CO2-natural gas-formation water three-phase coexistence diffusion coefficient testing device

Abstract

A CO2-natural gas-formation water three-phase coexistence diffusion coefficient testing device relates to the technical field of oil and gas reservoir development, and comprises a natural gas source, a CO2 gas source, a core holder, a vacuum pump and a confining pressure pump, the core holder is respectively communicated with the natural gas source and the CO2 gas source, the vacuum pump is communicated to the interior of the core holder, the confining pressure pump is used for providing confining pressure for the core holder, and the confining pressure pump is used for providing confining pressure for the core holder. When a rock core in the rock core holder is in a clamping state, the plurality of groups of isolation ferrules are coaxially paved on the side surface of the rock core in a manner that two adjacent groups of isolation ferrules are in contact with each other, and a fastening ring is also clamped between two adjacent groups of isolation ferrules; the pressure-bearing structure on the surface of the rock core is a plurality of groups of isolation ferrules which are in contact distribution side by side, and the fastening rings are arranged between the adjacent isolation ferrules for improving the pressure-bearing strength, so that the pressure-bearing upper limit of the testing device is improved, the device can accurately simulate the high-pressure condition in an actual stratum, and the accuracy of an experimental result is further improved.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas reservoir development, and in particular to a device for testing the diffusion coefficient of three-phase coexistence of CO2, natural gas and formation water. Background Art

[0002] The oil and gas components in the reservoir in the formation can diffuse through the cover layer, and the diffusion effect can effectively reflect the preservation conditions of the oil and gas reservoir. Therefore, the diffusion coefficient of the oil and gas reservoir has received extensive attention in the field of geological research. By studying the diffusion ability of natural gas in the oil and gas reservoir through the cover layer under different conditions, the sealing performance of the cover layer and the preservation conditions of the oil and gas reservoir can be comprehensively evaluated, which can provide effective help in guiding the subsequent oil and gas development work.

[0003] CO2 has been widely used in oil and gas development at present. It is usually introduced into the development process as a displacement means. Therefore, it is of great practical significance to study the diffusion effect of natural gas under the complex conditions where CO2 and water coexist in the formation. For this purpose, the corresponding natural gas-CO2 diffusion coefficient test device is usually used for research. The basic structure is: a core with gas chambers on both sides is set in the core holder, and the corresponding confining pressure and temperature are applied to simulate the formation conditions. According to the experimental conditions, formation water is introduced into the core, and various compositions of natural gas and CO2 are introduced into the gas chamber to observe the diffusion state of natural gas under the complex conditions of the simulated formation. However, there are the following main problems in the current experimental device: First, the confining pressure on the core is provided by the one-piece rubber cylinder and the confining pressure cavity. The pressure bearing capacity of the integrated rubber cylinder is limited, and it is easy to break under high pressure conditions, resulting in a low upper limit of the pressure of the diffusion experiment, which is difficult to accurately simulate the high-pressure experimental conditions of the real formation; Second, the size of the tested core must meet the specifications of the holder, resulting in the size of the test core cannot be adjusted according to needs, limiting the test range. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a CO2-natural gas-formation water three-phase coexistence diffusion coefficient testing device, which increases the upper pressure limit of the testing device through a specific structure, so that the testing device can simulate the high-pressure conditions in the real formation, thereby improving the accuracy of the experimental results. At the same time, the testing device can also be applicable to cores of different sizes and has a wider range of applications.

[0005] In order to solve at least one of the above technical problems, the technical solution provided by the present invention is:

[0006] Provided is a CO2-natural gas-formation water three-phase coexistence diffusion coefficient testing device, comprising a natural gas source, a CO2 gas source, a core holder, a vacuum pump, and a confining pressure pump, wherein the core holder is provided with two groups of air chambers on both sides of a core therein, the two groups of air chambers being connected to the natural gas source and the CO2 gas source, respectively; the vacuum pump is connected to the inside of the core holder; and the confining pressure pump is used to provide confining pressure to the core holder.

[0007] The core clamp comprises a clamp barrel and movable end covers and fixed end covers which are detachably arranged at both ends of the clamp barrel, and the three constitute a closed core clamp, wherein the fixed end cover is provided with a group of cylindrical clamping members extending into the interior of the core clamp, and the movable end cover is provided with a movable air inlet head for connecting the inside and outside of the core clamp, the movable air inlet head can move axially relative to the movable end cover, and the movable air inlet head is detachably connected with another group of cylindrical clamping members.

