact surface.

[0011] By adopting the above technical solutions, the eccentric design and arc-shaped contact surface ensure that the instrument can stably and closely adhere to the wellbore wall over a large area, minimizing the gap between the instrument and the formation in the drilling mud (drilling fluid). Drilling mud significantly affects gamma-ray measurement results; therefore, close contact with the wellbore significantly improves the accuracy of density measurements. Compared to line contact or point contact, "surface contact" (arc-shaped contact surface) makes the instrument more stable during downhole movement, less prone to shaking or rotation, and also reduces wear on the wellbore wall and the instrument itself. The shielding and radiation source are housed within the eccentric block, resulting in a compact structure and unified protection by a protective cover, enhancing the overall robustness and reliability of the device.

[0012] Optionally, the column is a semi-cylinder, and the semi-cylinder has a semi-circular arc surface on the side away from the center of gravity offset portion. The center of gravity offset portion includes a plane, and the plane connects the semi-circular arc surface and the arc mating surface. The opening of the first mounting hole is located on one side of the plane.

[0013] By adopting the above technical solution, the semi-cylindrical structure can be easily connected to other standard logging instrument strings. Setting the first mounting hole on a flat surface provides a smooth working surface for installing the radioactive source, facilitating tool positioning and operation, and reducing the difficulty and risk of installing and replacing the radioactive source. Simultaneously, the flat surface connecting the semi-circular arc surface and the arc-shaped mating surface, with the opening of the first mounting hole located on one side of the flat surface, aims to reduce the contact area between the radioactive source and the well wall, ensuring the radioactive source is completely enclosed within the shielding body, further reducing wear on the radioactive source.

[0014] Optionally, the shielding body has a mounting groove on the side near the plane, the mounting groove is connected to the first mounting hole, the radiation source includes a fixing part, the fixing part is placed in the mounting groove and is detachably connected to the shielding body through the mounting groove, and the side of the fixing part facing away from the first mounting hole is located inside the groove opening of the mounting groove.

[0015] By adopting the above technical solution, the detachable design makes replacing the radioactive source feasible and convenient, without having to replace the entire expensive shielding. By completely housing the fixing part within the mounting groove, the radioactive source's fixing part is prevented from protruding from the mounting groove, allowing the radioactive source to be embedded within the shielding. This reduces the risk of the fixing part being scratched or damaged due to prolonged collision and friction with the well wall downhole. Simultaneously, while ensuring that the fixing part remains unworn, it further ensures the radioactive source is securely installed in the mounting groove.

[0016] Optionally, a second mounting hole is provided on the side of the mounting groove away from the fixing part, and a connecting hole is provided at the bottom of the mounting groove. Fasteners can be inserted into the second mounting hole and the connecting hole, wherein the opening of the second mounting hole is exposed on the outside of the shield.

[0017] By adopting the above technical solution and using standard fasteners such as bolts, a strong and stable locking force can be provided, ensuring that the radioactive source will not loosen or fall off under the severe vibration and impact environment downhole, thus guaranteeing the stability and safety of the measurement. This is a reliable mechanical connection method that is easy to implement and convenient for on-site technicians to operate using standard tools. Because the second mounting hole is exposed on the outside of the shielding body, technicians can use long-sized tools for remote operation, reducing radiation exposure to technicians.

[0018] Optionally, the extension direction of the first mounting hole is perpendicular to the axial direction of the column.

[0019] By adopting the above technical solution, the radiation source and shielding can be compactly arranged on the off-center side of the instrument without occupying the axial length of the instrument. This helps to shorten the overall length of the instrument, leaving more axial space for other electronic circuits and sensors. Combined with the side-mounted design, this allows the instrument to be laid flat and operated from above when installed and maintained on the ground, which is ergonomic and safer.

[0020] Optionally, the radial holes are inclined so that when the logging tool structure is placed in the well for measurement, the radial holes are inclined downwards.

