CN113047828B - Visual simulation method of clay expansion and migration during depressurization mining of argillaceous silt type hydrate - Google Patents

Abstract

The invention relates to a hydrate simulation experiment, in particular to a visual simulation method for clay expansion and migration in a depressurization exploitation process of a argillaceous powder sand mold hydrate. The method comprises the following steps: preparing clay suspension, soaking a glass etching model in saline water, injecting the clay suspension into the glass etching model, driving out clay particles which are not firmly attached to the surfaces of the pore passages of the glass etching model, soaking the glass etching model in the saline water again, and generating hydrate which is gradually decomposed. The method can effectively control the variation of the pore structure, and realize the visual observation of the behaviors such as clay expansion, migration and the like in the depressurization exploitation process of the hydrate, thereby clarifying the behavior evolution law of the clay and providing technical support for the regulation and control of the behavior of the clay in the actual depressurization exploitation process of the argillaceous powder sand mold hydrate.

Description

Visualization of clay swelling and migration during depressurization mining of argillaceous silt-type hydrate simulation method

technical field

The invention relates to a hydrate simulation experiment, in particular to a visual simulation method for clay expansion and migration during depressurization mining of argillaceous silt type hydrate.

Background technique

More than 90% of the world's natural gas hydrates are distributed in argillaceous silt reservoirs, which are characterized by small porosity, low permeability, and high clay content, and clay minerals are prone to hydration expansion and dispersion during mining Migration, resulting in the reduction of seepage space in reservoir pores, and the serious decrease of reservoir permeability.

Aiming at the problem of reservoir damage caused by clay during decompression mining of argillaceous silt type hydrates, there are literatures that have carried out hydrate depressurization mining simulation experiments using clay-bearing sediments, and found that during the process of hydrate decompression decompression, clay does indeed Volume expansion and particle migration occurred, resulting in a decrease in sediment permeability. However, the existing technical means and research methods can only obtain the final result of whether the clay expands and (or) migrates. For the behavioral evolution process of clay, such as how clay particles expand and migrate in the pores, the expansion and migration How the displaced clay particles affect hydrate decomposition and gas-water seepage cannot be described yet.

In addition, the pore media currently used to simulate argillaceous silt type reservoirs are all natural cores or artificially filled cores, and it is difficult to ensure that the pore structures of different cores are completely consistent. Since clay expansion and migration have a strong dependence on sediment pore structure, the difference in pore structure between cores will inevitably have a great impact on clay behavior, which seriously interferes with the accuracy of the research results.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned defects existing in the prior art, and propose a visual simulation method for clay expansion and migration during depressurization mining of argillaceous silt type hydrates, which can effectively control pore structure variables and realize hydration control. The intuitive observation of clay expansion and migration behaviors during the process of depressurization mining, so as to clarify the evolution law of clay behavior, and provide technical support for the regulation of clay behavior in the process of actual argillaceous silt type hydrate depressurization mining.

The technical solution of the present invention is: a visual simulation method for clay expansion and migration during the depressurization mining process of argillaceous silt type hydrate, which includes the following steps:

S1. configure the clay suspension;

S2. Glass etching model of rinse visualization simulation device:

The visual simulation device includes injection system, visual reactor, glass etching model, cooling circulation pump, output system, confining pressure control system, back pressure control system and image data acquisition system, and the glass etching model is located in the visual reactor;

The injection system includes a gas injection unit, a liquid injection unit, and a six-way valve 1, and the gas injection unit includes a methane cylinder, a pressure reducing valve, a gas flow meter and a one-way valve connected in sequence, and the one-way valve is connected with the six-way valve 1 , the liquid injection unit includes a straight-flow pump, a six-way valve II, an intermediate container I, an intermediate container II, and an intermediate container III, and the flat-flow pump, the intermediate container I, the intermediate container II, and the intermediate container III are respectively connected to the six-way valve II, and the intermediate container I Deionized water is contained inside, brine is contained in intermediate container II, and clay suspension is contained in intermediate container III, which has a stirring function. The outlets of the three intermediate containers are respectively connected to six-way valve I, and six-way valve I is also Connect with visualization reactor and pressure sensor I;

