Hydrate deposit sample ultragrain preparation device and method at different stratum depths, and sample stability-maintaining transfer method

Abstract

The application discloses a hydrate sediment sample preparation device and method at different stratum depths, and a sample stability-maintaining transfer method. The device comprises a sample preparation kettle placed in a constant-temperature water bath box, an axial pressure loading assembly connected with the sample preparation kettle and used for applying axial pressure load to the sediment sample, and a pore pressure generating assembly connected with a cavity in the sample preparation kettle. The preparation process comprises the following steps: preparing the sediment in the sample container; transferring the sediment sample to a centrifuge; adding axial pressure consolidation; injecting high-pressure methane gas; preparing the sample under supergravity; stopping the centrifuge and moving to liquid nitrogen; sampling under normal gravity while maintaining stability; and transferring the sample while maintaining stability. The application can simulate the preparation of hydrate-containing sediment samples under effective stress levels at different stratum depths in a laboratory supergravity environment, and can transfer the samples to a scanning electron microscope or other microscopic observation device for testing while maintaining the stability of the hydrates.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of energy engineering and geotechnical engineering, and particularly relates to a device and method for preparing hydrate sediments at different depths, and a method for transferring the prepared hydrate sediments. BACKGROUND

[0002] Natural gas hydrate is a clathrate compound formed by methane gas molecules and water molecules under low temperature and high pressure. Natural gas hydrate mainly exists in sediments under high pressure and low temperature. Natural gas hydrate has multiple modes and forms of occurrence in sediments. The main modes of occurrence include the particle extrusion mode and the pore intrusion mode. The particle extrusion mode often forms block-shaped, vein-shaped, and prism-shaped hydrates, while the pore intrusion mode forms pore filling type, particle cementation type, and particle coating type.

[0003] Geological exploration and experimental research show that the mode of occurrence of hydrate in sediments is affected by effective stress and type of sediments. In particular, in fine-grained sediments, the effective stress often becomes the main controlling factor for the mode of occurrence and form of hydrate. With the change of the burial depth of hydrate reservoirs, the effective stress of sediments changes along the depth, forming a layered hydrate distribution along the depth.

[0004] In laboratory hydrate preparation, the effective stress level in small-scale sediment models under normal gravity remains basically unchanged, and the characteristics of hydrate occurrence along the depth cannot be simulated. By using the supergravity effect of the supergravity model test, the stress field of the prototype field reservoir can be reproduced on the model scale by using a large-scale soil centrifuge. Preparing hydrate reservoir models with different occurrence characteristics on the model scale in the laboratory becomes an innovative method.

[0005] At present, a variety of microscopic observation means and techniques are used to study the occurrence form of natural gas hydrate in sediment pores, wherein a scanning electron microscope can be used to observe the microscopic occurrence form of hydrate in sediment pores by magnifying the sample by tens to tens of thousands of times. The generation conditions of natural gas hydrate are generally near-zero temperature and megapascal high pressure environment, and the scanning electron microscope experiment needs to be carried out in a near-vacuum environment, at this time, the temperature condition of the hydrate is as low as-90 DEG C or lower. After the preparation of the hydrate sample, the sample is transferred from the high-pressure container in the-90 DEG C low-temperature environment to the near-vacuum environment of the scanning electron microscope for observation, and the transfer process becomes the technical key point and difficulty of the whole experiment. The experimental device and experimental technical method which can simulate the preparation of hydrate-containing sediment samples at different formation depths and transfer to the microscopic observation device such as a scanning electron microscope while keeping the hydrate stable are blank.

[0006] At present, limited by the experimental device and method, the research on the genesis of different hydrate occurrence forms is not perfect, especially the experimental research on the influence law of effective stress on the occurrence characteristics of hydrate is lacking. SUMMARY

[0007] In view of the deficiencies in the prior art, the embodiments of the present application provide a different formation depth hydrate sediment sample supergravity preparation device and method and a sample stable transfer method.

[0008] In a first aspect, the embodiments of the present application provide a different formation depth hydrate sediment sample supergravity preparation device, which comprises:

[0009] A sample preparation kettle placed in a constant temperature water bath box, which contains a sediment sample;

[0010] An axial pressure loading assembly connected with the sample preparation kettle, used for applying axial pressure load to the sediment sample;

[0011] A pore pressure generating assembly connected with the cavity in the sample preparation kettle, used for simulating the pore pressure of the hydrate reservoir in the sample preparation kettle.

[0012] Further, the sample preparation kettle comprises:

[0013] A kettle cover connected with the axial pressure loading assembly;

[0014] A kettle body connected with the kettle cover through a kettle cover clamp; a handle is further installed on the kettle cover clamp

[0015] A sample container arranged in the kettle body.

[0016] Further, the sample container comprises:

[0017] The sample container upper box is fixed by a trapezoidal groove and a sample container upper box limiter; the sample container upper box limiter is connected with the kettle body;

[0018] The sample container lower box is arranged below the sample container upper box and is installed in a limiting groove at the bottom of the kettle body; a lifting ring is further installed on the sample container lower box;

[0019] The sample container upper box and the sample container lower box are sequentially provided from top to bottom with a sample shaft pressure loading cover, a first water-permeable stone, a sample, and a second water-permeable stone;

[0020] Further, the shaft pressure loading assembly comprises:

[0021] an upper end cover,

[0022] a lower end cover connected with a kettle cover in the sample preparation kettle;

[0023] a shaft pressure loading piston arranged between the upper end cover and the lower end cover;

[0024] The pressure balance cavity is connected with a cavity in the sample preparation kettle through a pressure balance channel in the shaft pressure loading piston.