[0021] By employing the above-described technical solution, the downward-tilted emission of the X-ray beam increases the path of interaction between the X-ray and the formation, and optimizes the geometric path of the gamma rays scattered back to the detector. This helps to improve the sensitivity to changes in formation density and increase the detection depth. The downward-tilted design helps to reduce the amount of "useless" gamma rays that are rapidly scattered back from the instrument body or wellbore surface, thereby improving the signal-to-noise ratio and measurement quality.

[0022] Optionally, the first mounting hole and the radiation hole are round holes, the radiation source protection component is a sealing plug, and the end of the sealing plug near the first mounting hole has an arc surface structure, which can contact the radiation source.

[0023] By adopting the above technical solution, the sealing plug can effectively isolate the harsh downhole environment, protect the radioactive source, and extend the instrument's lifespan. The arc-shaped contact ensures that when the sealing plug is tightened, the force is evenly applied to the radioactive source, providing final positioning and buffering, preventing the radioactive source from shaking inside the borehole, and avoiding stress concentration that could damage the fragile radioactive source casing.

[0024] Optionally, the receiving cavity is provided with a horizontal mounting plane and an inclined mounting plane on one side near the cavity wall. When the logging tool structure is placed in the well for measurement, the horizontal mounting plane is set horizontally and the inclined mounting plane is set inclined downward. The side wall of the shield is in contact with the horizontal mounting plane and the inclined mounting plane, and the shield is detachably connected to the center of gravity offset part at the horizontal mounting plane and the inclined mounting plane.

[0025] By employing the above technical solution and positioning it using two planes, the shielding body, weighing tens of kilograms, can be very stably and precisely fixed in its designed position. This ensures that the angle and position of the radiation holes are consistent after each assembly, which is crucial for the repeatability and accuracy of measurement results. When the shielding body needs repair or replacement, this design makes the disassembly and assembly process more convenient and standardized.

[0026] This application also discloses an assembly method for a density logging tool structure, which, based on the above-mentioned density logging tool structure, includes the following steps:

[0027] S1. Fix the shielding body to the housing of the logging instrument;

[0028] S2. Insert the radiation source protection component into the radiation hole;

[0029] S3. Insert the radiation source into the first mounting hole from the side of the shield and tighten the radiation source to the shield;

[0030] S4. Install the protective cover plate on the side of the center of gravity offset part away from the column, and use the protective cover plate to completely press the radiation source protection component into the radiation hole.

[0031] By adopting the above technical solution, a portion of the protective components are first placed in, then the radiation source is placed from the side, and finally the protective components are completely tightened with a protective cover. This method ensures maximum operating space when installing the radiation source, and the final cover installation step can simultaneously complete the final tightening of internal components. The process is reasonable and reduces the risk and time that operators have to come into contact with the radiation source.

[0032] A method for assembling a density logging tool structure, wherein step S3 includes:

[0033] S31. Use a remote operating tool to clamp the radiation source and place it into the first mounting hole;

[0034] S32. Secure the radiation source to the shielding body using a remote operating tool.

[0035] By adopting the above technical solutions, using remote tools can keep operators at a safe distance from radiation sources, minimizing the radiation dose received, which is a key measure for radiation protection.

[0036] In summary, this application includes at least one of the following beneficial technical effects:

[0037] This application uses a center-of-gravity offset section to shift the center of gravity of the logging instrument casing towards one side of the well wall, and the arc-shaped contact surface forms a surface contact with the well wall, which improves the fit between the instrument and the well wall, enhances the stability of X-ray emission and reception, and improves the accuracy and reliability of formation density measurement.

[0038] This application uses a downward-sloping radial aperture, which allows the rays to better act on the formation and improves the measurement results.

[0039] This application uses a shield installed inside the receiving cavity and a radiation source protection component installed inside the radiation hole to reduce the impact of radiation on other parts of the instrument and operators. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the overall structure of this application;

[0041] Figure 2 yes Figure 1 Partial sectional view;

[0042] Figure 3 yes Figure 1 A cross-sectional schematic diagram;

[0043] Figure 4 yes Figure 1 Partial schematic diagram;

[0044] Figure 5 This is a schematic diagram of the structure of the radioactive source described in Example 1.

