CN111691856A - Device and method for simulating influence of overlying and marginal low water layers on methane hydrate exploitation - Google Patents

Abstract

The invention discloses a simulation device and an experimental method for influence of an upper water-covering layer and a lower water-covering layer on exploitation of methane hydrate, wherein the simulation device comprises a gas injection unit, a water injection unit, a reservoir simulation unit, a gas-liquid separation unit and a data acquisition system; the reservoir simulation unit is immersed in the water bath heating tank and comprises a sealed box body in a cubic shape, an inner cavity of the box body is divided into an upper layer cavity, a middle layer cavity and a lower layer cavity by two partition plates which are horizontally arranged, the upper layer cavity, the middle layer cavity and the lower layer cavity are respectively used as an upper water covering layer area, a hydrate storage layer area and a side low water layer area, each area is provided with a water injection port, an air inlet, a pressure gauge and a thermometer, the water injection ports are connected with the water injection unit, and the air inlets are connected with the air injection unit. And a vertical shaft and a horizontal shaft in the horizontal direction are arranged in the box body. The simulation device can be used for researching the influence of the upper water-layer area and the lower water-layer area on the exploitation of the hydrate reservoir area.

Description

Device and method for simulating influence of overlying and marginal low water layers on methane hydrate exploitation

Technical Field

The invention relates to the technical field of methane hydrate exploitation, in particular to a simulation device and an experimental method for researching influence of an upper water layer and a lower water layer on methane hydrate exploitation.

Background

From the condition of hydrate pilot production in the past, the water yield is greatly improved compared with that of the traditional oil-gas reservoir in the methane hydrate production process, and the gas-water co-production becomes an obvious characteristic in the hydrate production process. Due to the decomposition of hydrate, the rock skeleton of a reservoir containing hydrate is changed greatly, and the sand grains are moved in a near wellbore area due to the large yield of water, so that the sand production of a perforation section is serious, even collapse occurs, and matched equipment is further damaged. Meanwhile, a large amount of water is easy to form a water cone near the bottom of the well, so that gas is bound in a reservoir stratum, the trial production time is greatly reduced, and the trial production condition of the hydrate is poor directly. For this reason, for hydrate production, effective control of water production during hydrate production has a significant impact on commercial production of hydrate reservoirs. In combination with the current knowledge, the water produced during hydrate production comes not only from the hydrate decomposition and hydrate-bearing reservoirs, but also from overlying and marginal low water layers, mainly due to the fact that the hydrate reservoir is shallow in depth, so that the compaction effect of the rock is not strong. However, at present, the water production law in the hydrate exploitation process is not sufficiently known, so that an effective water control measure is lacked to indicate the pilot production of the hydrate. .

Disclosure of Invention

The invention aims to provide a simulation device and a simulation experiment method for influence of overlying and side low water layers on methane hydrate exploitation, aiming at solving the problem that the existing water production law in the hydrate exploitation process is not sufficiently known, so that the problem that the effective water control measure is lacked to indicate the pilot exploitation of the hydrate is solved.

The simulation device for the influence of the overlying and side low water layers on the exploitation of the methane hydrate, provided by the invention, has the following structure: the simulation device comprises a gas injection unit, a water injection unit, a reservoir simulation unit, a gas-liquid separation unit and a data acquisition system.

The gas injection unit comprises a methane storage tank, a gas booster pump and a high-pressure gas storage tank which are sequentially connected, the gas booster pump is further connected with an air compressor, and the high-pressure gas storage tank is connected to the reservoir simulation unit.

The water injection unit comprises a deionized water tank with a constant-temperature water bath and a water injection pump connected with the water tank, and an outlet of the water injection pump is connected to the reservoir simulation unit.

The reservoir simulation unit is immersed in the water bath heating tank and comprises a sealed box body in a cubic shape, an inner cavity of the box body is divided into an upper layer cavity, a middle layer cavity and a lower layer cavity by two horizontal partition plates, the upper layer cavity, the middle layer cavity and the lower layer cavity are respectively used as an upper water covering layer area, a hydrate storage layer area and a side low water layer area, and each area is provided with a water injection port, an air inlet, a pressure gauge and a thermometer. And the gas outlet of the high-pressure gas storage tank is simultaneously connected with the gas inlets of the upper water layer area, the hydrate storage area and the side low water layer area. The outlet of the water injection pump is simultaneously connected with the water injection ports of the upper water layer area, the hydrate storage area and the side low water layer area. Each region is filled with a dry porous medium, which may be quartz sand or sea mud.