[0008] Two groups of cylindrical clamps are used to coaxially clamp the core, and when the core is in a clamped state, a closed active air chamber is formed between the core and the cylindrical clamp connected to the movable air inlet head, and the movable air inlet head extends into the interior of the active air chamber, and a closed fixed air chamber is formed between the core and the cylindrical clamp connected to the fixed end cover, and the fixed air chamber is connected to the outside of the core clamp through the fixed air inlet head.

[0009] When the core is in a clamping state, multiple groups of isolation rings are arranged between the two groups of cylindrical clamps. The isolation rings are coaxially spread on the surface of the core in the form of two adjacent groups contacting each other, wherein a fastening ring is also clamped between the two adjacent groups of isolation rings, the fastening ring includes an annular portion surrounding the core and a splitting portion pointing to the core, the splitting portion is a "V"-shaped groove structure, arranged in the middle of the annular portion and distributed along the annular portion, the splitting portion is in contact with the side surfaces of the two adjacent groups of isolation rings respectively, and at least part of the two ends of the annular portion overlap.

[0010] A confining pressure cavity is arranged in the part between the clamp tube, the cylindrical clamp and the core, and a confining pressure inlet is arranged on the clamp tube body to communicate with the confining pressure cavity and the confining pressure pump.

[0011] An implementation manner of the present invention is that the cross section of the isolation ring is a trapezoid whose long side contacts the core and whose trapezoidal side contacts the splitting portion.

[0012] An embodiment of the present invention is that a fixing hook and a fixing groove are provided on the annular portion of the fastening ring, and the annular portion located at the overlapping part far from the axis can extend its fixing hook into the fixing groove of the annular portion located at the overlapping part close to the axis.

[0013] One implementation mode of the present invention is that the natural gas source and the CO2 gas source are both connected to a gas mixer, and the gas mixer is respectively connected to the movable gas chamber and the fixed gas chamber on both sides of the core.

[0014] An implementation manner of the present invention is that a sampler and a pressure gauge are respectively provided on both sides of the core holder.

[0015] An implementation mode of the present invention is that a temperature control sleeve is provided on the outer surface of the core holder, and a temperature controller connected to the temperature control sleeve is also provided outside the core holder, and the temperature control sleeve can heat the core holder under the control of the temperature controller.

[0016] An implementation manner of the present invention is that a sealing ring is sleeved on the contact surface between the cylindrical clamp and the core.

[0017] An implementation mode of the present invention is that a sealing sleeve is embedded in the movable end cover, the sealing sleeve coaxially fits around the movable air inlet head, and the sealing sleeve is fixed in the movable end cover via a limiting cover which is also detachably arranged on the surface of the movable end cover around the movable air inlet head.

[0018] An implementation manner of the present invention is that the isolation ring is made of a high temperature and high pressure resistant rubber material, and the fastening ring is made of an elastic metal material.

[0019] The technical effects of the present invention are:

[0020] 1. The pressure-bearing structure on the surface of the core in the present invention is a plurality of isolation rings distributed in parallel contact, and fastening rings are arranged between adjacent isolation rings to improve the pressure-bearing strength. Compared with the integrated rubber sleeve in the conventional pressure-bearing structure, the pressure-bearing structure in the present invention can better disperse the pressure, avoiding the breakage and fragmentation of the conventional integrated rubber sleeve due to uneven local pressure under high-pressure conditions, while also ensuring the airtightness of the core, thereby increasing the upper pressure limit of the test device, so that the device can accurately simulate the high-pressure conditions in the actual formation, and further improving the accuracy of the experimental results.

[0021] 2. The clamping structure size of the clamp in the present invention is adjustable, and can be applied to cores of different sizes according to experimental requirements, thereby increasing the application range of the test device. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0024] Figure 2It is a structural schematic diagram of the core holder of the present invention;

[0025] Figure 3 It is a schematic structural diagram of a core having an isolation ring and a fastening ring sleeved on the surface in the present invention;

[0026] Figure 4 It is a schematic diagram of the three-dimensional structure of the isolation ring in the present invention;

[0027] Figure 5 is a distribution diagram of the fastening ring on the isolation ferrule in the present invention;

[0028] Figure 6 It is a schematic diagram of the three-dimensional structure of a core with an isolation ring and a fastening ring sleeved on the surface in the present invention;

[0029] In the figure, 1-natural gas source, 2-CO2 gas source, 3-gas mixer, 4-sampler, 5-core clamp, 6-vacuum pump, 7-confining pressure pump, 8-temperature controller, 9-pressure gauge, 501-clamp barrel, 502-movable end cover, 503-movable gas inlet head, 504-fixed end cover, 505-fixed gas inlet head, 506-movable air chamber, 507-fixed air chamber, 508-cylindrical clamp, 509-core, 510-sealing ring, 511-confining pressure chamber, 512-confining pressure inlet, 513-temperature control sleeve, 514-limiting cover, 515-sealing sleeve, 516-isolating sleeve, 517-fastening ring, 518-annular part, 519-splitting part, 520-fixing hook, 521-fixing groove. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below in conjunction with the embodiments and drawings.