[0045] In the diagram: 1. Logging instrument housing; 11. Column; 111. Semi-cylinder; 1111. Semi-circular arc surface; 12. Center of gravity offset part; 121. Receiving cavity; 1211. Horizontal mounting plane; 1212. Inclined mounting plane; 122. Arc-shaped mating surface; 123. Plane; 2. Shielding body; 21. First mounting hole; 22. Radiation hole; 23. Radiation source protection component; 24. Mounting groove; 25. Second mounting hole; 26. Connecting hole; 3. Protective cover plate; 31. Radiation window cover plate; 4. Radiation source; 41. Fixing part. Detailed Implementation

[0046] The following will be combined with the appendix Figure 1-5 The technical solutions of the various embodiments of this application have been clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0047] 1) Current status of related technologies in this field:

[0048] Radioactive density logging tools are key equipment in the field of oil well logging, primarily used to accurately measure formation density parameters through the interaction of radiation emitted from a radioactive source with the formation. As oil and gas exploration and development extend to complex formations and deep reservoirs, the requirements for the accuracy of logging data and the safety of instruments are becoming increasingly stringent. Traditional 80-density logging tools use a source chamber made of tungsten-nickel-iron alloy to enclose the density source, acquiring data through a direct-push logging method. Tungsten-nickel-iron material is widely used due to its high density and radiation shielding properties, but its non-magnetic properties pose a significant safety hazard in instrument design. During logging operations, the instrument needs to be in close contact with the wellbore to ensure directional radiation emission, resulting in the source chamber and wellbore being subjected to high-intensity friction for extended periods. Currently, the industry practice is to use an openable source chamber structure and mechanical fasteners to load and fix the radioactive source, but this design has revealed serious deficiencies in complex downhole environments. In recent years, international oil companies have faced substantial environmental compensation claims due to source chamber detachment accidents, prompting the industry to accelerate research into more reliable source chamber fixation technologies. Meanwhile, the development of unconventional resources such as shale oil and gas places higher demands on logging accuracy. The existing linear contact source chamber design can no longer meet the needs of thin interlayer measurement, and it is urgent to break through the technical bottleneck from the structural design level.

[0049] 2) Specific solutions based on existing technologies:

[0050] Currently, the industry mainly employs three technical solutions for securing the source chamber of radioactive density logging tools: The first is a split-type openable source chamber design, which uses threaded holes machined on both sides of the tungsten-nickel-iron source chamber and stainless steel set screws for mechanical locking. The advantage of this solution is ample space for source loading, but it suffers from fatal flaws such as metal fatigue of the set screw threads under high-frequency downhole vibrations and attenuation of locking torque. The second is an integrated welded source chamber solution, fixing the source chamber to the instrument body using electron beam welding. While this solves the problem of loosening mechanical fasteners, it necessitates cutting the entire instrument casing when replacing the radioactive source, significantly increasing maintenance costs and radiation exposure risks. The third is a modified sliding contact design, plating the source chamber surface with hard chrome or tungsten carbide coatings to reduce the coefficient of friction. However, this cannot fundamentally change the pressure concentration phenomenon caused by linear contact; in fact, coating peeling may accelerate the risk of stuck drill bits in the well. In terms of emergency measures to prevent detachment, existing technologies mainly rely on three methods: First, increasing the number of top screws to 4-6 to improve the theoretical locking force, but this results in a reduction of the source chamber wall thickness by more than 20%, and a decrease in impact resistance; Second, using spring pre-tightening anti-loosening washers, but the elastic elements are prone to failure under high temperature and high pressure well conditions; Third, binding tungsten wire ropes to the outside of the source chamber as a secondary safety measure, but this seriously hinders the logging tool from passing through the casing coupling.