The inner portion of the partition board is provided with an interlayer control mechanism, the interlayer control mechanism comprises a square through hole which is formed in the partition board and is through up and down, a threaded hole perpendicular to the side face of the partition board is formed in one side face of the partition board, the central axis of the threaded hole is overlapped with the central axis of the square through hole in the horizontal direction, and the threaded hole penetrates through the square through hole and extends to the inner portion of the other side face of the square through hole in a straight. The bottom end in the threaded hole is provided with a spring, the screw rod is inserted into the threaded hole from the outside of the box body, and the front end of the screw rod positioned outside the box body is provided with a bolt. The diameter of screw rod is greater than square through hole's width, can be with the complete shutoff of square through hole, and is provided with another square through hole the same with square through hole size on the screw rod, changes screw rod square through hole and baffle square through hole's alignment degree through rotatory adjusting bolt, realizes opening or closing of baffle square through hole to between the realization upper water layer region and hydrate reservoir region, the intercommunication or the isolation between hydrate reservoir region and the limit low water layer region. And the through holes in the direction of the partition board are provided with anti-sand cloth.

The vertical well shaft penetrates through the upper water covering layer area, the hydrate storage layer area and the lower water layer area, and the horizontal well shaft is located in the hydrate storage layer area. And the horizontal well shaft and the vertical well shaft are wrapped by sand control cloth and are provided with perforations. The vertical shaft in the upper water covering area and the lower water area may be perforated or not perforated. And the production outlet of the vertical well shaft and the production outlet of the horizontal well shaft are both connected to the gas-liquid separation unit. And back pressure valves are arranged on pipelines between the production outlets of the vertical well shaft and the horizontal well shaft and the gas-liquid separation unit.

The gas-liquid separation unit comprises a gas-liquid separator, a gas outlet of the gas-liquid separator is connected with a gas flowmeter, and a balance is arranged at the bottom of the gas-liquid separator.

The data acquisition system is connected with all pressure gauges, thermometers, gas flow meters and back pressure valves and is used for acquiring data information such as pressure and temperature, and the data acquisition system is finally connected to a computer.

Preferably, the sealed box body is formed by splicing a first box body unit with an opening at the upper end, a second box body unit with a square opening, a third box body unit with a square opening and a square top cover. The second box body unit and the third box body unit are identical in structure, the upper end and the lower end of the second box body unit are open, and the middle in the second box body is provided with a partition board integrally formed with the box body to divide the inner space of the box body into an upper layer and a lower layer. The opening position of the upper end of the first box body unit is provided with a lower end opening of a second box body unit, the upper end opening of the second box body unit is connected with the lower end opening of a third box body unit, and the upper end opening of the third box body unit is connected with a square cover plate; the junction of first box unit and second box unit, the junction between second box unit and the third box unit, the junction between third box unit and the square apron all are equipped with the sealing washer and pass through square clamp fixed connection, finally form complete sealed box. The center of the square cover plate, the center of the partition plate of the third box body and the center of the partition plate of the second box body are respectively provided with a mounting hole for mounting a vertical shaft, and the three mounting holes are vertically overlapped and aligned and are positioned on the vertical central line of the sealing box body. The surface of the vertical shaft is provided with threads, the inner wall of the mounting hole is provided with threads, and the vertical shaft is rotated to be mounted by matching the threads on the surface of the vertical shaft and the threads on the inner wall of the mounting hole. And a fastening sealing element is arranged at the mounting hole position at the center of the outer side of the square cover plate and used for fastening the vertical shaft.

The method for carrying out the simulation experiment by adopting the simulation device comprises the following steps:

s1, installing a reservoir simulation unit: filling porous media in the boundary low-water layer area, the hydrate storage area and the upper water covering layer area in sequence, installing a horizontal well shaft and a vertical well shaft, and finally installing a square top cover for sealing;

s2, placing the reservoir simulation unit in a water bath heating tank, adjusting the temperature to the experimental temperature and keeping the temperature constant;

s3, injecting water in the deionized water tank into the low-water-level area, opening a production outlet of the vertical shaft to discharge air in the vertical shaft until the deionized water is completely immersed, and adding a tracer; then sequentially injecting deionized water containing different tracers into the hydrate storage area and the overlying water layer area, wherein the pressure of the three areas is kept similar to the actual formation pressure, and the deionized water containing the tracers is ensured to be fully contacted with the porous medium;

s4, closing air inlets of the upper water covering layer area and the lower water layer area, and injecting methane gas into the hydrate reservoir area;

