A gas logging experiment system simulating real downhole environment

Abstract

This invention relates to a gas logging experimental system simulating a real downhole environment. Its features include a wellbore undulation device, a drilling fluid injection device, a drilling fluid preparation device, and a drilling fluid treatment device. The wellbore undulation device simulates the unevenness of the wellbore during real drilling. The drilling fluid preparation device injects drilling fluid. The drilling fluid injection device forms concentric spiral flows of drilling fluid in different shapes within the wellbore undulation device. The drilling fluid treatment device is used for degassing and gas logging analysis. The wellbore undulation device is equipped with a microbubble injection device. This invention simulates the unevenness of the wellbore during real drilling, overcoming the shortcomings of existing devices that use smooth cylinders to simulate the wellbore; it solves the problem of existing devices failing to achieve concentric spiral flow of drilling fluid; and it also addresses the issue that existing devices have not yet achieved the injection of hydrocarbon gas into the drilling fluid in the form of microbubbles.

Description

Technical Field

[0001] This invention belongs to the technical field of oil and gas engineering, and in particular to a gas logging experimental system that simulates the real downhole environment. Background Technology

[0002] Gas logging is a key technology in oil and gas development. This technology obtains reservoir oil and gas information at different depths in real time by measuring the content of hydrocarbon gases in the drilling fluid returned to the wellhead. Compared with other oil and gas content evaluation technologies, it has obvious advantages. However, hydrocarbon gases are affected by many factors during the return process with the drilling fluid, making it difficult to compare the characteristics of oil and gas reservoirs in both horizontal and vertical directions. As a result, the methods and levels of oil and gas reservoir evaluation and interpretation based on gas logging data have not been significantly improved.

[0003] Considering that hydrocarbon gases migrate with drilling fluid in the annulus between the wellbore and the drill string, parameters related to the wellbore annulus or the flow behavior of drilling fluid will affect hydrocarbon gas migration, causing fluctuations in gas logging data measured at the wellhead for the same reservoir's oil and gas content.

[0004] Existing gas logging experimental devices are used to improve the interpretation accuracy of gas logging data or to discuss the impact of different factors on gas logging data. However, these devices operate on smooth wellbore surfaces, making it difficult to assess the impact of actual wellbore irregularities on gas logging data. Furthermore, these devices have not yet achieved concentric spiral flow of drilling fluid within the wellbore annulus, making it difficult to capture the influence of concentric spiral flow on gas logging data in the actual downhole environment. Finally, these devices use a single tube to directly inject hydrocarbon gas into the drilling fluid, which differs from the complex three-dimensional network of hydrocarbon gas infiltrating into the drilling fluid through rock pores and channels in a reservoir environment. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a gas logging experimental system that simulates the real downhole environment, which can accurately measure and acquire the impact of the wellbore environment on gas logging data during the simulated real drilling process.

[0006] The technical problem solved by this invention is achieved through the following technical solution:

[0007] On the one hand, this invention provides a gas logging experimental system that simulates the real downhole environment, characterized by comprising a wellbore undulation device, a drilling fluid injection device, a drilling fluid preparation device, and a drilling fluid treatment device.

[0008] The drilling fluid treatment device is positioned on top of the wellbore undulation device, forming a sealed space. One end of the drilling fluid injection device penetrates the drilling fluid treatment device and is located inside the wellbore undulation device. The other end of the drilling fluid injection device is connected to the drilling fluid preparation device. The wellbore undulation device simulates the uneven characteristics of the wellbore during actual drilling. The drilling fluid injection device forms concentric spiral flows of drilling fluid of different shapes inside the wellbore undulation device. The drilling fluid preparation device injects drilling fluid into the drilling fluid injection device. The drilling fluid treatment device degasses the drilling fluid inside the wellbore undulation device and performs gas analysis on the degassed drilling fluid.

[0009] The lower part of the wellbore oscillation device is equipped with a microbubble injection device, which is used to inject hydrocarbon gas into the interior of the wellbore oscillation device in the form of microbubbles, so as to realize the simulation of hydrocarbon gas infiltrating into the drilling fluid through the complex three-dimensional network of rock pores and channels in the real reservoir environment.

