AU2015271890A1

AU2015271890A1 - Ground cold exchange injection system and coal reservoir phase change reconstructing method

Info

Publication number: AU2015271890A1
Application number: AU2015271890A
Authority: AU
Inventors: Hang Che; Guohua Liu; Mengmeng NING; Yihan Yang; Yong Yang; Donghe Yu
Original assignee: Petrochina Co Ltd
Current assignee: Petrochina Co Ltd
Priority date: 2014-12-19
Filing date: 2015-12-17
Publication date: 2016-07-07
Anticipated expiration: 2035-12-17
Also published as: CN105756648B; CN105756648A; AU2015271890B2

Abstract

Abstract The present invention provides a ground cold exchange injection system and a coal reservoir phase change reconstructing method, belonging to the technical field of reconstructing coal reservoir. In the present invention, spacer liquid, phase change liquid, 5 spacer liquid and coolant liquid are injected successively into oillets in the coal reservoir, so that the coolant liquid conducts the cold energy to the phase change liquid to produce the phase change and volumetric expansion, therefore netshaped crack is formed on the coal reservoir around the oillets under a swelling stress due to low temperature and phase change liquid, the netshaped crack has many branches, which increases mining passages 10 for the coal bed gas and thus better helps mining of the coal bed gas absorbed in the coal reservoir; moreover, the method causes the coal reservoir to be expanded from the oillets to produce the crack and to be free from washing by external objects, thereby reducing coal powder generated by coal rock and thus avoiding blocking of the crack, so that the crack formed by the present invention has a strong flow conductivity, which helps the drainage 15 works after the coal reservoir phase change reconstruction and improves mining efficiency of the coal bed gas. 7240430_1 (GHMatters) P101851.AU LYNT 3,/"t 14 15 8 9 10 180- 11 14 15 18 I T, _Fig 4 '4 142 1 01 0 113 17l Fig. 4

Description

GROUND COLD EXCHANGE INJECTION SYSTEM AND COAL RESERVOIR PHASE CHANGE RECONSTRUCTING METHOD

Technical Field

The present invention relates to the technical field of reconstructing coal reservoir, and in particular, to a ground cold exchange injection system and a coal reservoir phase change reconstructing method.

Background of the Invention

In mining of coal bed gas, coal reservoir has characteristics such as low hardness, being easily breakable, low permeability and the like, coal bed gas is not easy to mine, so that it is necessary to reconstruct the coal reservoir, with the purpose of enlarging coal reservoir fracture on the premise of not destroying the coal reservoir so that the absorbed coal bed gas is mined through a passage.

Generally in the prior art, the coal reservoir is reconstructed in a manner of hydraulic fracturing, in which water in large discharge capacity is injected into the coal reservoir by a fracturing pump truck, after bottom hole pressure is larger than a bursting pressure of the coal reservoir, a crack occurs in the coal reservoir, so as to improve flow conductivity of the coal reservoir, so that the absorbed coal bed gas is mined through a passage.

In the process of implementing the present invention, the inventor finds that the prior art at least has the following defects:

In the manner of hydraulic fracturing, water is injected into the coal reservoir in a large discharge capacity, however, coal rock may be easily scoured and a large amount of coal powder may be produced, thus the crack formed through fracturing may be easily blocked, thereby reducing the flow conductivity of the crack and impacting on the drainage work subsequent to the fracturing.

