Experimental device and method for monitoring phase change of natural gas hydrate

Abstract

The invention discloses a natural gas hydrate phase change monitoring experiment device and method. The device comprises a core holder, the core holder comprises a shell, plugs are arranged at the two ends of the shell, a sleeve is arranged in the shell, a core is arranged in the sleeve, a pressure chamber is arranged between the shell and the sleeve, and a plurality of through holes are formed in the peripheral side wall of the sleeve; the testing system comprises a phase change promoter arranged on the shell, and the phase change promoter is a gas injection interface; the monitoring system comprises a pressure sensor and an acoustoelectric probe arranged in the core holder, and the acoustoelectric probe is connected with a bridge instrument, a sound wave pulse transmitter and an oscilloscope; during use, the natural gas hydrate is prepared in the pressure chamber, then the natural gas hydrate is decomposed through the phase change promoter, and the resistivity and sound wave changes in the process are recorded. The sound wave and resistivity change in the natural gas generation and decomposition process can be effectively recorded, and powerful data support is provided for the actual production process and mechanism research.

Description

Technical Field

[0001] The invention relates to the technical field of development of natural gas hydrates, in particular to a natural gas hydrate phase change monitoring experimental device and method. Background Art

[0002] Natural gas hydrate, also known as combustible ice, is an ice-like crystalline substance formed by natural gas and water under high pressure and low temperature conditions. Because it looks like ice and burns when exposed to fire, it is called "combustible ice", "solid gas" and "gas ice". Natural gas hydrate is distributed in deep sea or permafrost on land. After burning, it only produces a small amount of carbon dioxide and water, and the pollution is far less than coal, oil, etc., and the reserves are huge. Therefore, it is internationally recognized as a successor energy source to oil, etc.

[0003] Natural gas hydrates are generally found in sedimentary layers on the seafloor surface at a depth of no more than 2,000 meters. They are solid in form. If pressure-maintained sampling is not implemented, they will quickly volatilize and degrade after the original low-temperature and high-pressure environment changes. Therefore, it is difficult and costly to directly extract natural gas hydrate samples from the reservoir and preserve them for a long time, making it difficult to conduct subsequent research on the extracted natural gas hydrates.

[0004] There are many methods for the development of natural gas hydrates, including conventional hot fluid injection development, decompression development, and microwave heating in recent years. Although these methods are different, their purpose is usually to promote the decomposition of natural gas hydrates to generate natural gas and water for their exploitation. However, there is little research on the decomposition process of natural gas hydrates.

[0005] At the same time, existing technicians have conducted relatively little research on the natural gas hydrate formation process. Summary of the invention

[0006] In order to solve at least one of the above problems, the present invention provides an experimental device and method for monitoring the phase change of natural gas hydrate.

[0007] The technical solution of the present invention is: a natural gas hydrate phase change monitoring experimental device, comprising:

[0008] A core holder, the core holder comprising a shell, plugs are provided at both ends of the shell, a sleeve is provided in the shell, a core is provided in the sleeve, a pressure chamber is provided between the shell and the sleeve, and a plurality of through holes are provided on the peripheral side wall of the sleeve;

[0009] The test system comprises a phase change accelerator disposed on the housing, wherein the phase change accelerator is a gas injection interface, and one end of the gas injection interface is connected to the pressure chamber;

[0010] The monitoring system comprises a pressure sensor arranged in a pressure chamber and an acoustic-electric probe arranged in the core holder, wherein the acoustic-electric probe is arranged between the core and the plug, and the acoustic-electric probe is electrically connected to a bridge instrument, an acoustic pulse transmitter and an oscilloscope.

[0011] One implementation mode of the present invention is that a coupling piston with a variable diameter is further provided between the plug and the core, the larger end of the coupling piston is fitted with the plug, and the smaller end is fitted with the acoustic and electric probe; the diameter of the contact surface between the acoustic and electric probe and the core is the same as the diameter of the core; and the sleeve is a heat shrink tube.