[0031] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention.

[0032] Example:

[0033] See also Figure 1 , a CO2-natural gas-formation water three-phase coexistence diffusion coefficient test device,

[0034] The basic structure of the device refers to the conventional diffusion coefficient testing device. The core holder 5 is provided with two sets of air chambers on both sides of the core 509 inside it. The two sets of air chambers are connected to the natural gas source 1 and the CO2 gas source 2 respectively. The vacuum pump 6 is connected to the inside of the core holder 5 to provide the vacuum environment required for the experiment. It is usually used to provide a vacuum environment when the core is saturated with formation water to improve the saturation efficiency. The confining pressure pump 7 is used to provide confining pressure to the core holder 5. When conducting the test, natural gas or CO2 is injected into the two groups of gas chambers respectively to conduct a diffusion experiment. After the experiment is completed, the gas composition in the gas chamber is measured to determine the diffusion effect of a single component or a mixed component gas. In this embodiment, the natural gas source 1 and the CO2 gas source connection 2 are both connected to the gas mixer 3, and the gas mixer 3 is respectively connected to the movable gas chamber 506 and the fixed gas chamber 507 on both sides of the core 508. The gas mixer 3 allows the natural gas and CO2 to be mixed according to the experimental requirements. Then, the pipeline switch is adjusted to introduce the configured mixed gas into the two groups of gas chambers respectively, thereby simulating the natural gas diffusion state in the presence of CO2; in addition, with reference to similar test devices in the prior art, samplers 4 and pressure gauges 9 are respectively provided on both sides of the core holder 5, which are convenient for sampling and pressure testing of diffusion samples in the two groups of gas chambers.

[0035] See also Figure 2 The core holder 5 comprises a holder barrel 501 and movable end covers 502 and a fixed end cover 504 which are detachably arranged at both ends of the holder barrel 501, and the three constitute a closed core holder 5. The disassembly structure thereof is preferably a threaded disassembly structure, wherein the fixed end cover 504 is provided with a group of cylindrical clamping members 508 extending into the interior of the core holder 5, and the movable end cover 502 is provided with a movable air inlet head 503 for connecting the inside and outside of the core holder 5, the movable air inlet head 503 can move axially relative to the movable end cover 502, and the movable air inlet head 503 is detachably connected with another group of cylindrical clamping members 508, and the function of the cylindrical clamping members 508 is to fix the core in the closed space of the core holder 5, and when the core 509 is set, the core 509 is coaxially inserted into the cylindrical clamping member 508;

[0036] The two sets of cylindrical clamping members 508 are used to coaxially clamp the core 509, and when the core 509 is in the clamping state, a closed active air chamber 506 is formed between the core 509 and the cylindrical clamping member 508 connected to the active air inlet head 503, and the active air inlet head 503 extends into the active air chamber 506, and a closed fixed air chamber 507 is formed between the core 509 and the cylindrical clamping member 508 connected to the fixed end cover 504, and the fixed air chamber 507 is connected to the outside of the core clamp 5 through the fixed air inlet head 505. Figure 2It can be seen that if an active air chamber 506 and a fixed air chamber 507 are to be arranged between the cylindrical clamp 508 and the core 509, a coaxial discontinuous diameter-changing structure can be arranged on the cylindrical clamp 508, and it is ensured that the diameter of the core 509 conforms to the larger inner diameter of the cylindrical clamp 508, so that the active air chamber 506 and the fixed air chamber 507 can be retained while the core 509 is fixed, and the active air chamber 506 and the fixed air chamber 507 are respectively connected to the movable air inlet head 503 and the fixed air inlet head 505. Figure 1 In the external pipeline shown, in addition, since the cylindrical clamp 508 is detachably connected to the movable air inlet head 503, by adjusting the position of the movable air inlet head 503 on the movable end cover 502, the position of the cylindrical clamp 508 connected thereto can be axially adjusted to match the cores 509 with different lengths.