Summary of the Invention

In order to solve the problem of the prior art that coal powder may be easily produced due to the hydraulic fracturing to block the crack, an embodiment of the present invention provides a ground cold exchange injection system and a coal reservoir phase change reconstructing method. Technical solution of the embodiment is as follows: on one hand, the present invention provides a ground cold exchange injection system, comprising: an ultra-low temperature cold source circulation system, a cold exchange device, a coolant liquid circulation system and a reconstruction liquid injection system, wherein the ultra-low temperature cold source circulation system is used for transporting the cold source and is connected to the cold exchange device, the coolant liquid circulation system and the cold exchange device are connected in succession to a wellhead through an oil pipe in the wellhead, the oil pipe is further connected to the reconstruction liquid injection system, and a sleeve outside the oil pipe is connected to the coolant liquid circulation system; the ultra-low temperature cold source circulation system transfers cold energy of the cold source through the cold exchange device to the coolant liquid transported from the coolant liquid circulation system to the cold exchange device; the coolant liquid that obtains the cold energy enters the coal reservoir via the oil pipe; phase change liquid that is transported from the reconstruction liquid injection system to the coal reservoir receives the cold energy, and reconstructs the stratum, and the coolant liquid flows from the sleeve outside the oil pipe into the coolant liquid circulation system.

On the other hand, the present invention provides a coal reservoir phase change reconstructing method, comprising: step 1: lowering the sleeve into a coal bed gas well, perforating the coal reservoir, lowering a thermal insulation oil pipe and a thermo-pressure meter into the sleeve, and providing an annular gap between the sleeve and the thermal insulation oil pipe; step 2: injecting a certain amount of spacer liquid into the thermal insulation oil pipe by the ground cold exchange injection system; step 3: injecting a certain amount of phase change liquid into the thermal insulation oil pipe by the ground cold exchange injection system; step 4: continuing to inject a certain amount of spacer liquid into the thermal insulation oil pipe; step 5: cooling the coolant liquid by the ground cold exchange injection system, and injecting the cooled coolant liquid into the thermal insulation oil pipe, wherein the coolant liquid conducts the cold energy to the phase change liquid to cause the phase change liquid to reach a phase change temperature and to produce volume expansion, when the thermo-pressure meter shows that the bottom hole temperature is not decreased any more, stopping injection of the coolant liquid; step 6: injecting once again a certain amount of spacer liquid into the thermal insulation oil pipe, if the thermo-pressure meter shows that the bottom hole pressure is higher than or equal to the fracturing pressure of the coal reservoir, then repeating the steps 3 to 6, continuing phase change reconstruction of the coal reservoir outside the sleeve; if the thermo-pressure meter shows that the bottom hole pressure is lower than the fracturing pressure of the coal reservoir, then ending phase change reconstruction of the coal reservoir outside the sleeve.

The technical solution provided by the embodiment of the present invention produces the following beneficial effects:

In the present invention, spacer liquid, phase change liquid, spacer liquid and coolant liquid are injected successively into oillets in the coal reservoir, so that the coolant liquid conducts the cold energy to the phase change liquid to produce the phase change and volumetric expansion, therefore netshaped crack is formed on the coal reservoir around the oillets under a swelling stress due to low temperature and phase change liquid, the netshaped crack has many branches, which increases mining passages for the coal bed gas and thus better helps mining of the coal bed gas absorbed in the coal reservoir; moreover, the method causes the coal reservoir to be expanded from the oillets to produce the crack and to be free from washing by external objects, thereby reducing coal powder generated by coal rock and thus avoiding blocking of the crack, so that the crack formed by the present invention has a strong flow conductivity, which helps the drainage works after the coal reservoir phase change reconstruction and improves mining efficiency of the coal bed gas.

Brief Description of the Drawings

In order to describe the technical solutions in the embodiments of the invention more clearly, hereinafter accompanying figures required to be used in descriptions of the embodiments will be introduced briefly. Obviously, the accompanying figures in the following descriptions are merely some embodiments of the invention, and it is practicable for those skilled in the art to obtain other accompanying figures according to these ones in the premise of making no creative efforts.

