Natural gas hydrate artificial core as well as preparation method and application thereof

Abstract

The invention belongs to the field of rock physics, and discloses a natural gas hydrate artificial core and a preparation method and application thereof. The method comprises the following steps: uniformly mixing, stirring and rubbing dried kaolin mineral powder and a cementing agent, then putting the mixture into a mold, carrying out pressurization treatment to obtain a pressurized material, and crushing and screening the pressurized material to obtain pretreated kaolin particles; putting the pretreated kaolin particles into a rock core holder, pouring a solvent aqueous solution into the rock core holder until the solvent aqueous solution submerges the pretreated kaolin particles in the rock core holder, providing a low-temperature environment for the interior of the rock core holder, and preparing the natural gas hydrate artificial rock core. According to the present invention, the mineral matrix is improved based on the natural gas hydrate occurrence characteristics and the artificial rock core preparation technology, such that the artificial rock core conforming to the natural gas hydrate reservoir characteristics is prepared, and the similarity between the artificial rock core and the natural gas hydrate reservoir is improved.

Description

Technical Field

[0001] The present invention belongs to the field of petrophysics, and more specifically, relates to a synthetic core for natural gas hydrate, a preparation method thereof, and an application thereof. Background Art

[0002] Natural gas hydrate is a new type of unconventional clean energy. According to research data, there are extensive hydrate ore bodies distributed in some sea areas, which have great exploration and development potential. However, its unique geological and mineralization conditions make it significantly different from the occurrence forms and seismic reflection characteristics of conventional oil and gas resources.

[0003] Geophysical technology is the core technology for the identification of natural gas hydrates. Through seismic exploration or acoustic logging, the seismic wave velocity of the sediment layer containing natural gas hydrates can be obtained, but it is difficult to directly obtain the saturation and occurrence form of natural gas hydrates, and a quantitative relationship between the seismic wave velocity of sediments containing natural gas hydrates and the saturation and occurrence form of natural gas hydrates has not been established. Therefore, it is necessary to carry out petrophysical research on hydrates to establish a quantitative relationship.

[0004] To carry out petrophysical research on natural gas hydrates, it is necessary to obtain synthetic cores for natural gas hydrates. Synthetic cores for natural gas hydrates decompose immediately when the temperature and pressure change beyond the stable phase boundary conditions, and it is very difficult to coring under constant temperature and pressure. At present, domestic laboratories all use synthetic cores to carry out research on natural gas hydrates. Natural gas hydrates are present in the muddy sediments on the seabed at a depth of about 500 m (pressure of 5 MPa) in the offshore area. At present, there are mainly two types of matrix minerals for preparing synthetic cores, quartz sand and kaolin. The mineral velocity of quartz sand is significantly higher than that of the muddy minerals where natural gas hydrates occur, and the mesh number of kaolin is above 2000 mesh, and the porosity is very small under a pressure of 5 MPa, making it difficult to form a synthetic core for natural gas hydrates.

[0005] Therefore, there is an urgent need to provide a synthetic core for natural gas hydrates, a preparation method thereof, and an application thereof. Summary of the Invention

[0006] The object of the present invention is to provide a synthetic core for natural gas hydrates, a preparation method thereof, and an application thereof in view of the deficiencies of the prior art. In view of the occurrence characteristics of natural gas hydrates and based on the synthetic core preparation technology, the present invention improves the mineral matrix, thereby preparing a synthetic core that conforms to the characteristics of natural gas hydrate reservoirs and improving the similarity between the synthetic core and natural gas hydrate reservoirs.

[0007] To achieve the above object, the first aspect of the present invention provides a preparation method for a synthetic core for natural gas hydrates, the method comprising the following steps:

[0008] S1: Mix the dried kaolin mineral powder with a binder, stir and knead evenly, then put it into a mold, perform pressure treatment to obtain a pressed material, and then crush and screen it to obtain pretreated kaolin particles.

[0009] S2: Put the pretreated kaolin particles into a core holder, pour a solvent aqueous solution into the core holder until it covers the pretreated kaolin particles in the core holder, and provide a low-temperature environment inside the core holder to prepare the artificial core of natural gas hydrate.

[0010] The second aspect of the present invention provides an artificial core of natural gas hydrate prepared by the preparation method of the artificial core of natural gas hydrate described above.

[0011] The third aspect of the present invention provides the application of the artificial core of natural gas hydrate in the petrophysical research of natural gas hydrate.

