Device and method for testing microscopic deformation of hydrate sediment under stress-seepage coupling

Abstract

The invention relates to the technical field of marine natural gas hydrate resource exploration and development engineering, in particular to a device and a method for testing microscopic deformation of hydrate sediment under stress-seepage coupling. Comprising a high-pressure reaction kettle system, two ends of the high-pressure reaction kettle system are respectively provided with an axial loading-shearing system, each axial loading-shearing system comprises a propelling module for locally shearing a sample and a loading module for integrally loading different stresses on the sample, the loading module is connected with an integral loading part, and the propelling module is connected with a local loading part. The microstructure change of the sediment can be observed while the mechanical and seepage characteristics of the hydrate-containing sediment are synchronously tested, the requirement for macro-micro combined testing of the hydrate-containing sediment under the seepage-deformation coupling effect is met, and a new thought is provided for research of a sea area hydrate reservoir failure mechanism and engineering geological risk prevention and control.

Description

Technical Field

[0001] The present invention relates to the technical field of marine natural gas hydrate resource exploration and development engineering, in particular to a device and method for testing microscopic deformation of hydrate sediments under stress-seepage coupling. Background Art

[0002] The mechanical properties of natural gas hydrate reservoirs are the basis for potential geological risk analysis and prediction, and their deformation and failure mechanisms are a prerequisite for revealing the geological risk induction mechanisms and the evolution of geological hazards. Currently, researchers are using indoor mechanical experiments to determine the strength and deformation properties of hydrate sediments, preliminarily revealing the deformation and failure mechanisms of hydrate sediments and conducting preliminary exploration of the geological risk induction mechanisms of hydrate reservoirs. However, existing experimental equipment and testing technologies make it difficult to detect changes in the microstructure of hydrate sediments under complex working conditions, especially the impact of the seepage-deformation coupling process on the sediment microstructure, which limits in-depth research on the deformation and failure mechanisms of hydrate sediments.

[0003] At present, the study of the seepage-deformation coupling process is mainly concentrated in the traditional geotechnical field, and the macroscopic deformation failure characteristics and seepage characteristics are obtained through triaxial shear, direct shear and other methods. Patent CN113267411 B discloses a cyclic shear seepage test system and method for soil-rock mixtures, which can realize the study of the water-mechanical coupling characteristics of soil-rock mixtures; Patents CN112710554B and CN219391743U respectively propose a triaxial shear-seepage combined test device and method for hydrate sediments, which can analyze the permeability change law of hydrate sediments during shear deformation. However, due to the limitations of the test device and technology, the existing equipment can only realize the test of the macroscopic mechanical behavior and permeability of hydrate sediments, and cannot realize the analysis of the microstructural change characteristics of sediments under seepage-deformation conditions. There is an urgent need to design a test device that can realize macro-micro synchronous testing. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and propose a device and method for testing the microscopic deformation of hydrate sediments under stress-seepage coupling. The device and method can realize the simultaneous testing of the mechanical and seepage characteristics of hydrate sediments while observing the changes in the microstructure of the sediments, meet the needs of macro-micro joint testing of hydrate sediments under seepage-deformation coupling, and provide new ideas for the study of the destruction mechanism of marine hydrate reservoirs and the prevention and control of engineering geological risks.

[0005] The technical solution of the present invention is: a stress-seepage coupling hydrate sediment micro-deformation testing device, comprising a high-pressure reactor system, and axial loading-shear systems are respectively provided at both ends of the high-pressure reactor system, wherein,

[0006] The axial loading-shearing system includes a propulsion module for shearing a local sample and a loading module for loading different stresses on the entire sample. The loading module is connected to the overall loading part, and the propulsion module is connected to the local loading part.

[0007] In the present invention, the loading module includes:

[0008] a loading rod, one end of which is located outside the autoclave system and the other end of which is movably disposed inside the autoclave system;

[0009] A pressure head is provided between the loading rod and the hydrate-containing sediment, and the loading rod acts on the hydrate-containing sediment through the pressure head.

[0010] The propulsion module includes shear blocks, and shear blocks are respectively provided at the upper and lower ends of the hydrate-containing sediment;

[0011] A groove is provided on the side of the pressure head facing the hydrate-containing sediment, and the shear block is slidably arranged in the groove, and the shear block directly contacts the hydrate-containing sediment;

[0012] The upper and lower shear blocks are arranged asymmetrically to achieve asymmetric local shearing of hydrate-containing sediments.

[0013] The overall loading unit includes:

[0014] The loading cylinder housing has an annular protrusion on the annular outer side of the loading rod, the annular protrusion is slidably arranged in the loading cylinder housing, and the side wall of the annular protrusion is dynamically sealed with the corresponding inner wall of the loading cylinder housing;

[0015] The loading cylinder is formed between the annular protrusion and the side wall of the loading cylinder shell facing away from the hydrate-containing sediment, and a closed loading cylinder is provided on the loading cylinder.

[0016] The local loading section includes:

[0017] The propulsion cylinder housing is located between the loading cylinder housing and the autoclave body, one end of the propulsion cylinder housing is fixedly connected to the autoclave body, and the other end of the propulsion cylinder housing is fixedly connected to the loading cylinder housing through the propulsion cylinder base;

[0018] The propulsion piston is reciprocatingly arranged in the propulsion cylinder housing, and a propulsion cylinder is formed between one end of the propulsion piston and the propulsion cylinder base. The other end of the propulsion piston is arranged in the autoclave body and contacts the shear block. A high-pressure liquid inlet is provided on the propulsion cylinder base, and the high-pressure liquid inlet is connected to the propulsion cylinder.

