Hydrate sediment sample preparation and mechanical property testing device and method

Abstract

The invention provides a hydrate sediment sample preparation and mechanical property testing device and method. The hydrate sediment sample preparation and mechanical property testing device comprises a base, a base, a jacking force application assembly, a plurality of annular assemblies, a water pipe branch and an air pipe branch. The base is arranged above the base and is connected with the base in a sliding manner; a shearing rod is arranged on one side of the base in the horizontal direction. The annular assemblies are arranged above the base, and a columnar cavity is defined by the annular assemblies and used for providing a filling space for a hydrate sample; the height of the columnar cavity is smaller than the radius of the columnar cavity, so that the length-diameter ratio of the hydrate sample is smaller than or equal to 1; the water pipe branch and the air pipe branch are respectively communicated with the columnar cavity; and the jacking force application assembly is arranged above the annular assembly. According to the invention, by arranging the equipment with small length-diameter ratio, the length-diameter ratio of the prepared hydrate sediment sample is ensured to be small, so that the permeation efficiency of gas and moisture in the sample is higher, and the distribution of hydrate in the sediment is more uniform.

Description

Technical Field

[0001] The present invention relates to the technical field of natural gas hydrate exploration, and in particular to a device and method for preparing a hydrate sediment sample and testing mechanical properties. Background Art

[0002] Natural gas hydrate is an ice-like cage formed by water and gas (mainly methane) under high pressure and low temperature conditions. It is mainly distributed in deep sea and permafrost areas. Due to its huge reserves, it is considered a potential energy source. However, the exploitation of natural gas hydrate faces many problems. The uncontrollable decomposition of hydrates during the exploitation process will lead to a decrease in the shear strength of hydrate sediments, which may lead to submarine landslides. Therefore, in-depth research on the engineering mechanical properties of hydrate-containing soils is a prerequisite for the safe exploitation of natural gas hydrates.

[0003] The in-situ test method is expensive and difficult to test mechanical properties. The current internationally accepted method is to conduct research by synthesizing hydrates indoors. The most commonly used equipment is the high-pressure and low-temperature triaxial instrument. This type of equipment has been used to conduct many studies on the mechanical properties of sandy hydrates at home and abroad, and many valuable results have been achieved. However, more than 90% of the total amount of hydrates in the world is stored in clay silt or silt sediments on the seabed. Therefore, it is more valuable to study the mechanical properties of muddy silt hydrates. However, the biggest difficulty faced by the mechanical property test of muddy silt hydrates is the preparation of hydrate samples. Low permeability is one of the main differences between muddy silt hydrates and sandy hydrates. It is very difficult to prepare muddy silt high-pressure and low-temperature triaxial samples using traditional hydrate preparation methods such as saturated water and saturated gas. The efficiency of methane gas ventilation in the process of traditional saturated water and saturated gas sample preparation is low, and the saturation of the prepared samples is not high, and it is easy to cause hydrates to form at the inlet end, while no hydrates are generated at the far end. This is mainly due to the low permeability of muddy silt sand hydrate and the large aspect ratio of the existing high-pressure and low-temperature triaxial instrument. Tetrahydrofuran (THF) hydrate has also been used to study the mechanical properties of hydrates. Since THF is a water-soluble liquid, it is easier to prepare hydrates with it, and the mechanical properties of the prepared hydrates are consistent with the in-situ hydrate properties. However, because THF is a liquid, it is impossible to carry out mechanical property research on hydrate decomposition. In view of the above reasons, it is very necessary to develop new low-permeability muddy silt sand hydrate sample preparation and mechanical property testing technologies. Summary of the invention

[0004] In view of this, the present invention proposes a hydrate sediment sample preparation and mechanical property testing device and method, aiming to solve the technical problems in the prior art that the efficiency of muddy silt hydrate sample preparation is low and the generated hydrate is unevenly distributed.

[0005] In one aspect, the present invention provides a hydrate sediment sample preparation and mechanical property testing device, comprising: a base, a pedestal, a top pressure force component, a plurality of annular components, a water pipe branch and an air pipe branch; wherein,

[0006] The base is arranged above the pedestal and is slidably connected to the pedestal; a shear rod is arranged on one side of the base in a horizontal direction to apply a shear force to the hydrate sample;

[0007] Each of the annular components is arranged above the base and encloses a columnar cavity to provide a filling space for the hydrate sample; the height of the columnar cavity is smaller than the radius of the columnar cavity, so that the aspect ratio of the hydrate sample is ≤1;

[0008] The water pipe branch and the air pipe branch are respectively connected to the columnar cavity, and are used to inject water and drain water, and inject air and exhaust air into the columnar cavity to prepare the hydrate sample;

[0009] The top pressure force application component is arranged above the annular component to form a closed cavity with the annular component and apply force to the hydrate sample.