Fig. lisa flowchart illustrating a coal reservoir phase change reconstructing method provided in an embodiment of the invention;

Fig. 2 is a schematic illustrating installations of a sleeve in a coal bed gas well, a thermal insulation oil pipe and a thermo-pressure meter provided in another embodiment of the present invention;

Fig. 3 is a schematic illustrating overall structure of a ground cold exchange injection system provided in the embodiment of the present invention;

Fig. 4 is a structural schematic illustrating an ultra-low temperature cold source circulation system provided in another embodiment of the present invention;

Fig. 5 is a structural schematic illustrating a coolant liquid circulation system provided in another embodiment of the present invention;

Fig. 6 is a structural schematic illustrating a reconstruction liquid injection system provided in another embodiment of the present invention; wherein, 1: ultra-low temperature cold source circulation system; 2: cold exchange device; 3: coolant liquid circulation system; 4: reconstruction liquid injection system; 5: wellhead; 6: cold source tank; 7: first metering injection device; 8: first check valve; 9: cold source three-way valve; 10: evaporator; 11: second metering injection device; 12: condenser; 13: compressor; 14: pressure meter; 15: thermometer; 16: cold source passage; 17: coolant liquid passage; 18: throttle control valve; 19: first coolant liquid tank; 20: second check valve; 21: coolant liquid three-way valve; 22: third metering injection device; 23: second coolant liquid tank; 24: fourth metering injection device; 25: third check valve; 26: first wellhead oil pipe gate; 27: wellhead sleeve gate; 28: fourth check valve; 29: coolant liquid flowback tank; 30: second wellhead oil pipe gate; 31: spacer liquid tank; 32: fifth metering injection device; 33: fifth check valve; 34: reconstruction liquid three-way valve; 35: phase change liquid tank; 36: sixth metering injection device; 37: sixth check valve; 38: sleeve; 39: thermal insulation oil pipe; 40: coal reservoir; 41: oillet; 42: thermo-pressure meter.

Detailed Description of the Embodiment

Hereinafter, the embodiment of the present invention is further described in detail in combination with the accompanying drawings, in order to describe purpose, technical solution and advantages of the present invention more clearly.

Embodiment 1

On one hand, as shown in Fig. 3, the embodiment of the present invention provides a ground cold exchange injection system which is disposed on the ground and is characterized in comprising: an ultra-low temperature cold source circulation system 1 for transporting the cold source, a cold exchange device 2, a coolant liquid circulation system 3 for transporting coolant liquid, and a reconstruction liquid injection system 4 for transporting phase change liquid and spacer liquid, wherein the ultra-low temperature cold source circulation system 1 is connected to the cold exchange device 2, the coolant liquid circulation system3, the cold exchange device 2 and an oil pipe in a wellhead 5 are connected in succession, the oil pipe is further connected to the reconstruction liquid injection system 4, and a sleeve outside the oil pipe is connected to the coolant liquid circulation system 3; the ultra-low temperature cold source circulation system 1 transfers cold energy of the cold source to the coolant liquid that is transported from the coolant liquid circulation system 3 through the cold exchange device 2, the coolant liquid that obtains the cold energy enters the coal reservoir via the oil pipe, the phase change liquid that is transported from the reconstruction liquid injection system 4 to the coal reservoir receives the cold energy and reconstructs the stratum, and the coolant liquid flows from the sleeve outside the oil pipe into the coolant liquid circulation system 3.