[0019] The high pressure reactor system includes:

[0020] The top of the autoclave is sealed with an upper end cover, and the bottom of the autoclave is sealed with a lower end cover. The upper and lower end covers are connected to a permeability testing system. A CT scanning system is provided on the outside of the autoclave.

[0021] The rubber sleeve is arranged in the cylindrical cavity of the autoclave body, and contains hydrate-containing sediments. The rubber sleeve and the autoclave body are coaxially arranged. A confining pressure cavity is formed between the annular outer wall of the rubber sleeve and the annular inner wall of the autoclave body. The confining pressure cavity is connected to the temperature and confining pressure control system.

[0022] The pressure head and loading rod above the high-pressure reactor system are both provided with interconnected gas channels, which are connected to the gas supply system;

[0023] The gas supply system transports high-pressure gas to the high-pressure reactor system through the gas channel to provide the gas required for hydrate synthesis.

[0024] A flow channel is provided in the axial middle of the loading rod and the pressure head, and the flow channel is connected to the permeability test system;

[0025] The fluid provided by the permeability testing system is injected into the hydrate-containing sediment through the loading rod and flow channel in the pressure head below the high-pressure reactor system, and flows out through the loading rod and flow channel in the pressure head above the high-pressure reactor system to test the permeability change pattern of the sediment under different deformation conditions.

[0026] The present application also includes a method for testing using the above-mentioned stress-seepage coupling hydrate sediment micro-deformation testing device, which includes the following steps:

[0027] S1. Air tightness check;

[0028] S2, specimen preparation and pre-consolidation;

[0029] S3, hydrate synthesis;

[0030] S4. Mechanical testing of hydrate sediments: Inject loading fluid into the loading cylinder, push the loading rod toward the hydrate sediment, and apply axial load to the hydrate sediment simultaneously above and below the hydrate sediment through the pressure head;

[0031] High-pressure fluid is injected into the thrust cylinder, and the thrust piston pushes the shear block toward the hydrate-bearing sediment. The upper and lower shear blocks simulate the shear failure process of the hydrate-bearing sediment.

[0032] S5. Permeability test of hydrate-containing sediments under deformation conditions;

[0033] S6. Microstructural detection of hydrate-bearing sediments;

[0034] S7. End the experiment and organize the equipment.

[0035] In step S4, the calculation formula for the deviatoric stress σ* of the hydrate-containing sediment is:

[0036]

[0037] Where N is the axial load, S is the sediment cross-sectional area, ε is the axial strain, and σ3 is the confining pressure;

[0038] In step S5, the calculation formula for the permeability k of the hydrate-containing sediment is:

[0039]

[0040] Where Q is the volume flow rate of the fluid, μ is the fluid viscosity, L is the sediment length, P i is the pressure value at the inflow interface; P o is the pressure value at the outflow interface.

[0041] The beneficial effects of the present invention are:

[0042] (1) By combining the autoclave with a high-precision CT detection device, the macroscopic seepage-deformation behavior and microstructural changes of hydrate-bearing sediments during sliding friction were simultaneously tested. A macro-micro comprehensive analysis method for the seepage-deformation behavior of hydrate-bearing sediments was established, which helps to reveal the permeability damage mechanism during sliding friction of hydrate-bearing sediments.

[0043] (2) By designing an axial loading-shear system, overall loading and local shearing of hydrate-containing sediments are achieved. At the same time, combined with the permeability test system proposed in this application, the deformation characteristics and permeability changes of hydrate-containing sediments during sliding friction are tested simultaneously, which is closer to actual working conditions and the experimental results are clearer.

[0044] (3) The axial force loading at both ends of the hydrate-containing sediment was achieved through the loading cylinder in the axial loading-shear system; the sliding friction pushing of the hydrate-containing sediment was achieved through the propulsion cylinder in the axial loading-shear system, thus realizing the integrated seepage-deformation test of the hydrate-containing sediment under sliding friction conditions;

[0045] (4) By rationally designing the structures of the propulsion module, the local loading part, the loading module, and the overall loading part, the high-pressure reactor body is miniaturized, so that the high-pressure reactor in this application can be used with CT scanning equipment.

[0046] In summary, based on the demand for joint seepage-deformation testing of hydrate-containing sediments under sliding friction conditions, this application designs a multifunctional high-pressure reactor, and cooperates with a high-precision X-CT detection device to realize the integrated testing of the seepage and deformation characteristics of hydrate-containing sediments during sliding friction. At the same time, it can monitor the microstructural change characteristics of the sediments during the sliding friction process in real time, and can realize the analysis of the permeability change law during the sliding friction process, providing a reference for the evaluation of the mechanical properties of marine natural gas hydrate reservoirs and the identification of potential engineering geological risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a structural schematic diagram of the device of the present invention;

[0048] Figure 2 It is a structural diagram of the high-pressure reactor system;

[0049] Figure 3 It is a structural diagram of the upper loading cylinder and the upper thrust cylinder;

[0050] Figure 4 It is a structural diagram of the lower loading rod and the lower thrust cylinder.