The visualization reaction kettle includes a kettle body, an upper top cover and a lower bottom cover, and the central positions of the upper top cover and the lower bottom cover are respectively provided with a visual window, the upper top cover is fixedly connected to the top of the kettle body, and the lower bottom cover is connected to the bottom of the kettle body. The bottom of the kettle body is fixedly connected, the center of the kettle body is provided with a hollow cavity, the wall of the kettle body is provided with an annular cavity, and the kettle body is provided with a circulating fluid inlet and a circulating fluid outlet, which are respectively connected to the cooling circulation pump Connection, so that the cooling circulating fluid circulates in the annular cavity of the kettle body. There are openings I and II on the upper top cover. The opening I is connected to the confining pressure control system. The opening II is connected to the temperature sensor. There is an opening on the lower bottom cover. III and port IV, port III is connected to the six-way valve I, port IV is connected to the output system, the inlet of the glass etching model is connected to port III, and the outlet of the glass etching model is connected to port IV;

The output system includes a six-way valve III, a pressure sensor II, a recovery tank, a solid phase separator, a back pressure valve, a gas-liquid separator, a gas collection bottle and a liquid collection bottle, and the six-way valve III is connected to the bottom cover respectively. The inlet of opening IV, the recovery tank, and the solid phase separator are connected to the pressure sensor II, the inlet of the back pressure valve is connected to the outlet of the solid phase separator, the outlet of the back pressure valve is connected to the inlet of the gas-liquid separator, and the gas-liquid separator The gas outlet of the gas-liquid separator is connected to the gas collecting bottle, and the liquid outlet of the gas-liquid separator is connected to the liquid collecting bottle;

The confining pressure control system includes a confining pressure control pump and a three-way valve I, the confining pressure control pump communicates with the opening I of the upper top cover through the three-way valve I, the pressure sensor III is connected to the three-way valve I, and the back pressure control The system includes a back pressure control pump and a three-way valve II, the back pressure control pump communicates with the pressure port of the back pressure valve through the three-way valve II, and the pressure sensor IV is connected to the three-way valve II;

The image data acquisition system includes a video microscope, a light source and a computer, the video microscope is connected to the computer through a data transmission line, and the computer is also connected to the pressure sensor I, the pressure sensor II, the pressure sensor III, the pressure sensor IV and the temperature sensor through the data line;

Adjust the six-way valve II and the six-way valve I to connect the advection pump, the intermediate container I and the opening III of the lower bottom cover, adjust the six-way valve III to make the output fluid of the glass etching model flow into the recovery pool, and the liquid in the intermediate container I Inject deionized water into the glass etching model, rinse the glass etching model repeatedly, and remove the bubbles and residues in the glass etching model;

S3. Salt water immersion glass etching model:

Adjust the six-way valve I to connect the advection pump, the intermediate container II and the opening III of the lower bottom cover, and inject the salt water in the intermediate container II into the glass etching model to fully soak the glass etching model;

S4. Inject the clay suspension into the glass etching model:

Adjust the six-way valve II to connect the advection pump, the intermediate container III and the opening III of the lower bottom cover, inject the clay suspension in the intermediate container III into the glass etching model, and observe the channels inside the glass etching model through a video microscope After the surface absorbs a layer of clay, turn off the advection pump and stop injecting the clay suspension;

S5. Drive out the clay particles that are not firmly attached to the channel surface of the glass etching model:

Adjust the six-way valve I to connect the gas injection unit with the opening III of the lower bottom cover, open the methane gas cylinder, pressure reducing valve, check valve and gas flow meter in turn, inject gas into the glass etching model, and drive out the glass etching model. Clay particles that are not firmly attached to the channel surface of the erosion model;

S6. Repeat S4 and S5, repeatedly inject clay suspension and gas into the glass etching model, and stop injecting clay suspension and gas after observing the clay content and distribution on the surface of the channel through a video microscope to become stable;