[0012] The beneficial effects of the technical solution of the present invention are as follows:

[0013] Natural gas hydrate only forms under specific conditions and can only be stored for a long time under specific conditions. It is quite difficult to conduct petrophysical tests and analyses on its actual samples. Therefore, in view of the occurrence characteristics of natural gas hydrate and based on the artificial core preparation technology, the present invention improves the mineral matrix, thereby preparing an artificial core that conforms to the characteristics of natural gas hydrate reservoirs, improving the similarity between the artificial core and natural gas hydrate reservoirs, and on this basis, petrophysical research on hydrates can be carried out.

[0014] Other features and advantages of the present invention will be described in detail in the following specific implementation manner section. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] By describing the exemplary embodiments of the present invention in more detail in conjunction with the drawings, the above and other objects, features, and advantages of the present invention will become more obvious. Among them, in the exemplary embodiments of the present invention, the same reference numerals generally represent the same components.

[0016] Figure 1 Shows the kaolin mineral powder used in the preparation method of an artificial core of natural gas hydrate provided by the present invention.

[0017] Figure 2 Shows the device for preparing the artificial core of natural gas hydrate used in the preparation method of an artificial core of natural gas hydrate provided by the present invention.

[0018] Figure 3 Shows the core holder used in the preparation method of an artificial core of natural gas hydrate provided by the present invention.

[0019] Figure 4Shows the low-temperature constant temperature bath used in a method for preparing an artificial core of natural gas hydrate provided by the present invention.

[0020] Figure 5 Shows the artificial core of natural gas hydrate prepared by a method for preparing an artificial core of natural gas hydrate provided in Embodiment 1 of the present invention.

[0021] Figure 6 Shows the waveform data measured during the preparation process of the artificial core of natural gas hydrate in Embodiment 1 of the present invention.

[0022] Figure 7 Shows the artificial core of natural gas hydrate prepared by a method for preparing an artificial core of natural gas hydrate provided in Embodiment 2 of the present invention.

[0023] Figure 8 Shows the waveform data measured during the preparation process of the artificial core of natural gas hydrate in Embodiment 2 of the present invention.

[0024] Figure 9 Shows the waveform data measured during the preparation process of the artificial core of natural gas hydrate in Embodiment 3 of the present invention.

[0025] Figure 10 Shows the waveform data measured during the preparation process of the artificial core of natural gas hydrate in Embodiment 4 of the present invention.

[0026] Figure 11 Shows the artificial core of natural gas hydrate prepared by a method for preparing an artificial core of natural gas hydrate provided in Comparative Example 1 of the present invention.

[0027] Figure 12 Shows the waveform data measured during the preparation process of the artificial core of natural gas hydrate in Comparative Example 1 of the present invention. Detailed implementation manners

[0028] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0029] The first aspect of the present invention provides a method for preparing an artificial core of natural gas hydrate, and the method includes the following steps:

[0030] S1: Mix the dried kaolin mineral powder and a binder, stir and knead them evenly, then put them into a mold, perform a pressure treatment to obtain a pressured material, and then crush and screen the pressured material to obtain pretreated kaolin particles;

[0031] S2: Place the pretreated kaolin particles into a core holder, pour an aqueous solvent solution into the core holder until it covers the pretreated kaolin particles in the core holder, and provide a low-temperature environment inside the core holder to prepare the artificial core of natural gas hydrate.

[0032] According to the present invention, preferably, the particle size of the kaolin mineral powder is 1800 - 2200 mesh, as Figure 1 shown.

[0033] According to the present invention, preferably, the drying temperature is 45 - 55 °C and the time is 12 - 36 h.

[0034] According to the present invention, preferably, the dosage ratio of the dried kaolin mineral powder to the binder is (8 - 9.5):(0.5 - 2).

[0035] According to the present invention, preferably, the binder is a mixture of epoxy resin and curing agent, and the dosage ratio of the epoxy resin to the curing agent is (1.5 - 2.5):(0.5 - 1.5).

[0036] According to the present invention, preferably, the mold is an iron mold; the equipment for pressure treatment includes a high-precision hydraulic press, the pressure of the pressure treatment is 4.5 - 5.5 MPa, and the pressure is maintained for 12 - 36 h during the pressure treatment.

[0037] According to the present invention, preferably, the particle size of the pretreated kaolin particles is 60 - 80 mesh.

[0038] According to the present invention, preferably, the aqueous solvent solution is a tetrahydrofuran aqueous solution.

[0039] According to the present invention, preferably, the mass fraction of the tetrahydrofuran aqueous solution is 0.1 - 19%.

[0040] According to the present invention, preferably, the axial pressure of the core holder is 4.9 - 5.5 MPa. In the present invention, as a preferred solution, the core holder is Figure 2 the core holder provided by the natural gas hydrate core preparation device shown, and the core holder is as Figure 3 shown.