[0051] In the figure: 11 autoclave body, 12 rubber sleeve, 13 confining pressure chamber, 14 hydrate-containing sediment, 15 upper end cover, 16 lower end cover, 17 fixing bolts, 18 confining pressure liquid inlet, 19 confining pressure liquid outlet, 21 lower pressure head, 22 lower shear block, 23 lower flow channel, 24 lower loading rod, 25 lower propulsion piston, 26 lower propulsion cylinder, 27 lower propulsion cylinder housing, 28 lower centralizer, 29 lower propulsion cylinder base, 210 lower loading cylinder housing, 211 lower loading cylinder, 212 high-pressure liquid inlet, 213 No. 1 valve, 214 No. 1 high-pressure pump, 215 loading liquid Lower inlet, 216 No. 2 valve, 217 No. 2 high-pressure pump, 218 upper pressure head, 219 upper shear block, 220 upper flow channel, 221 upper loading rod, 222 upper propulsion piston, 223 upper propulsion cylinder, 224 upper propulsion cylinder housing, 225 upper centralizer, 226, upper propulsion cylinder base, 227 upper loading cylinder housing, 228 upper loading cylinder, 229 high-pressure liquid upper inlet, 230 loading liquid upper inlet, 231 gas channel, 232 No. 3 valve, 233 No. 3 high-pressure pump, 234 No. 4 valve, 235 No. 4 high-pressure pump, 236, liquid storage tank,

[0052] 31 Low temperature water bath, 32 High pressure pump No. 5, 33 Valve No. 5, 34 Pressure gauge No. 1, 35 Thermometer No. 1,

[0053] 41 Low temperature water tank, 42 ​​No. 6 high pressure pump, 43 No. 6 internal valve, 44 No. 1 flow meter, 45 No. 2 pressure gauge, 46 No. 2 thermometer, 47 Inflow interface, 48 Outflow interface, 49 No. 3 pressure gauge, 410 Back pressure valve, 411 No. 2 flow meter,

[0054] 51 gas cylinder, 52 valve No. 7, 53 flow meter No. 3, 54 pressure gauge No. 4,

[0055] 61 ray source, 62 ray detector, 63 connector, 64 turntable,

[0056] 71 Computer, 72 Data processor. DETAILED DESCRIPTION

[0057] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0058] The following description sets forth specific details to facilitate a thorough understanding of the present invention. However, the present invention can be implemented in a variety of other ways than those described herein, and those skilled in the art will be able to make similar generalizations without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0059] like Figures 1 to 4 As shown, the apparatus for testing microstructural changes in hydrate-bearing sediments under seepage-deformation coupling described herein includes a high-pressure reactor system, an axial loading-shear system, a temperature and confining pressure control system, a permeability testing system, an air supply system, a CT scanning system, and a data processing system. The high-pressure reactor system is connected to the temperature and confining pressure control system, the permeability testing system, the air supply system, and the data processing system.

[0060] Hydrate-containing sediment samples can be synthesized in situ within the autoclave system. Axial loading and shear systems, located at both axial ends of the autoclave, enable axial loading of the hydrates, both in a single loading process and in a localized loading process. A temperature and confining pressure control system provides a low-temperature, high-pressure environment conducive to hydrate formation and survival. A permeability testing system measures permeability changes during shear deformation of the sediment. A CT scanning system, installed outside the autoclave system, provides the microstructure of the sediment during the seepage-deformation process.

[0061] The autoclave reactor system includes an autoclave body 11. An upper end cover 15 is provided at the upper end of the autoclave body 11, and a lower end cover 16 is provided at the lower end of the autoclave body 11. The upper end cover 15 and the lower end cover 16 are fixedly connected and sealed to the autoclave body 11 by fixing bolts 17. The autoclave body 11 is cylindrical and has a cylindrical cavity inside. A rubber sleeve 12 is provided in the cylindrical cavity of the autoclave body, and the rubber sleeve 12 is coaxially arranged with the autoclave body 11. A confining pressure chamber 13 is formed between the annular outer wall of the rubber sleeve 12 and the annular inner wall of the autoclave body 11, and the confining pressure chamber 13 is connected to the temperature and confining pressure control system.

[0062] In this embodiment, a confining pressure liquid inlet 18 is provided at the bottom of the autoclave body 11, and a confining pressure liquid outlet 19 is provided at the top of the autoclave body 11. The confining pressure liquid inlet 18 and the confining pressure liquid outlet 19 are connected to the temperature and confining pressure control systems, respectively. The confining pressure liquid inlet 18 and the confining pressure liquid outlet 19 are also connected to the confining pressure chamber 13.

[0063] The rubber sleeve 12 contains hydrate-containing sediment 14 , and both axial ends of the rubber sleeve 12 are respectively connected to the axial loading-shear system.

[0064] In this embodiment, the skeleton material used in the preparation of the hydrate-containing sediment 14 can be selected from materials such as quartz sand, clay, and glass balls. The gas used to synthesize the hydrate can be selected from gases such as methane, ethane, and carbon dioxide. The water used for hydrate synthesis and permeability testing can be selected from distilled water or deionized water. In addition, a promoter such as sodium dodecyl sulfate (SDS) can be reasonably selected to accelerate hydrate synthesis.

[0065] The autoclave body 11 can be made of titanium alloy or aluminum alloy, and its outer surface is wrapped with carbon fiber and resin to enhance its rigidity.