S7. soak the glass etching model in salt water again;

S8. Keep the brine injected, adjust the six-way valve III so that the inlet of the solid phase separator communicates with the opening IV of the lower bottom cover, and adjust the back pressure control pump and the confining pressure control pump synchronously to gradually increase the back pressure and confining pressure to Preset the pressure, and always keep the back pressure less than 1MPa of the confining pressure, and adjust the temperature of the cooling circulation pump to the preset temperature;

S9. Generate hydrate:

When the pressure value measured by pressure sensor I, pressure sensor II, and the temperature value measured by the temperature sensor are stable, adjust the six-way valve I so that the gas injection unit and the liquid injection unit are connected to the opening III of the lower bottom cover at the same time. Proportionally inject methane gas and brine into the glass etching model. After the gas-water seepage is stable, stop the injection, close the valve connecting the six-way valve I to the gas injection unit and the liquid injection unit, and close the six-way valve III to the recovery pool, The valve connected to the solid phase separator keeps the glass etching model closed and waits for the formation of hydrate;

S10. After observing the hydrate formation and stability in the glass etching model through a video microscope, adjust the six-way valve III to connect the inlet of the solid phase separator to the opening IV of the lower bottom cover, and adjust the back pressure control pump to make the return pressure The pressure gradually decreases, and at the same time adjust the confining pressure control pump to make the confining pressure drop synchronously, and always keep the confining pressure 1Mpa higher than the back pressure;

S11. As the back pressure decreases, the hydrate gradually decomposes. The video microscope is used to observe the behavioral response of the clay during the hydrate decomposition process in real time, and the pressure sensor I and pressure sensor II measure the front and rear pressure of the glass etching model in real time.

In the present invention, in step S1, according to the ion type and concentration of the formation water, configure brine that can replace the formation water, then add clay to the brine, and stir with a magnetic stirrer for more than 30 minutes to initially obtain a clay suspension, and then suspend the clay Ultrasonic dispersion of liquid for more than 1h.

In step S8, the set pressure of the back pressure control pump is 7MPa, the set pressure of the confining pressure control pump is 8MPa, and the set temperature of the cooling circulation pump is -1°C.

The light source is located below the viewing window II, and the video microscope is located above the viewing window I.

Ethylene glycol can be used as the cooling circulating fluid.

The beneficial effects of the present invention are:

(1) Using the adsorption characteristics of clay and the strong interfacial tension between air and water, a glass etching model can be obtained that uniformly adsorbs clay on the pore surface, thereby simulating the muddy silt type reservoir and ensuring the pore structure of the simulated reservoir Constant, avoiding the influence of pore structure changes on clay expansion and migration;

(2) By using visual research methods, the whole process of clay expansion and migration in the process of hydrate decompression mining is intuitively displayed, and the real-time observation of clay expansion and migration behaviors is realized, thus clearly revealing the relationship between clay expansion and migration. The migration and other behavioral evolution laws provide scientific guidance for the effective regulation of clay behavior in the process of depressurization mining of argillaceous silt type hydrates.

Description of drawings

Fig. 1 is a schematic structural diagram of a visual simulation device;

Fig. 2 is a top view structural schematic diagram of a visual reactor;

Fig. 3 is a schematic cross-sectional structure diagram of the visualization reactor.

In the figure: 1 advection pump; 2 six-way valve II; 3 intermediate container I; 4 intermediate container II; 5 intermediate container III; 6 methane cylinder; 7 pressure reducing valve; 8 gas flow meter; Through valve I; 11 pressure sensor I; 12 visual reaction kettle; 12-1 kettle body; 12-2 upper top cover; 12-3 visual window I; ;12-7 Circulating fluid inlet; 12-8 Circulating fluid outlet; 12-9 Bottom cover; 12-10 Opening III; 12-11 Visual window II; 12-12 Opening IV; 13 Glass etching model; 14 Six-way Valve III; 15 Cooling circulation pump; 16 Confining pressure control pump; 17 Three-way valve I; 18 Solid phase separator; 19 Back pressure valve; 20 Back pressure control pump; 21 Three-way valve II; 22 Gas-liquid separator; 23 Liquid collecting bottle; 24 gas collecting bottle; 25 video microscope; 26 computer; 27 temperature sensor; 28 pressure sensor II; 29 pressure sensor III; 30 pressure sensor IV; 31 recovery pool.

detailed description

In order to make the above objects, features and advantages of the present invention more comprehensible, specific implementations of the present invention will be described in detail below in conjunction with the accompanying drawings.