[0051] 3) Deficiencies of existing technology:

[0052] The existing technology system suffers from multiple structural defects: First, regarding mechanical fixation, the top-screw fixing method relied upon by the openable source chamber has inherent flaws. The axial vibration acceleration experienced by the downhole tool can reach 5-7 times the surface test value, causing slight relative movement of the threaded pair, which in turn triggers the typical "vibration loosening" failure mode. Second, regarding contact mechanics, the line contact design results in contact stress between the source chamber and the wellbore that is 8-10 times higher than that under surface contact conditions. This not only accelerates the wear of the tungsten-nickel-iron alloy, generating metal debris that contaminates the wellbore, but also causes a deterioration of the signal-to-noise ratio of the gamma-ray detector signal by more than 15% due to contact pressure fluctuations. Third, regarding safety protection, the compact design of the existing source chamber means that its volume is only about 60% of the minimum capture size of a standard retrieval basket. In addition, the magnetic permeability of the tungsten-nickel-iron alloy is less than 1.002, resulting in the strong magnetic retrieval device having an adsorption force of less than 3% of the rated value. More seriously, the detached source chamber may embed itself in formation fractures under the impact of wellbore fluid, in which case the success rate of conventional core retrieval operations is less than 20%. Finally, regarding maintainability, the existing source loading process requires complete exposure to the radioactive source for 15-20 minutes, resulting in a cumulative radiation dose to operators that can reach 3-4 times the limit. Furthermore, the failure rate of precision parts in the opening and closing mechanism remains high in field operations. These shortcomings collectively constitute a systemic technical obstacle restricting the development of radioactive logging technology.

[0053] Therefore, this application provides a density logging tool structure, which mainly solves the following technical problems:

[0054] 1) The source chamber fixing structure of traditional density logging tools poses a significant safety hazard. Current technology employs a side-mounted, openable source chamber design, which is highly susceptible to screw delamination under long-term downhole vibration and friction conditions, leading to the entire source chamber detaching. This mechanical connection method cannot meet the long-term stability requirements of radioactive instruments under harsh well conditions, and the frequent opening and closing of the source chamber during loading further increases the risk of fixing failure. Once the source chamber detaches, it will not only interrupt logging operations but also trigger a serious uncontrolled radioactive source accident.

[0055] 2) The wellbore contact method of existing density logging tools severely limits measurement accuracy. Instruments with a linear casing design form only a narrow linear contact area with the wellbore. This limited contact area results in an excessively low signal-to-noise ratio for the formation reflection signal received by the gamma-ray detector. Especially in irregular wellbore or fractured formation conditions, the linear contact is difficult to maintain a stable coupling state, causing large fluctuations and poor repeatability in measurement data, directly affecting the accuracy of reservoir evaluation.

[0056] 3) There are significant technical deficiencies in the emergency response to the accidental detachment of the radioactive source container. Due to the non-magnetic nature of the tungsten-nickel-iron material of the container, traditional strong magnetic retrieval tools are completely ineffective. Furthermore, the spatial positioning of the small-sized container in the complex wellbore environment is extremely difficult, making it difficult for conventional retrieval tools to effectively capture it. This lack of retrieval technology under these special conditions significantly increases the risk of radioactive source 4 remaining at the bottom of the well, potentially leading to long-term groundwater and soil radiation pollution.

[0057] 4) Existing source loading procedures have radiation protection loopholes. Traditional open-type source loading methods require operators to be exposed to the vicinity of the open source chamber for extended periods, and the complex fastening process prolongs the exposure time. This operating mode not only increases the radiation dose to personnel but also exacerbates the mechanical wear of the fixed structure during repeated loading and unloading, creating a vicious cycle of safety hazards.

[0058] 5) Defects in adhesion performance due to unreasonable instrument center of gravity distribution. The center of gravity position of the linear casing design cannot adapt to the measurement requirements under different well inclination conditions. Especially in horizontal well sections, the instrument is prone to rotational displacement, resulting in a measurement gap between the source window and the formation. This structural defect causes systematic errors in the measurement results, seriously affecting the accuracy of porosity calculation. Example

[0059] Reference Figures 1-2 This application discloses a density logging instrument structure, including a logging instrument housing 1, a shield 2, and a protective cover 3.

[0060] Specifically, the logging instrument housing 1 includes a column 11 and a center of gravity offset part 12. The center of gravity offset part 12 is located on one side of the column 11 and is used to offset the center of gravity of the logging instrument housing 1 towards the well wall. A receiving cavity 121 is provided inside the center of gravity offset part 12.