s5, adjusting the temperature of the water bath heating tank to the temperature of an actual reservoir, closing an air inlet of a hydrate reservoir area, and starting generating a hydrate;

s6, sequentially injecting deionized water containing a tracer into the upper water layer area and the lower water layer area to reach the final pressure of hydrate formation during the hydrate formation;

s7, opening a back pressure valve to reduce the pressure;

s8, adjusting bolts located outside the sealing box body according to experimental requirements, changing the overlapping alignment degree of the square through holes of the screw rods and the direction through holes of the partition plates so as to change the mutual connectivity among the three areas and verify the influence of the upper water layer area and the lower water layer area on the exploitation of the hydrate reservoir area;

s9, opening a production outlet of the vertical well shaft or a production outlet of the horizontal well shaft, and starting depressurization production;

s10, the produced methane and water enter a gas-liquid separator for separation, the produced methane gas is measured by a gas flowmeter, and the produced water is weighed by a balance; during the whole experiment process, the data of the pressure gauge and the temperature gauge are collected by the data collecting system and transmitted to the computer.

Compared with the prior art, the invention has the advantages that:

1. the simulation device of the invention integrally designs the upper water-covering layer, the hydrate reservoir and the lower water-covering layer, and is convenient to disassemble and assemble; and the interlayer control mechanism is adopted to realize the communication of the three storage areas.

2. The vertical shaft adopts a sectional design, so that different exploitation effects of different perforation in three reservoirs are realized, and the horizontal shaft is also designed for comparing the exploitation effects of the three reservoirs under different well types. And the influence of a single water body on the exploitation of a hydrate reservoir can be realized through the arrangement of different perforation sections and the control of different interlayer control mechanisms.

3. By adding different tracers into different injected water, the method can be used for detecting the content of methane hydrate exploitation of the upper water layer and the lower water layer at the edge, and realizes the evaluation of hydrate exploitation of the upper water layer and the lower water layer at the edge.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.

Drawings

FIG. 1, upper and lower water layers with simulated process flow diagram for methane hydrate production impact.

Fig. 2 is a perspective view of a reservoir simulation unit.

Fig. 3 is a schematic sectional structure diagram of a reservoir simulation unit.

Fig. 4 is a schematic structural view of the screw.

Reference numbers in the figures:

1. a deionized water tank; 2. an inlet control valve of the water injection pump; 3 and 5, a water injection pump; 4 and 6, a water injection pump outlet control valve; 7. a methane storage tank; 8. an outlet control valve; 9. an inlet control valve of the gas booster pump; 13. an outlet control valve of the gas booster pump; 10. a gas booster pump; 11. an air compressor outlet control valve; 12. an air compressor; 14. an inlet control valve for the high-pressure gas storage tank; 15. a pressure gauge; 16. an outlet control valve of the high-pressure gas storage tank; 17. a high-pressure gas storage tank; 18. a methane injection control main valve; 19. a water bath heating tank; 20-22 parts of a water injection port control valve; 23-25, an air inlet control valve; 26-28 parts of pressure gauge; 29-36, thermometer; 37. a vertical well bore; 38. a horizontal well bore; 39. a vertical shaft production outlet control valve; 40. a horizontal well shaft production outlet control valve; 41. an inlet control valve of the back pressure valve; 42. a back pressure valve; 43. a back pressure valve outlet control valve; 44. a gas separator; 45. a balance; 46. a gas flow meter; 47. discharging the gas; 48. a data acquisition system; 49. computer, 50, sealed box; 51. a partition plate; 52. an upper water layer area; 53. a hydrate reservoir region; 54. a marginal low water area; 55. water injection ports are arranged in the area of the upper cladding layer; 56. a water injection port of the hydrate reservoir region; 57. a water injection port is arranged at the lower water layer area; 58. an upper cladding area air inlet; 59. a hydrate reservoir zone air inlet; 60. a marginal low water region air inlet; 61. a square through hole of the partition plate; 62. a spring; 63. a screw; 64. a bolt; 65. a square through hole of the screw; 66. a sand control cloth; 67. perforating; 68. a first case unit; 69. a second case unit; 70. a third case unit; 71. a square top cover; 72. a seal ring; 73. a square hoop; 74. mounting holes; 75. a thread; 76 securing a seal; 77. a pressure test tube; 78. testing the sand prevention head by pressure; 79. an interlayer control mechanism; 80. a single layer temperature probe distribution layer.