[0066] The autoclave body 11 and the upper end cover 15, and the autoclave body 11 and the lower end cover 16 are respectively fixedly connected by bolts 17. At the same time, the autoclave body 11 and the upper end cover 15, and the autoclave body 11 and the lower end cover 16 are both sealed. In this embodiment, sealing rings are respectively provided between the autoclave body 11 and the upper end cover 15, and between the autoclave body 11 and the lower end cover 16, and lubricating oil is applied.

[0067] The temperature and confining pressure control system includes a low-temperature water bath 31. The water outlet of the low-temperature water bath 31 is connected to the confining pressure liquid inlet 18 on the autoclave. A high-pressure pump 32, a valve 33, a pressure gauge 34, and a thermometer 35 are installed on the high-pressure pipeline connecting the low-temperature water bath 31 and the confining pressure liquid inlet 18. The water inlet of the low-temperature water bath 31 is connected to the confining pressure liquid outlet 19 on the autoclave.

[0068] A low-temperature water bath 31 allows for low-temperature circulation of the confining fluid. A high-pressure pump 32 is used to pressurize the confining fluid, a valve 33 controls the flow of the confining fluid, a pressure gauge 34 monitors the pressure of the confining fluid flowing into the confining chamber in real time, and a thermometer 35 monitors the temperature of the confining fluid flowing into the chamber in real time. The temperature and confining pressure control system enables precise control of the temperature and pressure of the confining fluid, thereby providing a low-temperature, high-pressure environment ideal for the formation and existence of hydrates.

[0069] Both ends of the autoclave system are connected to an axial loading-shear system. This system consists of a propulsion module and a loading module. The loading module applies varying stresses to the entire specimen, while the propulsion module applies shear to a specific area of ​​the specimen, simulating the shear process under varying stress conditions.

[0070] This axial loading-shearing system can achieve both overall loading and local shearing of hydrate-containing sediments, thus realizing a complex loading process for hydrate-containing sediments. The loading module is connected to the overall loading part, and the propulsion module is connected to the local loading part.

[0071] The loading module includes a loading rod and a pressure head. One end of the loading rod is located outside the autoclave body 11, and the other end of the loading rod is movably arranged in the autoclave body. A pressure head is provided between the loading rod and the hydrate-containing sediment. The loading rod acts on the hydrate-containing sediment through the pressure head.

[0072] Loading modules are provided above and below the autoclave system. In this embodiment, the loading module above the autoclave system includes an upper loading rod 221 and an upper pressure head 218. The lower end of the upper loading rod 221 passes through the upper end cover 15 and extends into the autoclave body 11. The upper pressure head 218 is provided between the bottom end of the upper loading rod 221 and the top of the hydrate-containing sediment 14. The upper pressure head 218 is located within the autoclave body 11.

[0073] The loading module below the autoclave system includes a lower loading rod 24 and a lower pressure head 21. The upper end of the lower loading rod 24 passes through the lower end cover 15 and extends into the autoclave body 11. The lower pressure head 21 is provided between the top of the lower loading rod 24 and the bottom of the hydrate-containing sediment 14. The lower pressure head 21 is located inside the autoclave body 11.

[0074] The integrated loading unit includes a loading cylinder housing and a loading cylinder. An annular protrusion is provided on the annular outer side of the loading rod, which is slidably disposed within the loading cylinder housing. A sealing ring is provided between the sidewall of the annular protrusion and the corresponding inner wall of the loading cylinder housing. The annular protrusion and the sidewall of the loading cylinder housing facing away from the hydrate deposit form a closed loading cylinder. The loading cylinder is provided with a loading liquid inlet. When the loading liquid flows into the loading cylinder through the loading liquid inlet, it pushes the loading rod with the annular protrusion toward the hydrate deposit. The loading rod pushes the pressure head toward the hydrate deposit, thereby achieving integrated loading of the hydrate deposit.

[0075] During the assembly process of the loading rod and the loading cylinder housing, a certain amount of lubricating oil is applied to play a sealing and lubricating role to ensure that the loading rod can move up and down in the loading cylinder housing.

[0076] The entire device is equipped with integral loading sections at the top and bottom. In this embodiment, the integral loading section at the top of the device comprises an upper loading cylinder housing 227. The annular protrusion of the upper loading rod 221 and the upper loading cylinder housing 227 form an upper loading cylinder 228. An upper inlet 230 is provided on the upper loading cylinder 228. Loading fluid flows into the upper loading cylinder 228 through the upper inlet 230, pushing the upper loading rod 221 and the upper pressure head 218 toward the hydrate-containing sediment.

[0077] The integrated loading section at the bottom of the device consists of a lower loading cylinder housing 210. The annular protrusion of the lower loading rod 24 and the lower loading cylinder housing 210 form a lower loading cylinder 211. A loading liquid lower inlet 215 is provided in the lower loading cylinder 211. Loading liquid flows into the lower loading cylinder 211 through the loading liquid lower inlet 215, pushing the lower loading rod 24 and the lower pressure head 21 toward the hydrate-containing sediment. The simultaneous operation of the integrated loading sections above and below the hydrate-containing sediment achieves integrated loading of the hydrate-containing sediment.