[0010] Furthermore, in the above-mentioned hydrate sediment sample preparation and mechanical property testing device, the top pressure force application component includes: a vertical loading rod and a top cover connected to each other; wherein,

[0011] The top cover is arranged toward the top opening of the annular assembly, and the vertical loading rod is arranged above the top cover.

[0012] Furthermore, in the above-mentioned hydrate sediment sample preparation and mechanical property testing device, the water pipe branch includes: a water injection pipe section and a drainage pipe section; wherein,

[0013] The inlet end of the water injection pipe section is connected to the water source, and the outlet end of the water injection pipe section is connected to the inlet of the first pipeline in the base; the inlet end of the drainage pipe section is connected to the second pipeline in the top pressure force component, and the water injection pipe section is provided with a water injection valve and a water injection meter; the outlet end of the drainage pipe section is connected to the discharge end, and the drainage pipe section is provided with a drainage valve and a drainage meter.

[0014] Furthermore, in the above-mentioned hydrate sediment sample preparation and mechanical property testing device, a clay plate is provided on the drainage pipe section upstream of the drainage meter to prevent gas discharge.

[0015] Furthermore, in the above-mentioned hydrate sediment sample preparation and mechanical property testing device, the air pipe branch includes: an air injection pipe section and an exhaust pipe section; wherein,

[0016] The inlet end of the gas injection pipe section is connected to the gas source, the outlet end of the gas injection pipe section is connected to the inlet of the first pipeline in the base, and the gas injection pipe section is provided with a gas injection valve and a gas injection meter; a second pipeline is provided in the top pressure force component, the inlet end of the second pipeline is connected to the outlet end of the first pipeline, the inlet end of the exhaust pipe section is connected to the outlet end of the second pipeline, and the exhaust pipe section is provided with an exhaust valve and an exhaust meter.

[0017] Furthermore, in the above-mentioned hydrate sediment sample preparation and mechanical property testing device, a first heat conduction pipe is also provided in the top pressure force application component, and a second heat conduction pipe is provided in the base, and the first heat conduction pipe and the second heat conduction pipe are both connected to an external temperature control device.

[0018] Furthermore, the above-mentioned hydrate sediment sample preparation and mechanical property testing device also includes: a heat insulation cover; wherein,

[0019] The pedestal, the base, each of the annular components and the top pressure force component are all placed in the heat insulation cover, the vertical loading rod of the top pressure force component vertically passes through the heat insulation cover, and the heat insulation cover is also filled with silicone oil.

[0020] The hydrate sediment mechanical property testing device of the present invention ensures that the prepared hydrate sediment sample has a smaller aspect ratio by setting a device with a smaller aspect ratio, so that the penetration efficiency of gas and water in the sample is faster and the distribution of hydrate in the sediment is more uniform.

[0021] On the other hand, the present invention also proposes a method for testing the mechanical properties of hydrate sediments, comprising the following steps: Step 1, calculating the mass m of dry soil required in the hydrate sediment to be prepared according to the required saturation and particle component content percentage; sd and the volume of water V w1 ;

[0022] Step 2: For sediments with a high clay content, the required dry soil and an appropriate amount of water are prepared in advance, the volume of the prepared water being greater than the water content in the hydrate sample to be prepared, the dry soil is evenly sprinkled into the sample preparation device, filter paper and permeable stone are laid on the upper end cover of the sample preparation device, and pre-compression and consolidation are performed for a preset time to keep the soil sample at a high compressibility and permeability;

[0023] Step 3: Take the soil sample out of the sample preparation device and directly put it into the film holding tube and weigh it. The weight of the soil sample can be calculated based on the weight of the film holding tube and the latex film. sw , the volume of water in the soil sample V can be calculated based on the weight of the soil sample and the weight of the dry soil w ;

[0024] Step 4, after the base and the top cover in the top pressure force component are filled with water and exhausted, the latex film containing the soil sample is sealed with the base and the top cover and then placed in the columnar cavity surrounded by each of the annular components;

[0025] Step 5, adjusting the stress and strain of the shear rod and the vertical loading rod of the top pressure force component to zero, and exhausting the impurity gas in each circuit. After the impurities are exhausted, the water injection and gas injection circuit and the water drainage and exhaust circuit are connected to the base and the top pressure force component respectively;