Detailed Description

The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.

As shown in fig. 1 to 3, the simulation apparatus for the influence of the overlying and edge low water layers on the exploitation of methane hydrate provided by the invention has the following structure: the simulation device comprises a gas injection unit, a water injection unit, a reservoir simulation unit, a gas-liquid separation unit and a data acquisition system.

The water injection unit comprises a deionized water tank 1 with a constant-temperature water bath and two water injection pumps (a water injection pump 3 and a water injection pump 5) connected with the water tank 1 in parallel. Be equipped with water injection pump import control valve 2 on the pipeline that is close to water injection pump 3 and 5 imports of water injection pump, set up water injection pump export control valve 4 and water injection pump export control valve 6 on the pipeline that is close to water injection pump 3 and 5 exports of water injection pump respectively, two water injection pump exit linkage to reservoir simulation unit, to reservoir simulation unit injection deionized water.

The gas injection unit comprises a methane storage tank 7, a gas booster pump 10 and a high-pressure gas storage tank 17 which are sequentially connected, and the gas booster pump is further connected with an air compressor 12. An outlet control valve 8 is arranged at the outlet position of the methane storage tank 7. The inlet end and the outlet end of the gas booster pump 10 are respectively provided with a gas booster pump inlet control valve 9 and a gas booster pump outlet control valve 13. An air compressor outlet control valve 11 is arranged on a pipeline between the air compressor and the gas booster pump. The inlet end of the high-pressure gas tank 17 is provided with a high-pressure gas tank inlet control valve 14. The high-pressure gas storage tank 17 is connected to a reservoir simulation unit to which high-pressure methane gas is injected. A pressure gauge 15, a high-pressure gas storage tank outlet control valve 16 and a methane injection control main valve 18 are sequentially arranged on a pipeline between the outlet end of the high-pressure gas storage tank 17 and the reservoir simulation unit.

The reservoir simulation unit is immersed in a water bath heating tank 19. The reservoir simulation unit comprises a sealed box body 50 in a cubic shape, an inner cavity of the box body is divided into an upper layer cavity, a middle layer cavity and a lower layer cavity by two partition plates 51 which are horizontally arranged, the upper layer cavity, the middle layer cavity and the lower layer cavity are respectively used as an upper water covering layer area 52, a hydrate storage layer area 53 and a side low water layer area 54, and each area is provided with a water filling port, an air inlet, a pressure gauge and a thermometer. Wherein, the water injection port comprises an upper water layer water injection port 55, a hydrate reservoir region water injection port 56 and a side low water layer water injection port 57. The air inlets comprise an overlying water zone air inlet 58, a hydrate reservoir zone air inlet 59, and a boundary low water zone air inlet 60. The pressure gauges include an upper water-layer region pressure gauge 26, a hydrate reservoir region pressure gauge 27, and a side low water region pressure gauge 28. The pressure gauge also includes a pressure test tube 77 and a pressure test sand control head 78 located inside the tank. The thermometers include an overburden zone thermometer 29, hydrate reservoir zone thermometers 30, 31, 32, 33, 34, 35, and a boundary low zone thermometer 36. And a plurality of rows of thermometers are distributed in the hydrate reservoir area and used for monitoring the distribution of the temperature, and the rows and the distribution of the thermometers can be carried out according to the actual condition. The perspective view of fig. 2 shows the temperature probe distribution for a single layer only, see the single layer temperature probe distribution layer 80. The gas outlet of the high-pressure gas storage tank is connected with the gas inlets of the upper water layer area, the hydrate storage area and the side low water layer area simultaneously by using a four-way joint or two three-way joints. And an intake port control valve 23, 24, 25 is mounted at the front end of each intake port. The outlet of the water injection pump is simultaneously connected with the water injection ports of the upper water layer area, the hydrate storage area and the side low water layer area by using one four-way joint or two three-way joints. And a water inlet control valve 20, 21, 22 is installed at the front end of each water inlet. Each region is filled with a dry porous medium (not shown), which may be quartz sand or sea mud.