[0078] The propulsion module includes shear blocks, one at each end of the hydrate-containing sediment. A groove is provided on the side of the pressure head facing the hydrate-containing sediment, within which the shear blocks slide, allowing them to directly contact the hydrate-containing sediment. The upper and lower shear blocks are asymmetrically positioned, so when they are simultaneously applied to the hydrate-containing sediment, asymmetric localized shearing of the sediment is achieved.

[0079] In this embodiment, an upper shear block 219 is positioned above the hydrate-containing sediment. The upper shear block 219 is slidably disposed within a groove in an upper pressure head 218 and contacts the upper surface of the hydrate-containing sediment. A lower shear block 22 is positioned below the hydrate-containing sediment. The lower shear block 22 is slidably disposed within a groove in a lower pressure head 21 and contacts the upper surface of the hydrate-containing sediment. The upper shear block 219 and the lower shear block 22 are positioned asymmetrically.

[0080] The local loading section includes a thrust piston and a thrust cylinder housing. The thrust cylinder housing is located between the loading cylinder housing and the autoclave body. One end of the thrust cylinder housing is fixedly connected to the autoclave body, while the other end of the thrust cylinder housing is fixedly connected to the loading cylinder housing via a thrust cylinder base. The thrust piston is reciprocally disposed within the thrust cylinder housing. A thrust cylinder is formed between one end of the thrust piston and the thrust cylinder base, while the other end of the thrust piston is disposed within the autoclave body and contacts the shear block. A high-pressure liquid inlet is provided on the thrust cylinder base, which is connected to the thrust cylinder. After the high-pressure liquid enters the thrust cylinder through the high-pressure liquid inlet, it pushes the thrust piston toward the hydrate-containing sediment, pulling in the piston to push the shear block toward the hydrate-containing sediment, thereby achieving local loading of the hydrate-containing sediment. When the upper and lower shear blocks simultaneously move toward the hydrate-containing sediment, asymmetric shearing of the hydrate-containing sediment is achieved.

[0081] The loading rod is arranged through the propulsion cylinder base and the propulsion piston. In this application, the middle parts of the propulsion cylinder base and the propulsion piston are provided with through holes, and the loading rod is slidably arranged in the through holes, and the loading rod can reciprocate in the through holes.

[0082] A centralizer is also fixed to the thrust cylinder housing, and the inner end of the centralizer contacts the outer surface of the thrust piston, thereby guiding the reciprocating movement of the thrust piston.

[0083] In this embodiment, an upper thrust cylinder housing 224 is disposed between the upper loading cylinder housing 227 and the upper end of the autoclave body 11. The upper end of the upper thrust cylinder housing 224 is fixedly connected to the upper loading cylinder housing 227 via an upper thrust cylinder base 226, while the lower end of the upper thrust cylinder housing 224 is fixedly connected to the upper end cover 15 of the autoclave body. An upper thrust piston 222 is disposed within the upper thrust cylinder housing 224 and is capable of reciprocating up and down within the upper thrust cylinder housing 224. An upper thrust cylinder 223 is formed between the upper end of the upper thrust piston 222 and the upper thrust cylinder base 226. The lower end of the upper thrust piston 222 extends into the autoclave body and contacts the upper shear block 219.

[0084] An upper centralizer 225 is fixed on the upper thrust piston 222 . The upper centralizer 225 contacts the outer surface of the upper thrust piston 222 . During the reciprocating movement of the upper thrust piston 222 , the upper centralizer plays a guiding role.

[0085] A high-pressure liquid upper inlet 229 is provided on the upper thrust cylinder base 226, and the high-pressure liquid upper inlet 229 is connected to the upper thrust cylinder 223. After the high-pressure liquid enters the upper thrust cylinder 223 through the high-pressure liquid upper inlet 229, it pushes the upper thrust piston 222 to move downward, thereby pushing the upper shear block 219 to move toward the hydrate-containing sediment.

[0086] The upper loading rod 221 passes through the upper propulsion cylinder base 226 and the upper propulsion piston 222 in sequence, and the upper loading rod 221 can reciprocate in the upper propulsion cylinder base and the upper propulsion piston.

[0087] A lower thrust cylinder housing 27 is disposed between the lower loading cylinder housing 210 and the upper end of the autoclave body 11. The lower end of the lower thrust cylinder housing 27 is fixedly connected to the lower loading cylinder housing 210 via a lower thrust cylinder base 29, while the upper end of the lower thrust cylinder housing 27 is fixedly connected to the lower end cover 16 of the autoclave body. A lower thrust piston 25 is disposed within the lower thrust cylinder housing 27 and is capable of reciprocating up and down within the lower thrust cylinder housing 27. A lower thrust cylinder 26 is formed between the upper end of the lower thrust piston 25 and the lower thrust cylinder base 29. The upper end of the lower thrust piston 25 extends into the autoclave body and contacts the lower shear block 22.

[0088] A lower centralizer 28 is fixed on the lower thrust piston 25 . The lower centralizer 28 contacts the outer surface of the lower thrust piston 25 . During the reciprocating movement of the lower thrust piston 25 , the lower centralizer plays a guiding role.

[0089] A high-pressure liquid inlet 212 is provided on the lower thrust cylinder base 29, and the high-pressure liquid inlet 212 is connected to the lower thrust cylinder 26. After the high-pressure liquid enters the lower thrust cylinder 26 through the high-pressure liquid inlet 212, it pushes the lower thrust piston 25 to move upward, thereby pushing the lower shear block 22 to move toward the hydrate-containing sediment.