[0026] Step 6, start the top pressure force application component, and apply a vertical load to the hydrate sample according to the temperature-pressure phase equilibrium relationship of the gas component hydrate; after the vertical load is applied to a specified value, change the vertical loading rod of the top pressure force application component from force control to displacement control, and keep the position unchanged;

[0027] Step 7: Start injecting gas into the cylindrical cavity and measure the injected gas volume Va in real time. in , Exhaust volume value Va out and the discharge water value V wout , until V w1≥ V w- V wout , close the air injection valve, drain valve and exhaust valve, open the water injection valve and continue to inject water until the water volume is V wout At this time, the methane gas that had not formed hydrates before has formed hydrates, and the volume of gas in the formed hydrate is Va in -Va out The hydrate saturation can be calculated according to Va1=Va in -Va out Perform calculations;

[0028] Step 8, close the water injection valve, open the gas injection valve, the drain valve and the exhaust valve, repeat steps 7 and 8 until the saturation reaches the required value, and obtain a hydrate sample;

[0029] Step 9, the vertical loading rod of the top pressure force assembly is still set to displacement control, the water is drained, and the vertical loading rod is slowly moved downward, and the moving speed is controlled at a strain rate of 0.5% / hour. At the same time, the temperature value is increased according to the axial pressure value and the temperature-pressure phase equilibrium relationship of the hydrate, so that the temperature-pressure relationship of the soil sample is always on the phase equilibrium critical line;

[0030] Step 10: After reaching the set sample height, stop the movement of the vertical loading rod and measure the drainage volume until the volume of water in the sample reaches V w , stop draining, and after stabilizing for a period of time, prepare to start the sample shear test;

[0031] Step 11, during the shear test, the vertical loading rod is adjusted to displacement control, the air inlet valve, the exhaust valve, the water inlet valve, and the drain valve are closed, the vertical displacement, the shear displacement, the vertical force, and the shear force are recorded, and the hydrate sample is sheared by the shear rod, and the shear speed is controlled at a shear strain rate of 5% / hour. The sample is sheared continuously until the shear strain reaches 20% or the shear force drops to less than 80% of the maximum value, and the shearing is stopped. During this process, the vertical displacement, shear displacement, vertical force, and shear force are measured and recorded in real time;

[0032] Step 12, analyzing the hydrate sample according to the vertical displacement, shear displacement, vertical force, shear force and other data recorded during the shearing process, drawing vertical and transverse stress-strain relationship curves, so as to determine the shear strength and other mechanical properties of the hydrate sample.

[0033] Furthermore, in the above mechanical property testing method, the volume of the pre-prepared water is twice the water content in the hydrate sample to be prepared.

[0034] Furthermore, in the above mechanical property testing method, the consolidation pressure is 5-10 kPa, and the preset time is greater than or equal to 24 hours.

[0035] The method for testing the mechanical properties of hydrate sediments provided by the present invention first prepares a soil sample with high water content and high porosity, and adjusts the temperature and pressure according to the temperature and pressure phase equilibrium relationship during the aeration process, and keeps the volume unchanged during the whole process, thereby fully increasing the content of combustible ice in the sediment sample. The saturation of the hydrate sample can be effectively improved by optimizing the equipment and test methods, and the uniformity of the hydrate distribution in the sediment can be improved; at the same time, the stress state of the hydrate sample during the shear test using the equipment is closer to the state of the hydrate in the actual formation, which effectively ensures the accuracy of the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0037] Figure 1 A schematic diagram of the initial state structure of a hydrate sediment sample preparation and mechanical property testing device provided by an embodiment of the present invention;

[0038] Figure 2 A schematic diagram of the structure of the hydrate sediment sample preparation and mechanical property testing device provided in an embodiment of the present invention shearing the hydrate sample;

[0039] Figure 3A schematic structural diagram of a drainage pipe section and an exhaust pipe section in a hydrate sediment sample preparation and mechanical property testing device provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to be able to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0041] Device Example:

[0042] See also Figure 1 and Figure 2 The hydrate sediment sample preparation and mechanical property testing device of the embodiment of the present invention comprises: a base 1, a base 2, a top pressure force component 3, a plurality of annular components 4, a water pipe branch 5 and an air pipe branch 6; wherein the base 2 is arranged above the base 1 and is slidably connected to the base 1; a shear rod 7 is arranged on one side of the base 2 in the horizontal direction to apply a shear force to the hydrate sample; each of the annular components 4 is arranged above the base 2 and is surrounded by a columnar cavity to provide a filling space for the hydrate sample; the height of the columnar cavity is less than the radius of the columnar cavity so that the aspect ratio of the hydrate sample is ≤1; the water pipe branch 5 and the air pipe branch 6 are respectively connected to the columnar cavity 10 to inject water and drain water and inject gas and exhaust gas into the columnar cavity to prepare the hydrate sample; the top pressure force component 3 is arranged above the annular component 4 to form a closed cavity with the annular component 4 and apply a force to the hydrate sample.