[0025] The lower end cover and the shaft pressure loading piston are provided with a shaft pressure cavity; the shaft pressure cavity is connected with a high-pressure nitrogen cylinder through a shaft pressure gas path interface, a shaft pressure loading valve, and a shaft pressure adjusting valve; the gas pressure in the shaft pressure cavity acts on the shaft pressure loading piston, and under the action of gravity, the shaft pressure loading piston is pushed downward to extrude the sample shaft pressure loading cover, and then the shaft pressure load is transmitted to the sample.

[0026] Further, the pore pressure generation assembly comprises:

[0027] An air compressor is used to drive a gas booster pump, so that the methane gas in the methane cylinder is pressurized by the gas booster pump into a pressurized container;

[0028] The pressurized container is connected with one end of a first injection valve and a second injection valve through an injection adjusting valve;

[0029] The other end of the first injection valve pressurizes the sample through an opening in the upper part of the upper end cover of the shaft pressure loading assembly and an injection channel in the shaft pressure loading piston;

[0030] The other end of the second injection valve is connected with the cavity in the sample preparation kettle through an injection channel arranged in the lower part of the kettle body.

[0031] Further, the device further comprises:

[0032] A shaft pressure sensor is used to monitor the size of the shaft pressure load in real time;

[0033] an injection pressure sensor for monitoring the gas pressure in the sample preparation kettle in real time;

[0034] an axial displacement sensor for monitoring the axial movement of the axial pressure loading piston in real time.

[0035] In a second aspect, the embodiments of the present application provide a method for preparing hydrate samples of different formation depths, which is realized based on the above-mentioned device for preparing hydrate samples of different formation depths under supergravity, and the method comprises the following steps:

[0036] S1, a sediment with a target mass and a target water content is prepared, the sediment is loaded into a sample container, and is compacted to a target porosity; the sample container is installed into the sample preparation kettle;

[0037] S2, the sample preparation kettle is placed in a constant-temperature water bath box; the sample preparation device under supergravity is arranged in a centrifuge basket; the axial pressure loading valve, the first injection valve and the second injection valve are closed, and the high-pressure nitrogen cylinder and the methane cylinder are opened; the centrifuge is started to accelerate to a supergravity of n times the earth's surface gravity acceleration g;

[0038] S3, the target pressure p F is set by the axial pressure adjusting valve, and acts on the axial pressure loading piston to press the sample axial pressure loading cover downward, so as to transmit the axial pressure load to the sample; the axial settlement of the sediment sample is monitored, and when the settlement speed is less than 0.005 mm / h, the consolidation is completed, and the axial pressure load is maintained;

[0039] S4, the air compressor is started to drive the gas booster pump, so that the methane gas in the methane cylinder is pressurized by the gas booster pump into the booster container; the first injection valve and the second injection valve are opened, the injection adjusting valve is used to adjust the gas pressure to simulate the hydrate reservoir pore pressure p g consistent with the formation depth;

[0040] S5, the constant-temperature water bath box is started to simulate the hydrate reservoir formation temperature; when the first injection valve and the second injection valve are closed, and the injection pressure decreases by less than 0.05 MPa, the preparation of the hydrate sample is completed.

[0041] Further, the process that the target pressure p F is set by the axial pressure adjusting valve and acts on the axial pressure loading piston to press the sample axial pressure loading cover downward, so as to transmit the axial pressure load to the sample comprises:

[0042] wherein the target pressure p F set by the axial pressure adjusting valve is expressed as follows:

[0043]

[0044]

[0045] where p' is the effective stress at the top surface of the sample, S is the cross-sectional area of the sample, S F is the cross-sectional area of the axial pressure chamber, p m is the pressure generated by the gravity of the axial pressure loading piston, m is the mass of the axial pressure loading piston, g is the acceleration of the earth's surface gravity, n is the ratio of the acceleration generated by the centrifuge to the acceleration of the earth's surface gravity, and p* is the frictional resistance of the axial pressure loading piston.

[0046] The expression of the simulated effective stress p' of the formation at a certain depth of the reservoir at the top surface of the sample is as follows:

[0047] p' = p a 'gz

[0048] where p a ' is the average effective density of the upper formation at the place, determined by drilling the formation, g is the acceleration of gravity, and z is the burial depth of the deposit at the place.

[0049] The expression of the effective stress p l ' at the depth l of the sample is as follows:

[0050] p l ' = p' + p s '·ng·l

[0051] where p' is the effective stress at the top of the sample, l is the depth inside the sample from the top surface of the sample, ng is the centrifugal acceleration suffered by the sample, and p s ' is the effective density of the sample deposit.

[0052] Further, the expression of the simulated pore pressure p g of the formation at the depth is as follows:

[0053] p g = p w g(h+z)

[0054] where p w is the average density of seawater, g is the acceleration of the earth's surface gravity, h is the depth of the overlying seawater at the place, and z is the burial depth of the deposit at the place.

