Methane hydrate in calcareous sand particles and preparation method thereof

Abstract

The invention provides a methane hydrate in calcareous sand particles and a preparation method thereof, and the preparation method comprises the following specific steps: (1) adding dry calcareous sand particles into air-free water, and carrying out vacuum saturation until no bubble is generated in the air-free water to obtain saturated calcareous sand particles; (2) the saturated calcareous sand particles are flatly laid and stood, moisture on the surfaces of the particles is naturally air-dried, pores in the calcareous sand are filled with air-free water, and dispersed calcareous sand particles are obtained; (3) freezing the dispersed calcareous sand particles to enable air-free water in the calcareous sand particles to be in a bulk state, preparing a sample in the reaction kettle, and vacuumizing to enable no air among the calcareous sand particles; and (4) filling high-pressure methane gas into the reaction kettle, raising the temperature for reaction, and obtaining the methane hydrate when the methane pressure value is stable and unchanged. And the prepared sand particle inner filling type distribution form is obviously different from the traditional inter-particle filling type distribution form, so that the artificial synthesis range of the methane hydrate distribution form is effectively expanded, and the method has a relatively good application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of natural gas hydrates, and in particular to methane hydrate in calcareous sand particles and a preparation method thereof. Background Art

[0002] Methane hydrate is a kind of ice-like natural gas deposit, also known as "combustible ice". It is a cage-like crystalline compound formed by methane gas and water molecules. Its formation is not through the strong attraction between molecules, but the cage-like structure formed by water molecules tightly wraps the methane molecules. It is formed under high pressure and low temperature conditions. It will slowly decompose and release methane at room temperature and pressure. The carbon content of methane hydrates formed naturally in nature is much greater than the sum of the carbon content of all fossil fuels currently. Studies have found that 1 volume of methane hydrate contains more than 160 volumes of methane gas. The space required for methane hydrate storage is small and the conditions are easy to obtain, and the storage conditions are mild. However, the induction period of methane hydrate formation is long, usually several days or even weeks. The hydrate grows slowly, the water conversion rate is low, and the amount of methane stored per unit volume of water is small, which becomes a barrier to its application. How to achieve its rapid generation and high storage capacity is the key to using this technology. Therefore, the study of methane hydrate is of great significance to the development and utilization of new energy.

[0003] Hydrate technology can be applied to natural gas storage and transportation, sewage treatment, seawater desalination, mixed gas separation, solution concentration, methane hydrate cold storage and replacement mining. With the continuous deepening of research on the basic physical properties, microstructure, thermodynamics and kinetics of methane hydrates, methane hydrates have attracted great attention all over the world.

[0004] At present, methane hydrates filled with calcareous sand particles are generally intergranular filling types. For the foraminiferal shell-rich area in the Shenhu Sea area of ​​the South China Sea, the distribution patterns of different filling types have different effects on the pore structure of the reservoir soil. Therefore, it is necessary to find a method that can simply and efficiently synthesize methane hydrates in a general laboratory, expand the range of artificial synthesis of methane hydrate distribution patterns, and assist in the research on natural gas hydrate exploitation in the South China Sea, which is of great significance. Summary of the invention

[0005] In view of this, the present invention proposes methane hydrate in calcareous sand particles and a preparation method thereof.

[0006] The technical solution of the present invention is achieved in this way:

[0007] A method for preparing methane hydrate in calcareous sand particles, the specific steps comprising:

[0008] (1) adding dry calcareous sand particles into air-free water and saturating the water under vacuum until no bubbles are generated in the air-free water, thereby obtaining saturated calcareous sand particles;

[0009] (2) Spreading the saturated calcareous sand particles flat, leaving them to stand, and allowing the moisture on the surface of the particles to dry naturally, so that the pores in the calcareous sand are filled with air-free water, thereby obtaining dispersed calcareous sand particles;

[0010] (3) freezing the dispersed calcareous sand particles so that the airless water in the calcareous sand particles is in a dispersed state, and evacuating the sample in a reaction kettle so that there is no air between the calcareous sand particles;

[0011] (4) High-pressure methane gas is charged into the reactor and the temperature is raised to react. When the methane pressure value remains stable, methane hydrate is obtained.