[0010] Preferably, the wellbore undulation device includes a simulated wellbore body, an electromagnet, an iron block, and an inner wellbore cylinder. The inner wellbore cylinder is fitted inside the simulated wellbore body and is an annular cylindrical structure. The electromagnets are arranged at intervals from top to bottom on the inner wall of the simulated wellbore body, and the iron blocks are arranged at intervals from top to bottom on the outer wall of the inner wellbore cylinder. The electromagnets and the iron blocks cooperate to form attraction and repulsion. The electromagnets are connected to an AC motor, which is used to exert the attraction force of the electromagnets. The cooperation of the electromagnets, iron blocks, and AC motor is used to simulate the uneven characteristics of the wellbore wall during the actual drilling process inside the simulated wellbore body.

[0011] Preferably, the drilling fluid injection device includes a drill string, casing, drilling fluid tank, auger assembly, and bending device. One end of the drill string is connected to the drilling fluid tank via a water pipe, and the other end passes through the auger assembly and is fitted inside the wellbore undulating device, where a screw drill bit is mounted. The bending device is spaced apart on the outer wall of the drill string fitted inside the wellbore undulating device. The drilling fluid tank is used to inject drilling fluid into the drill string. The auger assembly is used to rotate the drill string longitudinally. The bending device is used to simulate the bending characteristics of the drill string during actual drilling.

[0012] The spiral device includes a multi-stage motor and a rotary table. The drill string passes through the rotary table, and the multi-stage motor is meshed with the rotary table. The multi-stage motor controls the rotary table to rotate in the same direction, thereby driving the drill string to rotate longitudinally.

[0013] The bending device includes a casing tightener, a lead casing, and a casing connecting line. The lead casings are sequentially spaced on the outer wall of the drill string. The casing tightener is located at the bottom of the rotary table and is connected through the drill string. The casing tightener and the lead casing are connected by the casing connecting line. The casing tightener controls the lead casing to generate additional centrifugal force through the casing connecting line, causing the drill string to bend at the location where the lead casing is set. Through the cooperation of the spiral device and the bending device, the drill string, which is fitted inside the wellbore oscillation device, achieves concentric spiral flow within the wellbore oscillation device.

[0014] Preferably, the microbubble injection device includes a methane gas tank, a gas pipe, an annular injection cylinder, and a capillary tube. The methane gas tank is connected to the annular injection cylinder through the gas pipe. One end of the capillary tube is connected to the annular injection cylinder, and the other end is connected to the internal space of the wellbore oscillation device. The top and bottom ends of the annular injection cylinder are respectively provided with reinforcing rings. The reinforcing rings are used to fix the annular injection cylinder inside the wellbore oscillation device. The methane gas tank is used to store methane gas. The capillary tube is used to inject the methane gas stored in the methane gas tank into the internal space of the wellbore oscillation device in the form of microbubbles, so as to establish a three-dimensional pore network to simulate the pores and channels in the formation.

[0015] Preferably, the drilling fluid treatment device includes a drilling fluid guide, a degassing tank, and a drilling fluid storage tank. The drilling fluid guide and the degassing tank are connected by a connecting pipe, which extends into the interior of the drilling fluid storage tank to form a discharge pipe.

[0016] The lower part of the drilling fluid guide is located at the top of the wellbore undulation device, forming a sealed space. A degasser is installed inside the degassing tank to degas the drilling fluid inside. A chromatograph is installed at the top of the degassing tank to analyze the degassed drilling fluid gas and transmit the data parameters to a host computer via communication equipment.

[0017] A controllable valve is provided at the connection between the outlet pipe and the degassing tank. The controllable valve is used to control the drilling fluid after degassing to be discharged into the drilling fluid storage tank.

[0018] Preferably, a positioning ball is provided inside the drill string, and the positioning ball is equipped with a signal receiver. The signal receiver is used to receive the real-time position information of the positioning ball, and the cooperation between the positioning ball and the signal receiver is used to determine whether the drilling fluid inside the drill string forms a concentric spiral flow.