[0043] Specifically, the height of the columnar cavity formed by each of the annular components 4 is smaller than the radius of the columnar cavity, which can make the aspect ratio of the prepared hydrate sample ≤1, which is more conducive to the penetration of gas and water, thereby improving the saturation and distribution uniformity of the hydrate in the sample and greatly improving the efficiency of sample preparation.

[0044] The base 1 may be a square structure, the base 2 may be a disc structure, and the base 1 and the base 2 may be made of metal materials with high hardness and high thermal conductivity. A slide rail 9 is provided between the top of the base 1 and the bottom of the base 2, so that the base 2 slides along the base 1 driven by the shear rod 7 to achieve shearing of the hydrate sample.

[0045] The annular assembly 4 is a stacked ring, and each stacked ring may be an annular structure with the same size.

[0046] The top pressure force application component 3 includes: a vertical loading rod 31 and a top cover 32 connected to each other; wherein the top cover 32 is arranged toward the top opening of the annular component 4 , and the vertical loading rod 31 is arranged above the top cover 32 .

[0047] Specifically, the top cover 32 may be a circular structure, and its diameter may be adapted to the top opening of the annular assembly 4. The vertical loading rod 31 may be integrally formed with the top cover 32.

[0048] In order to communicate with the water pipe branch 5 and the gas pipe branch 6, in this embodiment, a first pipeline is arranged in the base 2, and the first pipeline may include: a first main pipeline and various first branches that are connected. The various first branches may be arranged in parallel and at intervals on the upper side of the first main pipeline.

[0049] A second pipeline is arranged in the top cover 32 of the top pressure force applying assembly 3, and the second pipeline may include: a second main pipeline and each second branch pipeline connected to each other. Each second branch pipeline may be arranged in parallel and at intervals on the lower side of the second main pipeline. The second main pipeline and the first main pipeline may be arranged symmetrically about the columnar cavity.

[0050] The top pressure component 3 is also provided with a first heat conducting pipe 33, and the base 2 is provided with a second heat conducting pipe 34, and both the first heat conducting pipe 33 and the second heat conducting pipe 34 are connected to the external temperature control device 100. The first heat conducting pipe 33 and the second heat conducting pipe 34 are respectively connected to the top cover 32 and the base 2 in the top pressure component 3, so that the base 2, the top cover 32 and the stacking ring transfer the temperature to the internal sample through temperature conduction.

[0051] The water pipe branch 5 includes: an injection pipe section 51 and a drainage pipe section 52; wherein, the inlet end of the injection pipe section 51 is connected to the water source 50, and the outlet end of the injection pipe section 51 is connected to the inlet of the first pipeline in the base 2; the inlet end of the drainage pipe section 52 is connected to the second pipeline in the top pressure force component 3, and the injection pipe section 51 is provided with an injection valve 511 and an injection meter 512; the outlet end of the drainage pipe section 52 is connected to the discharge end 520, and the drainage pipe section 52 is provided with a drainage valve 521 and a drainage meter 522.

[0052] See also Figure 3 Preferably, a clay plate 523 is provided on the drainage pipe section 52 at the upstream of the drainage meter to prevent gas discharge. In specific implementation, due to the clay plate, only water is discharged without gas discharge after the drainage valve is opened, so that the sample is consolidated by discharging water while keeping the gas from being discharged during the consolidation stage, and the hydrate content in the sample is kept unchanged because the gas cannot be discharged.

[0053] The air pipe branch 6 includes: an air injection pipe section 61 and an exhaust pipe section 62; wherein, the inlet end of the air injection pipe section 61 is connected to the air source 60, the outlet end of the air injection pipe section 61 is connected to the inlet of the first pipeline in the base 2, and the air injection pipe section 61 is provided with an air injection valve 611 and an air injection meter 612; a second pipeline is provided in the top pressure force component 3, the inlet end of the second pipeline is connected to the outlet end of the first pipeline, the inlet end of the exhaust pipe section 62 is connected to the outlet end of the second pipeline, and the exhaust valve 621 and an exhaust meter 622 are provided on the exhaust pipe section 62.

[0054] It can be clearly concluded from the above that the hydrate sediment sample preparation and mechanical property testing device provided in this embodiment ensures that the prepared hydrate sediment sample has a smaller aspect ratio by setting a device with a smaller aspect ratio, so that the penetration efficiency of gas and water in the sample is faster and the distribution of hydrates in the sediment is more uniform.