[0012] Furthermore, in step (1), the solid-liquid ratio of the dried calcareous sand particles to the air-free water is 1:10-20 g / mL.

[0013] Furthermore, in step (1), the vacuum degree of the vacuum saturation is 0.02-0.05 MPa, and the temperature is 15-25°C.

[0014] Furthermore, in step (2), the saturated calcareous sand particles are spread on a metal filter screen inclined at 45 degrees.

[0015] Furthermore, in step (2), the standing time is 2-6 hours.

[0016] Furthermore, in step (3), the freezing is carried out at -10 to -5°C for 2 to 4 hours.

[0017] If any calcareous sand particles freeze into clumps during freezing, tap them gently to disperse them.

[0018] Furthermore, in step (3), the vacuum degree of the vacuum extraction is 0.05-0.08 MPa.

[0019] Furthermore, in step (4), the pressure of the high-pressure methane gas is 4-6 MPa; and the temperature-raising reaction is to raise the temperature to 1-3° C. and react for 8-12 hours.

[0020] A methane hydrate in calcareous sand particles is prepared by any of the preparation methods described above.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention prepares methane hydrate in calcareous sand particles, which can be easily and efficiently achieved under laboratory conditions. The prepared methane hydrate distribution form is filled in the sand particles, which is significantly different from the traditional distribution form filled between sand particles. It effectively expands the artificial synthesis range of methane hydrate distribution forms, helps the research on natural gas hydrate exploitation in the South China Sea, and has good application prospects.

[0023] (2) The method for preparing methane hydrate in calcareous sand particles of the present invention involves a controllable quantity of raw materials. Combined with the collected data of the methane gas after decomposition, the methane hydrate saturation value in the sample can be accurately calculated. Based on the relevant data, the optimal conditions for the synthesis of methane hydrate can be determined. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagrams of the morphology of the intra-particle filling type methane hydrate synthesized in Example 1 of the present invention (a) and the inter-particle filling type methane hydrate synthesized in a conventional manner (b). DETAILED DESCRIPTION

[0025] In order to better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0026] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0027] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial sources.

[0028] Example 1

[0029] A method for preparing methane hydrate in calcareous sand particles, the specific steps comprising:

[0030] (1) adding dry calcareous sand particles to air-free water at a solid-liquid ratio of 1:15 g / mL, and performing vacuum saturation at a temperature of 20° C. and a vacuum degree of 0.03 MPa until no bubbles are generated in the air-free water and the pores in the particles are filled with air-free water, thereby obtaining saturated calcareous sand particles;

[0031] (2) Spreading saturated calcareous sand particles on a metal filter screen inclined at 45 degrees, leaving gaps between the particles, and letting them stand for 4 hours to naturally air-dry the surface moisture of the particles. No obvious moisture is left on the surface of the particles, and the pores in the calcareous sand are filled with air-free water, thereby obtaining dispersed calcareous sand particles;

[0032] (3) Freeze the dispersed calcareous sand particles at -7°C for 3 h. If any calcareous sand particles freeze into a mass during freezing, tap them gently to disperse them. Freezing makes the airless water in the calcareous sand particles present a dispersed state. According to the test requirements, the frozen calcareous sand is made into a sample that meets the test requirements in a closed reactor, and then the vacuum degree is 0.07 MPa, and vacuum is drawn to make no air between the calcareous sand particles.

[0033] (4) High-pressure methane gas is charged into the reactor to a pressure of 5 MPa. When the temperature is raised to 2°C, the ice in the particles melts into water and forms methane hydrates with the methane gas. During the reaction, methane gas needs to be supplemented and monitored in real time by a computer until the methane pressure value no longer decreases and the methane hydrates are completely formed.