Wherein, in the present invention, the ultra-low temperature cold source circulation system 1 for transporting the cold source, the cold exchange device 2, the coolant liquid circulation system 3 for transporting coolant liquid, and the reconstruction liquid injection system 4 for transporting phase change liquid and spacer liquid are combined to form the ground cold exchange injection system; wherein, the ultra-low temperature cold source circulation system 1 and the cold exchange device 2 are connected to each other at head and tail thereof to form a loop to realize cyclic utilization of the cold source, the coolant liquid circulation system 3 is connected successively to the cold exchange device 2 and the wellhead 5, the wellhead 5 is then connected to the coolant liquid circulation system 3 to form a loop to realize cooling, injection and recycling of the coolant liquid, the wellhead 5 is further connected with the reconstruction liquid injection system 4 to realize injection of the reconstruction liquid; the coolant liquid circulation system 3 performs heat exchange circulation with the ultra-low temperature cold source circulation system 1 by the cold exchange device 2, that is, the ultra-low temperature cold source and the coolant liquid are both injected into the cold exchange device 2 to perform cold exchange, the coolant liquid absorbs cooling energy of the coolant and then flows out of the cold exchange device 2 to be injected into the oil pipe in the well, which can achieve cooling of the coolant liquid at the construction site without the need of transportation and thermal insulation in a large amount by a tank truck, thereby saving time and cost for transportation and reducing great cost, and on-site production and use of the low temperature coolant liquid can absolutely meet the construction demand directly, and the coolant liquid can be maintained at the temperature required for the construction all the time before going down to the well without the need to worry about cold energy loss during the transportation; after the cold exchange is performed, the ultra-low temperature cold source flows back to the ultra-low temperature cold source circulation system 1 to be recycled and re-cooled, then it can be injected into the cold exchange device 2 together with a new cold source to again perform cold exchange with the coolant liquid, which realizes recycling of the cold source without repetitively transporting it from a warehouse to the site to be heat exchanged and then transporting it back to be cooled, thereby also saving a series of transportation time and cost and also saving production cost; temperature of the low-temperature coolant liquid rises after being used, which can be drained out of the well and can flow back to the coolant liquid circulation system 3 to be recycled, thereby saving the cost; the reconstruction liquid injection system 4 can provide an injecting device for injection of the phase change liquid, the spacer liquid or other medium required in the well, which can not only satisfy the demand of the ultra-low temperature ground cold exchange but also increase a plurality of branches in the system so that the whole ground cold exchange injection system is more completed, to realize injection of various mediums; in addition, in this way the above several systems are used comprehensively, transportation problem can be solved, and such new and overall ground cold exchange injection system can meet the demand of ground injection of ultra-low temperature reconstruction of the coal reservoir and can realize application of other various coal reservoir reconstructing methods and thus according with the actual needs very much.

As shown in Fig. 4, also with reference to Fig. 5, furthermore, the cold exchange device 2 comprises a cold source passage 6 and a coolant liquid passage 17, wherein the ultra-low temperature cold source circulation system 1 is connected to the cold source passage 16, the coolant liquid circulation system 3 is connected to the coolant liquid passage 17, the cold energy of the cold source is transferred to the coolant liquid in the coolant liquid passage 17 through the cold source passage 16.

Wherein, the cold exchange device 2 is a device which transfers cold energy of a fluid to another fluid, i.e., reverse transfer of heat, which is divided into a mixing type and a surface type. Heat transfer process in the mixing-type cold exchange device 2 refers to direct mixing of hot fluid and cold fluid, while in the surface-type cold exchange device 2, heat is transferred from a fluid to another fluid through solid wall, i.e., the cold energy is transferred from a cold fluid to a hot fluid. The present invention adopts the surface-type cold exchange device 2 which includes two pipelines therein: the cold source passage 16 and the coolant liquid passage 17, wherein the cold source passage 16 is connected to the ultra-low temperature cold source circulation system 1, the coolant liquid passage 17 is connected to the coolant liquid circulation system 3, the ultra-low temperature cold source and the coolant liquid are injected into the cold exchange device 2 respectively from the cold source passage 16 and the coolant liquid passage 17, the ultra-low temperature cold source absorbs heat of the coolant liquid, i .e., transfers cold energy to the coolant liquid, then the ultra-low temperature cold source and the coolant liquid flow out respectively from exits of respective passages, the ultra-low temperature cold source is recycled and re-cooled in the ultra-low temperature cold source circulation system 1, the coolant liquid becomes low-temperature coolant liquid after heat exchange, which then can be injected into the well for ultra-low temperature reconstructing work of the coal reservoir.