[0055] The above embodiments also include: a heat-insulating cover 8; wherein the base 1, the base 2, each of the annular components 4 and the top pressure force component 3 are all placed in the heat-insulating cover, the vertical loading rod 31 of the top pressure force component 3 vertically passes through the heat-insulating cover, and the heat-insulating cover is also filled with silicone oil 9.

[0056] Specifically, the heat preservation cover can be a square structure. An injection hole can be provided at the bottom of the heat preservation cover 9 to inject silicone oil 9. The external heat preservation cover only serves as a heat insulation. Since it will not withstand megapascal pressure, the heat preservation cover can be made of transparent materials such as acrylic glass and plastic coated with a heat preservation coating. While ensuring the safety of the test, the changes in the sample during the test can be directly seen, thereby improving the reliability of the test. The addition of silicone oil can play a role in heat preservation and uniform distribution of the sample temperature.

[0057] Method Example:

[0058] The present invention also provides a method for testing the mechanical properties of a hydrate sediment sample, comprising the following steps:

[0059] Step 1: Calculate the mass m of dry soil required in the hydrate sediment to be prepared according to the required saturation and particle component content percentage. sd and the volume of water V w1 In practice, the mass of each particle group in the hydrate sediment soil skeleton and the volume of water required can be calculated based on the required saturation and particle component content percentage.

[0060] Step 2: For sediments with a high clay content, prepare the required dry soil and an appropriate amount of water in advance. The volume of the pre-prepared water is greater than the water content in the hydrate sample to be prepared. The dry soil is evenly sprinkled into the sample preparation device, and filter paper and permeable stone are laid on the upper end cover of the sample preparation device. Pre-compression and consolidation are performed for a preset time to keep the soil sample at a high compressibility and permeability.

[0061] Specifically, the volume of the pre-prepared water is twice the water content in the hydrate sample to be prepared, which can increase the porosity of the soil sample, improve the air permeability, and increase the permeability. The consolidation pressure is 5-10kPa, and the preset time is greater than or equal to 24h, so that the water and the soil sample are evenly distributed. In practice, a pre-loading instrument or directly placing weights can be used for pre-loading consolidation.

[0062] It should be noted that, in this embodiment, sediment samples with low clay content can be directly prepared by the sand-rain method according to geotechnical test specifications.

[0063] Step 3: Take the soil sample out of the sample preparation device and directly put it into the film holding tube and weigh it. The weight of the soil sample can be calculated based on the weight of the film holding tube and the latex film. sw , the volume of water in the soil sample V can be calculated based on the weight of the soil sample and the weight of the dry soil w .

[0064] Specifically, v w =(m sw -m sd ) / ρ w , where m sw is the weight of wet soil sample, m sd is the dry soil weight, ρ w is the water density.

[0065] Step 4, after the base 2 and the top cover 32 in the top pressure force component 3 are filled with water and exhausted, the latex membrane containing the soil sample is sealed with the base 2 and the top cover 32 and then placed in the columnar cavity surrounded by each of the annular components 4;

[0066] During specific implementation, after the base 2 is filled with water to exhaust the air, the sample is loaded into the base 2 through the membrane tube. After the membrane tube is removed, the base 2 and the latex film are fastened together by an O-ring to prevent air or water leakage. Then, multiple stacked rings are placed, and the final height of the stacked rings should be slightly higher than the soil sample. After the top cover 32 is filled with water to exhaust the air, the top cover 32 is lowered to make it contact with the soil sample, and the upper top cap and the latex film are fastened together by an O-ring to prevent air or water leakage.

[0067] Step 5, adjust the stress and strain of the shear rod 7 and the vertical loading rod 31 of the top pressure force assembly 3 to zero, and discharge the impurity gas in each circuit. After the impurities are removed, connect the water injection and gas injection circuit and the water drainage and exhaust circuit to the base 2 and the top pressure force assembly 3 respectively.

[0068] In specific implementation, the stress and strain of the vertical loading rod 31 and the stress and strain of the shear rod 7 are adjusted to zero, the water injection valve and the drainage valve are opened, and water is injected to exhaust gas to exhaust the gas in the water pipeline, and the gas injection valve 611 and the exhaust pipe valve are opened to inject methane gas to exhaust the gas in the gas branch; after the zeroing and exhaust are completed, the water injection pipe section 51, the drainage pipe section 52, the gas injection pipe section 61, and the exhaust pipe section 62 are connected to the equipment, and the water injection valve, the drainage valve, the gas injection valve 611, and the exhaust valve 621 are closed. The first heat pipe 33 and the second heat pipe 34 are connected to the temperature control device, the heat insulation cover is installed, and silicone oil is injected.