[0061] The shield 2 is installed in the receiving cavity 121. The side wall of the shield 2 has a first mounting hole 21 for installing the radiation source 4 and a radiation hole 22. The radiation hole 22 is connected to the first mounting hole 21. A radiation source protection component 23 is installed in the radiation hole 22.

[0062] The protective cover plate 3 is installed on the side of the center of gravity offset part 12 away from the column 11. The protective cover plate 3 is provided with a radiation window cover plate 31, which is arranged opposite to the radiation hole 22.

[0063] Among them, the side of the center of gravity bias 12 away from the column 11 is provided as an arc-shaped contact surface 122. The arc-shaped contact surface 122 can form a surface contact with the well wall, and the plate surface of the protective cover plate 3 and the arc-shaped contact surface 122 are located on the same arc surface.

[0064] Specifically, the function of the receiving cavity 121 is to provide installation space for the shield 2. The setting of the center of gravity offset part 12 is one of the key designs of this instrument. It enables the center of gravity of the logging instrument housing 1 to be offset towards one side of the well wall, thereby allowing the instrument to better fit against the well wall when measuring inside the well. For example, in actual measurement, when the instrument is placed in the well, because the center of gravity is offset towards one side of the well wall, the instrument will naturally move towards the well wall, increasing the contact area with the well wall. The side of the center of gravity offset part 12 away from the column 11 is set as an arc-shaped contact surface 122. The arc-shaped contact surface 122 can form a surface contact with the well wall, and the surface of the protective cover plate 3 is located on the same arc surface as the arc-shaped contact surface 122. The design of the arc-shaped contact surface 122 ensures a stable surface contact between the instrument and the well wall, which greatly improves the stability of the measurement compared with the traditional point contact or small area contact method. The function of the X-ray window cover plate 31 is to allow X-rays to pass through while protecting the radiation source 4 and the shield 2 from the intrusion of external substances. The installation method of the protective cover 3 and the center of gravity offset part 12 makes the structure of the entire instrument more complete and stable.

[0065] Reference Figures 1-3 Preferably, the column 11 is a semi-cylinder 111, and the semi-cylinder 111 has a semi-circular arc surface 1111 on the side away from the center of gravity bias portion 12. The center of gravity bias portion 12 includes a plane 123, which connects the semi-circular arc surface 1111 and the arc-shaped contact surface 122. The opening of the first mounting hole 21 is located on one side of the plane 123.

[0066] The first mounting hole 21 is positioned on the plane 123, providing a flat working surface for installing the radiation source 4, facilitating tool positioning and operation, and reducing the difficulty and risk of installing and replacing the radiation source 4. Simultaneously, the plane 123 connects the semi-circular arc surface 1111 and the arc-shaped mating surface 122, with the opening of the first mounting hole 21 located on one side of the plane 123. This aims to reduce the contact area between the radiation source 4 and the well wall, allowing the radiation source 4 to be completely placed within the shielding body 2, further reducing wear on the radiation source 4.

[0067] Reference Figures 2-4 A mounting groove 24 is provided on the side of the shield 2 closest to the plane 123, and the mounting groove 24 communicates with the first mounting hole 21. (Refer to...) Figure 4 and Figure 5 The radiation source 4 includes a fixing part 41, which is placed in the mounting groove 24 and detachably connected to the shield 2 through the mounting groove 24. The side of the fixing part 41 facing away from the first mounting hole 21 is located inside the groove of the mounting groove 24.

[0068] Reference Figure 4 and Figure 5 A second mounting hole 25 is provided on the side of the mounting groove 24 opposite to the fixing part 41, and a connecting hole 26 is provided at the bottom of the mounting groove 24. Fasteners can be inserted into the second mounting hole 25 and the connecting hole 26. The opening of the second mounting hole 25 is exposed on the outside of the shield 2. Because the opening of the second mounting hole 25 is exposed on the outside of the shield 2, technicians can use long tools to perform remote operations, which can reduce the radiation from the radiation source 4 to the technicians.

[0069] Preferably, the extension direction of the first mounting hole 21 is perpendicular to the axial direction of the column 11. This arrangement makes the installation of the radiation source 4 and the emission direction of the radiation more reasonable, which is beneficial to the interaction between the radiation and the strata.