[0055] In a third aspect, the embodiments of the present application provide a hydrate deposit sample preservation and transfer method at different formation depths, which is realized based on the above-mentioned hydrate deposit sample supergravity preparation device at different formation depths, and the method comprises the following steps.

[0056] Step S100, when the hydrate sample preparation is completed, disconnect all pipes connected with the sample preparation kettle; open the shaft pressure loading valve to release the pressure in the shaft pressure chamber, take the sample preparation kettle out of the constant temperature water bath and quickly put it into the liquid nitrogen tank;

[0057] Step S200, the methane gas in the sample preparation kettle is quickly condensed by liquid nitrogen low temperature, when the pressure in the sample preparation kettle is reduced to less than 0.05 MPa, the first injection valve and the second injection valve are opened to release the residual methane gas pressure which is not completely condensed; the kettle cover clamp is released and taken out of the liquid nitrogen tank by the handle; the kettle cover is lifted by holding the shaft pressure loading assembly, so that the sample preparation kettle is opened, and the liquid nitrogen is poured into the kettle until it is over the sample container;

[0058] Step S300, the sample container is taken out of the sample preparation kettle by the lifting ring, and the sample container upper box, the sample shaft pressure loading cover and the first water permeable stone are removed in liquid nitrogen; the sample and the second water permeable stone are pushed out through the through hole in the sample container lower box, so that the sample is separated from the sample container, and then the sample is stored in liquid nitrogen; the sample is transferred to an external test device for testing under the liquid nitrogen atmosphere.

[0059] Compared with the prior art, the beneficial effects of the present application are:

[0060] The present application provides a different formation depth hydrate deposit sample supergravity preparation device and method, and a sample stability maintaining and transferring method, wherein the device comprises: a sample preparation kettle placed in a constant temperature water bath; a shaft pressure loading assembly connected with the sample preparation kettle, used for applying shaft pressure load to the deposit sample; and a pore pressure generating assembly connected with the cavity in the sample preparation kettle. The preparation process comprises: preparing the deposit in a sample container; transferring the deposit sample to a centrifuge; applying shaft pressure consolidation; injecting high-pressure methane gas; preparing the sample under supergravity; stopping the centrifuge and moving it to liquid nitrogen; sampling under normal gravity while maintaining stability; and transferring the sample while maintaining stability. The present application can simulate the preparation of hydrate-containing deposit samples under different formation depth effective stress levels in a laboratory supergravity environment, and can transfer the samples to a scanning electron microscope and other microscopic observation devices for testing while maintaining the stability of the hydrates. The present application fills the gap in the field of laboratory experimental research methods for the influence of the effective stress level of natural gas hydrate reservoirs on the occurrence characteristics of generated hydrate-containing deposits, and provides a new research method for deep-sea natural gas hydrate accumulation mechanism and safe and efficient exploitation technology. BRIEF DESCRIPTION OF DRAWINGS

[0061] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0062] Figure 1 The schematic diagram of the sample hypergravity preparation device provided by the embodiment of the present application is arranged on a centrifuge.

[0063] Figure 2 The schematic diagram of the sample hypergravity preparation device provided by the embodiment of the present application is arranged on a centrifuge.

[0064] Figure 3 The schematic diagram of the sample hypergravity preparation device provided by the embodiment of the present application is arranged on a centrifuge.

[0065] Figure 4 The schematic diagram of the sample hypergravity preparation device provided by the embodiment of the present application is arranged on a centrifuge.

[0066] Figure 5 The schematic diagram of the sample hypergravity preparation device provided by the embodiment of the present application is arranged on a centrifuge. Figure 5 (a) in the drawings is a top view of the sample container, Figure 5 (b) in the drawings is a vertical sectional view of the sample container, Figure 5 (c) in the drawings is an exploded view of the sample container.

[0067] Figure 6 The schematic diagram of the sample hypergravity preparation device provided by the embodiment of the present application is arranged on a centrifuge.

[0068] Figure 7 The schematic diagram of the sample hypergravity preparation device provided by the embodiment of the present application is arranged on a centrifuge.

[0069] In the figure, 1-sample preparation kettle, 101-kettle cover, 102-kettle body, 103-kettle cover clamp, 104-handle, 105-sample container, 1051-sample container upper box, 1052-sample container upper box limiter, 1053-sample container lower box, 1054-sample shaft pressure loading cover, 1055-first water-permeable stone, 1056-sample, 1057-second water-permeable stone, 1058-suspension ring, 2-shaft pressure loading assembly, 201-upper end cover, 202-lower end cover, 203-shaft pressure loading piston, 204-pressure balance cavity, 205-pressure balance channel, 206-shaft pressure cavity, 207-shaft pressure gas path interface, 208-shaft pressure loading valve, 209-shaft pressure adjusting valve, 2010-high pressure nitrogen cylinder, 3-pore pressure generation assembly, 301-air compressor, 302-methane cylinder, 303-gas booster pump, 304-boosting container, 305-injection adjusting valve, 306-first injection valve, 307-second injection valve, 4-constant temperature water bath box, 5-data acquisition assembly, 501-shaft pressure sensor, 502-injection pressure sensor, 503-axial displacement sensor, 6-controller, 701-liquid nitrogen tank, 702-liquid nitrogen tank, 801-centrifuge rotating shaft, 802-circuit, 803-centrifuge rotating arm, 804-device components, 805-centrifuge basket. DETAILED DESCRIPTION

[0070] The exemplary embodiments will be described in detail herein with reference to the attached drawings. In the following description, like reference numerals refer to like elements throughout the description. The following exemplary embodiments are not representative of all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the present invention as detailed in the appended claims.