In the following description, specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention can be implemented in many other ways than those described here, and those skilled in the art can make similar extensions without departing from the connotation of the present invention. Accordingly, the present invention is not limited to the specific embodiments disclosed below.

The invention discloses a visual simulation method for clay expansion and migration in the process of depressurization mining of argillaceous silt type hydrate. The method comprises the following steps.

The first step is to configure the clay suspension.

According to the ion type and concentration of the formation water, prepare brine that can replace the formation water, then add clay to the brine, and stir with a magnetic stirrer for more than 30 minutes to initially obtain a clay suspension, and then ultrasonically disperse the clay suspension for more than 1 hour.

In the second step, the glass etching model of the visual simulation device is rinsed.

As shown in Figure 1, the visual simulation device includes an injection system, a visual reactor 12, a glass etching model 13, a cooling circulation pump 15, an output system, a confining pressure control system, a back pressure control system and an image data acquisition system. The glass etching model 13 is located in the visualization reactor 12 .

The injection system includes a gas injection unit, a liquid injection unit, and a six-way valve I10, wherein the gas injection unit includes a methane cylinder 6, a pressure reducing valve 7, a gas flow meter 8, and a one-way valve 9 connected in sequence, and the one-way valve 9 is connected to the six-way valve. Through the valve I10 connection. The liquid injection unit includes a horizontal flow pump 1, a six-way valve II2, an intermediate container I3, an intermediate container II4, and an intermediate container III5. The horizontal flow pump 1, the intermediate container I3, the intermediate container II4, and the intermediate container III5 are respectively connected to the six-way valve II2. I3 holds deionized water, intermediate container II4 holds brine, and intermediate container III5 holds clay suspension with stirring function. The outlets of the three intermediate containers are directly connected to the six-way valve I10 respectively. The six-way valve I10 is also connected with the visualization reactor 12 and the pressure sensor I11, through which the pressure sensor I11 measures the injection pressure when the liquid enters the glass etching model.

As shown in Figures 2 and 3, the visualization reactor 12 includes a still body 12-1, an upper top cover 12-2 and a lower bottom cover 12-9, and the center position of the upper top cover 12-2 and the lower bottom cover 12-9 Visible windows are respectively provided, the center of the upper top cover 12-2 is provided with a visual window I12-3, and the center of the lower bottom cover 12-9 is provided with a visual window II12-11. The upper top cover 12-2 is fixedly connected with the top of the kettle body 12-1 by several screws and nuts 12-4, and the lower bottom cover 12-9 is fixedly connected with the bottom of the kettle body 12-1 by several screws and nuts. The central hollow cavity of the kettle body 12 - 1 , the upper top cover 12 - 2 , the kettle body 12 - 1 and the lower bottom cover 12 - 9 constitute the internal space of the visualization reaction kettle 12 . An annular cavity is arranged in the wall of the kettle body, and a circulating fluid inlet 12-7 and a circulating fluid outlet 12-8 are arranged on the kettle body 12-1, and the circulating fluid inlet 12-7 and the circulating fluid outlet 12-8 are connected with the cooling cycle The pump 15 is connected, so that the cooling circulating fluid can circulate in the annular cavity of the kettle body, so as to realize the control of the temperature of the visualized reaction kettle. In this embodiment, ethylene glycol may be used as the cooling circulating fluid. The upper top cover 12-2 is provided with an opening I12-5 and an opening II12-6. The opening I12-5 is connected to the confining pressure control system. The confining pressure liquid enters the hollow cavity of the kettle body through the opening I12-5, and the opening II12-6 It is connected with the temperature sensor 27, and the temperature sensor 27 is used to measure the temperature of the confining pressure fluid. The lower bottom cover 12-9 is provided with an opening III12-10 and an opening IV12-12, the opening III12-10 is connected to the six-way valve I10 of the injection system, and the opening IV12-12 is connected to the output system.