[0070] Reference Figure 2 and Figure 5 The first mounting hole 21 and the radiation hole 22 are round holes, and the radiation source protection component 23 is a sealing plug. The end of the sealing plug near the first mounting hole 21 has an arc surface structure, which can contact the radiation source 4.

[0071] The first mounting hole 21 and the radiation hole 22 are circular holes. This circular hole design facilitates the installation and placement of the radiation source 4 and the radiation source protection component 23. The sealing plug protects the radiation source 4 from external influences and also reduces radiation leakage. The curved surface structure makes better contact with the radiation source 4, improving the sealing effect.

[0072] The radial aperture 22 is inclined so that when the logging tool structure is placed in the well for measurement, the radial aperture 22 is tilted downwards. The inclined radial aperture 22 design allows the rays to better penetrate the formation, improving the accuracy of the measurement.

[0073] Reference Figure 1 and Figure 2 The receiving cavity 121 has a horizontal mounting plane 1211 and an inclined mounting plane 1212 on one side near the cavity wall. When the logging tool structure is placed in the well for measurement, the horizontal mounting plane 1211 is horizontally positioned, and the inclined mounting plane 1212 is inclined downwards. The sidewall of the shield 2 is in contact with both the horizontal mounting plane 1211 and the inclined mounting plane 1212, and the shield 2 is detachably connected to the center of gravity offset part 12 at both the horizontal mounting plane 1211 and the inclined mounting plane 1212. This detachable connection is achieved by fasteners such as bolts at these planes 123. This dual-plane 123 positioning method ensures that the shield 2 is always installed in the same position, thus ensuring that the geometric orientation of the radial hole 22 remains unchanged, providing a guarantee for the repeatability of the measurement results.

[0074] Finally, the protective cover 3 is placed over the surface of the shield 2 to further fix and protect the shield 2.

[0075] The implementation principle of this embodiment is as follows: through an asymmetrical structural design, the physical center of gravity is offset to achieve stable and large-area contact (surface contact) between the logging tool and the wellbore, thereby overcoming the problems of unstable measurement and severe wear caused by traditional "line contact," ultimately improving the accuracy of formation density measurement and equipment reliability. By setting the center of gravity offset part 12, the center of gravity of the entire logging tool housing 1 is artificially offset to one side. In the downhole environment, gravity will cause this offset side to naturally and continuously move towards and press against the wellbore. An arc-shaped contact surface 122 is provided in the center of gravity offset part 12, the curvature of which is designed to form a large-area "surface contact" with the inner wall of the wellbore. Compared to the traditional "line contact" design, surface contact disperses the contact force over a wider area, significantly reducing contact stress and thus substantially reducing wear on the instrument and wellbore. The increased contact area effectively prevents the instrument from swaying, rotating, or jumping during downhole movement, ensuring the geometric stability of the measurement path from the radioactive source 4 to the formation and detector. The high-density shielding 2 and the radioactive source 4 are integrated and installed in the receiving cavity 121 inside the center-of-gravity offset section 12. This design combines functional components with the counterweight structure, optimizing space utilization. It ensures a constant relative position between the emission window (radiation aperture 22) of the radioactive source 4 and the contact surface, which is fundamental to measurement accuracy. The radioactive source 4 is layered with the shielding 2, the radioactive source protection component 23 (sealing plug), the protective cover 3, and the ray window cover 31, providing excellent radiation shielding and physical protection, effectively isolating it from the harsh downhole environment. The radiation aperture 22 is tilted downwards to optimize the path of the gamma rays. Inclined emission can increase the path length of the radiation interaction with the formation; reduce rapid scattering noise from the wellbore or the instrument body, and enable the detector to receive more effective signals from deep within the formation. Example

[0076] This application also discloses an assembly method for a density logging tool structure, using the density logging tool structure in Embodiment 1, including the following steps:

[0077] S1. Fix the shield 2 to the logging instrument housing 1.