[0041] According to the present invention, preferably, the equipment for providing a low-temperature environment inside the core holder includes a low-temperature constant temperature bath. In the present invention, as a preferred solution, the equipment for providing a low-temperature environment inside the core holder includes a low-temperature constant temperature bath as Figure 4 shown, and some components of the low-temperature constant temperature bath are arranged on the outer wall of the core holder to provide a low-temperature environment.

[0042] According to the present invention, preferably, the operation of providing a low-temperature environment inside the core holder includes first maintaining a low temperature of -12°C to -8°C for 5 - 7 hours, and then maintaining a low temperature of 0.5 - 1.5°C for 11 - 13 hours to prepare the artificial core of natural gas hydrate.

[0043] The second aspect of the present invention provides an artificial core of natural gas hydrate prepared by the preparation method of the artificial core of natural gas hydrate described above.

[0044] The third aspect of the present invention provides the application of the artificial core of natural gas hydrate in the petrophysical research of natural gas hydrate.

[0045] The present invention will be specifically described below through examples.

[0046] In the following examples:

[0047] The epoxy resin is the Phoenix brand epoxy resin of Nantong Xingchen Synthetic Materials Co., Ltd.

[0048] The curing agent is R-2269 of Richy (Guangdong) Technology Co., Ltd.

[0049] The tetrahydrofuran is T818767 of Macklin.

[0050] Example 1

[0051] This example provides a preparation method of an artificial core of natural gas hydrate, and the method includes the following steps:

[0052] S1: Place the kaolin mineral powder (2000 mesh) as shown in Figure 1 in a drying oven and dry it at 50°C for 24 hours to obtain the dried kaolin mineral powder. Mix the dried kaolin mineral powder and the binder in a ratio of 9:1, stir and knead evenly, then put it into an iron mold, apply a pressure of 5 MPa under a high-precision hydraulic press and keep the pressure for 24 hours to obtain a kaolin plate. Take out the kaolin plate from the iron mold and put it into a crusher, and sieve out the kaolin particles of 60 - 80 mesh with a sample splitter to obtain the pretreated kaolin particles;

[0053] Among them, the binder is a mixture of epoxy resin and curing agent, and the dosage ratio of the epoxy resin and the curing agent is 2:1.

[0054] S2: Place 300 g of pretreated kaolin particles into a core holder, and pour a tetrahydrofuran aqueous solution (the mass ratio of tetrahydrofuran to water is 1:4.26, so that the mass fraction of the tetrahydrofuran aqueous solution is 19%) into the core holder until the pretreated kaolin particles in the core holder are submerged. Set the axial pressure to 5 MPa, and provide a low-temperature environment inside the core holder, that is, first maintain a low temperature of -10 °C for 6 h, and then maintain a low temperature of 1 °C for 12 h to prepare the artificial core of natural gas hydrate, as Figure 5 shown.

[0055] Among them, the core holder is Figure 2 the core holder set by the natural gas hydrate core preparation device shown, and the core holder is as Figure 3 shown.

[0056] The equipment for providing a low-temperature environment inside the core holder includes a low-temperature constant temperature bath as Figure 4 shown, and some components of the low-temperature constant temperature bath are arranged on the outer wall of the core holder to provide a low-temperature environment.

[0057] Moreover, during the preparation process of the artificial core in this embodiment, a high-voltage pulse generator is used to test the artificial core in this embodiment, and the results are as Figure 6 shown, which are the waveform data measured during the preparation process of the natural gas hydrate artificial core in the first embodiment of the present invention (measured once every 30 min, and the pulse signal is -5 to 5 V).

[0058] Example 2

[0059] This embodiment provides a method for preparing an artificial core of natural gas hydrate, and the method includes the following steps:

[0060] S1: Place the kaolin mineral powder (2000 mesh) as Figure 1 shown in a drying oven and dry it at 50 °C for 24 h to obtain the dried kaolin mineral powder. Mix the dried kaolin mineral powder and the binder in a ratio of 9:1, stir and knead evenly, then put it into an iron mold, apply a pressure of 5 MPa under a high-precision hydraulic press and keep the pressure for 24 h to obtain a kaolin plate. Take out the kaolin plate from the iron mold and put it into a crusher to crush it, and sieve out the kaolin particles with a particle size of 60 - 80 mesh with a sample sieve to obtain the pretreated kaolin particles;

[0061] Among them, the binder is a mixture of epoxy resin and curing agent, and the dosage ratio of the epoxy resin to the curing agent is 2:1.