[0069] Step 6, open the top pressure force application component 3, and apply a vertical load to the hydrate sample according to the temperature-pressure phase equilibrium relationship of the gas component hydrate; after the vertical load is applied to a specified value, the vertical loading rod 31 of the top pressure force application component 3 is changed from force control to displacement control, and the position is kept unchanged.

[0070] During the specific implementation, turn on the vertical loading rod 31, adjust it to force control, apply an axial load of 5kPa-10kPa, make the vertical loading rod 31 tightly combined with the sample, measure the displacement s1 of the vertical loading rod 31, and at the same time turn on the temperature control device to start cooling. The cooling temperature is controlled at 0℃-5℃, and stand for 1 hour to maintain uniform temperature distribution; then start to apply vertical force, and the size of the vertical load needs to be determined according to the temperature-pressure phase equilibrium relationship of the gas component hydrate. Taking methane hydrate as an example, when the temperature drops to 2 degrees Celsius, the axial load is applied to the critical value of 3.2MPa. The application of the axial load should be controlled at 0.5MPa / min.

[0071] After the vertical load is applied to the specified value, the vertical loading rod 31 is changed from force control to displacement control, and the position is kept unchanged, and the vertical pressure value is measured in real time, that is, the vertical loading rod 31 is kept stationary, the volume is kept constant, and the porosity is large, which is conducive to accelerating the ventilation speed.

[0072] Step 7: Start injecting gas into the cylindrical cavity and measure the injected gas volume Va in real time. in , Exhaust volume value Va out and the discharge water value V wout , until V w1≥ V w- V wout , close the air injection valve, drain valve and exhaust valve, open the water injection valve and continue to inject water until the water volume is V wout At this time, the methane gas that had not formed hydrates before has formed hydrates, and the volume of gas in the formed hydrate is Va in -Va out The hydrate saturation can be calculated according to Va1=Va in -Va outThe injected gas can be methane, carbon dioxide or other gases that can synthesize combustible ice.

[0073] In the specific implementation, the gas injection valve, the gas exhaust valve and the water discharge valve are opened, the gas injection is started and the value of the gas injection meter Vain, the value of the gas discharge meter Vaout and the value of the water discharge meter Vwout are measured in real time to facilitate the entry of methane into the soil sample. Since the volume remains unchanged, the water discharged is the compressed gas injected into the soil sample that has not formed hydrates.

[0074] Step 8, close the water injection valve, open the gas injection valve, the drain valve and the exhaust valve, repeat steps 7 and 8 until the saturation reaches the required value, and obtain a hydrate sample.

[0075] Step 9, continue to set the vertical loading rod 31 of the top pressure force assembly 3 to displacement control, start drainage, and slowly move the vertical loading rod 31 downward. The moving speed is controlled at a strain rate of 0.5% / hour. At the same time, the temperature value is increased according to the axial pressure value and the temperature-pressure phase equilibrium relationship of the hydrate, so that the temperature-pressure relationship of the soil sample is always on the phase equilibrium critical line.

[0076] During specific implementation, the vertical loading rod 31 continues to be set to displacement control, the drain valve is opened, and the vertical loading rod 31 is slowly moved downward. The moving speed is controlled at a strain rate of 0.5% / hour. At the same time, the temperature value is increased according to the axial pressure value and the temperature-pressure phase equilibrium relationship of the hydrate, so that the temperature-pressure relationship of the soil sample is always on the phase equilibrium critical line.

[0077] Step 10: After reaching the set sample height, stop the movement of the vertical loading rod and measure the drainage volume until the volume of water in the sample reaches V w , stop draining, and after stabilizing for a period of time, prepare to start the sample shear test.

[0078] Specifically, after reaching the set sample height, the vertical loading rod 31 stops moving, that is, keeps its constant height unchanged, and measures the drainage volume until the volume of water in the sample is reached, then closes the drainage valve, and prepares for shearing after stabilization for 5 hours.

[0079] Step 11, during the shear test, the vertical loading rod is adjusted to displacement control, the air inlet valve, the exhaust valve, the water inlet valve, and the drain valve are closed, the vertical displacement, shear displacement, vertical force, and shear force are recorded, and the hydrate sample is sheared by the shear rod. The shear speed is controlled at a shear strain rate of 5% / hour, and the sample is sheared continuously until the shear strain reaches 20% or the shear force drops to less than 80% of the maximum value, and the shearing is stopped. During this process, the vertical displacement, shear displacement, vertical force, and shear force are measured and recorded in real time.