[0019] Preferably, a stirrer is provided at the bottom of the drilling fluid tank. The stirrer is used to stir the drilling fluid to ensure the uniformity of the drilling fluid density and viscosity. A water pump is provided at the connection between the water pipe and the drilling fluid tank. A sliding bearing is provided between the drill string and the water pipe. The sliding bearing is used to allow the water pipe to rotate without being rotated by the drill string.

[0020] Preferably, the inner cylinder of the well is made of aluminum, and the iron block is spherical;

[0021] Preferably, an air pump is installed on the gas pipe, the air pump being used to pump methane gas from inside the methane tank into the annular gas injection cylinder.

[0022] On the other hand, the present invention also provides a method for calculating the horizontal flow velocity of drilling fluid in a gas logging experimental system that simulates the real downhole environment. The drilling fluid in the drill string forms a concentric spiral flow under the control of the rotary table. The formula for calculating the horizontal flow velocity of the drilling fluid is as follows:

[0023] ;

[0024] In the formula:

[0025] v is the horizontal flow velocity of the drilling fluid at a certain point, in m / s;

[0026] r is the distance from the point to the drill string axis, in meters;

[0027] e is the eccentricity of the drill string's revolution, in meters;

[0028] R is the radius of the wellbore, in meters (m).

[0029] ω is the rotational speed of the turntable, in r / s.

[0030] The advantages and positive effects of this invention are:

[0031] This invention proposes a gas logging experimental system that simulates the real downhole environment. Compared with existing technologies, it incorporates a wellbore undulation device consisting of an electromagnet and an iron block. An AC motor controls the electromagnet to generate attractive and repulsive forces, causing the aluminum wellbore inner cylinder to undulate within a pre-reserved gap between the electromagnet and the spherical iron block. This simulates the unevenness of the wellbore during actual drilling, overcoming the shortcomings of existing devices that use smooth cylinders to simulate the wellbore. Furthermore, this invention adds a spiral and bending device to the drill string. The combination of these devices creates concentric spiral flows of drilling fluid in different shapes. A positioning ball confirms the formed concentric spiral flow, solving the problem of existing devices failing to achieve concentric spiral flow of drilling fluid. Finally, this invention adds a microbubble injection device to simulate the process of hydrocarbon gases infiltrating into the drilling fluid from formation pores in the form of microbubbles, solving the problem that existing devices have not yet achieved the injection of hydrocarbon gases into the drilling fluid in the form of microbubbles. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the overall structure and connection of the gas logging experimental system for simulating the real downhole environment of the present invention;

[0033] Figure 2 This is a schematic diagram of the structural connection between the drill string and the wellbore undulation device of the present invention;

[0034] Figure 3 yes Figure 2 Top view;

[0035] Figure 4 This is a schematic diagram of the structural connection of the drilling fluid injection device of the present invention in the wellbore oscillation device to simulate the real environment;

[0036] Figure 5 This is a schematic diagram of the structural connection of the microbubble injection device of the present invention;

[0037] Figure 6 This is a top view of the annular air injection cylinder of the present invention;

[0038] Figure 7 This is a schematic diagram of the structural connection of the drilling fluid treatment device of the present invention;

[0039] Figure 8 This is a top view of the drilling fluid guide and the connection between the drill string and the wellbore body of the present invention.

[0040] The components include: 1. Drilling fluid tank; 2. Agitator; 3. Methane gas tank; 4. Gas pump; 5. Gas pipe; 6. Annular gas injection cylinder; 7. Capillary tube; 8. Wellbore body; 801. Electromagnet; 802. Iron block; 803. Inner cylinder of wellbore; 9. Drill string; 10. Drilling fluid storage tank; 11. Liquid outlet pipe; 12. Controllable valve; 13. Host computer; 14. Degasser; 15. Degassing tank; 16. Multi-stage motor; 17. Rotary table; 18. Connecting pipe; 19. Water pipe; 20. Water pump; 21. Sliding bearing; 22. Drilling fluid guide; 23. Chromatograph; 24. AC motor; 25. Positioning ball; 26. Signal receiver; 27. Tubing tightener; 28. Tubing; 29. ​​Tubing connection line; 30. Screw drill bit; 31. Reinforcing ring. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to the accompanying drawings.