[0078] Specifically, in this step, first ensure that the receiving cavity 121 is clean and free of debris. Then, accurately place the shielding body 2 into the receiving cavity 121 according to the positions of the horizontal mounting plane 1211 and the inclined mounting plane 1212. Use suitable fasteners such as bolts to fix the shielding body 2 to the center-of-gravity offset part 12. In actual operation, if necessary, some auxiliary tools can be used to ensure the accuracy and stability of the installation of the shielding body 2.

[0079] S2. Insert the radiation source protection component 23 into the radiation hole 22.

[0080] Specifically, in this step, a suitable radiation source protector 23, i.e., a sealing plug, is selected and slowly inserted into the radiation hole 22. During insertion, attention should be paid to the fit between the curved surface of the sealing plug and the radiation hole 22 to ensure a good seal. Small tools can be used to assist in the operation and prevent damage to the sealing plug during insertion.

[0081] S3. Insert the radiation source 4 into the first mounting hole 21 from the side of the shield 2, and tighten the radiation source 4 and the shield 2.

[0082] Specifically, the S3 steps include:

[0083] S31. Use a remote operating tool to hold the radioactive source 4 and place it into the first mounting hole 21. Since the radioactive source 4 is radioactive, to reduce the risk of radiation exposure to the operator, use a remote operating tool such as a long-handled clamp to hold the radioactive source 4. During placement, exercise caution to ensure that the radioactive source 4 is accurately placed into the first mounting hole 21.

[0084] S32. Secure the radiation source 4 to the shield 2 using a remote operating tool. After the radiation source 4 is inserted into the first mounting hole 21, use a suitable fastening method, such as inserting fasteners (bolts) through the second mounting hole 25 and the connecting hole 26, and tighten the fasteners using a remote operating tool to securely connect the radiation source 4 to the shield 2.

[0085] S4. Install the protective cover plate 3 on the side of the center of gravity offset part 12 away from the column 11, and use the protective cover plate 3 to completely press the radiation source protection component 23 into the radiation hole 22.

[0086] Specifically, the protective cover 3 is accurately installed on the offset part 12, so that its ray window cover 31 is opposite to the radiation hole 22. During installation, attention should be paid to the alignment of the protective cover 3 with the arc-shaped contact surface 122, ensuring that the plate surface and the arc-shaped contact surface 122 are on the same arc surface. After installation, the protective cover 3 will further press the radiation source protection component 23 into the radiation hole 22, enhancing the sealing effect.

[0087] The implementation principle of this embodiment is as follows: A step-by-step, isolated, and safe assembly process is designed. This process follows the principle of "outer before inner, auxiliary before main, and remote operation," aiming to maximize the safety of operators, ensure the accuracy of the installation of the radioactive source 4, and simplify the difficulty of on-site operation. S1 (fixing the shield 2), S2 (pre-installing the protective component), S3 (installing the radioactive source 4), S4 (installing the cover plate and finally tightening it). First, insert the protective component (sealing plug) (S2): Before installing the radioactive source 4, the protective component is placed in advance, which plays a role in preliminary positioning and isolation. Install the radioactive source 4 from the side (S3): At this time, the operating space is the largest, which makes it easy to use tools to accurately place the radioactive source 4 into the first mounting hole 21. Finally, install the protective cover plate 3 to complete the pressing (S4): The action of installing the protective cover plate 3 has the dual function of sealing the entire cavity and completely pressing the radioactive source protective component 23 into place. This "final step to complete the final tightening" design ensures that all internal components are firmly fixed without the risk of loosening, and the process is efficient and reliable. Step S3 explicitly requires the use of remote operating tools to clamp and secure the radiation source 4 (S31, S32). The principle is to increase the physical distance between the operator and the radiation source, utilizing the "inverse square law of distance" to drastically reduce the radiation dose received by the operator, thereby ensuring personnel safety. The entire assembly process is essentially a modular operation. First, the shielding body 2, the "base," is installed; then, the radiation source 4 and protective components, among other "functional components," are installed; finally, the "outer shell" is placed on top.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of this application.