[0012] Furthermore, at least one of the plugs is provided with a fluid injection connector, which passes through the plug, and one end of the fluid injection connector away from the plug is connected to a pressurizing device.

[0013] One embodiment of the present invention is that the phase change accelerator further includes a microwave generator, the emitting end of which passes through the shell and is aimed at the core; and / or the phase change accelerator further includes an exhaust pipe, one end of which is connected to the inside of the pressure chamber and the other end is connected to a back pressure valve, and the outlet of the back pressure valve is connected to a gas meter. .

[0014] An implementation manner of the present invention is that the test system further comprises a heater, the core holder is arranged inside the heater, and a temperature sensor is also arranged inside the acoustic and electrical probe.

[0015] Another object of the present invention is to disclose an experimental method for monitoring the phase change of natural gas hydrate, which is based on any of the above-mentioned devices and comprises the following steps:

[0016] S1. Take a core saturated with water and install the equipment, start the bridge instrument, acoustic pulse transmitter, oscilloscope and acoustic probe, inject natural gas into the pressure chamber until the pressure chamber reaches the target pressure, let it stand for a period of time to form natural gas hydrate in the core, and record the changes in acoustic waves and resistivity during the formation of natural gas hydrate;

[0017] S2, starting the phase change promoter and adjusting the parameters in the pressure chamber and the core to the target values ​​to promote the decomposition of natural gas hydrates, and recording the changes in acoustic waves and resistivity during the process;

[0018] S3. Repeat the above operation and adjust the parameters in the pressure chamber and the core to another target value through the phase change promoter to obtain the changes in the acoustic wave and resistivity of the natural gas hydrate under different parameter conditions.

[0019] One implementation of the present invention is that the core sleeve is a heat shrink tube, and before the core is saturated with water, the heat shrink tube is heated so that the heat shrink tube fixes the core; axial pressure is applied to the core through a fluid injection joint provided on the plug and a booster device connected to the fluid injection joint.

[0020] One implementation of the present invention is that in S1, after natural gas is injected into the pressure chamber to reach the target pressure, the pressure is left to stand, and the natural gas pressure gradually decreases and natural gas hydrates are generated in the core until the pressure in the pressure chamber remains unchanged for a period of time, and the pressure change of the process is recorded.

[0021] One implementation of the present invention is that in S2, in S2, hot fluid is injected into the pressure chamber through the gas injection interface to a target value, the hot fluid causes the natural gas hydrate in the core to decompose, and the changes in sound waves and resistivity in the process are recorded.

[0022] One implementation mode of the present invention is that, in S2, when the phase change promoter includes a microwave generator, the microwave generator is started to heat the core, and the changes in sound waves and resistivity in the process are recorded; when the phase change promoter includes an exhaust pipe, the exhaust pipe is opened, the pressure in the pressure chamber is adjusted to a target pressure, the target pressure is less than the initial pressure in the pressure chamber, and the changes in sound waves and resistivity in the process are recorded.

[0023] Beneficial effects: The device and method of the present invention can effectively record the acoustic waves and resistivity changes during the generation and decomposition of natural gas, providing strong data support for the actual production process and mechanism research. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the structure of the device of Example 1.

[0025] In the figure, 1 is a shell, 2 is a pressure chamber, 3 is a core, 4 is a sleeve, 5 is a coupling piston, 6 is a plug, 7 is an acoustic pulse transmitter, 8 is a bridge instrument, 9 is an oscilloscope, 10 is an acoustic probe, 11 is a fluid injection pipe, 12 is a gas injection interface, 13 is a temperature regulator, 14 is an exhaust pipe, 15 is a back pressure valve, 16 is a gas meter, and 17 is a microwave generator. DETAILED DESCRIPTION

[0026] The specific implementation modes of the present invention will be described clearly and completely below with reference to examples and drawings. Obviously, the described examples are only some embodiments of the present invention, rather than all embodiments.