[0042] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0043] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when we say an element is “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or there may be intermediate elements. Furthermore, “connected” or “coupled” as used herein can include wireless connections or couplings. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0044] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0045] To facilitate understanding of the embodiments of the present invention, the following will provide further explanation and description with reference to the accompanying drawings and several specific embodiments. These embodiments do not constitute a limitation on the embodiments of the present invention.

[0046] This invention proposes a gas logging experimental system that simulates the real downhole environment, such as... Figure 1 As shown, it includes a wellbore undulation device, a drilling fluid injection device, a drilling fluid preparation device, and a drilling fluid treatment device.

[0047] The drilling fluid treatment device is positioned on top of the wellbore undulation device, forming a sealed space. One end of the drilling fluid injection device penetrates the drilling fluid treatment device and is located inside the wellbore undulation device. The other end of the drilling fluid injection device is connected to the drilling fluid preparation device. The wellbore undulation device simulates the uneven characteristics of the wellbore during actual drilling. The drilling fluid injection device forms concentric spiral flows of drilling fluid of different shapes inside the wellbore undulation device. The drilling fluid preparation device injects drilling fluid into the drilling fluid injection device. The drilling fluid treatment device degasses the drilling fluid inside the wellbore undulation device and performs gas analysis on the degassed drilling fluid.

[0048] The lower part of the wellbore oscillation device is equipped with a microbubble injection device, which is used to inject hydrocarbon gas into the interior of the wellbore oscillation device in the form of microbubbles, so as to realize the infiltration of hydrocarbon gas into the drilling fluid through the complex three-dimensional network of rock pores and channels in a simulated real reservoir environment.

[0049] In this embodiment, as Figure 2 As shown, the wellbore undulation device includes a simulated wellbore body 8, an electromagnet 801, an iron block 802, and an inner wellbore cylinder 803. The inner wellbore cylinder 803 is fitted inside the simulated wellbore body 8 and is an annular cylindrical structure. The electromagnets 801 are arranged at intervals from top to bottom on the inner wall of the simulated wellbore body 8, and the iron blocks 802 are arranged at intervals from top to bottom on the outer wall of the inner wellbore cylinder 803. The electromagnets 801 and the iron blocks 802 cooperate to form attraction and repulsion. The electromagnets 801 are connected to an AC motor 24, which is used to exert the attraction force of the electromagnets 801. The cooperation of the electromagnets 801, the iron blocks 802, and the AC motor 24 is used to simulate the uneven characteristics of the wellbore wall during the actual drilling process inside the simulated wellbore body 8.

[0050] In this embodiment, the inner cylinder 803 of the well is made of aluminum, and the iron block 802 is spherical.

[0051] In this embodiment, as Figure 3 As shown, the drilling fluid injection device includes a drill string 9, a casing 28, a drilling fluid tank 1, a spiral device, and a bending device. One end of the drill string 9 is connected to the drilling fluid tank 1 via a water pipe 19, and the other end passes through the spiral device and is fitted inside the wellbore undulating device, where a screw drill bit 30 is installed. The bending devices are spaced apart on the outer wall of the drill string 9, which is fitted inside the wellbore undulating device. The drilling fluid tank 1 is used to inject drilling fluid into the drill string 9. The spiral device is used to rotate the drill string 9 longitudinally. The bending devices are used to simulate the bending characteristics of the drill string 9 during actual drilling.

[0052] The spiral device includes a multi-stage motor 16 and a turntable 17. The drill string 9 passes through the turntable 17. The multi-stage motor 16 is meshed with the turntable 17. The multi-stage motor 16 controls the turntable 17 to rotate in the same direction, thereby driving the drill string 9 to rotate longitudinally.