The partition plate 51 has a certain thickness, and an interlayer control mechanism 79 is provided inside the partition plate. The interlayer control mechanism comprises a square through hole 61 which is formed in the partition plate and penetrates up and down. A threaded hole perpendicular to the side face of the partition board is formed in one side face of the partition board, the central axis of the threaded hole is overlapped with the central axis of the square through hole in the horizontal direction, and the threaded hole penetrates through the square through hole and extends to the inside of the other side face of the square through hole in a straight line mode. The bottom end in the threaded hole is provided with a spring 62, a screw 63 is inserted into the threaded hole from the outside of the box body, and the front end of the screw positioned outside the box body is provided with a bolt 64. The diameter of the screw 63 is larger than the width of the square through hole, the square through hole 61 can be completely plugged, another square through hole 65 with the same size as the square through hole is arranged on the screw 63, the alignment degree of the screw square through hole 65 and the partition plate square through hole 61 is changed by rotating the adjusting bolt, and the partition plate square through hole is opened or closed, so that communication or isolation between the upper water layer area and the hydrate storage area and between the hydrate storage area and the side low water layer area is realized. A sand cloth (not shown) is provided on the directional through hole 61 of the partition. The purpose of the interlayer control mechanism 79 is to control the communication pattern of the overburden and boundary low water zones with the hydrate reservoir zone as desired.

A vertical shaft 37 and a horizontal shaft 38 are arranged in the box 50, and the vertical shaft penetrates through the upper water covering layer area 52, the hydrate storage layer area 53 and the lower water layer area 54. A horizontal well bore is located in the hydrate reservoir zone 53. A horizontal well bore is disposed in the lateral middle of the hydrate reservoir zone, while a vertical well bore is disposed longitudinally through the three zones, with different perforation locations. The horizontal well shaft and the vertical well shaft are wrapped by the sand control cloth 66 and are provided with the perforation 67. The manner of perforation may be square, circular, etc., but the interval of perforation should be according to a simulation scheme. For example, vertical wellbores in overburden and marginal low water zones may or may not be perforated. And the production outlet of the vertical well shaft and the production outlet of the horizontal well shaft are both connected to the gas-liquid separation unit. The gas-liquid separation unit comprises a gas-liquid separator 44, a gas outlet of the gas-liquid separator is connected with a gas flowmeter 46, and the bottom of the gas-liquid separator is provided with a balance 45. The production outlets of both the vertical and horizontal well bores are connected to a gas-liquid separator 44. And a vertical well shaft production outlet control valve 39 and a horizontal well shaft production outlet control valve 40 are arranged at the production outlet positions of the vertical well shaft and the horizontal well shaft. A back pressure valve 42 is arranged on a pipeline between the two control valves and the gas-liquid separator, and the front end and the rear end of the back pressure valve 42 are respectively provided with a back pressure valve inlet control valve 41 and a back pressure valve outlet control valve 43. The gas passing through the gas flow meter 46 is discharged from the gas discharge port 47.

The data acquisition system 48 is connected with all pressure gauges, thermometers, gas flow meters and back pressure valves for acquiring data information such as pressure and temperature, and is finally connected to the computer 49.

In another embodiment, the sealed box 50 is formed by splicing a first box unit 68 with a square upper end opening, a second box unit 69 with a square upper end opening, a third box unit 70 with a square upper end opening, and a square top cover 71 with a square upper end opening. The second box unit 69 and the third box unit 70 have the same structure, the upper end and the lower end of the second box unit 69 are open, and the middle part in the second box body is provided with a partition plate 51 which is integrally formed with the box body to divide the inner space of the box body into an upper layer and a lower layer. The upper end opening of the first box body unit is provided with a lower end opening of the second box body unit, the upper end opening of the second box body unit is connected with a lower end opening of the third box body unit, and the upper end opening of the third box body unit is connected with the square cover plate. The junction of first box unit and second box unit, the junction between second box unit and the third box unit, the junction between third box unit and the square apron all are equipped with sealing washer 72 and pass through square clamp 73 fixed connection, finally form complete sealed box. Mounting holes 74 for mounting a vertical shaft are formed in the center of the square cover plate, the center of the partition plate of the third box body and the center of the partition plate of the second box body, the three mounting holes are vertically overlapped and aligned and are located on the vertical central line of the sealing box body. The surface of the vertical shaft is provided with threads, and the inner wall of the mounting hole 74 is provided with threads 75 matched with the threads on the surface of the vertical shaft, so that the vertical shaft can be rotatably mounted through the threads. And a fastening sealing member 76 is arranged at the position of the mounting hole in the center of the outer side of the square cover plate and used for fastening the vertical shaft. Similarly, the horizontal well shaft is horizontally inserted into the hydrate reservoir area through a mounting hole on one side face of the box body, and a fastening sealing member 76 is arranged at the position of the mounting hole on the side face of the box body and used for fastening the horizontal well shaft.