[0027] Example 1

[0028] A natural gas hydrate phase change monitoring experimental device, comprising:

[0029] A core holder, the core holder comprising a shell 1, plugs 6 are provided at both ends of the shell 1, a sleeve 4 is provided inside the shell 1, a core 3 is provided inside the sleeve 4, a pressure chamber 2 is provided between the shell 1 and the sleeve 4, and a plurality of through holes are provided on the side wall of the sleeve 4;

[0030] The test system comprises a gas injection interface 12 and a phase change accelerator provided on the housing 1, wherein one end of the gas injection interface 12 is connected to the pressure chamber 2, and the phase change accelerator is at least one of a microwave generator 17 and a heater;

[0031] The monitoring system includes a pressure sensor arranged in the pressure chamber 2 and an acoustic-electric probe 10 arranged in the core holder. The acoustic-electric probe 10 is arranged between the core 3 and the plug 6. The acoustic-electric probe 10 is electrically connected to a bridge instrument 8, an acoustic pulse transmitter 7 and an oscilloscope 9.

[0032] Specifically, in this embodiment, the shell 1 is a pressure-bearing shell, which is made of pressure-bearing material. The pressure chamber 2 is the main place for the experiment in this embodiment, and the generation and decomposition of natural gas hydrates are carried out in the pressure chamber 2. The function of the plug 6 is to cooperate with the shell 1 to form a relatively closed pressure chamber 2. In order to monitor the pressure in the pressure chamber, a pressure sensor (not shown in the figure) is arranged in the pressure chamber to monitor the pressure change in the pressure chamber during the generation and decomposition of natural gas hydrates.

[0033] The function of the sleeve 4 is to fix the core 3 and the acoustic and electrical probe 10, wherein the diameter of the acoustic and electrical probe 10 is equal to the diameter of the core 3, one end of the acoustic and electrical probe 10 is close to the core 3, and the other end is connected to the bridge instrument 8, the acoustic pulse transmitter 7 and the oscilloscope 9, and the acoustic and electrical probe 10 can test the acoustic wave and the core resistivity at the same time. For the sleeve 4, its inner diameter is the same as the diameter of the core 3, so that the sleeve 4 can better tighten the core 3; at the same time, in order to be able to observe the process of the core 3 generating natural gas hydrates and the performance changes of the core 3 in the process, the core 3 is required to generate natural gas hydrates in the pressure chamber 2. For this purpose, the inventors set a number of through holes on the sleeve 4 so that the external gas can enter the core 3 through the through holes. When there is high-pressure natural gas in the pressure chamber 2, these natural gases can enter the core 3 through the through holes. Under certain pressure and temperature conditions, the natural gas and the water inside the core 3 react to generate natural gas hydrates. Preferably, the sleeve 4 is a heat shrink tube provided with a plurality of through holes.

[0034] The main function of the bridge meter 8 and the acoustic pulse transmitter 7 is to monitor the formation and degradation process of natural gas hydrates in the core, so as to provide corresponding data support for the theoretical analysis of the formation and degradation of natural gas hydrates. The bridge meter 8, in conjunction with the acoustic and electrical probe 10, can detect the resistivity change of the core 3; the acoustic pulse transmitter 7, in conjunction with the acoustic and electrical probe 10, can detect the change of the acoustic wave in the core 3 to simulate the process of acoustic logging. As for the oscilloscope 9, its function is to record and display the resistivity change and the acoustic wave change process.

[0035] As shown above, in order to enable the core 3 to generate natural gas hydrates, corresponding natural gas is also required. In order to ensure that there is enough natural gas in the pressure chamber 2, in this embodiment, at least one gas injection interface 12 is provided on the shell 1. Through the gas injection interface 12, high-pressure natural gas can be injected into the pressure chamber 2 to promote the water in the core and the high-pressure natural gas in the pressure chamber to generate natural gas hydrates; at the same time, in the prior art, when developing natural gas hydrates, the following methods are usually included: hot fluid injection, decompression development, electromagnetic heating development, etc. Therefore, in order to simulate these development methods, the gas injection interface 12 as a phase change promoter can also be used as a channel for injecting hot fluid to promote the phase change of natural gas hydrates in the core and simulate the development process of hot fluid injection.