[0090] The lower loading rod 24 is sequentially arranged through the lower propulsion cylinder base 29 and the lower propulsion piston 25, and the lower loading rod 24 can reciprocate in the lower propulsion cylinder base and the lower propulsion piston.

[0091] The loading liquid upper inlet 230 is connected to the No. 3 high-pressure pump 233 via a high-pressure pipeline. A No. 3 valve 232 is installed on the high-pressure pipeline connecting the loading liquid upper inlet 230 and the No. 3 high-pressure pump 23. The high-pressure liquid upper inlet 229 is connected to the No. 4 high-pressure pump 235 via a high-pressure pipeline. A No. 4 valve 234 is installed on the high-pressure pipeline connecting the high-pressure liquid upper inlet 229 and the No. 4 high-pressure pump 235.

[0092] The loading liquid submersible inlet 215 is connected to the second high-pressure pump 217 via a high-pressure pipeline. A second valve 216 is installed on the high-pressure pipeline connecting the loading liquid submersible inlet 217 and the second high-pressure pump 217. The high-pressure submersible inlet 212 is connected to the first high-pressure pump 214 via a high-pressure pipeline. A first valve 213 is installed on the high-pressure pipeline connecting the high-pressure submersible inlet 212 and the first high-pressure pump 214.

[0093] The No. 1 high-pressure pump 214, the No. 2 high-pressure pump 217, the No. 3 high-pressure pump 233 and the No. 4 high-pressure pump 235 are respectively connected to the liquid storage tank 236 through high-pressure pipelines. The liquid storage tank 236 injects a certain amount of high-pressure liquid into the lower thrust cylinder 26, the lower loading cylinder 211, the upper thrust cylinder 223 and the upper loading cylinder 228 respectively to achieve axial loading of the hydrate-containing sediment 14, including overall loading and local loading.

[0094] The loading rod and pressure head are both equipped with flow channels in the middle of their axis, which are connected to the permeability testing system. Fluid provided by the permeability testing system is injected into the hydrate-bearing sediment through the lower flow channel and exits through the upper flow channel, testing the permeability changes of the sediment under different deformation conditions.

[0095] In this embodiment, a lower flow channel 23 is provided in the center of the lower loading rod 24 and the lower pressure head 21. The flow channel opening on the lower loading rod 24 is an inflow interface 47. The fluid provided by the permeability testing system is injected into the lower flow channel 23 through the inflow interface 47 and injected into the hydrate-containing sediment.

[0096] An upper flow channel 220 is provided at the center of the upper loading rod 221 and the upper pressure head 218 , and the flow channel opening on the upper loading rod 221 is an outflow interface 48 .

[0097] The permeability testing system includes a cryogenic water tank 41, which is connected to the inlet port 47 of the lower loading rod via a connecting pipeline. The connecting pipeline between the cryogenic water tank 41 and the inlet port 47 is equipped with a sixth high-pressure pump 42, a sixth valve 43, a first flowmeter 44, a second pressure gauge 45, and a second thermometer 46. The outflow port of the upper loading rod 221 is equipped with an outflow pipeline, which is equipped with a third pressure gauge 49, a back-pressure valve 410, and a second flowmeter 411. Cryogenic fluid provided by the cryogenic water tank 41 flows through the connecting pipeline into the lower flow channel 23 and is then injected into the hydrate-containing sediment 14. After exiting the hydrate-containing sediment 14, it is discharged along the upper flow channel 220. The outflow port 48 is connected to a third pressure gauge 49 and a back-pressure valve 410, and finally, the fluid is measured by the second flowmeter 411 before being discharged into a specific container. Parameters such as the inflow volume, temperature, and pressure at a specific time are simultaneously recorded. The permeability testing system is used to test the permeability change pattern of sediments under different deformation conditions.

[0098] The temperature of the injected liquid can be controlled by setting the initial temperature of the low-temperature water tank 41 and adjusting the flow rate of high-pressure pump 42. During the experiment, the injected liquid temperature should be kept below the hydrate phase equilibrium temperature in the hydrate-bearing sediment to prevent hydrate decomposition. The low-temperature fluid in the low-temperature water tank 41 is primarily distilled or purified water.

[0099] The upper pressure head 218 and the upper loading rod 221 are both provided with gas passages 231 that are interconnected, and the gas passages 231 are connected to the gas supply system.

[0100] The gas supply system includes a gas cylinder 51, which is connected to the gas channel 231 via a gas pipeline. This provides a gas source for the preparation of the hydrate-containing sediment 14. The gas pipeline is equipped with a valve 52, a flowmeter 53, and a pressure gauge 54. The gas cylinder 51 contains high-pressure gas, which the gas supply system delivers to the autoclave, providing the gas required for hydrate synthesis and maintaining stable pore pressure.

[0101] A CT scanning system is installed outside the autoclave. It includes a radiation source 61 and a radiation detector 62. The autoclave system is located between the radiation source 61 and the radiation detector 62, scanning the hydrate-containing sediment 14 within the autoclave system. The radiation source 61 and radiation detector 62 also work in conjunction with a connector 63 and a turntable 64 to scan and analyze the microstructure of the hydrate-containing sediment 14. The turntable 64 is located below the autoclave system and is connected to the lower loading rod 24 above it via the connector 63. Rotating the turntable 64 drives the hydrate-containing sediment 14 within the autoclave system to rotate at a constant speed.