As shown in Fig. 4, furthermore, the ultra-low temperature cold source circulation system 1 comprises: a cold source tank 6, a first metering injection device 7, a first check valve 8, a cold source three-way valve, an evaporator 10, a second metering injection device 11, the cold source passage 16, a condenser 12 and a compressor 13 which are connected in succession, wherein the compressor 13 is further connected to the cold source three-way valve.

Wherein, an outlet of the cold source tank 6 is connected to an inlet of the first metering injection device 7, an outlet of the first metering injection device 7 is connected to an inlet of the first check valve 8, an outlet of the first check valve 8 is connected to an inlet of the evaporator 10 and an outlet of the compressor 13 respectively through the cold source three-way valve, an outlet of the evaporator 10 is connected to an inlet of the second metering injection device 11, an outlet of the second metering injection device 11 is connected to an inlet of the cold source passage 16 of the cold exchange device 2, an outlet of the cold source passage 16 of the cold exchange device 2 is connected to an inlet of the condenser 12, an outlet of the condenser 12 is connected to an inlet of the compressor 13, an outlet of the compressor 13 is connected to the cold source three-way valve to form a loop; besides the above elements, the ultra-low temperature cold source circulation system 1 further comprises a plurality of throttle control valves 18 of which the number is preferably 5 and each of which only has two ports, wherein one throttle control valve 18 is provided on each of pipelines between the cold source tank 6 and the first metering injection device 7, between the evaporator 10 and the second metering injection device 11, and between the second metering injection device 11 and the cold exchange device 2, elements at two ends of the throttle control valve 18 are communicated with the throttle control valve 18 by the pipelines, and two throttle control valves 18 are provided between the cold source passage of the cold exchange device 2 and the condenser 12 to communicate the cold source passage 16 and the condenser 12; pipelines for connection between elements in the system all adopt low temperature resistant pipelines, and are connected in the manner of union connection.

Wherein, the cold source tank 6 is used for storing ultra-low temperature cold source; the throttle control valves 18 are used for controlling on/off of the pipelines; the metering injection device corresponds to a pump which supplies power to the output of the ultra-low temperature cold source; the evaporator 10 is standby for another cooling of the ultra-low temperature cold source, to prevent insufficient cold energy that possibly occurs in the ultra-low temperature cold source when transported in the pipelines; the condenser 12 and the compressor 13 are used in cooperation for recycling and cooling of the ultra-low temperature cold source after the cold exchange, to make the ultra-low temperature cold source can satisfy the temperature requirement to be recycled.

As shown in Fig. 5, furthermore, the coolant liquid circulation system 3 comprises a first coolant liquid tank 19, a second check valve 20, a coolant liquid three-way valve 21, a third metering injection device 22, the coolant liquid passage 17, a second coolant liquid tank 23, a fourth metering injection device 24 and a third check valve 25 which are connected in succession, wherein the third check valve 25 is connected to the oil pipe in the wellhead 5, the coolant liquid circulation system 3 further comprises a fourth check valve 28 and a coolant liquid flowback tank 29 that are connected to each other, the fourth check valve 28 is further connected to the sleeve outside the oil pipe, and the coolant liquid flowback tank 29 is further connected to the coolant liquid three-way valve 21.