[0036] In order to further simulate other development methods of natural gas hydrates, two other phase change promoters are also provided in this embodiment: an exhaust pipe and a variable frequency microwave generator. Among them, one end of the exhaust pipe is connected to the inside of the pressure chamber, and the other end is arranged outside the core holder and is connected to a back pressure valve and a meter in sequence; through the exhaust pipe, the process of decompression development can be simulated. The transmitting end of the microwave generator is arranged inside the shell and facing the core. Through the microwave generator, microwaves of different frequencies can be emitted to heat the core to explore the influence of microwaves of different frequencies on the development of natural gas hydrates.

[0037] In actual use, the inventor found that if the plug 6 is directly contacted with the acoustic and electric probe 10, the acoustic and electric probe 10 and the core 3 may have a low fit, resulting in a relatively poor ability of the acoustic and electric probe 10 to receive signals. In order to solve this problem, in the present embodiment, a coupling piston 5 with a variable diameter is provided between the acoustic and electric probe 10 and one of the plugs 6. One end of the coupling piston 5 is larger and fits with the plug 6, and the other end is smaller and fits with the acoustic and electric probe 10. Under the action of the coupling piston 5 of such a shape, the acoustic and electric probe 10 can be better coupled with the core 3 to improve its signal receiving ability. Preferably, the area of ​​the larger end of the coupling piston 5 is at least 5 times the area of ​​the smaller end. For the other plug 6, a coupling piston 5 can also be provided, or the plug 6 and the acoustic and electric probe 10 can be directly fit. Those skilled in the art can make arrangements according to actual conditions.

[0038] In particular, at least one of the plugs 6 is further provided with a fluid injection joint 11, which penetrates the plug 6, and one end of the fluid injection joint 11 away from the plug 6 is connected to a booster (not shown in the figure). Through the fluid injection joint 11 and the booster, axial pressure can be applied to the coupling piston 5, so that the core 3 is subjected to triaxial pressure. For the booster, a conventional hydraulic booster can be used.

[0039] For the formation and decomposition of natural gas hydrates, the two most important influencing factors are pressure and temperature. For pressure, it can be controlled by adding natural gas, so an additional temperature controller is also required. For this reason, the inventors set a temperature regulator 13, which is large in size and can maintain a relatively constant temperature. The shell 1 is set inside the temperature regulator 13 to facilitate heating and temperature control of the pressure chamber 2 and the core 3 inside the shell 1. In order to facilitate monitoring the temperature of the core 3, a temperature sensor (not shown in the figure) is also set inside the acoustic and electrical probe 10 to monitor the temperature and changes inside the pressure chamber 2 and the core 3. For the temperature regulator 13, a conventional air bath constant temperature test box can be set.

[0040] Example 2

[0041] A method for monitoring the phase change of natural gas hydrates is provided. The method is based on the device disclosed in Example 1 and comprises the following steps:

[0042] S1. Take a core saturated with water and install the equipment, start the bridge instrument, acoustic pulse transmitter, oscilloscope and acoustic probe, inject natural gas into the pressure chamber until the pressure chamber reaches the target pressure, let it stand for a period of time to form natural gas hydrate in the core, and record the changes in acoustic waves and resistivity during the formation of natural gas hydrate;

[0043] In this process, saturating the core with water is a conventional operation in the art, and those skilled in the art can saturate it with water using existing methods. At the same time, we can saturate the core with water in other devices and then place it in the device of this method.

[0044] During the installation of the core, since the sleeve used in this embodiment is a heat shrink tube, in order to fix the core so that the core does not move during the experiment, it is also necessary to use heating to cause the heat shrink tube to deform, thereby tightening the core.

[0045] The formation process of natural gas hydrate needs to be carried out under certain pressure and temperature conditions. Therefore, during the experiment, it can be adjusted to the appropriate temperature and pressure according to the actual reservoir conditions.