[0062] S2: Place 300 g of pretreated kaolin particles into a core holder, and pour a tetrahydrofuran aqueous solution (the mass fraction of the tetrahydrofuran aqueous solution is 15.2%) into the core holder until the pretreated kaolin particles in the core holder are submerged. Set the axial pressure to 5 MPa, and provide a low-temperature environment inside the core holder, that is, first maintain a low temperature of -10 °C for 6 h, and then maintain a low temperature of 1 °C for 12 h to prepare the artificial core of natural gas hydrate, as Figure 7 shown.

[0063] Among them, the core holder is the core holder set in the natural gas hydrate core preparation device as Figure 2 shown, and the core holder is as Figure 3 shown.

[0064] The equipment for providing a low-temperature environment inside the core holder includes a low-temperature constant temperature bath as Figure 4 shown, and some components of the low-temperature constant temperature bath are arranged on the outer wall of the core holder to provide a low-temperature environment.

[0065] Moreover, during the preparation process of the artificial core in this embodiment, a high-voltage pulse generator is used to test the artificial core in this embodiment, and the results are as Figure 8 shown, which are the waveform data measured during the preparation process of the artificial core of natural gas hydrate in the second embodiment of the present invention (measured once every 30 min, and the pulse signal is -5 to 5 V).

[0066] Example 3

[0067] This embodiment provides a method for preparing an artificial core of natural gas hydrate, and the method includes the following steps:

[0068] S1: Place the kaolin mineral powder (2000 mesh) as Figure 1 shown in a drying oven and dry it at 50 °C for 24 h to obtain the dried kaolin mineral powder. Mix the dried kaolin mineral powder and the binder in a ratio of 9:1, stir and knead evenly, then put them into an iron mold, apply a pressure of 5 MPa under a high-precision hydraulic press and keep the pressure for 24 h to obtain a kaolin plate. Take out the kaolin plate from the iron mold and put it into a crusher to crush it, and sieve out the kaolin particles with a particle size of 60 - 80 mesh with a sample sieve to obtain the pretreated kaolin particles;

[0069] Among them, the binder is a mixture of epoxy resin and curing agent, and the dosage ratio of the epoxy resin to the curing agent is 2:1.

[0070] S2: Place 300 g of pretreated kaolin particles into a core holder, and pour a tetrahydrofuran aqueous solution (the mass fraction of the tetrahydrofuran aqueous solution is 11.3%) into the core holder until the pretreated kaolin particles in the core holder are submerged. Set the axial pressure to 5 MPa, and provide a low-temperature environment inside the core holder, that is, first maintain a low temperature of -10°C for 6 h, and then maintain a low temperature of 1°C for 12 h to prepare the artificial core of natural gas hydrate.

[0071] Among them, the core holder is Figure 2 the core holder set by the natural gas hydrate core preparation device shown, and the core holder is as Figure 3 shown.

[0072] The equipment for providing a low-temperature environment inside the core holder includes a low-temperature constant temperature bath as Figure 4 shown, and some components of the low-temperature constant temperature bath are arranged on the outer wall of the core holder to provide a low-temperature environment.

[0073] Moreover, during the preparation process of the artificial core in this embodiment, a high-voltage pulse generator is used to test the artificial core in this embodiment, and the results are as Figure 9 shown, which are the waveform data measured during the preparation process of the artificial core of natural gas hydrate in the third embodiment of the present invention (measured once every 30 min, and the pulse signal is -5 to 5 V).

[0074] Example 4

[0075] This embodiment provides a method for preparing an artificial core of natural gas hydrate, and the method includes the following steps:

[0076] S1: Place the kaolin mineral powder (2000 mesh) as Figure 1 shown in a drying oven and dry it at 50°C for 24 h to obtain the dried kaolin mineral powder. Mix the dried kaolin mineral powder and the binder in a ratio of 9:1, stir and knead evenly, then put it into an iron mold, apply a pressure of 5 MPa under a high-precision hydraulic press and hold the pressure for 24 h to obtain a kaolin plate. Take out the kaolin plate from the iron mold and put it into a crusher to crush it, and sieve out the kaolin particles with a particle size of 60 - 80 mesh with a sample splitter to obtain the pretreated kaolin particles;

[0077] Among them, the binder is a mixture of epoxy resin and curing agent, and the dosage ratio of the epoxy resin to the curing agent is 2:1.