More preferably, the interlayer control mechanism 79 may have a structure in which: one, two or more square through holes can be formed in each partition plate, the square through holes are distributed on the partition plates at equal intervals, and each square through hole is provided with an anti-sand cloth. The number of the square through holes can be arranged and distributed according to actual needs. The side face of the partition board is provided with a plurality of threaded holes perpendicular to the side face of the partition board, each threaded hole corresponds to each square through hole one by one, each square through hole is provided with a corresponding screw rod and a corresponding bolt in a matched mode, the screw rod is provided with another square through hole with the same size as the through hole in the direction of the partition board, the central axis of each threaded hole coincides with the central axis of one horizontal direction of the corresponding square through hole, and the threaded hole penetrates through the corresponding square through hole and extends to the inside of the other side face of the corresponding. The bottom end in the threaded hole is provided with a spring 62, a screw 63 is inserted into the threaded hole from the outside of the box body, and the front end of the screw positioned outside the box body is provided with a bolt 64. The diameter of the screw 63 is larger than the width of the square through hole, so that the square through hole 61 can be completely blocked, and another square through hole 65 (see fig. 4) with the same size as the square through hole is arranged on the screw 63. The alignment degree of the screw rod square through hole 65 and the partition plate square through hole 61 is changed by rotating the adjusting bolt, so that the partition plate square through hole is opened or closed, and the communication or isolation between the upper water covering layer area and the hydrate storage layer area and between the hydrate storage layer area and the side low water layer area is realized. A sand cloth (not shown) is provided on the directional through hole 61 of the partition.

The method for carrying out the experiment by adopting the simulation device comprises the following steps:

(1) filling dry porous medium such as quartz sand, sea mud, etc. Firstly, installing a corresponding vertical shaft in a low water area on the side, filling a porous medium, compacting, and then installing a square clamp 73 and an elastic sealing ring 72; secondly, installing a horizontal shaft and a vertical shaft of the hydrate reservoir area, filling corresponding porous media, and installing a square clamp 73 and an elastic sealing ring 72; and finally, installing a vertical shaft in the water-covering layer area, filling and installing porous media, compacting, installing a square top cover 71, a square clamp 73 and an elastic sealing ring 72, and completely installing the reservoir simulation unit.

(2) And (3) immersing the reservoir simulation unit installed in the step (1) in a water bath heating tank 19, and adjusting the temperature to the temperature required by the experiment and keeping the temperature constant.

(3) Opening outlet control valves 4 and 6 of the water injection pump, opening a water injection inlet control valve 22 of a side low-water layer area, opening a water injection pump 3 or 5, injecting deionized water into the side low-water layer area from a deionized water tank with constant-temperature water bath, opening a production outlet control valve 39 of a vertical shaft, discharging air in the deionized water until the deionized water is completely immersed, and starting to add a tracer; by adopting the same measures, a hydrate reservoir region water injection inlet control valve 21 and an upper water covering region water injection inlet control valve 20 are sequentially opened, deionized water with different tracers is injected into the hydrate reservoir region and the upper water covering region, and finally a certain pressure (similar to the actual formation pressure) is kept in the three regions, so that the trace agent-containing deionized water is fully contacted with the porous medium.

(4) And closing the gas injection inlet control valve 25 of the overlying water layer area and the gas injection inlet control valve of the boundary water layer area, and opening the gas injection inlet control valve 24 of the hydrate reservoir area. Opening inlet and outlet control valves 4 and 6 of the gas booster pump, opening an air compressor and a gas booster pump 10, opening an inlet control valve 14 of the high-pressure gas storage tank, opening an outlet control valve 8 of the methane tank, and injecting methane into the high-pressure gas storage tank to 25 MPa. The methane injection control main valve 18 is opened and methane is injected to the hydrate reservoir area to a certain pressure through the high-pressure gas storage tank control valve 16.

(5) And adjusting the temperature of the water bath heating tank 19 to the temperature of the actual reservoir, closing the gas injection inlet control valve 24 of the hydrate reservoir area, and starting to generate the hydrate.

(6) During the generation of the hydrate, the water injection inlet control valve 20 of the upper water covering zone and the water injection inlet control valve 22 of the lower water side zone are opened in sequence, and deionized water containing tracer is injected into the corresponding zones until the final pressure of the generation of the hydrate.

(7) The back-pressure valve inlet control valve 41 and the back-pressure valve outlet control valve 43 are opened to adjust the back-pressure valve 42 to a desired reduced pressure value.