[0053] The bending device includes a tubing tightener 27, a lead tubing 28, and a tubing connecting line 29. The lead tubing 28 are sequentially spaced on the outer wall of the drill string 9. The tubing tightener 27 is located at the bottom of the rotary table 17 and is connected through the drill string 9. The tubing tightener 27 and the lead tubing 28 are connected by the tubing connecting line 29. The tubing tightener 27 controls the lead tubing 28 to generate additional centrifugal force through the tubing connecting line 29, causing the drill string 9 to bend at the location where the lead tubing 28 is located.

[0054] In practice, the drill string 9, which is fitted inside the wellbore wave device, achieves concentric spiral flow within the wellbore wave device through the cooperation of the spiral device and the bending device.

[0055] In this embodiment, a stirrer 2 is provided at the bottom of the drilling fluid tank 1. The stirrer 2 is used to stir the drilling fluid to ensure the uniformity of the drilling fluid density and viscosity. A water pump 20 is provided at the connection between the water pipe 19 and the drilling fluid tank 1.

[0056] In this embodiment, a sliding bearing 21 is provided between the drill string 9 and the water pipe 19, and the sliding bearing 21 is used to allow the water pipe 19 to rotate without being rotated by the drill string 9.

[0057] In this embodiment, as Figure 4 As shown, the microbubble injection device includes a methane tank 3, a gas pipe 5, an annular injection cylinder 6, and a capillary tube 7. The methane tank 3 is connected to the annular injection cylinder 6 through the gas pipe 5. One end of the capillary tube 7 is connected to the annular injection cylinder 6, and the other end is connected to the internal space of the wellbore undulating device through the inner cylinder 803 of the wellbore. The top and bottom ends of the annular injection cylinder 6 are respectively provided with reinforcing rings 31. The reinforcing rings 31 are used to fix the annular injection cylinder 6 inside the wellbore undulating device. The methane tank 3 is used to store methane gas. The capillary tube 7 is used to inject the methane gas stored in the methane tank 3 into the internal space of the wellbore undulating device in the form of microbubbles, so as to establish a three-dimensional pore network to simulate the pores and channels in the formation.

[0058] In this embodiment, an air pump 4 is provided on the gas pipe 5 to pump the methane gas inside the methane gas tank 3 into the annular gas injection cylinder 6.

[0059] In this embodiment, as Figure 5 As shown, the drilling fluid treatment device includes a drilling fluid guide 22, a degassing tank 15, and a drilling fluid storage tank 10. The drilling fluid guide 22 and the degassing tank 15 are connected by a connecting pipe 18, which extends into the interior of the drilling fluid storage tank 10 to form a discharge pipe 11.

[0060] The lower middle part of the drilling fluid guide 22 is located at the top of the wellbore undulation device, forming a sealed space. A degasser 14 is installed inside the degassing tank 15. The degasser 14 is used to degas the drilling fluid inside the degassing tank 15. A chromatograph 23 is installed at the top of the interior of the degassing tank 15. The chromatograph 23 is used to analyze the degassed drilling fluid gas and transmit the data parameters to the host computer 13 via communication equipment.

[0061] A controllable valve 12 is provided at the connection between the outlet pipe 11 and the degassing tank 15. The controllable valve 12 is used to control the drilling fluid after degassing to be discharged into the drilling fluid storage tank 10.

[0062] In this embodiment, a positioning ball 25 is provided inside the drill string 9. The positioning ball 25 is equipped with a signal receiver 26. The signal receiver 26 is used to receive the real-time position information of the positioning ball 25. The cooperation between the positioning ball 25 and the signal receiver 26 is used to determine whether the drilling fluid inside the drill string 9 forms a concentric spiral flow.

[0063] In this embodiment, the drilling fluid in the drill string 9 forms a concentric spiral flow under the control of the rotary table 17. The formula for calculating the horizontal flow velocity of the drilling fluid is as follows:

[0064] ;

[0065] In the formula:

[0066] v is the horizontal flow velocity of the drilling fluid at a certain point, in m / s;

[0067] r is the distance from the point to the drill string axis, in meters;

[0068] e is the eccentricity of the drill string's revolution, in meters;

[0069] R is the radius of the wellbore, in meters (m).