[0037] In this embodiment, a sealing ring 510 is also provided on the contact surface between the cylindrical clamp 508 and the core 509 to ensure the sealing effect of the movable air chamber 506 and the fixed air chamber 507 and to improve the placement stability of the core 509 in the cylindrical clamp 508.

[0038] See also Figure 2 , Figure 3 , Figure 6 When the core 509 is in the clamping state, multiple groups of isolation rings 516 are arranged between the two groups of cylindrical clamps 508. The isolation rings 516 are coaxially spread on the surface of the core 509 in the form of two adjacent groups contacting each other. A fastening ring 517 is also clamped between the two adjacent groups of isolation rings 516. Figure 4 , Figure 5The fastening ring 517 includes an annular portion 518 surrounding the core and a splitting portion 519 pointing to the core. The splitting portion 519 is a "V"-shaped groove structure, which is arranged in the middle of the annular portion 518 and distributed along the annular portion 518. The splitting portion 519 contacts the side surfaces of the two adjacent groups of isolation rings 516 respectively, and at least part of the two ends of the annular portion 518 overlaps. In this embodiment, the cross-section of the isolation ring 516 is a trapezoid whose long side contacts the core 509, and its trapezoidal side contacts the splitting portion 519. It can be seen that the part of the core 509 exposed from the cylindrical clamp 508 is completely covered by the trapezoidal isolation rings arranged in contact side by side, which is used to replace the rubber tube in the conventional setting to bear the confining pressure. The confining pressure bearing end in the conventional test device is usually an integrally formed rubber tube that can completely cover the core. The way it bears the confining pressure is that the surface is subjected to pressure as a whole. When a certain point is subjected to uneven force during the pressure bearing process, such as the pressure received is higher than the surface pressure, the pressure on the surface of the core 509 is greater than that on the surface of the core 509. When pressure is applied to other points, tearing or surface damage may occur due to excessive local pressure, and the damage surface may be further expanded on the basis of the tearing or damage, resulting in failure to provide normal pressure to the core 509. To avoid this problem, conventional test devices will not apply a large confining pressure, which limits the upper limit of the confining pressure of the experimental device, resulting in the device being difficult to accurately simulate the high-pressure conditions in the formation; the surface of the core 509 in the present invention is a contact-distributed isolation ring 516, which will produce an isolation ring 516 layer on the surface of the core 509 after the setting is completed, which also ensures the side sealing of the core 509. The trapezoidal structure has a good pressure-bearing effect and can effectively withstand a large confining pressure. At the same time, the setting of multiple groups of isolation rings 516 is less likely to cause chain damage than an integrally formed rubber tube, avoiding the overall loss of function due to the continuous expansion of one damage. In addition, the adjacent gaps of the isolation rings 516 are also provided with Figure 4 The fastening ring 517 shown, from Figure 6 As can be seen from the figure, the annular portion 518 of the fastening ring 517 is arranged closely to the short sides of the trapezoids of the two adjacent isolation rings 516 to withstand the radially applied confining pressure, while the splitting portion 519 of the fastening ring 517 is inserted into the annular gap between the two adjacent isolation rings 516 along the radial direction, thereby completely filling the annular gap between the two adjacent isolation rings 516. Figure 4It can also be seen that the fastening ring 517 is an involute circle. When the fastening ring 517 is subjected to radially applied confining pressure, the split portion 519 of the annular portion 518 located on the outer ring in the overlapping portion will extend into the "V"-shaped groove structure of the annular portion 518 located on the inner ring, so that the fastening ring 517 as a whole approaches a perfect circle from an involute circle. At this time, the split portion 519 will transfer the pressure to the two groups of trapezoidal isolation rings 516 in contact with it, thereby strengthening the isolation ring 516 layer and making the isolation ring 516 further tightened in all directions by the lateral force, thereby improving the strength of the isolation ring 516. It can be seen that by providing the isolation ring 516 and the fastening ring 517, the strength of the part directly subjected to the confining pressure outside the core 509 is significantly improved, thereby effectively improving the upper limit of the confining pressure that the core can withstand.

[0039] In addition, when an integrally molded rubber tube is used as a component to withstand confining pressure, the length of the core 509 needs to be adjusted according to the length of the rubber tube. In the present invention, the coverage of the isolation ring 516 is controlled after the length of the core 509 is determined, so that the device can be suitable for cores 509 of various sizes.