[0080] The specific method of shearing is as follows: keep the air inlet valve, exhaust valve, water inlet pipe and drain pipe closed, open the shear loading rod, slowly shear, control the shear strain rate at 2% / hour, and record the axial stress, shear stress and shear strain in real time. Draw the axial stress-shear stress curve and the shear stress-shear strain curve. Shear the sample until the shear strain reaches 20% or the shear force drops 20% below the maximum value.

[0081] Step 12, analyzing the hydrate sample according to the vertical displacement, shear displacement, vertical force, shear force and other data recorded during the shearing process, drawing vertical and transverse stress-strain relationship curves, so as to determine the shear strength and other mechanical properties of the hydrate sample.

[0082] Finally, the shear modulus, shear strength, etc. of hydrate-containing sediments can be determined using soil mechanics methods based on axial stress, shear stress, and shear strain.

[0083] The related parts of the method embodiment and the above-mentioned device embodiment can be referred to each other and will not be described in detail here.

[0084] In summary, the method for testing the mechanical properties of hydrate sediments provided by the present invention first configures a soil sample with a high water content and a high porosity ratio, and adjusts the temperature and pressure according to the temperature-pressure phase equilibrium relationship during the aeration process, and keeps the volume unchanged during the entire process, thereby fully increasing the content of combustible ice in the sediment sample. The saturation of the hydrate sample can be effectively improved by optimizing the equipment and test methods, and the uniformity of the hydrate distribution in the sediment can be improved; at the same time, the stress state of the hydrate sample during the shear test using the equipment is closer to the state of the hydrate in the actual formation, which effectively ensures the accuracy of the measurement results.

[0085] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A hydrate sediment sample preparation and mechanical properties testing device, characterized in that: include: Base, pedestal, top pressure force component, multiple annular components, water pipe branch and air pipe branch; wherein, The base is arranged above the pedestal and is slidably connected to the pedestal; a shear rod is arranged on one side of the base in a horizontal direction to apply a shear force to the hydrate sample; Each of the annular components is arranged above the base and encloses a columnar cavity to provide a filling space for the hydrate sample; the height of the columnar cavity is smaller than the radius of the columnar cavity, so that the aspect ratio of the hydrate sample is ≤1; The water pipe branch and the air pipe branch are respectively connected to the columnar cavity, and are used to inject water and drain water, and inject air and exhaust air into the columnar cavity to prepare the hydrate sample; The top pressure force application component is arranged above the annular component to form a closed cavity with the annular component and apply force to the hydrate sample.

2. The hydrate sediment sample preparation and mechanical property testing device according to claim 1, characterized in that: The top pressure force application assembly includes: a vertical loading rod and a top cover connected to each other; wherein, The top cover is arranged toward the top opening of the annular assembly, and the vertical loading rod is arranged above the top cover.

3. The hydrate sediment sample preparation and mechanical property testing device according to claim 1, characterized in that: The water pipe branch includes: a water injection pipe section and a drainage pipe section; wherein, The inlet end of the water injection pipe section is connected to the water source, and the outlet end of the water injection pipe section is connected to the inlet of the first pipeline in the base; the inlet end of the drainage pipe section is connected to the second pipeline in the top pressure force component, and the water injection pipe section is provided with a water injection valve and a water injection meter; the outlet end of the drainage pipe section is connected to the discharge end, and the drainage pipe section is provided with a drainage valve and a drainage meter.

4. The hydrate sediment sample preparation and mechanical property testing device according to claim 3, characterized in that: A clay plate is provided on the drainage pipe section upstream of the drainage meter to prevent gas from being discharged.

5. The hydrate sediment sample preparation and mechanical property testing device according to claim 1, characterized in that: The tracheal branch includes: an air injection pipe section and an exhaust pipe section; wherein, The inlet end of the gas injection pipe section is connected to the gas source, the outlet end of the gas injection pipe section is connected to the inlet of the first pipeline in the base, and the gas injection pipe section is provided with a gas injection valve and a gas injection meter; a second pipeline is provided in the top pressure force component, the inlet end of the second pipeline is connected to the outlet end of the first pipeline, the inlet end of the exhaust pipe section is connected to the outlet end of the second pipeline, and the exhaust pipe section is provided with an exhaust valve and an exhaust meter.

6. The hydrate sediment sample preparation and mechanical property testing device according to claim 1, characterized in that: A first heat conducting pipe is also provided in the top pressure applying component, and a second heat conducting pipe is provided in the base. Both the first heat conducting pipe and the second heat conducting pipe are connected to an external temperature control device.