[0070] ω is the rotational speed of the turntable, in r / s.

[0071] Unless otherwise specifically stated, the relative steps, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention.

[0072] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process of the system and apparatus described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0073] In summary, the content of this invention is not limited to the above-described embodiments. Those skilled in the art can propose other embodiments within the technical guiding principles of this invention, but these embodiments are all included within the scope of this invention.

[0074] It should be emphasized that the embodiments described in this invention are illustrative rather than limiting. Therefore, this invention includes, but is not limited to, the embodiments described in the specific implementation. Any other implementations derived by those skilled in the art based on the technical solutions of this invention are also within the scope of protection of this invention.

Claims

1. A gas logging experiment system for simulating the real downhole environment, characterized in that: It includes a wellbore fluctuation device, a drilling fluid injection device, a drilling fluid preparation device, and a drilling fluid treatment device. The drilling fluid treatment device is arranged at the top of the wellbore fluctuation device to form a sealed space. One end of the drilling fluid injection device penetrates through the drilling fluid treatment device and is arranged inside the wellbore fluctuation device. The other end of the drilling fluid injection device is connected to the drilling fluid preparation device. The wellbore fluctuation device is used to simulate the uneven characteristics of the wellbore in the real drilling process. The drilling fluid injection device is used to form different forms of drilling fluid concentric spiral flow inside the wellbore fluctuation device. The drilling fluid preparation device is used to inject drilling fluid into the drilling fluid injection device. The drilling fluid treatment device is used to degas the drilling fluid inside the wellbore fluctuation device and conduct gas logging analysis on the degassed drilling fluid gas. A microbubble injection device is arranged in the middle and lower part of the wellbore fluctuation device. The microbubble injection device is used to inject hydrocarbon gas in the form of microbubbles into the inside of the wellbore fluctuation device to simulate the infiltration of hydrocarbon gas through the complex three-dimensional network of rock pores and throats into the drilling fluid under the real reservoir environment. The wellbore fluctuation device includes a simulated wellbore body, electromagnets, iron blocks, and an inner wellbore cylinder. The inner wellbore cylinder is sleeved inside the simulated wellbore body and both are of annular cylinder structures. The electromagnets are sequentially arranged at intervals from the top to the bottom on the inner wall of the simulated wellbore body. The iron blocks are sequentially arranged at intervals from the top to the bottom on the outer wall of the inner wellbore cylinder. The electromagnets and the iron blocks cooperate to form attraction and repulsion forces. The electromagnets are connected to an AC motor, and the AC motor is used for the attraction force of the electromagnets. The cooperation of the electromagnets, iron blocks, and the AC motor is used to simulate the uneven characteristics of the wellbore in the real drilling process inside the simulated wellbore body.

2. The gas logging experiment system for simulating the real downhole environment according to claim 1, wherein: The drilling fluid injection device includes a drill string, a pipe sleeve, a drilling fluid tank, a spiral device, and a bending device. One end of the drill string is connected to the drilling fluid tank through a water pipe, and the other end penetrates through the spiral device and is sleeved in the internal space of the wellbore fluctuation device and is provided with a screw drill bit. The bending devices are arranged at intervals on the outer wall of the drill string sleeved in the internal space of the wellbore fluctuation device. The drilling fluid tank is used to inject drilling fluid into the drill string. The spiral device is used to rotate the drill string longitudinally. The bending device is used to simulate the bending characteristics of the drill string in the real drilling process. The spiral device includes a multi-stage motor and a turntable. The drill string penetrates through the turntable, and the multi-stage motor is meshed with the turntable. By controlling the turntable to rotate in the same direction through the multi-stage motor, the drill string is driven to rotate longitudinally. The bending device includes a casing tightener, a lead casing, and a casing connecting line. The lead casings are arranged on the outer wall of the drill string at intervals. The casing tightener is arranged at the bottom end of the rotary table and is connected through the drill string. The casing tightener and the lead casing are connected by the casing connecting line. The casing tightener controls the lead casing to generate additional centrifugal force through the casing connecting line, so that the drill string bends at the position where the lead casing is arranged. Through the cooperation of the spiral device and the bending device, the drill string sleeved in the internal space of the wellbore fluctuation device realizes concentric spiral flow in the internal space of the wellbore fluctuation device.