[0046] When natural gas hydrates are generated, as the natural gas is gradually consumed, the pressure inside the pressure chamber will gradually decrease. We can calculate the natural gas consumption based on the pressure reduction and the volume inside the pressure chamber, and thus obtain the amount of natural gas hydrate generated in the process.

[0047] During the process of natural gas hydrate formation, the acoustic logging data and resistivity of the core will change. Based on the changes in these values ​​and the degree of reduction in natural gas pressure, we can deduce the impact of natural gas hydrate formation on the reservoir, providing data support for research on the formation mechanism of natural gas hydrates.

[0048] S2, starting the phase change promoter and adjusting the parameters in the pressure chamber and the core to the target values ​​to promote the decomposition of natural gas hydrates, and recording the changes in acoustic waves and resistivity during the process;

[0049] In this process, as microwave heating proceeds, natural gas hydrates gradually decompose, and the decomposed natural gas hydrates will enter the interior of the pressure chamber, increasing the pressure of the pressure chamber. However, the increase in pressure will limit the decomposition of natural gas hydrates, resulting in distortion of the final measured result. In order to solve this problem, in this embodiment, the back pressure valve on the exhaust pipe can also be opened, and the corresponding first pressure is set on the back pressure valve as the exhaust pressure. When the pressure in the pressure chamber exceeds the first pressure, the excess natural gas will be discharged through the exhaust pipe and the back pressure valve, and the amount of the discharged gas will be measured by the gas meter.

[0050] In this embodiment, since the phase change accelerator includes a gas injection interface, a microwave generator and an exhaust pipe, there are many different operations for adjusting the parameters in the pressure chamber and the core through the phase change accelerator:

[0051] When only the gas injection interface is used as a phase change promoter, hot fluid is injected into the pressure chamber through the gas injection interface to a target value. The hot fluid causes the natural gas hydrate in the core to decompose, and the changes in acoustic waves and resistivity in the process are recorded.

[0052] When only a microwave generator is used as a phase change promoter, the microwave generator is started to heat the core, and the changes in sound waves and resistivity during the process are recorded; when the phase change promoter includes an exhaust pipe, the exhaust pipe is opened, the pressure in the pressure chamber is adjusted to a target pressure that is less than the initial pressure in the pressure chamber, and the changes in sound waves and resistivity during the process are recorded.

[0053] At the same time, during the operation, multiple phase change promoters can also be used in combination, such as the coordination of gas injection interface and microwave generator, the coordination of microwave generator and exhaust pipe, etc.

[0054] At the same time, for the exhaust pipe, it can not only serve as a phase change promoter, but also simulate the constant pressure environment in the wellbore during mining through the back pressure valve.

[0055] S3. Repeat the above operation and adjust the parameters in the pressure chamber and the core to another target value through the phase change promoter to obtain the changes in the acoustic wave and resistivity of the natural gas hydrate under different parameter conditions.

[0056] In summary, the device of the embodiment of the present invention can simulate the phase change of natural gas hydrate under different development conditions, so the data obtained can provide guidance for actual production. At the same time, since corresponding acoustic wave monitoring and resistivity monitoring are carried out, and acoustic wave and resistivity are common means in the process of natural gas hydrate logging, therefore, this embodiment can also explain the logging results based on acoustic wave and resistivity, and has a relatively wide range of application value; there are also some means of predicting natural gas hydrate reservoirs based on acoustic wave and resistivity logging results. Through the device and method of this embodiment, these means can also be provided with real data support to calibrate these prediction means.

[0057] At the same time, in the above-mentioned experimental process, axial pressure can be applied to the core through the fluid injection joint provided on the plug and the booster device connected to the fluid injection joint. The axial pressure usually needs to be greater than the pressure in the pressure chamber, and the difference can be set to 0-2MPa. Of course, technical personnel in this field can also set different axial pressures according to actual conditions.