In this embodiment, the glass etching model 13 is a square, the side length of the glass etching model 13 is 40 mm, the thickness is 4 mm, and the pressure resistance is 2 MPa. When placing the glass etching model 13 in the visualization reactor 12, the inlet of the glass etching model 13 is connected to the opening III12-10, and the outlet of the glass etching model 13 is connected to the opening IV12-12. There are micron-scale pores in the glass etching model for simulating the porous medium of the reservoir. In this embodiment, the kettle body 12-1 is made of stainless steel, with a height of 150 mm and an outer diameter of 200 mm. The internal space of the visualization reactor 12 is 60 mm in height, with an inner diameter of 100 mm and a pressure resistance of 30 MPa. The diameters of the viewing window I12-3 and the viewing window II12-11 are both 50mm.

The output system includes six-way valve III14, pressure sensor II28, recovery tank 31, solid phase separator 18, back pressure valve 19, gas-liquid separator 22, gas collection bottle 23 and liquid collection bottle 24, and six-way valve III14 is connected with The opening IV12-12 of the lower bottom cover 12-9, the recovery tank 31, the inlet of the solid phase separator 18 are connected with the pressure sensor II28, and the pressure sensor II28 is used to measure the outflow pressure of the glass etching model. The inlet of the back pressure valve 19 is connected with the outlet of the solid phase separator 18, the outlet of the back pressure valve 19 is connected with the inlet of the gas-liquid separator 22, and the gas outlet of the gas-liquid separator 22 is connected with the gas collecting bottle 23, and the gas-liquid separation The liquid outlet of device 22 is connected with liquid collection bottle 24.

The confining pressure control system includes a confining pressure control pump 16 and a three-way valve I17. The confining pressure control pump 16 communicates with the opening I12-5 of the upper top cover 12-2 through the three-way valve I17. The pressure sensor III29 is connected to the three-way valve I17. The pressure sensor III29 is used to measure the pressure of the hydraulic fluid inside the kettle body. Through the confining pressure control system, the confining pressure liquid is injected into the hollow cavity of the visualization reactor. During the simulation process, the hollow cavity of the visualization reactor is filled with confining pressure fluid, and the glass etching model is surrounded by confining pressure fluid. The confining pressure fluid provides external confining pressure for the glass etching model to protect the glass etching model and prevent The glass etching model was too high internal pressure and shattered.

The back pressure control system includes a back pressure control pump 20 and a three-way valve II21. The back pressure control pump 20 communicates with the pressure port of the back pressure valve 19 through the three-way valve II21. The pressure sensor IV30 is connected to the three-way valve II21. The pressure transducer IV30 is used to measure the back pressure exerted by the back pressure control pump.

Image-data acquisition system comprises video microscope 25, light source and computer 26, and video microscope 25 is connected computer 26 by data transmission line, and computer 26 is also by data line and pressure sensor I11, pressure sensor II28, pressure sensor III29, pressure sensor IV30 and temperature Sensor 27 is connected. The light source is located below the viewing window II12-11, and the intensity and color of the light source are adjustable. The video microscope 25 is located above the viewing window I12-3, which can photograph the simulated experimental phenomena in the glass etching model.

Adjust the six-way valve II2 and the six-way valve I10 to connect the advection pump 1, the intermediate container I3 and the opening III12-10 of the lower bottom cover 12-9, and adjust the six-way valve III14 to make the output fluid of the glass etching model flow into the recovery pool 31. Under the action of the advection pump 1, inject the deionized water in the intermediate container I3 into the glass etching model 13, rinse the glass etching model 13 repeatedly, and drain the air bubbles and residues in the glass etching model 13.