[0040] In this embodiment, a fixing hook 520 and a fixing groove 521 are provided on the annular portion 518 of the fastening ring 517. The annular portion 518 located at the overlapping part far from the axis can extend its fixing hook 520 into the fixing groove 521 of the annular portion 518 located at the overlapping part close to the axis. When the annular portion 518 is in the overlapping part, it can make the fastening ring 517 as a whole approach a perfect circle from an involute circle after being compressed. If the overlapping part of the annular portion 518 is separated, it may cause the fastening ring 517 to fall off from the isolation ring 516. Therefore, the following configuration is provided: Figure 5 The fixing hook 520 and the fixing groove 521 are used to ensure that at least a portion of the annular portion 518 can overlap.

[0041] A confining pressure chamber 511 is provided in the portion between the clamp cylinder 501 and the cylindrical clamp 508 and the core 509. A confining pressure inlet 512 is provided on the clamp cylinder 501 to connect the confining pressure chamber 511 and the confining pressure pump 7. The confining pressure chamber 511 is used to accommodate the confining pressure medium, and the confining pressure medium is transported to the confining pressure chamber 511 through the confining pressure pump 7.

[0042] The outer surface of the core holder 5 is covered with a temperature control sleeve 513, and a temperature controller 8 connected to the temperature control sleeve 513 is also arranged outside the core holder 5. The temperature control sleeve 513 can heat the core holder 5 under the control of the temperature controller 8. The temperature control sleeve 513 is preferably heated by an electric heating wire and is powered and controlled by the temperature controller 8.

[0043] The movable end cover 502 is embedded with a sealing sleeve 515, which coaxially fits around the movable air inlet head 503, and the sealing sleeve 515 is fixed in the movable end cover 502 through a limit cover 514 which is also detachably arranged on the surface of the movable end cover 502 around the movable air inlet head 503, see Figure 2 The position of the cylindrical clamp 508 is adjusted by adjusting the extension and contraction degree of the movable air inlet head 503. When the position is determined, a sealing sleeve 515 is placed in the movable end cover 502 and fixed by a limiting cover 514, so that the movable air inlet head 503 can be fixed and sealed.

[0044] In this embodiment, the sealing performance and the pressure bearing performance are comprehensively considered, and the isolation ring 516 is made of a high temperature and high pressure resistant rubber material, and the fastening ring 517 is made of an elastic metal material.

[0045] In summary, before use, the present invention is Figure 1 Assemble the entire device according to the structure shown Figure 2 The structure shown assembles the core clamp 5, wherein the movable air inlet head 503 and the cylindrical clamp 508 are adjusted according to the length of the core 509 so that the core 509 can be accurately clamped, and before the core 509 is completely placed in the cylindrical clamp 508, an isolation ring 516 and a fastening ring 517 are sequentially sleeved on the surface of the core 509, and then the core 509 and the cylindrical clamp 508 are assembled to ensure that the surface of the core 509 does not contact the confining pressure chamber 511, and the assembly of the core clamp 5 is completed.

[0046] Specifically, when in use, the pipeline is evacuated according to experimental needs, and the core is saturated with formation water. Then, the natural gas, CO2, or a mixture of the two that need to be injected into the air chambers on both sides of the core 509 are mixed in the gas mixer 3, the core holder is heated and confining pressure is applied, and the diffusion coefficient test is carried out. After the test time reaches the limit, the gas concentrations of the air chambers on both sides are sampled and analyzed from the sampler 4, and then the results of the diffusion experiment of natural gas and CO2 in the presence of formation water are obtained. Compared with similar devices in the prior art, the device in the present invention has a larger upper limit of confining pressure and a larger applicable range of the core, so that the experimental conditions can be closer to the actual situation in the formation, thereby improving the accuracy of the final result.

[0047] In the description of the present invention, it should be pointed out that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside" and "outside" etc. indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and should not be understood as a limitation on the present invention.