Wherein, an outlet of the first coolant liquid tank 19 is connected to an inlet of the second check valve 20, an outlet of the second check valve 20 is connected to an inlet of the third metering injection device 22 and an outlet of the coolant liquid flowback tank 29 respectively through the coolant liquid three-way valve 21, an outlet of the third metering injection device 22 is connected to an inlet of the coolant liquid passage 17 of the cold exchange device 2, an outlet of the coolant liquid passage 17 is connected to an inlet of the second coolant liquid tank 23, an outlet of the second coolant liquid tank 23 is connected to an inlet of the fourth metering injection device 24, the fourth metering injection device 24 is connected to an inlet of the third check valve 25, an outlet of the third check valve 25 is connected to the oil pipe in the well through a first wellhead oil pipe gate 26, a sleeve is provided outside the oil pipe, a wellhead sleeve gate 27 is provided on the sleeve at a position of the wellhead 5, an outlet of the wellhead sleeve gate 27 is connected to an inlet of the fourth check valve 28, an outlet of the fourth check valve 28 is connected to an inlet of the coolant liquid flowback tank 29, an outlet of the coolant liquid flowback tank 29 is connected to the coolant liquid three-way valve 21; besides the above elements, the coolant liquid circulation system 3 further comprises a plurality of throttle control valves 18 of which the number is preferably 7, and each of which has only two ports to form the coolant liquid circulation system 3, wherein one throttle control valve 18 is provided on each of pipelines between the first coolant liquid tank 19 and the second check valve 20, between the third metering injection device 22 and the coolant liquid passage 17, between the second coolant liquid tank 23 and the fourth metering injection device 24, between the fourth check valve 28 and the coolant liquid flowback tank 29 and between the coolant liquid flowback tank 29 and the coolant liquid three-way valve 21, elements at two ends of the throttle control valve 18 are communicated with the throttle control valve 18 by the pipelines, and two throttle control valves 18 are provided between the outlet of the coolant liquid passage 17 and the second coolant liquid tank 23, which communicate the pipelines therebetween; and the third check valve 25 is communicated into the wellhead 5 by the pipeline, where the first wellhead oil pipe gate 26 is provided, which is a throttle control valve 18, like the above wellhead sleeve gate 27; wherein, the first coolant liquid tank 19 is used for storing coolant liquid before heat exchange cooling, the second coolant liquid tank 23 is used for temporarily storing low-temperature coolant liquid after the heat exchange cooling, the coolant liquid flowback tank 29 is used for temporarily storing coolant liquid that is drained out of the well after coal reservoir reconstructing work is performed; all pipelines for connection between elements in the system adopt low temperature resistant pipelines, and are connected in the manner of union connection.

As shown in Fig. 6, furthermore, the reconstruction liquid injection system 4 comprises a spacer liquid tank 31, a fifth metering injection device 32, a fifth check valve 33 and a reconstruction liquid three-way valve 34 which are connected in succession, wherein the reconstruction liquid three way valve 34 is further connected to the oil pipe in the wellhead 5, the reconstruction liquid injection system 4 further comprises a phase change liquid tank 35, a sixth metering injection device 36 and a sixth check valve 37 in succession, the sixth check valve 37 is further connected to the reconstruction liquid three-way valve 34.

Wherein, besides the above elements, the system further comprises a plurality of throttle control valves 18 of which the number is preferably 4, and each of two ends of the throttle control valve 18 is connected to one element; an outlet of the spacer liquid tank 31 is connected to an inlet of the fifth metering injection device 32 through the throttle control valve 18, an outlet of the fifth metering injection device 32 is connected to an inlet of the fifth check valve 33, an outlet of the fifth check valve 33 is connected to the reconstructed three-way valve 34 through the throttle control valve 18, the reconstruction liquid three-way valve 34 is further connected to an outlet of the sixth check valve 37 and the second wellhead oil pipe gate 30 respectively, the second wellhead oil pipe gate 30 is connected onto the oil pipe of the wellhead 5; an outlet of the phase change liquid tank 35 is connected to an inlet of the sixth metering injection device 36 through one throttle control valve 18, an outlet of the sixth metering injection device 36 is connected to an inlet of the sixth check valve 37, one throttle control valve is connected between an outlet of the sixth check valve 37 and the reconstruction liquid three-way valve 34; the second wellhead oil pipe gate 30 also uses the throttle control valve 18; all pipelines for connection between elements adopt low temperature resistant pipelines, and are connected in the manner of union connection.