(8) According to experimental needs, adjusting bolts outside the sealing box body, enabling the square through holes of the screw rods to be coincident and aligned with the direction through holes of the partition plates, enabling the regions to be communicated with each other, enabling the hydrate storage region to be communicated with the upper water covering region, or the hydrate storage region to be communicated with the side low water layer region, or all three regions to be communicated, and verifying influences of different water layers on hydrate reservoir exploitation.

(9) The control valve for the production outlet 39 of the vertical well shaft or the control valve 40 for the production outlet of the horizontal well shaft is opened, and the depressurization production is started.

(10) The produced methane and water enter a gas-liquid separator 44 for separation, a gas outlet of the gas-liquid separator 44 is connected with a gas flowmeter 46, and the methane gas is discharged through a gas discharge outlet 47; and the produced water is metered by a balance 45; during the whole experiment, the data of the pressure gauges 26, 27, 28 and the thermometers 29-36 are collected by the data collection system and transmitted to the computer 49.

In conclusion, the simulation device provided by the invention has the advantages that the upper water-covering layer, the hydrate reservoir and the lower water-covering layer are integrally designed, so that the device is convenient to disassemble and assemble; and the interlayer control mechanism is adopted to realize the communication of the three reservoir regions, and the interlayer control mechanism can be used for researching the influence of the upper water layer region and the lower water layer region on the exploitation of the hydrate reservoir region.

Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (10)

1. A simulation device for influence of overlying and marginal low water layers on exploitation of methane hydrates is characterized by comprising a gas injection unit, a water injection unit, a reservoir simulation unit, a gas-liquid separation unit and a data acquisition system;

the reservoir simulation unit is immersed in the water bath heating tank and comprises a cubic sealed box body, an inner cavity of the box body is divided into an upper layer cavity, a middle layer cavity and a lower layer cavity by two horizontally arranged partition plates, the upper layer cavity, the middle layer cavity and the lower layer cavity are respectively used as an upper water covering layer area, a hydrate storage layer area and a side low water layer area, each area is provided with a water injection port, an air inlet, a pressure gauge and a thermometer, the water injection port is connected with the water injection unit, and the air inlet is connected with the air injection unit; each region is filled with porous medium;

an interlayer control mechanism is arranged in the partition plate and comprises a square through hole which is formed in the partition plate and is through up and down, a threaded hole which is perpendicular to the side face of the partition plate is formed in one side face of the partition plate, the central axis of the threaded hole is overlapped with the central axis of the square through hole in the horizontal direction, the threaded hole penetrates through the square through hole and extends to the inside of the other side face of the square through hole in a straight line, a spring is arranged at the bottom end in the threaded hole, a screw rod is inserted into the threaded hole from the outside of the box body, a bolt is arranged at the front end of the screw rod which is positioned outside the box body, the diameter of the screw rod is larger than the width of the square through hole and can completely block the square through hole, another square through hole with the same size as the square through hole is arranged on the screw rod, the alignment degree of, the hydrate storage area is communicated or isolated with the boundary low water area; the through holes in the direction of the partition board are provided with anti-sand cloth;

a vertical shaft and a horizontal shaft in the horizontal direction are arranged in the box body, the vertical shaft penetrates through the upper water covering layer area, the hydrate storage area and the lower water layer area, and the horizontal shaft is located in the hydrate storage area; both the horizontal well shaft and the vertical well shaft are wrapped by sand control cloth and are provided with perforations; the production outlet of the vertical shaft and the production outlet of the horizontal shaft are both connected to the gas-liquid separation unit, and back pressure valves are arranged on pipelines between the production outlets of the vertical shaft and the horizontal shaft and the gas-liquid separation unit.

2. The device for simulating the influence of the overlying and bordering low water layers on methane hydrate exploitation as claimed in claim 1, wherein the gas-liquid separation unit comprises a gas-liquid separator, a gas outlet of the gas-liquid separator is connected with a gas flow meter, and a balance is arranged at the bottom of the gas-liquid separator.

3. The apparatus for simulating the effect of overburden and boundary low water layers on methane hydrate production as recited in claim 2 wherein said data acquisition system is connected to all pressure gauges, thermometers, gas flow meters, back pressure valves.

4. The simulation device for simulating the influence of the overlying and bordering low water layers on the exploitation of the methane hydrate as claimed in claim 1, wherein the gas injection unit comprises a methane storage tank, a gas booster pump and a high-pressure gas storage tank which are connected in sequence, the gas booster pump is further connected with an air compressor, and a gas outlet of the high-pressure gas storage tank is simultaneously connected with gas inlets of the overlying water layer area, the hydrate storage area and the bordering low water layer area.