[0071] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "and / or", as used herein, refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0072] It will be understood that, although the terms first, second, third, etc. can be used herein to describe various information, these terms are not intended to denote a temporal or chronological order. Rather, these terms are used only as labels to identify particular information. For example, a first information could be termed a second information, and, similarly, a second information could be termed a first information without departing from the scope of the present invention. As used herein, the word "if" can be interpreted to mean "when" or "upon" or "in response to determining" depending on the context.

[0073] The application will be described in detail below with reference to the drawings. The features in the following examples and embodiments can be combined with each other without conflict.

[0074] As shown in Figure 1 and Figure 2 , in a first aspect, the embodiments of the application provide a device for preparing hydrate deposits of different stratum depths under supergravity, which comprises:

[0075] A sample preparation kettle 1 is placed in a constant-temperature water bath box 4, and the sample preparation kettle 1 contains a deposit sample;

[0076] An axial pressure loading assembly 2 is connected with the sample preparation kettle 1, and is used for applying an axial pressure load to the deposit sample;

[0077] A pore pressure generating assembly 3 is connected with a cavity in the sample preparation kettle 1, and is used for simulating the pore pressure of a hydrate reservoir in the sample preparation kettle 1.

[0078] Further, the sample preparation kettle 1 comprises:

[0079] A kettle cover 101 is connected with the axial pressure loading assembly 2;

[0080] A kettle body 102 is connected with the kettle cover 101 through a kettle cover clamp 103, and a handle 104 is further installed on the kettle cover clamp 103;

[0081] A sample container 105 is arranged in the kettle body 102.

[0082] It should be noted that the sample preparation kettle 1 is a high-pressure container made of stainless steel forging, and a quick-release design is adopted to quickly open the kettle at a low temperature for maintaining the stability of hydrates without decomposition. When the kettle is opened, the bolt does not need to be twisted, and the kettle cover 101 can be quickly opened through the kettle cover clamp 103 after the pressure in the kettle is reduced.

[0083] Further, as shown in Figure 5 , the sample container 105 comprises:

[0084] A sample container upper box 1051 is fixed through a trapezoidal groove and a sample container upper box limiter 1052, so as to limit the horizontal displacement of the sample container upper box 1051; the sample container upper box limiter 1052 is connected with the side wall of the kettle body 102 through a bolt;

[0085] A sample container lower box 1053 is arranged below the sample container upper box 1051 and is installed in a limiting groove at the bottom of the kettle body 102; a lifting ring 1058 is further installed on the sample container lower box 1053;

[0086] The sample container upper box 1051 and the sample container lower box 1053 are sequentially provided from top to bottom with a sample shaft pressure loading cover 1054, a first water permeable stone 1055, a sample 1056, and a second water permeable stone 1057.

[0087] Further, as shown in Figure 4 The shaft pressure loading assembly 2 comprises:

[0088] an upper end cover 201,

[0089] a lower end cover 202 connected with the pot cover 101 in the sample preparation pot 1;

[0090] a shaft pressure loading piston 203 arranged between the upper end cover 201 and the lower end cover 202;

[0091] The upper end cover 201 and the shaft pressure loading piston 203 are provided with a pressure balance cavity 204, and the shaft pressure loading piston 203 is provided with a pressure balance channel 205, so that the pressure balance cavity 204 and the cavity in the sample preparation pot 1 are communicated through the pressure balance channel 205.

[0092] The lower end cover 202 and the shaft pressure loading piston 203 are provided with a shaft pressure cavity 206; the shaft pressure cavity 206 is connected with a high-pressure nitrogen cylinder 2010 through a shaft pressure gas path interface 207, a shaft pressure loading valve 208, and a shaft pressure adjusting valve 209; the high-pressure nitrogen cylinder 2010 applies gas pressure to the shaft pressure cavity 206 through the shaft pressure gas path interface 207; the gas pressure in the shaft pressure cavity 206 acts on the shaft pressure loading piston 203, which is pushed downward to extrude the sample shaft pressure loading cover 1054 under the action of gravity, and then the shaft pressure load is transmitted to the sample.

[0093] It should be noted that the pressure balance cavity 204 is used to balance the pressure of the shaft pressure loading piston, and to eliminate the influence of the pressure in the sample preparation pot 1 on the shaft pressure loading. One end of the shaft pressure adjusting valve 209 is connected with the high-pressure nitrogen cylinder 2010 through a pipeline, and the other end is connected with the shaft pressure loading valve 208 through a pipeline, so as to adjust and control the pressure in the shaft pressure cavity.

[0094] Further, the pore pressure generating assembly 3 comprises:

[0095] An air compressor 301 is used to drive a gas booster pump 303, so that the methane gas in a methane cylinder 302 is pressurized by the gas booster pump 303 into a pressurized container 304.