[0034] Example 2

[0035] A method for preparing methane hydrate in calcareous sand particles, the specific steps comprising:

[0036] (1) adding dry calcareous sand particles to air-free water at a solid-liquid ratio of 1:10 g / mL, and performing vacuum saturation at a temperature of 15° C. and a vacuum degree of 0.02 MPa until no bubbles are generated in the air-free water and the pores in the particles are filled with air-free water, thereby obtaining saturated calcareous sand particles;

[0037] (2) Spreading saturated calcareous sand particles on a metal filter screen inclined at 45 degrees, leaving gaps between the particles, and letting them stand for 2 hours to naturally air-dry the surface moisture of the particles. No obvious moisture is left on the surface of the particles, and the pores in the calcareous sand are filled with air-free water, thereby obtaining dispersed calcareous sand particles;

[0038] (3) Freeze the dispersed calcareous sand particles at -10°C for 2 hours. If the calcareous sand particles are frozen into a mass during the freezing period, tap them gently to disperse them. Freezing makes the airless water in the calcareous sand particles present a dispersed state. According to the test requirements, the frozen calcareous sand is made into a sample that meets the test requirements in a closed reactor, and then the vacuum degree is 0.05MPa, and vacuum is drawn to make no air between the calcareous sand particles;

[0039] (4) High-pressure methane gas is charged into the reactor to a pressure of 4 MPa. When the temperature is raised to 1°C, the ice in the particles melts into water and forms methane hydrates with the methane gas. During the reaction, methane gas needs to be supplemented and monitored in real time by a computer until the methane pressure value no longer decreases and the methane hydrates are completely formed.

[0040] Example 3

[0041] A method for preparing methane hydrate in calcareous sand particles, the specific steps comprising:

[0042] (1) adding dry calcareous sand particles to air-free water at a solid-liquid ratio of 1:20 g / mL, and performing vacuum saturation at a temperature of 25° C. and a vacuum degree of 0.05 MPa until no bubbles are generated in the air-free water and the pores in the particles are filled with air-free water, thereby obtaining saturated calcareous sand particles;

[0043] (2) Spreading saturated calcareous sand particles on a metal filter screen inclined at 45 degrees, leaving gaps between the particles, and letting them stand for 6 hours to naturally air-dry the surface moisture of the particles. No obvious moisture is left on the surface of the particles, and the pores in the calcareous sand are filled with air-free water, thereby obtaining dispersed calcareous sand particles;

[0044] (3) Freeze the dispersed calcareous sand particles at -5°C for 4 hours. If the calcareous sand particles are frozen into a mass during the freezing period, tap them gently to disperse them. Freezing makes the airless water in the calcareous sand particles present a dispersed state. According to the test requirements, the frozen calcareous sand is made into a sample that meets the test requirements in a closed reactor, and then the vacuum degree is 0.08MPa, and vacuum is drawn to make no air between the calcareous sand particles.

[0045] (4) High-pressure methane gas is charged into the reactor to a pressure of 6 MPa. When the temperature is raised to 3°C, the ice in the particles melts into water and forms methane hydrates with the methane gas. During the reaction, methane gas needs to be supplemented and monitored in real time by a computer until the methane pressure value no longer decreases and the methane hydrates are completely formed.

[0046] Test example

[0047] Gas storage multiple C of methane hydrate prepared by the preparation method of Example 1-3 s It is calculated according to the following formula based on temperature and pressure.