[0078] S2: Put 300 g of pretreated kaolin particles into a core holder, and pour a tetrahydrofuran aqueous solution (the mass fraction of the tetrahydrofuran aqueous solution is 7.5%) into the core holder until the pretreated kaolin particles in the core holder are submerged. Set the axial pressure to 5 MPa, and provide a low-temperature environment inside the core holder, that is, first maintain a low temperature of -10°C for 6 h, and then maintain a low temperature of 1°C for 12 h to prepare the artificial core of natural gas hydrate.

[0079] Among them, the core holder is Figure 2 the core holder set in the natural gas hydrate core preparation device shown, and the core holder is as Figure 3 shown.

[0080] The equipment for providing a low-temperature environment inside the core holder includes a low-temperature constant temperature bath as Figure 4 shown, and some components of the low-temperature constant temperature bath are arranged on the outer wall of the core holder to provide a low-temperature environment.

[0081] Moreover, during the preparation of the artificial core in this embodiment, a high-voltage pulse generator is used to test the artificial core in this embodiment, and the results are as Figure 10 shown, which are the waveform data measured during the preparation of the artificial core of natural gas hydrate in Example 4 of the present invention (measured once every 30 min, and the pulse signal is -5 to 5 V).

[0082] Comparative Example 1

[0083] This comparative example provides a method for preparing an artificial core of natural gas hydrate. The difference between this comparative example and Example 1 is only that: the kaolin mineral powder is replaced with quartz sand to prepare an artificial core of natural gas hydrate, as Figure 11 shown.

[0084] Moreover, during the preparation of the artificial core in the comparative example, a high-voltage pulse generator is used to test the artificial core in this comparative example, and the results are as Figure 12 shown, which are the waveform data measured during the preparation of the artificial core of natural gas hydrate in Comparative Example 1 of the present invention (measured once every 30 min, the pulse signal is -5 to 5 V, and 1 sample point corresponds to 1 μs).

[0085] The above has described the embodiments of the present invention. The above description is exemplary and not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those of ordinary skill in the art in the technical field without departing from the scope and spirit of the described embodiments.

Claims

1. A method for preparing an artificial core of natural gas hydrate, characterized in that, the method comprises the following steps: S1: Mix the dried kaolin mineral powder and the binder, stir and knead evenly, then put them into a mold, perform pressure treatment, obtain the pressurized material, pulverize and screen it to obtain pretreated kaolin particles; S2: Put the pretreated kaolin particles into a core holder, pour a solvent aqueous solution into the core holder until the pretreated kaolin particles in the core holder are covered, provide a low-temperature environment inside the core holder, and prepare the artificial core of natural gas hydrate.

2. The method for preparing an artificial core of natural gas hydrate according to claim 1, wherein, the particle size of the kaolin mineral powder is 1800 - 2200 mesh; the drying temperature is 45 - 55 °C and the time is 12 - 36 h.

3. The method for preparing an artificial core of natural gas hydrate according to claim 1, wherein, the dosage ratio of the dried kaolin mineral powder to the binder is (8 - 9.5):(0.5 - 2); the binder is a mixture of epoxy resin and curing agent, and the dosage ratio of the epoxy resin to the curing agent is (1.5 - 2.5):(0.5 - 1.5).

4. The method for preparing an artificial core of natural gas hydrate according to claim 1, wherein, the mold is an iron mold; the equipment for the pressure treatment includes a high-precision hydraulic press, the pressure of the pressure treatment is 4.5 - 5.5 MPa, and the pressure treatment is kept for 12 - 36 h.

5. The method for preparing an artificial core of natural gas hydrate according to claim 1, wherein, the particle size of the pretreated kaolin particles is 60 - 80 mesh.

6. The method for preparing an artificial core of natural gas hydrate according to claim 1, wherein, the solvent aqueous solution is a tetrahydrofuran aqueous solution; the mass fraction of the tetrahydrofuran aqueous solution is 0.1 - 19%.

7. The method for preparing an artificial core of natural gas hydrate according to claim 1, wherein, the axial pressure of the core holder is 4.9 - 5.5 MPa.

8. The method for preparing an artificial core of natural gas hydrate according to claim 1, wherein, the equipment for providing a low-temperature environment inside the core holder includes a low-temperature constant temperature bath; the operation of providing a low-temperature environment inside the core holder includes first maintaining a low temperature of -12 °C to -8 °C for 5 - 7 h, and then maintaining a low temperature of 0.5 - 1.5 °C for 11 - 13 h to prepare the artificial core of natural gas hydrate.

9. An artificial core of natural gas hydrate prepared by the method for preparing an artificial core of natural gas hydrate according to any one of claims 1 - 8.

10. Application of the artificial core of natural gas hydrate according to claim 9 in the rock physics research of natural gas hydrate.

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