[0096] The pressurized container 304 is connected with one end of a first injection valve 306 and a second injection valve 307 through an injection adjusting valve 305.

[0097] The other end of the first injection valve 306 is connected to the sample 1056 through the opening in the upper end cover 201 of the shaft pressure loading assembly 2, the injection channel in the shaft pressure loading piston 203, and the cavity in the sample preparation kettle 1.

[0098] The other end of the second injection valve 307 is connected to the sample preparation kettle 1 through the injection channel in the lower part of the kettle body 102.

[0099] It should be noted that in this example, the gas pressure in the sample preparation kettle is adjusted by the first injection valve 306 and the second injection valve 307 to simulate the pore pressure at different formation depths; at the same time, the design of the double injection port can ensure the uniformity of the gas inside the sample.

[0100] Further, the device further comprises:

[0101] The data acquisition assembly 5 monitors the size of the shaft pressure load in real time through the shaft pressure sensor 501, monitors the gas pressure in the sample preparation kettle 1 in real time through the injection pressure sensor 502, and monitors the axial movement of the shaft pressure loading piston 203 in real time through the axial displacement sensor 503.

[0102] The controller 6 is coupled with the data acquisition assembly 5, and controls the shaft pressure loading valve 208, the shaft pressure regulating valve 209, the air compressor 301, the injection regulating valve 305, the first injection valve 306, the second injection valve 307, and the constant temperature water bath 4 according to the data monitored by the data acquisition assembly 5 in real time.

[0103] As shown in Figure 6 the second aspect, the embodiments of the present application provide a different formation depth hydrate deposit sample supergravity preparation method, which is realized based on the above-mentioned different formation depth hydrate deposit sample supergravity preparation device, and the preparation method comprises the following steps:

[0104] Step S1, configure a sediment with a target mass and a target water content, load the sediment into the sample container 105, and compact it to a target porosity; install the sample container 105 into the sample preparation kettle 1.

[0105] Further, the sample container lower box 1053 is fixed in the limiting groove in the sample preparation kettle 1, the sample container upper box 1051 is connected with the sample container upper box limiter 1052 through the trapezoidal groove, and then the kettle cover 101 of the sample preparation kettle 1 is closed.

[0106] Step S2, place the sample preparation kettle 1 in the constant temperature water bath 4; arrange the sample supergravity preparation device in the centrifuge basket; close the shaft pressure loading valve 208, the first injection valve 306, and the second injection valve 307, open the high-pressure nitrogen cylinder 2010 and the methane cylinder 302; start the centrifuge to accelerate to a supergravity of n times the surface gravity acceleration g of the earth.

[0107] Furthermore, in this example, the controller 6 is arranged on the centrifuge shaft 801, the wiring 802 including the data acquisition component 5, the axial pressure sensor 501, the injection pressure sensor 502, the axial displacement sensor 503, the axial pressure loading valve 208, and the axial pressure regulating valve 209 is arranged on the centrifuge arm 803, and the remaining device components 804 of the preparation device are arranged in the centrifuge basket 805.

[0108] Step S3: Set the target pressure P using the axial pressure regulating valve 209. F The axial pressure loading piston 203 is applied to press the sample axial pressure loading cover 1054 downward, thereby transferring the axial pressure load to the sample; the axial settlement of the sediment sample is monitored, and consolidation is completed when the settlement rate is less than 0.005 mm per hour, and the axial pressure load is maintained.

[0109] Specifically, in this example, the pressure p within the axial pressure chamber F The pressure P inside the axial pressure chamber F The effective stress P′ corresponds to the effective stress at the top of the sample, while the effective stress p at the sample depth l corresponds to the effective stress at the top of the sample. l The effective stress p′ at the top of the sample, depth l, centrifugal acceleration ng, and effective sample density ρ are all factors. s The influence of the pressure inside the vessel on the magnitude of the axial pressure is negligible. Since the piston of the axial pressure loading assembly has a pressure balance chamber at its upper part and an axial pressure balance channel inside the piston, the influence of the pressure inside the vessel on the magnitude of the axial pressure need not be considered.

[0110] Among them, the target pressure p set by the axial pressure regulating valve 209 F The expression is as follows:

[0111]

[0112] In the formula, p′ is the effective stress at the upper surface of the sample, S is the cross-sectional area of ​​the sample, and S F p is the cross-sectional area of ​​the axial compression chamber. m ρ is the pressure generated by the gravity of the axially loaded piston, m is the mass of the axially loaded piston, g is the gravitational acceleration at the Earth's surface, n is the ratio of the acceleration generated by the centrifuge to the gravitational acceleration at the Earth's surface, and p* is the frictional resistance of the axially loaded piston.

[0113] The expression for the effective formation stress p′ at a certain depth in the reservoir, simulated at the upper surface of the sample, is as follows:

[0114] p'=ρ a 'gz

[0115] In the formula, ρ a ′ represents the average effective density of the upper strata at this location in the reservoir, determined by formation drilling; g represents the gravitational acceleration; and z represents the sediment burial depth at this location in the reservoir.

[0116] Effective stress p at sample depth l l The expression of p' is as follows:

[0117] p l '=p'+ρ s '·ng·l

[0118] In the formula, p' is the effective stress at the top of the sample, l is the depth inside the sample from the upper surface of the sample, ng is the centrifugal acceleration experienced by the sample, and ρ s ' is the effective density of the sample deposit.