[0058] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A natural gas hydrate phase change monitoring experimental device, characterized in that: include, A core holder, the core holder comprising a shell, plugs are provided at both ends of the shell, a sleeve is provided in the shell, a core is provided in the sleeve, a pressure chamber is provided between the shell and the sleeve, and a plurality of through holes are provided on the peripheral side wall of the sleeve; The test system comprises a phase change accelerator disposed on the housing, wherein the phase change accelerator is a gas injection interface, and one end of the gas injection interface is connected to the pressure chamber; The monitoring system comprises a pressure sensor arranged in a pressure chamber and an acoustic-electric probe arranged in the core holder, wherein the acoustic-electric probe is arranged between the core and the plug, and the acoustic-electric probe is electrically connected to a bridge instrument, an acoustic pulse transmitter and an oscilloscope.

2. The device according to claim 1, characterized in that A coupling piston with a variable diameter is also provided between at least one of the plugs and the core, the larger end of the coupling piston is fitted with the plug, and the smaller end is fitted with the acoustic and electric probe; the diameter of the contact surface between the acoustic and electric probe and the core is the same as the diameter of the core; and the sleeve is a heat shrink tube.

3. The device according to claim 2, characterized in that At least one of the plugs is also provided with a fluid injection joint, which passes through the plug, and one end of the fluid injection joint away from the plug is connected to a pressurizing device.

4. The device according to claim 1, characterized in that The phase change promoter also includes a microwave generator, the emitting end of which passes through the shell and is aimed at the core; and / or the phase change promoter also includes an exhaust pipe, one end of which is connected to the interior of the pressure chamber and the other end is connected to a back-pressure valve, and the outlet of the back-pressure valve is connected to a gas meter.

5. The device according to claim 1, characterized in that The testing system further comprises a heater, the core holder is arranged inside the heater, and a temperature sensor is also arranged inside the acoustic and electrical probe.

6. A method for monitoring the phase change of natural gas hydrate, characterized in that: The method is based on the device described in any one of claims 1 to 5, and comprises the following steps: S1. Take a core saturated with water and install the equipment, start the bridge instrument, acoustic pulse transmitter, oscilloscope and acoustic probe, inject natural gas into the pressure chamber until the pressure chamber reaches the target pressure, let it stand for a period of time to form natural gas hydrate in the core, and record the changes in acoustic waves and resistivity during the formation of natural gas hydrate; S2, starting the phase change promoter and adjusting the parameters in the pressure chamber and the core to the target values ​​to promote the decomposition of natural gas hydrates, and recording the changes in acoustic waves and resistivity during the process; S3. Repeat the above operation and adjust the parameters in the pressure chamber and the core to another target value through the phase change promoter to obtain the changes in the acoustic wave and resistivity of the natural gas hydrate under different parameter conditions.

7. The method according to claim 6, characterized in that The core sleeve is a heat shrink tube. Before the core is saturated with water, the heat shrink tube is heated so that the heat shrink tube fixes the core; axial pressure is applied to the core through a fluid injection joint provided on the plug and a booster device connected to the fluid injection joint.

8. The method according to claim 6, characterized in that In S1, after natural gas is injected into the pressure chamber to reach the target pressure, the pressure is left to stand, and the natural gas pressure gradually decreases and natural gas hydrates are generated in the core until the pressure in the pressure chamber remains unchanged for a period of time, and the pressure change of the process is recorded.

9. The method according to claim 6, characterized in that In S2, a hot fluid is injected into the pressure chamber through the gas injection interface to a target value. The hot fluid causes the natural gas hydrate in the core to decompose, and changes in the acoustic wave and resistivity during the process are recorded.

10. The method according to claim 6, characterized in that In S2, when the phase change promoter includes a microwave generator, the microwave generator is started to heat the core, and the changes in sound waves and resistivity during the process are recorded; when the phase change promoter includes an exhaust pipe, the exhaust pipe is opened, the pressure in the pressure chamber is adjusted to a target pressure, the target pressure is less than the initial pressure in the pressure chamber, and the changes in sound waves and resistivity during the process are recorded.

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