3. The gas logging experiment system for simulating the real downhole environment according to claim 1, wherein: The microbubble injection device includes a methane gas tank, a gas pipe, an annular gas injection cylinder, and a capillary tube. The methane gas tank is connected to the annular gas injection cylinder through the gas pipe. One end of the capillary tube is connected to the annular gas injection cylinder, and the other end is connected to the internal space of the wellbore fluctuation device. Reinforcing rings are respectively arranged at the top and bottom ends of the annular gas injection cylinder. The reinforcing rings are used to fix the annular gas injection cylinder in the internal space of the wellbore fluctuation device. The methane gas tank is used to store methane gas. The capillary tube is used to inject the methane gas stored in the methane gas tank into the internal space of the wellbore fluctuation device in the form of microbubbles, so as to establish a three-dimensional pore network for simulating pores and throats in the formation.

4. The gas logging experiment system for simulating the real downhole environment according to claim 1, wherein: The drilling fluid treatment device includes a drilling fluid diverter, a degassing tank, and a drilling fluid storage tank. The drilling fluid diverter and the degassing tank are connected through a connecting pipe, and the connecting pipe extends into the internal part of the drilling fluid storage tank to form a liquid discharge pipe. The middle and lower part of the drilling fluid diverter is arranged at the top of the wellbore fluctuation device to form a sealed space. A degasser is arranged inside the degassing tank. The degasser is used to transfer and degas the drilling fluid inside the degassing tank. A chromatograph is arranged at the top end inside the degassing tank. The chromatograph is used to analyze the data of the gas in the degassed drilling fluid and transmit the data parameters to the upper computer through communication equipment. A controllable valve is arranged at the connection between the liquid discharge pipe and the degassing tank. The controllable valve is used to control the discharged drilling fluid after degassing to be discharged into the internal part of the drilling fluid storage tank.

5. The gas logging experiment system for simulating the real downhole environment according to claim 2, wherein: A positioning ball is arranged inside the drill string. The positioning ball is equipped with a signal receiver. The signal receiver is used to receive the real-time position information of the positioning ball. The cooperation of the positioning ball and the signal receiver is used to judge whether the drilling fluid inside the drill string forms concentric spiral flow.

6. The gas logging experiment system for simulating the real downhole environment according to claim 2, wherein: A stirrer is arranged at the bottom end inside the drilling fluid tank. The stirrer is used to stir the drilling fluid to ensure the uniformity of the density and viscosity of the drilling fluid. A water pump is arranged at the connection between the water pipe and the drilling fluid tank. A sliding bearing is arranged between the drill string and the water pipe. The sliding bearing is used to prevent the water pipe from rotating due to the rotation of the drill string.

7. The gas logging experiment system for simulating the real downhole environment according to claim 1, wherein: The material of the inner cylinder of the wellbore is aluminum, and the iron block is spherical.

8. The gas logging experiment system for simulating the real downhole environment according to claim 3, characterized in that: An air pump is arranged on the gas pipe. The air pump is used to pump the methane gas inside the methane gas tank into the annular gas injection cylinder.

9. A method for calculating the horizontal flow velocity of drilling fluid in a gas logging experiment system for simulating the real downhole environment as described in claim 2, characterized in that: The drilling fluid in the drill string forms a concentric spiral flow under the control of the rotary table. The calculation formula for the horizontal flow velocity of the drilling fluid is as follows: ； In the formula: v is the horizontal flow velocity of the drilling fluid at a certain point, m / s; r is the distance from this point to the axis of the drill string, m; e is the eccentricity of the drill string revolution, m; R is the radius of the wellbore, m; ω is the rotary table speed, r / s.

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