[0119] Step S4, start the air compressor 301 to drive the gas booster pump 303, so that the methane gas in the methane cylinder 302 is pressurized to the pressurized container 304 through the gas booster pump 303; open the first injection valve 306 and the second injection valve 307, and adjust the gas pressure to simulate the formation depth pore pressure p g consistent high-pressure methane gas.

[0120] The expression of p g is as follows:

[0121] p g =ρ w g(h+z)

[0122] In the formula, ρ w is the average density of seawater, g is the surface gravity acceleration of the earth, h is the depth of the overlying seawater, and z is the burial depth of the deposit at the reservoir.

[0123] Step S5, start the constant-temperature water bath 4 to simulate the hydrate reservoir formation temperature; when the first injection valve 306 and the second injection valve 307 are closed and the injection pressure decreases by less than 0.05 MPa, the preparation of the hydrate sample is completed.

[0124] Specifically, the constant-temperature water bath 4 is started and the temperature is adjusted to a low temperature, thereby simulating the hydrate reservoir formation temperature, and the hydrate begins to generate in the sample deposit when the temperature drops; wait for several hours to allow the hydrate to generate.

[0125] As shown in Figure 3 and Figure 7 , in a third aspect, the embodiments of the present application provide a stable transfer method for hydrate deposit samples at different formation depths, which is realized based on the above-mentioned supergravity preparation device for hydrate deposit samples at different formation depths, and the method comprises:

[0126] Step S100, when the hydrate sample preparation is completed, the centrifuge speed is reduced until the centrifuge is stopped, and all pipelines connected with the sample preparation kettle 1 are disconnected after the centrifuge is stopped; the shaft pressure loading valve 208 is opened to release the pressure in the shaft pressure chamber 206, the sample preparation kettle 1 is taken out from the constant temperature water bath box 4 and quickly placed in the liquid nitrogen tank 701 connected with the external liquid nitrogen tank 702.

[0127] It should be noted that in the present example, the sample preparation kettle 1 is quickly taken out from the constant temperature water bath box 4 and placed in the liquid nitrogen tank 701, and the liquid nitrogen is used to control the ultra-low temperature in the sample preparation kettle 1, so that the sample can be taken out and stored under normal pressure.

[0128] Step S200, the methane gas in the sample preparation kettle 1 is quickly condensed by the low temperature of the liquid nitrogen, and when the pressure in the sample preparation kettle 1 is reduced to less than 0.05 MPa, it is considered that the temperature in the kettle is reduced to a temperature at which the hydrate can be stable under normal pressure; the first injection valve 306 and the second injection valve 307 are opened to release the pressure of the residual methane gas which is not completely condensed; the kettle cover clamp 103 is released and the kettle cover clamp 103 is taken out from the liquid nitrogen tank 701 by the handle 104; and the kettle cover 101 is lifted by holding the shaft pressure loading assembly 2, so that the sample preparation kettle 1 is opened, and the liquid nitrogen is poured into the kettle until it covers the sample container 105.

[0129] Further, the kettle cover 101 of the sample preparation kettle is designed with a quick release clamp 103, and after the pressure in the kettle is reduced to normal pressure, the clamp 103 can be quickly released by the handle 104 on the clamp 103 in the liquid nitrogen, and then the kettle cover 101 can be opened.

[0130] Step S300, the sample container 105 is taken out from the sample preparation kettle 1 from bottom to top by the lifting ring 1058, and the sample container upper box 1051, the sample shaft pressure loading cover 1054 and the first water permeable stone 1055 are sequentially removed in the liquid nitrogen; the sample 1056 and the second water permeable stone 1057 are pushed out through the through hole in the sample container lower box 1053, so that the sample 1056 is separated from the sample container 105, and then the sample 1056 is stored in the liquid nitrogen; the sample 1056 is transferred to an external test device under the liquid nitrogen atmosphere for testing.

[0131] It should be noted that the experimental device can be carried on the soil centrifuge to carry out the ultra-gravity experiment, or can be carried out on the ground to carry out the normal gravity experiment, and when the normal gravity experiment is carried out on the ground, the steps related to the centrifuge in the above steps can be ignored, and n is taken as 1 in all related calculation formulas.

[0132] In summary, the application innovatively proposes an experimental method and specific operation for preparing hydrate-bearing sediment samples under different formation depth stress levels in a laboratory, and then transferring the samples to a microscopic observation device such as a scanning electron microscope for testing, by means of the quick-opening design of the kettle body and the sample rapid removal method, thereby filling the gap in the field of laboratory experimental research methods for the influence of effective stress levels of natural gas hydrate reservoirs on the occurrence characteristics of generated hydrate-bearing sediments, and providing technical support for deep-sea natural gas hydrate accumulation mechanism research and safe and efficient exploitation of natural gas hydrate.

[0133] It should be noted that the embodiments of the present application have better implementation, and are not any form of limitation of the present application. The technical features or combinations of technical features described in the embodiments of the present application should not be considered in isolation, and they can be combined with each other to achieve better technical effects. The scope of the preferred embodiments of the present application can also include other implementations, and this should be understood by those skilled in the art to which the embodiments of the present application belong.