5. The device for simulating the influence of the overlying and surrounding low water layers on the exploitation of the methane hydrate according to claim 1, wherein the water injection unit comprises a deionized water tank with a constant-temperature water bath and a water injection pump connected with the water tank, and an outlet of the water injection pump is simultaneously connected with water injection ports of the overlying water layer area, the hydrate storage area and the surrounding low water layer area.

6. The device for simulating the influence of the overlying and bordering low water layers on methane hydrate exploitation according to claim 1, wherein the sealed box body is formed by splicing a first box body unit with a square upper end opening, a second box body unit with a square upper end opening, a third box body unit with a square upper end opening and a square top cover; the second box body unit and the third box body unit are identical in structure, the upper end and the lower end of the second box body unit are open, and the middle in the box body is provided with a partition plate integrally formed with the box body to divide the inner space of the box body into an upper layer and a lower layer.

7. The device for simulating the influence of the overlying and bordering low water layers on methane hydrate mining as recited in claim 6, wherein the opening of the upper end of the first box unit is provided with the opening of the lower end of the second box unit, the opening of the upper end of the second box unit is connected with the opening of the lower end of the third box unit, and the opening of the upper end of the third box unit is connected with the square cover plate; sealing rings are arranged at the joint of the first box body unit and the second box body unit, the joint between the second box body unit and the third box body unit and the joint between the third box body unit and the square cover plate and are fixedly connected through square hoops, and finally a sealed box body is formed; the center of the square cover plate, the center of the partition plate of the third box body and the center of the partition plate of the second box body are respectively provided with a mounting hole for mounting a vertical shaft, and the three mounting holes are vertically overlapped and aligned and are positioned on the vertical central line of the sealing box body.

8. The device for simulating the influence of the overlying and bordering low water layers on the methane hydrate production as recited in claim 6, wherein the surface of the vertical shaft is provided with screw threads, the inner wall of the installation hole is provided with screw threads, the vertical shaft is installed in the installation hole in a rotating manner, and a fastening sealing member is arranged at the position of the installation hole at the center of the outer side of the square cover plate for fastening the vertical shaft.

9. The apparatus for simulating methane hydrate production effects of overburden and boundary low water layers as recited in claim 1 wherein vertical well bores in overburden and boundary low water layers may or may not be perforated.

10. A method for performing an experiment using a simulation apparatus according to any of claims 1 to 9, characterized by the steps of:

s1, installing a reservoir simulation unit: filling porous media in the boundary low-water layer area, the hydrate storage area and the upper water covering layer area in sequence, installing a horizontal well shaft and a vertical well shaft, and finally installing a square top cover for sealing;

s2, placing the reservoir simulation unit in a water bath heating tank, adjusting the temperature to the experimental temperature and keeping the temperature constant;

s3, injecting water in the deionized water tank into the low-water-level area, opening a production outlet of the vertical shaft to discharge air in the vertical shaft until the deionized water is completely immersed, and adding a tracer; then sequentially injecting deionized water containing different tracers into the hydrate storage area and the overlying water layer area, wherein the pressure of the three areas is kept similar to the actual formation pressure, and the deionized water containing the tracers is ensured to be fully contacted with the porous medium;

s4, closing air inlets of the upper water covering layer area and the lower water layer area, and injecting methane gas into the hydrate reservoir area;

s5, adjusting the temperature of the water bath heating tank to the temperature of an actual reservoir, closing an air inlet of a hydrate reservoir area, and starting generating a hydrate;

s6, sequentially injecting deionized water containing a tracer into the upper water layer area and the lower water layer area to reach the final pressure of hydrate formation during the hydrate formation;

s7, opening a back pressure valve to reduce the pressure;

s8, adjusting bolts located outside the sealing box body according to experimental requirements, changing the overlapping alignment degree of the square through holes of the screw rods and the direction through holes of the partition plates so as to change the mutual connectivity among the three areas and verify the influence of the upper water layer area and the lower water layer area on the exploitation of the hydrate reservoir area;

s9, opening a production outlet of the vertical well shaft or a production outlet of the horizontal well shaft, and starting depressurization production;

s10, the produced methane and water enter a gas-liquid separator for separation, the produced methane gas is measured by a gas flowmeter, and the produced water is weighed by a balance; during the whole experiment process, the data of the pressure gauge and the temperature gauge are collected by the data collecting system and transmitted to the computer.

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