[0102] The data processing system includes a computer 71 and a data processor 72. The data processing system is connected to the high-pressure reactor system, axial loading-shear system, temperature and confining pressure control system, permeability test system, gas supply system, and CT scanning system through data lines to realize the control of each system and the monitoring and recording of experimental data.

[0103] The present invention also includes a method for testing microstructural changes of hydrate-containing sediments using the above device, comprising the following steps.

[0104] The first step is air tightness check.

[0105] Connect the entire device, flush a certain amount of nitrogen into the device and keep it constant, observe the pressure changes in the device. If there is no obvious pressure drop, it means that the airtightness of the entire device is good.

[0106] The second step is sample preparation and pre-consolidation.

[0107] A certain amount of deionized water and sediment is thoroughly mixed and placed inside a rubber sleeve 12. The mixture is then fully compacted. The required volume of deionized water is calculated based on the target hydrate saturation and sediment porosity. An axial load-shear system is used to apply axial stress to the target value and maintain it for a specified period of time to complete the consolidation process.

[0108] The third step is hydrate synthesis.

[0109] Using the temperature and confining pressure control system, the initial temperature of the low-temperature water bath 31 is set to maintain the temperature of the confining pressure liquid at a certain value. The pump pressure and flow rate of the No. 5 high-pressure pump 32 are set to circulate the confining pressure liquid into the confining pressure chamber 13, maintain the sediment temperature below the phase equilibrium temperature, maintain the sediment temperature and pore pressure unchanged, and synthesize the hydrate-containing sediment 14 in situ.

[0110] The fourth step is mechanical testing of hydrate-containing sediments.

[0111] Keeping the temperature and pressure of the fluid in the confining pressure chamber 13 unchanged, first control the No. 2 high-pressure pump 217 to inject loading liquid into the lower loading cylinder 211, pushing the lower loading rod 24 to move toward the hydrate-containing sediment. At the same time, control the No. 3 high-pressure pump 233 to inject loading liquid into the upper loading cylinder 228, pushing the upper loading rod 221 to move toward the hydrate-containing sediment 14, and apply axial loads to the hydrate-containing sediment 14 through the lower pressure head and the upper pressure head respectively, keeping a certain load unchanged.

[0112] High-pressure pump No. 1 214 was then controlled to inject high-pressure fluid into the lower thrust cylinder 26, which in turn pushed the lower shear block 22 toward the hydrate-bearing sediment via the lower thrust piston 25. High-pressure pump No. 4 234 was then controlled to inject high-pressure fluid into the upper thrust cylinder 223, which in turn pushed the upper shear block 219 toward the hydrate-bearing sediment via the upper thrust piston 222, simulating the shear failure process of the hydrate-bearing sediment. During the test, parameters such as axial load, displacement, temperature, and pressure were recorded in real time to determine the mechanical properties of the hydrate-bearing sediment 14.

[0113] The calculation formula of the deviatoric stress σ* of hydrate-containing sediments is:

[0114]

[0115] Where N is the axial load, S is the sediment cross-sectional area, ε is the axial strain, and σ3 is the confining pressure.

[0116] Step 5: Permeability test of hydrate-containing sediments under deformation conditions.

[0117] Maintain the state of the hydrate-containing sediment 14 and adjust the set temperature of the low-temperature water tank 41 to ensure that the internal fluid temperature is below the hydrate phase equilibrium temperature to prevent hydrate decomposition. Maintain the temperature and pressure of the fluid in the confining pressure chamber 13. Set the pump pressure and flow rate of the No. 6 high-pressure pump 42 so that the low-temperature fluid enters the hydrate-containing sediment 14 through the lower flow channel 23 and then exits through the upper flow channel 220. Monitor the temperature and pressure of the fluid at the inlet port 47 in real time using the No. 2 pressure gauge 45 and the No. 2 thermometer 46. Record the flow rate data of the fluid used for permeability testing at the inlet and outlet using the No. 1 flowmeter 44 and the No. 2 flowmeter 411, respectively.

[0118] The calculation formula for the permeability k of hydrate-containing sediments is:

[0119]

[0120] Where Q is the volume flow rate of the fluid, μ is the fluid viscosity, L is the sediment length, P i is the pressure value at the inflow interface; P o is the pressure value at the outflow interface.

[0121] Step 6: Detection of the microstructure of hydrate-containing sediments.

[0122] The turntable 64 is adjusted to place the hydrate-containing sediment 14 at a suitable position between the radiation source 61 and the radiation detector 62. The hydrate-containing sediment 14 is scanned and reconstructed at a specific moment. The microstructural changes of the hydrate-containing sediment 14 under the seepage-deformation coupling effect are analyzed to explore its deformation and failure mechanism.

[0123] Step 7: End the experiment and organize the equipment.

[0124] The high-pressure gas in the hydrate-containing sediment 14 is released, the confining pressure liquid in the confining pressure chamber 13 is discharged, the axial loading-shear system is adjusted, the hydrate-containing sediment 14 is unloaded, the device is disassembled, and the equipment is sorted.