The third step is to etch the model in salt water soaked glass.

Adjust the six-way valve II2 to communicate with the advection pump 1, the intermediate container II4 and the opening III12-10 of the lower bottom cover 12-9. Under the action of the advection pump 1, inject the brine in the intermediate container II4 into the glass etching model 13, The glass etching model 13 is fully soaked to ensure that the wettability of the channel wall surface inside the glass etching model 13 reaches a stable state.

In the fourth step, the clay suspension is injected into the glass etching model.

Adjust the six-way valve II2 to connect the advection pump 1, the intermediate container III5 and the opening III12-10 of the lower bottom cover 12-9, and inject the clay suspension in the intermediate container III into the glass etching model under the action of the advection pump 1 13 in. After observing through the video microscope 25 that a layer of clay is adsorbed on the surface of the pores inside the glass etching model 13, the advection pump 1 is turned off, and the injection of the clay suspension is stopped.

The fifth step is to drive out the loosely attached clay particles on the channel surface of the glass etching model.

Adjust the six-way valve I10 so that the gas injection unit communicates with the opening III12-10 of the lower bottom cover 12-9, open the methane gas cylinder 6, the pressure reducing valve 7, the one-way valve 8 and the gas flow meter 9 in sequence, and etch the gas to the glass. Gas is injected into the model 13 to drive out the loosely attached clay particles on the channel surface of the glass etching model 13 .

The sixth step, repeating the fourth and fifth steps, repeatedly injecting clay suspension and gas into the glass etching model 13, and stopping injecting the clay suspension after observing that the content and distribution of the clay on the surface of the pores tends to be stable through the video microscope 25 and gas.

The seventh step is to etch the model with salt water soaking glass again.

Adjust the six-way valve II2 and the six-way valve I10 to connect the advection pump 1, the intermediate container II4 and the opening III12-10 of the lower bottom cover 12-9, and inject salt water into the glass etching model 13 under the action of the advection pump 1 , to re-soak the glass etched model 13 in salt water.

The eighth step is to maintain the injection of brine and adjust the six-way valve III14 so that the inlet of the solid phase separator 18 communicates with the opening IV12-12 of the lower bottom cover 12-9. Synchronously adjust the back pressure control pump 20 and the confining pressure control pump 16 to gradually increase the back pressure and confining pressure to the preset pressure, and always keep the back pressure less than 1 MPa of the confining pressure, and adjust the temperature of the cooling circulation pump 15 to the preset temperature . In this embodiment, the set pressure of the back pressure control pump 20 is 7MPa, the set pressure of the confining pressure control pump 16 is 8MPa, and the set temperature of the cooling circulation pump is -1°C.

The ninth step is to generate hydrate.

When the pressure value measured by the pressure sensor I11, the pressure sensor II28, and the temperature value measured by the temperature sensor 27 reach a stable value, adjust the six-way valve I10 so that the gas injection unit and the liquid injection unit are simultaneously connected to the opening of the lower bottom cover 12-9. III12-10 is connected, and inject methane gas and brine into the glass etching model 13 according to the set ratio. After the gas-water percolation is stable, stop the injection, close the six-way valve I10 and communicate with the gas injection unit and the liquid injection unit Close the valve of the six-way valve III14 communicating with the recovery tank 31 and the solid phase separator 18, so that the glass etching model 13 remains closed and waits for the formation of hydrate.

In the tenth step, when the hydrate is observed to be formed and stabilized in the glass etching model 13 through the video microscope 25, adjust the six-way valve III14 so that the inlet of the solid phase separator 18 is connected to the opening IV12-12 of the lower bottom cover 12-9 Connected, then adjust the back pressure control pump 20 to make the back pressure gradually drop, during this period, adjust the confining pressure control pump 16 to make the confining pressure drop synchronously, and always keep the confining pressure higher than the back pressure 1Mpa.

In the eleventh step, as the back pressure decreases, the hydrate gradually decomposes, and the video microscope 25 is used to observe the behavioral response of the clay during the hydrate decomposition process in real time, and at the same time, the pressure sensor I11 and pressure sensor II28 measure the temperature of the glass etching model 13 in real time. front and rear pressure.