[0134] Techniques, methods, and equipment known to those of ordinary skill in the relevant art can not be discussed in detail, but should be considered part of the authorized description where appropriate. In all examples shown and discussed herein, any specific values should be interpreted as merely exemplary, not as limiting. Therefore, other examples of exemplary embodiments can have different values.

[0135] The drawings of the present application are very simplified and use non-precise proportions, only to facilitate and clarify the purpose of assisting in the description of the embodiments of the present application, and are not limiting conditions for the implementation of the present application. Any modification of structure, change of proportional relationship or adjustment of size, without affecting the effects and purposes that can be achieved by the present application, should be within the scope of the technical content disclosed by the present application.

[0136] The above description is only a description of the preferred embodiments of the present application, and is not any limitation of the scope of the present application. Any modification or modification made by any person skilled in the art according to the above disclosed technical content should be considered as an equivalent effective embodiment, and belongs to the scope of protection of the technical scheme of the present application.

Claims

1. A device for preparing hydrate sediments samples at different formation depths under hypergravity, characterized in that, The device is arranged in a centrifuge basket, and a centrifuge is started to accelerate to supergravity n times of the earth surface gravity acceleration g to realize supergravity preparation of different formation depth hydrate deposit samples, and the device comprises: A sample preparation kettle (1) placed in a constant temperature water bath box (4) contains a deposit sample; An axial pressure loading assembly (2) connected with the sample preparation kettle (1) is used for applying an axial pressure load to the deposit sample; A pore pressure generating assembly (3) connected with a cavity in the sample preparation kettle (1) is used for simulating the pore pressure of a hydrate reservoir in the sample preparation kettle (1); The sample preparation kettle (1) comprises: A kettle cover (101) connected with the axial pressure loading assembly (2); A kettle body (102) connected with the kettle cover (101) through a kettle cover clamp (103); a handle (104) is further installed on the kettle cover clamp (103); the handle (104) is used for taking the sample preparation kettle (1) out of the constant temperature water bath box (4) and quickly placing it in a liquid nitrogen tank (701), and after the kettle cover clamp (103) is removed in the liquid nitrogen, the kettle cover clamp (103) is taken out of the liquid nitrogen tank (701) by using the handle (104); A sample container (105) arranged in the kettle body (102); The sample container (105) comprises: A sample container upper box (1051) fixed through a trapezoidal groove and a sample container upper box limiter (1052); the sample container upper box limiter (1052) is connected with the kettle body (102), so as to limit the horizontal displacement of the sample container upper box (1051); A sample container lower box (1053) arranged below the sample container upper box (1051) and installed in a limiting groove at the bottom of the kettle body (102); a lifting ring (1058) is further installed on the sample container lower box (1053); the lifting ring (1058) is used for taking the sample container (105) out of the sample preparation kettle (1) in the liquid nitrogen; The sample container upper box (1051) and the sample container lower box (1053) are sequentially provided from top to bottom with a sample axial pressure loading cover (1054), a first water-permeable stone (1055), a sample (1056), and a second water-permeable stone (1057); The axial pressure loading assembly (2) comprises: An upper end cover (201), A lower end cover (202) connected with the kettle cover (101) in the sample preparation kettle (1); An axial pressure loading piston (203) arranged between the upper end cover (201) and the lower end cover (202); A pressure balance cavity (204) is arranged between the upper end cover (201) and the axial pressure loading piston (203), and a pressure balance channel (205) is opened in the axial pressure loading piston (203), so that the pressure balance cavity (204) and the cavity in the sample preparation kettle (1) are communicated through the pressure balance channel (205). The shaft pressure loading piston (203) is arranged between the lower end cover (202) and the shaft pressure loading piston (203), and the shaft pressure loading piston (203) is connected with the high-pressure nitrogen cylinder (2010) through the shaft pressure gas path interface (207), the shaft pressure loading valve (208) and the shaft pressure regulating valve (209); the gas pressure in the shaft pressure cavity (206) acts on the shaft pressure loading piston (203), and the shaft pressure loading piston (203) is pushed downward to extrude the sample shaft pressure loading cover (1054) under the action of gravity, so that the shaft pressure load is transmitted to the sample; The pore pressure generating assembly (3) comprises: The air compressor (301) is used to drive the gas booster pump (303), so that the methane gas in the methane cylinder (302) is pressurized to the booster container (304) through the gas booster pump (303); The booster container (304) is connected with one end of the first injection valve (306) and the second injection valve (307) through the injection adjusting valve (305); The other end of the first injection valve (306) is connected with the sample (1056) through the opening in the upper part of the upper end cover (201) of the shaft pressure loading assembly (2) and the injection channel in the shaft pressure loading piston (203); The other end of the second injection valve (307) is connected with the cavity in the sample preparation kettle (1) through the injection channel arranged in the lower part of the kettle body (102).

2. The device for preparation of hydrate sediments samples from different depths of the formation according to claim 1, characterized in that, The device further comprises: The shaft pressure sensor (501) is used to monitor the size of the shaft pressure load in real time; The injection pressure sensor (502) is used to monitor the gas pressure in the sample preparation kettle (1) in real time; The axial displacement sensor (503) is used to monitor the axial movement of the shaft pressure loading piston (203) in real time.