7. The hydrate sediment sample preparation and mechanical property testing device according to claim 1, characterized in that: Also includes: Insulation cover; wherein, The pedestal, the base, each of the annular components and the top pressure force component are all placed in the heat insulation cover, the vertical loading rod of the top pressure force component vertically passes through the heat insulation cover, and the heat insulation cover is also filled with silicone oil.

8. A method for performing mechanical property testing using the hydrate sediment sample preparation and mechanical property testing device according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1: Calculate the mass m of dry soil required in the hydrate sediment to be prepared according to the required saturation and particle component content percentage. sd and the volume of water V w1 ; Step 2: For sediments with a high clay content, the required dry soil and an appropriate amount of water are prepared in advance, the volume of the prepared water being greater than the water content in the hydrate sample to be prepared, the dry soil is evenly sprinkled into the sample preparation device, filter paper and permeable stone are laid on the upper end cover of the sample preparation device, and pre-compression and consolidation are performed for a preset time to keep the soil sample at a high compressibility and permeability; Step 3: Take the soil sample out of the sample preparation device and directly put it into the film holding tube and weigh it. The weight of the soil sample can be calculated based on the weight of the film holding tube and the latex film. sw , the volume of water in the soil sample V can be calculated based on the weight of the soil sample and the weight of the dry soil w ; Step 4, after the base and the top cover in the top pressure force component are filled with water and exhausted, the latex film containing the soil sample is sealed with the base and the top cover and then placed in the columnar cavity surrounded by each of the annular components; Step 5, adjusting the stress and strain of the shear rod and the vertical loading rod of the top pressure force component to zero, and exhausting the impurity gas in each circuit. After the impurities are exhausted, the water injection and gas injection circuit and the water drainage and exhaust circuit are connected to the base and the top pressure force component respectively; Step 6, start the top pressure force application component, and apply a vertical load to the hydrate sample according to the temperature-pressure phase equilibrium relationship of the gas component hydrate; After the vertical load is applied to the specified value, the vertical loading rod of the top pressure force application assembly is changed from force control to displacement control, and the position is kept unchanged; Step 7: Start injecting gas into the cylindrical cavity and measure the injected gas volume Va in real time. in , Exhaust volume value Va out and the discharge water value V wout , until V w1≥ V w- V wout , close the air injection valve, drain valve and exhaust valve, open the water injection valve and continue to inject water until the water volume is V wout At this time, the methane gas that had not formed hydrates before has formed hydrates, and the volume of gas in the formed hydrate is Va in -Va out The hydrate saturation can be calculated according to Va1=Va in -Va out Perform calculations; Step 8, close the water injection valve, open the gas injection valve, the drain valve and the exhaust valve, repeat steps 7 and 8 until the saturation reaches the required value, and obtain a hydrate sample; Step 9, the vertical loading rod of the top pressure force assembly is still set to displacement control, the water is drained, and the vertical loading rod is slowly moved downward, and the moving speed is controlled at a strain rate of 0.5% / hour. At the same time, the temperature value is increased according to the axial pressure value and the temperature-pressure phase equilibrium relationship of the hydrate, so that the temperature-pressure relationship of the soil sample is always on the phase equilibrium critical line; Step 10: After reaching the set sample height, stop the movement of the vertical loading rod and measure the drainage volume until the volume of water in the sample reaches V w , stop draining, and after stabilizing for a period of time, prepare to start the sample shear test; Step 11, during the shear test, the vertical loading rod is adjusted to displacement control, the air inlet valve, the exhaust valve, the water inlet valve, and the drain valve are closed, the vertical displacement, the shear displacement, the vertical force, and the shear force are recorded, and the hydrate sample is sheared by the shear rod, the shear speed is controlled at a shear strain rate of 5% / hour, and the sample is sheared continuously until the shear strain reaches 20% or the shear force drops to less than 80% of the maximum value, and the shearing is stopped. During this process, the vertical displacement, shear displacement, vertical force, and shear force are measured and recorded in real time; Step 12, analyzing the hydrate sample according to the vertical displacement, shear displacement, vertical force, shear force and other data recorded during the shearing process, drawing vertical and transverse stress-strain relationship curves, so as to determine the shear strength and other mechanical properties of the hydrate sample.

9. The method for testing mechanical properties of hydrate sediments according to claim 8, characterized in that: The volume of the pre-prepared water is twice the water content in the hydrate sample to be prepared.

10. The method for testing mechanical properties of hydrate sediments according to claim 8, characterized in that: The consolidation pressure is 5-10 kPa, and the preset time is greater than or equal to 24 hours.

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