As shown in Fig. 6, and also with reference to Figs. 4 and 5, furthermore, the ground cold exchange injection system further comprises a pressure meter 14 and a thermometer 15, which are provided between the first metering injection device 7 and the first check valve 8, between the second metering injection device 11 and the cold source passage 16, between the compressor 13 and the cold source three-way valve, between the third metering injection device 22 and the coolant liquid passage 17, between the third check valve 25 and the oil pipe, between the fourth check valve 28 and the coolant liquid flowback tank 29, and between the reconstruction liquid three way valve 34 and the oil pipe; and one thermometer 15 is provided between the coolant liquid passage 17 and the second coolant liquid tank 23.

Wherein, the pressure meter 14 and the thermometer 15 at different positions both function to immediately test internal temperature and pressure of the pipeline at the positions, and through collection of such data, it is possible to timely adjust discharge rate of the output liquid of the metering injection devices, so as to ensure that pressure of the liquid inputted to the well is not higher than the fracturing pressure of the coal reservoir, and by combining the actual needs, it is possible to select the optimal discharge rate of the liquid as 0.5-3.0 m3/min.

On the other hand, as shown in Fig. 1, the embodiment of the present invention provides a coal reservoir phase change reconstructing method, comprising: step 1: lowering a sleeve 38 into a coal bed gas well, perforating the coal reservoir 40, lowering a thermal insulation oil pipe 39 and a thermo-pressure meter 42 into the sleeve, and providing an annular space between the sleeve 38 and the thermal insulation oil pipe 39; wherein, diameters and lowering depths of the sleeve 38 and the thermal insulation oil pipe 39 are decided depending on drilling depth, thickness of coal seam, quality of coal seam and the like and thus can be flexibly selected according to actual situation, wherein the sleeve 38 can be selected to have a diameter of 139.7m and a lowering depth of 690m, the thermal insulation oil pipe 39 can be selected to have a diameter of 73-88.9m and a lowering depth of 665m, the coal reservoir 40 can be selected to be perforated at a position of 650-656m deep; the thermometer 42 is connected at the bottom of the thermal insulation oil pipe 39 through screw threads and is lowered together with the thermal insulation oil pipe 39 into the sleeve 38 in the coal bed gas well, the bottom of the thermal insulation oil pipe 39 is lower than the bottommost end of perforation position in the coal reservoir 40 with a distance that is preferably 5-25m, so that the thermometer 42 can get close to the perforation position in the coal reservoir 40, so as to measure temperature and pressure at the well bottom in real time, the thermo-pressure meter 42 is preferably a direct-reading and storage type electronic thermo-pressure meter that has a temperature measurement range of -50°C-100°C and a pressure measurement range of 0-70Mpa; in the vicinity of the perforation position of the coal reservoir 40, a plurality of thermo-pressure meters 42 can be provided each of which is connected outside the coal bed gas well by a low temperature resistant cable, to be helpful for a worker to collect temperature and pressure values of the bottom well directly on the ground; the thermal insulation oil pipe 39 is provided with a top opening at a position close to the wellhead 5, the thermal insulation oil pipe 39 is communicated with both of the first wellhead oil pipe gate 26 and the second wellhead oil pipe gate 30 in the ground cold exchange system through the top opening, and the first wellhead oil pipe gate 26 is used for controlling communication between the thermal insulation oil pipe 39 and the second coolant liquid tank 23 in the coolant liquid circulation system 3, the second wellhead oil pipe gate 30 is used for controlling communication between the thermal insulation oil pipe 39 and the reconstruction liquid injection system 4; the sleeve 38 is also provided with a top opening at a position close to the wellhead 5, and opening and closing of the annular gap between the sleeve 38 and the thermal insulation oil pipe 39 is controlled by the wellhead sleeve gate 27, and the sleeve 38 is communicated with the coolant liquid flowback tank 29 in the coolant liquid circulation system 3 through the wellhead sleeve gate 27.