[0125] The above is a detailed introduction to the device and method for testing the micro-deformation of hydrate sediments under stress-seepage coupling provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only intended to help understand the methods and core concepts of the present invention. It should be noted that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications may be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A stress-seepage coupled hydrate sediment micro-deformation testing device, comprising a high-pressure reactor system with axial loading-shear systems installed at both ends of the high-pressure reactor system, characterized by: The axial loading-shearing system includes a propulsion module for shearing a local sample and a loading module for loading different stresses on the entire sample. The loading module is connected to the overall loading part, and the propulsion module is connected to the local loading part.

2. The stress-seepage coupling hydrate sediment micro-deformation testing device according to claim 1 is characterized in that: Loading modules include: a loading rod, one end of which is located outside the autoclave system and the other end of which is movably disposed inside the autoclave system; A pressure head is provided between the loading rod and the hydrate-containing sediment, and the loading rod acts on the hydrate-containing sediment through the pressure head.

3. The stress-seepage coupling hydrate sediment micro-deformation testing device according to claim 2 is characterized in that: The propulsion module includes shear blocks, and shear blocks are respectively provided at the upper and lower ends of the hydrate-containing sediment; A groove is provided on the side of the pressure head facing the hydrate-containing sediment, and the shear block is slidably arranged in the groove, and the shear block directly contacts the hydrate-containing sediment; The upper and lower shear blocks are arranged asymmetrically to achieve asymmetric local shearing of hydrate-containing sediments.

4. The stress-seepage coupling hydrate sediment micro-deformation testing device according to claim 2 is characterized in that: The overall loading unit includes: The loading cylinder housing has an annular protrusion on the annular outer side of the loading rod, the annular protrusion is slidably arranged in the loading cylinder housing, and the side wall of the annular protrusion is dynamically sealed with the corresponding inner wall of the loading cylinder housing; The loading cylinder is formed between the annular protrusion and the side wall of the loading cylinder shell facing away from the hydrate-containing sediment, and a closed loading cylinder is provided on the loading cylinder.

5. The stress-seepage coupling hydrate sediment micro-deformation testing device according to claim 3 is characterized in that: The local loading section includes: The propulsion cylinder housing is located between the loading cylinder housing and the autoclave body, one end of the propulsion cylinder housing is fixedly connected to the autoclave body, and the other end of the propulsion cylinder housing is fixedly connected to the loading cylinder housing through the propulsion cylinder base; The propulsion piston is reciprocatingly arranged in the propulsion cylinder housing, and a propulsion cylinder is formed between one end of the propulsion piston and the propulsion cylinder base. The other end of the propulsion piston is arranged in the autoclave body and contacts the shear block. A high-pressure liquid inlet is provided on the propulsion cylinder base, and the high-pressure liquid inlet is connected to the propulsion cylinder.

6. The stress-seepage coupling hydrate sediment micro-deformation testing device according to claim 1, characterized in that: The high pressure reactor system includes: The top of the autoclave is sealed with an upper end cover, and the bottom of the autoclave is sealed with a lower end cover. The upper and lower end covers are connected to a permeability testing system. A CT scanning system is provided on the outside of the autoclave. The rubber sleeve is arranged in the cylindrical cavity of the autoclave body, and contains hydrate-containing sediments. The rubber sleeve and the autoclave body are coaxially arranged. A confining pressure cavity is formed between the annular outer wall of the rubber sleeve and the annular inner wall of the autoclave body. The confining pressure cavity is connected to the temperature and confining pressure control system.

7. The stress-seepage coupling hydrate sediment micro-deformation testing device according to claim 1 is characterized in that: The pressure head and loading rod above the high-pressure reactor system are both provided with interconnected gas channels, which are connected to the gas supply system; The gas supply system transports high-pressure gas to the high-pressure reactor system through the gas channel to provide the gas required for hydrate synthesis.

8. The stress-seepage coupling hydrate sediment micro-deformation testing device according to claim 1, characterized in that: A flow channel is provided in the axial middle of the loading rod and the pressure head, and the flow channel is connected to the permeability test system; The fluid provided by the permeability testing system is injected into the hydrate-containing sediment through the loading rod and flow channel in the pressure head below the high-pressure reactor system, and flows out through the loading rod and flow channel in the pressure head above the high-pressure reactor system to test the permeability change pattern of the sediment under different deformation conditions.

9. A method for testing hydrate sediment micro-deformation using the stress-seepage coupling testing device according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Air tightness check; S2, specimen preparation and pre-consolidation; S3, hydrate synthesis; S4. Mechanical testing of hydrate sediments: Inject loading fluid into the loading cylinder, push the loading rod toward the hydrate sediment, and apply axial load to the hydrate sediment simultaneously above and below the hydrate sediment through the pressure head; High-pressure fluid is injected into the thrust cylinder, and the thrust piston pushes the shear block toward the hydrate-bearing sediment. The upper and lower shear blocks simulate the shear failure process of the hydrate-bearing sediment. S5. Permeability test of hydrate-containing sediments under deformation conditions; S6. Microstructural detection of hydrate-bearing sediments; S7. End the experiment and organize the equipment.

10. The method according to claim 9, characterized in that In step S4, the calculation formula for the deviatoric stress σ* of the hydrate-containing sediment is: Where N is the axial load, S is the sediment cross-sectional area, ε is the axial strain, and σ3 is the confining pressure; In step S5, the calculation formula for the permeability k of the hydrate-containing sediment is: Where Q is the volume flow rate of the fluid, μ is the fluid viscosity, L is the sediment length, P i is the pressure value at the inflow interface; P o is the pressure value at the outflow interface.

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