3. A method of hypergravity preparation of samples of gas hydrate deposits at different depths of the formation, characterized in that, The different formation depth hydrate sediment sample supergravity preparation device based on any one of the above claims 1-2 is realized, and the preparation method comprises: Step S1, configuring a sediment with a target mass and a target water content, loading the sediment into a sample container (105), and compacting to a target porosity; installing the sample container (105) into the sample preparation kettle (1); Step S2, placing the sample preparation kettle (1) in a constant temperature water bath box (4); arranging the sample supergravity preparation device in a centrifuge basket; closing the shaft pressure loading valve (208), the first injection valve (306) and the second injection valve (307); opening the high-pressure nitrogen cylinder (2010) and the methane cylinder (302); starting the centrifuge to accelerate to a supergravity of n times the earth surface gravity acceleration g; Step S3, set the target pressure p through the axial pressure regulating valve (209) F And acts on the axial pressure loading piston (203) to extrude the sample axial pressure loading cover (1054), and further transmits the axial pressure load to the sample; monitors the axial settlement of the sediment sample, and when the settlement speed is less than 0.005 mm per hour, the consolidation is completed, and the loading axial pressure load is maintained; Step S4, start the air compressor (301) to drive the gas booster pump (303), so that the methane gas in the methane cylinder (302) is pressurized to the booster container (304) through the gas booster pump (303); open the first injection valve (306) and the second injection valve (307), adjust the gas pressure to simulate the hydrate reservoir pore pressure by using the injection adjusting valve (305), and inject the sample preparation kettle (1) with the simulated formation depth pore pressure p g Consistent high-pressure methane gas; Step S5, starting the constant temperature water bath box (4) to simulate the hydrate reservoir formation temperature; when the injection pressure decreases by less than 0.05 MPa after the first injection valve (306) and the second injection valve (307) are closed, the preparation of the hydrate sample is completed.

4. A method of preparing samples of hydrate deposits at different depths in a formation according to claim 3, characterized in that The target pressure p is set by the axial pressure regulating valve (209) F And acts on the axial pressure loading piston (203) to extrude the sample axial pressure loading cover (1054) downward, and further transmits the axial pressure load to the sample Comprise: wherein the target pressure p of the shaft pressure adjusting valve (209) is set F The expression is as follows: where p' is the effective stress at the upper surface of the sample, S is the cross-sectional area of the sample, S F is the cross-sectional area of the axial pressure chamber, p m is the pressure due to the weight of the axial loading piston, m is the mass of the axial loading piston, g is the acceleration due to gravity at the earth's surface, n is the ratio of the acceleration produced by the centrifuge to the acceleration due to gravity at the earth's surface, and p* is the frictional resistance of the axial loading piston. The expression of the simulated formation effective stress p' of the sample upper surface at a certain depth of the reservoir is as follows: p' = p a 'gz; In the formula, ρ a ′ represents the average effective density of the upper strata at this location in the reservoir, determined by formation drilling; g represents the gravitational acceleration; and z represents the sediment burial depth at this location in the reservoir. Effective stress p at sample depth i l The expression for p of the following: p l ' = p + p s ' · ng · l; where p' is the effective stress at the top of the sample, / is the depth within the sample from the top surface, ng is the centrifugal acceleration experienced by the sample, p s is the effective density of the sample sediment.

5. A method of preparing samples of hydrate deposits at different depths in a formation according to claim 4, characterized in that, simulated formation depth pore pressure p g The expression for p is as follows: p g = p w g(h + z); where p w is the average density of seawater, g is the acceleration of gravity at the Earth's surface, h is the depth of overlying seawater, and z is the depth of the sediment at the reservoir.

6. A method for stabilizing and transferring hydrate-bearing sediment samples from different formation depths, characterized in that, The different formation depth hydrate sediment sample supergravity preparation device based on any one of the above claims 1-2 is realized, and the method comprises: Step S100, when the hydrate sample preparation is completed, disconnect all pipes connected with the sample preparation kettle (1); open the shaft pressure loading valve (208) to release the pressure in the shaft pressure chamber (206), take out the sample preparation kettle (1) from the constant temperature water bath (4) and quickly place it in the liquid nitrogen tank (701); Step S200, make the methane gas in the sample preparation kettle (1) quickly condense by low temperature of liquid nitrogen, when the pressure in the sample preparation kettle (1) is reduced to less than 0.05 MPa, open the first injection valve (306) and the second injection valve (307) to release the residual methane gas pressure which is not completely condensed; remove the kettle cover clamp (103) and take it out from the liquid nitrogen tank (701) by the handle (104); then lift the kettle cover (101) by holding the shaft pressure loading assembly (2) to open the sample preparation kettle (1) and pour liquid nitrogen into the kettle until it covers the sample container (105); Step S300, take out the sample container (105) from the sample preparation kettle (1) by the lifting ring (1058) and remove the sample container upper box (1051), the sample shaft pressure loading cover (1054) and the first water permeable stone (1055) in sequence in liquid nitrogen; push out the sample (1056) and the second water permeable stone (1057) through the through hole in the sample container lower box (1053) to separate the sample (1056) from the sample container (105), then store the sample (1056) in liquid nitrogen; transfer the sample (1056) to the external testing device under the liquid nitrogen atmosphere to carry out testing.

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