The visual simulation method of clay expansion and migration during the depressurization mining process of argillaceous silt type hydrate provided by the present invention has been introduced in detail above. In this paper, specific examples are used to illustrate the principle and implementation of the present invention, and the descriptions of the above embodiments are only used to help understand the method and core idea of the present invention. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, some improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention. The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (5)

1. A visual simulation method for clay expansion and migration in a depressurization exploitation process of a argillaceous powder sand mold hydrate is characterized by comprising the following steps:

s1, preparing a clay suspension;

s2, washing a glass etching model of the visual simulation device:

the visual simulation device comprises an injection system, a visual reaction kettle, a glass etching model, a cooling circulating pump, an output system, a confining pressure control system, a back pressure control system and an image data acquisition system, wherein the glass etching model is positioned in the visual reaction kettle;

the injection system comprises a gas injection unit, a liquid injection unit and a six-way valve I, wherein the gas injection unit comprises a methane gas cylinder, a pressure reducing valve, a gas flowmeter and a one-way valve which are sequentially connected, the one-way valve is connected with the six-way valve I, the liquid injection unit comprises a constant flow pump, a six-way valve II, an intermediate container I, an intermediate container II and an intermediate container III, the constant flow pump, the intermediate container I, the intermediate container II and the intermediate container III are respectively connected with the six-way valve II, deionized water is contained in the intermediate container I, saline water is contained in the intermediate container II, clay suspension is contained in the intermediate container III, the intermediate container III has a stirring function, outlets of the three intermediate containers are respectively connected with the six-way valve I, and the six-way valve I is also connected with a visual reaction kettle and a pressure sensor I;

the visual reaction kettle comprises a kettle body, an upper top cover and a lower bottom cover, wherein the center positions of the upper top cover and the lower bottom cover are respectively provided with a visual window, the upper top cover is fixedly connected with the top of the kettle body, the lower bottom cover is fixedly connected with the bottom of the kettle body, the center of the kettle body is provided with a hollow cavity, an annular cavity is arranged in the wall of the kettle body, the kettle body is provided with a circulating liquid inlet and a circulating liquid outlet, the circulating liquid inlet and the circulating liquid outlet are respectively connected with a cooling circulating pump, so that cooling circulating liquid circulates in the annular cavity of the kettle body, the upper top cover is provided with an opening I and an opening II, the opening I is connected with a confining pressure control system, the opening II is connected with a temperature sensor, the lower bottom cover is provided with an opening III and an opening IV, the opening III is connected with a six-way valve I, the opening IV is connected with a production system, the inlet of a glass etching model is butted with the opening III, and the outlet of the glass etching model is butted with the opening IV;

the output system comprises a six-way valve III, a pressure sensor II, a recovery tank, a solid-phase separator, a back pressure valve, a gas-liquid separator, a gas collecting bottle and a liquid collecting bottle, wherein the six-way valve III is respectively connected with an opening IV of a lower bottom cover, the recovery tank, an inlet of the solid-phase separator and the pressure sensor II;

the confining pressure control system comprises a confining pressure control pump and a three-way valve I, the confining pressure control pump is communicated with an opening I of the upper top cover through the three-way valve I, a pressure sensor III is connected to the three-way valve I, the back pressure control system comprises a back pressure control pump and a three-way valve II, the back pressure control pump is communicated with a pressure interface of a back pressure valve through the three-way valve II, and a pressure sensor IV is connected to the three-way valve II;

the image data acquisition system comprises a video microscope, a light source and a computer, wherein the video microscope is connected with the computer through a data transmission line, and the computer is also connected with a pressure sensor I, a pressure sensor II, a pressure sensor III, a pressure sensor IV and a temperature sensor through data line connections;

adjusting the six-way valve II and the six-way valve I to enable the advection pump, the intermediate container I and the opening III of the lower bottom cover to be communicated, adjusting the six-way valve III to enable the produced fluid of the glass etching model to flow into the recovery tank, injecting deionized water in the intermediate container I into the glass etching model, repeatedly washing the glass etching model, and completely discharging bubbles and residues in the glass etching model;