[0048] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A CO2-natural gas-formation water three-phase coexistence diffusion coefficient testing device, comprising a natural gas source (1), a CO2 gas source (2), a core holder (5), a vacuum pump (6), and a confining pressure pump (7), wherein: The core holder (5) is provided with two groups of air chambers on both sides of the core (509) inside the core holder (5), respectively. The two groups of air chambers are connected to the natural gas source (1) and the CO2 gas source (2), respectively. The vacuum pump (6) is connected to the inside of the core holder (5), and the confining pressure pump (7) is used to provide confining pressure to the core holder (5). The core holder (5) comprises a holder barrel (501) and movable end covers (502) and fixed end covers (503) which are detachably arranged at both ends of the holder barrel (501). The fixed end cover (504) is provided with a group of cylindrical clamping members (508) extending into the interior of the core clamp (5), and the movable end cover (502) is provided with a movable air inlet head (503) for connecting the inside and outside of the core clamp (5), the movable air inlet head (503) can move axially relative to the movable end cover (502), and the movable air inlet head (503) is detachably connected with another group of cylindrical clamping members (508); Two groups of cylindrical clamping pieces (508) are used to coaxially clamp the core (509), and when the core (509) is in a clamping state, a closed active air chamber (506) is formed between the core (509) and the cylindrical clamping piece (508) connected to the active air inlet head (503), and the active air inlet head (503) extends into the active air chamber (506), and a closed fixed air chamber (507) is formed between the core (509) and the cylindrical clamping piece (508) connected to the fixed end cover (504), and the fixed air chamber (507) is connected to the outside of the core clamp (5) through the fixed air inlet head (505); When the core (509) is in a clamping state, multiple groups of isolation rings (516) are arranged between the two groups of cylindrical clamping members (508), and the isolation rings (516) are coaxially spread on the surface of the core (509) in the form of two adjacent groups contacting each other, wherein a fastening ring (517) is also clamped between the two adjacent groups of isolation rings (516), and the fastening ring (517) includes an annular portion (518) surrounding the core and a splitting portion (519) pointing to the core, and the splitting portion (519) is a "V"-shaped groove structure, arranged in the middle of the annular portion (518) and distributed along the annular portion (518), and the splitting portion (519) is respectively in contact with the side surfaces of the two adjacent groups of isolation rings (516), and at least part of the two ends of the annular portion (518) overlap; A confining pressure chamber (511) is provided between the clamp cylinder (501), the cylindrical clamp (508) and the core (509), and a confining pressure inlet (512) is provided on the clamp cylinder (501) to connect the confining pressure chamber (511) and the confining pressure pump (7).

2. A CO2-natural gas-formation water three-phase coexistence diffusion coefficient testing device according to claim 1, characterized in that: The cross section of the isolation ring (516) is a trapezoid whose long side contacts the core (509), and whose side surface contacts the splitting portion (519).

3. A CO2-natural gas-formation water three-phase coexistence diffusion coefficient testing device according to claim 1, characterized in that: The annular portion (518) of the fastening ring (517) is provided with a fixing hook (520) and a fixing groove (521), and the annular portion (518) located at the overlapping portion and far from the axis can extend its fixing hook (520) into the fixing groove (521) of the annular portion (518) located at the overlapping portion and close to the axis.

4. A CO2-natural gas-formation water three-phase coexistence diffusion coefficient testing device according to claim 1, characterized in that: The natural gas source (1) and the CO2 gas source connection (2) are both connected to a gas mixer (3), and the gas mixer (3) is respectively connected to a movable gas chamber (506) and a fixed gas chamber (507) on both sides of the core (508).

5. A CO2-natural gas-formation water three-phase coexistence diffusion coefficient testing device according to claim 1, characterized in that: A sampler (4) and a pressure gauge (9) are respectively arranged on both sides of the core holder (5).

6. A CO2-natural gas-formation water three-phase coexistence diffusion coefficient testing device according to claim 1, characterized in that: The outer surface of the core holder (5) is provided with a temperature control sleeve (513), and a temperature controller (8) connected to the temperature control sleeve (513) is also provided outside the core holder (5). The temperature control sleeve (513) can heat the core holder (5) under the control of the temperature controller (8).

7. A CO2-natural gas-formation water three-phase coexistence diffusion coefficient testing device according to claim 1, characterized in that: A sealing ring (510) is sleeved on the contact surface between the cylindrical clamp (508) and the rock core (509).

8. The CO2-natural gas-formation water three-phase coexistence diffusion coefficient testing device according to claim 1, characterized in that: The movable end cover (502) is embedded with a sealing sleeve (515), which coaxially fits around the movable air inlet head (503), and the sealing sleeve (515) is fixed in the movable end cover (502) via a limit cover (514) which is also detachably arranged on the surface of the movable end cover (502) around the movable air inlet head (503).

9. A CO2-natural gas-formation water three-phase coexistence diffusion coefficient testing device according to claim 1, characterized in that: The isolation ring (516) is made of a high temperature and high pressure resistant rubber material, and the fastening ring (517) is made of an elastic metal material.

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