[0048]

[0049] In the above formula, n is the methane consumption;

[0050] P0 and P t are the pressures of the autoclave at time 0 and time t respectively;

[0051] V0 and V t are the gas phase volumes in the autoclave at time 0 and time t respectively;

[0052] T0 and T t are the temperatures of the autoclave at time 0 and time t respectively;

[0053] R is the universal gas constant;

[0054] z0 and z t are the gas compressibility factors at time 0 and time t respectively;

[0055] m is the theoretical value of methane hydrate number, 5.75;

[0056] T c and P c They are the critical temperature of methane, 190.6K, and the critical pressure, 4.599MPa;

[0057] ω is the methane eccentricity factor 0.012;

[0058] V mg and V mw are the molar volumes of gas and water, respectively;

[0059] Vi and V u are the volume of the initial reaction solution and the volume of the reaction solution that did not participate in the reaction after the reaction was completed;

[0060] ΔV is the molar volume difference between methane hydrate and water, and the theoretical value is 4.6 cm 3 .

[0061] The gas storage multiples of the intra-particle filled methane hydrate prepared in Example 1-3 are shown in Table 1. At the same time, the time required for the start of methane hydrate generation, ie, the methane hydrate induction time, was statistically calculated.

[0062] Table 1

[0063]

[0064] It can be seen from Table 1 that the preparation methods of Examples 1-3 of the present invention can quickly and efficiently generate methane hydrate, and the gas storage multiple can reach up to 121 (V / V), the reaction rate is high, and the induction time is short.

[0065] The intragranular filling hydrate of the present invention is a special hydrate distribution form. In the foraminifera shell-enriched area in the Shenhu Sea area of ​​the South China Sea, hydrates are mainly distributed in the pores inside the foraminifera shells. The intragranular filling hydrate has a different effect on the pore structure of the reservoir soil than the intergranular filling hydrate, which effectively expands the artificial synthesis range of methane hydrate distribution forms, helps the research on natural gas hydrate exploitation in the South China Sea, and has good application prospects.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing methane hydrate in calcareous sand particles, characterized in that: The specific steps include: (1) adding dry calcareous sand particles into air-free water and saturating the water under vacuum until no bubbles are generated in the air-free water, thereby obtaining saturated calcareous sand particles; (2) Spreading the saturated calcareous sand particles flat, leaving them to stand, and allowing the moisture on the surface of the particles to dry naturally, so that the pores in the calcareous sand are filled with air-free water, thereby obtaining dispersed calcareous sand particles; (3) freezing the dispersed calcareous sand particles so that the airless water in the calcareous sand particles is in a dispersed state, and evacuating the sample in a reaction kettle so that there is no air between the calcareous sand particles; (4) High-pressure methane gas is charged into the reactor and the temperature is raised to react. When the methane pressure value remains stable, methane hydrate is obtained.

2. The method for preparing methane hydrate in calcareous sand particles according to claim 1, characterized in that: In step (1), the solid-to-liquid ratio of the dried calcareous sand particles to the air-free water is 1:10-20 g / mL.

3. The method for preparing methane hydrate in calcareous sand particles according to claim 1, characterized in that: In step (1), the vacuum degree of the vacuum saturation is 0.02-0.05 MPa, and the temperature is 15-25°C.

4. The method for preparing methane hydrate in calcareous sand particles according to claim 1, characterized in that: In step (2), the saturated calcareous sand particles are spread on a metal filter screen inclined at 45 degrees.

5. The method for preparing methane hydrate in calcareous sand particles according to claim 1, characterized in that: In step (2), the standing time is 2-6 hours.

6. The method for preparing methane hydrate in calcareous sand particles according to claim 1, characterized in that: In step (3), the freezing is carried out at -10 to -5°C for 2 to 4 hours.

7. The method for preparing methane hydrate in calcareous sand particles according to claim 1, characterized in that: In step (3), the vacuum degree of the vacuum extraction is 0.05-0.08 MPa.

8. The method for preparing methane hydrate in calcareous sand particles according to claim 1, characterized in that: In step (4), the pressure of the high-pressure methane gas is 4-6 MPa; the temperature-raising reaction is to raise the temperature to 1-3° C. and react for 8-12 hours.

9. Methane hydrate in calcareous sand particles, obtained by the preparation method according to any one of claims 1 to 8.

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