s3, a saline water soaking glass etching model:

adjusting the six-way valve I to communicate the constant flow pump, the intermediate container II and the opening III of the lower bottom cover, and injecting the saline water in the intermediate container II into the glass etching model to fully soak the glass etching model;

s4, injecting a clay suspension into the glass etching model:

adjusting the six-way valve II to enable the constant-flow pump, the intermediate container III and the opening III of the lower bottom cover to be communicated, injecting the clay suspension in the intermediate container III into the glass etching model, observing that the surface of a pore channel in the glass etching model adsorbs a layer of clay through a video microscope, closing the constant-flow pump, and stopping injecting the clay suspension;

s5, driving out the clay particles which are not firmly adhered to the surface of the pore channel of the glass etching model:

adjusting the six-way valve I to enable the gas injection unit to be communicated with the opening III of the lower bottom cover, sequentially opening the methane gas cylinder, the pressure reducing valve, the one-way valve and the gas flowmeter, injecting gas into the glass etching model, and driving out clay particles which are not firmly attached to the surface of the pore channel of the glass etching model;

s6, repeating S4 and S5, repeatedly injecting clay suspension and gas into the glass etching model, observing that the content and distribution of clay on the surface of the pore channel tend to be stable through a video microscope, and stopping injecting the clay suspension and the gas;

s7, soaking the glass etching model again by using saline water;

s8, keeping saline water injection, adjusting a six-way valve III to enable an inlet of the solid phase separator to be communicated with an opening IV of a lower bottom cover, synchronously adjusting a back pressure control pump and a confining pressure control pump to enable back pressure and confining pressure to be gradually increased to preset pressure, keeping the back pressure smaller than the confining pressure by 1MPa all the time, and adjusting the temperature of a cooling circulating pump to be at a preset temperature;

s9, hydrate generation:

when the pressure values measured by the pressure sensor I and the pressure sensor II and the temperature value measured by the temperature sensor are stable, adjusting the six-way valve I to simultaneously communicate the gas injection unit and the liquid injection unit with the opening III of the lower bottom cover, injecting methane gas and brine into the glass etching model in proportion, stopping injecting after gas-water seepage is stable, closing valves communicated with the gas injection unit and the liquid injection unit by the six-way valve I, and closing the valves communicated with the recovery tank and the solid phase separator by the six-way valve III to keep the glass etching model closed, and standing until hydrates are generated;

s10, when the generation and the stability of hydrates in the glass etching model are observed through a video microscope, adjusting a six-way valve III to enable an inlet of a solid phase separator to be communicated with an opening IV of a lower bottom cover, adjusting a back pressure control pump to enable the back pressure to be gradually reduced, adjusting a confining pressure control pump to enable the confining pressure to be synchronously reduced, and keeping the confining pressure higher than the back pressure by 1Mpa all the time;

s11, gradually decomposing the hydrate along with the reduction of the back pressure, observing the behavior response of clay in the decomposition process of the hydrate in real time by using a video microscope, and measuring the front and back pressures of the glass etching model in real time by using a pressure sensor I and a pressure sensor II.

2. The method of claim 1, wherein: in the step S1, saline water capable of replacing the formation water is prepared according to the ion type and concentration of the formation water, then clay is added into the saline water, a magnetic stirrer is used for stirring for more than 30min, a clay suspension is obtained preliminarily, and the clay suspension is subjected to ultrasonic dispersion for more than 1 h.

3. The method of claim 1, wherein: in step S8, the set pressure of the back pressure control pump is 7MPa, the set pressure of the confining pressure control pump is 8MPa, and the set temperature of the cooling circulating pump is-1 ℃.

4. The method of claim 1, wherein: the light source is positioned below the visual window II, and the video microscope is positioned above the visual window I.

5. The method of claim 1, wherein: the cooling circulating liquid adopts ethylene glycol.

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