Claims

1. A density logging tool structure, characterized in that, include: The logging instrument housing (1) includes a column (11) and a center-of-gravity offset part (12). The center-of-gravity offset part (12) is located on one side of the column (11) and is used to offset the center of gravity of the logging instrument housing (1) towards the well wall. A receiving cavity (121) is provided in the center-of-gravity offset part (12). A shielding body (2) is installed in the receiving cavity (121). The shielding body (2) has a first mounting hole (21) for installing a radioactive source (4) and a radioactive hole (22) on its side wall. The radioactive hole (22) communicates with the first mounting hole (21). A radioactive source protection component (23) is installed in the radioactive hole (22). A protective cover plate (3) is installed on the side of the center of gravity offset part (12) away from the column (11). The protective cover plate (3) is provided with a ray window cover plate (31), which is arranged opposite to the ray hole (22). The side of the center of gravity offset part (12) away from the column (11) is provided with an arc-shaped contact surface (122). The arc-shaped contact surface (122) can form a surface contact with the well wall. The plate surface of the protective cover plate (3) and the arc-shaped contact surface (122) are located on the same arc surface. The column (11) is a semi-cylinder (111), and a semi-circular arc surface (1111) is provided on the side of the semi-cylinder (111) away from the center of gravity bias part (12). The center of gravity bias part (12) includes a plane (123), and the plane (123) connects the semi-circular arc surface (1111) and the arc fitting surface (122). The opening of the first mounting hole (21) is located on one side of the plane (123). The shield (2) has an installation groove (24) on the side near the plane (123). The installation groove (24) is connected to the first installation hole (21). The radiation source (4) includes a fixing part (41). The fixing part (41) is placed in the installation groove (24) and is detachably connected to the shield (2) through the installation groove (24). The side of the fixing part (41) facing away from the first installation hole (21) is located inside the groove of the installation groove (24).

2. The density logging tool structure according to claim 1, characterized in that, The mounting groove (24) has a second mounting hole (25) on the side opposite to the fixing part (41). The bottom of the mounting groove (24) has a connecting hole (26). Fasteners can be inserted into the second mounting hole (25) and the connecting hole (26). The opening of the second mounting hole (25) is exposed outside the shield (2).

3. The density logging tool structure according to claim 1, characterized in that, The extension direction of the first mounting hole (21) is perpendicular to the axial direction of the column (11).

4. The density logging tool structure according to claim 1, characterized in that, The radial hole (22) is inclined so that when the logging instrument structure is placed in the well for measurement, the radial hole (22) is inclined downward.

5. The density logging tool structure according to claim 1, characterized in that, The first mounting hole (21) and the radiation hole (22) are round holes, and the radiation source protection component (23) is a sealing plug. The end of the sealing plug near the first mounting hole (21) has an arc surface structure, and the arc surface structure can contact the radiation source (4).

6. The density logging tool structure according to claim 1, characterized in that, The receiving cavity (121) is provided with a horizontal mounting plane (1211) and an inclined mounting plane (1212) on one side near the cavity wall. When the logging instrument structure is placed in the well for measurement, the horizontal mounting plane (1211) is set horizontally and the inclined mounting plane (1212) is set inclined downward. The side wall of the shield (2) is in contact with the horizontal mounting plane (1211) and the inclined mounting plane (1212), and the shield (2) is detachably connected to the center of gravity offset part (12) at the horizontal mounting plane (1211) and the inclined mounting plane (1212).

7. A method for assembling a density logging tool structure, based on the density logging tool structure according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Fix the shield (2) to the well logging instrument housing (1); S2. Insert the radiation source protection component (23) into the radiation hole (22); S3. Insert the radiation source (4) into the first mounting hole (21) from the side of the shield (2) and tighten the radiation source (4) and the shield (2); S4. Install the protective cover plate (3) on the side of the center of gravity offset part (12) away from the column (11), and press the radiation source protection component (23) completely into the radiation hole (22) through the protective cover plate (3).

8. The assembly method of the density logging tool structure according to claim 7, characterized in that, Step S3 includes: S31, using a remote operating tool to clamp the radiation source (4) and insert it into the first mounting hole (21); S32, using a remote operating tool to fasten the radiation source (4) to the shield (2).

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