Step 2: injecting a certain amount of spacer liquid into the thermal insulation oil pipe 39 by the ground cold exchange injection system;

Step 3: injecting a certain amount of phase change liquid into the thermal insulation oil pipe 39 by the ground cold exchange injection system;

Step 4: continuing to inject a certain amount of spacer liquid into the thermal insulation oil pipe 39; wherein the reconstruction liquid injection system 4 in the ground cold exchange injection system injects a certain amount of spacer liquid, phase change liquid and spacer liquid in sequence into the thermal insulation oil pipe 39 through the second wellhead oil pipe gate 30, at this time, the spacer liquid serves to make the phase change liquid not come into contact with the coal reservoir 40 directly, thereby avoiding the phase change liquid from having chemical reaction with the coal reservoir 40 to cause damage to the coal reservoir 40, and injection amount of the spacer liquid and the phase change liquid can be set flexibly according to the actual situation.

Step 5: cooling the coolant liquid by the ground cold exchange injection system, and injecting the cooled coolant liquid into the thermal insulation oil pipe 39, wherein the coolant liquid conducts the cold energy to the phase change liquid to cause the phase change liquid to reach a phase change temperature and to produce volume expansion, when the thermo-pressure meter 42 shows that the bottom hole temperature is not decreased any more, stopping injection of the coolant liquid; wherein, the spacer liquid injected between the coolant liquid and the phase change liquid serves to prevent the coolant liquid from having chemical reaction or ion exchange with the phase change liquid, thus avoiding mutual influence between the coolant liquid and the phase change liquid to reduce influence effects; the coolant liquid and the low-temperature cold source are input into the cold exchange device 2 respectively by the coolant liquid circulation system 3 and the ultra-low temperature cold source circulation system 1 in the ground cold exchange injection system, so that the coolant liquid absorbs the cold energy of the low-temperature cold source in the cold exchange device 2, therefore temperature of the coolant liquid is reduced to the temperature required for construction and is stored in the second coolant liquid tank 23 for standby application; the coolant liquid circulation system 3 injects the temperature-lowered coolant liquid stored in the second coolant liquid tank 23 into the thermal insulation oil pipe 39 through the first wellhead oil pipe gate 26, so as to enter the oillets 41 in the coal reservoir 40 at the bottom hole, the coolant liquid transfers cold energy to the phase change liquid to make the phase change liquid reach the phase change temperature to experience volume expansion, the expanded volume oppresses the coal reservoir 40 around the oillets 41 to cause the coal reservoir 40 to have crack; when the bottom hole temperature is not decreased any more, the injection of the coolant liquid is stopped.

Step 6: injecting once again a certain amount of spacer liquid into the thermal insulation oil pipe 39, if the thermo-pressure meter 42 shows that the bottom hole pressure rises to be higher than or equal to the fracturing pressure of the coal reservoir 40, it shows that the phase change reconstruction of the coal reservoir outside the sleeve 38 is not completed, then repeating the steps 3 to 6 and continuing phase change reconstruction of the coal reservoir outside the sleeve 38, if the thermo-pressure meter 42 shows that the bottom hole pressure is lower than the fracturing pressure all the time, it shows that the phase change reconstruction of the coal reservoir outside the sleeve 38 is completed, then waiting for a period of time, when the thermo-pressure meter 42 shows that the bottom hole temperature recovers to be higher than the phase change temperature of the liquid change liquid, ending the phase change reconstruction of the coal reservoir 40.

Wherein, after the coolant liquid have cold exchange with the phase change liquid and when the bottom hole temperature is not decreased any more, waiting for a period of time and after the phase change liquid goes through the phase change sufficiently, then a certain amount of spacer liquid is injected into the phase change liquid, and determining, according to the above condition, whether or not the phase change reconstruction of the coal reservoir 40 outside the sleeve 38 at the bottom hole is completed, if the coal reservoir 40 can continue to form crack, then repeating the steps 3 to 6, and if the coal reservoir 40 cannot continue to form crack, then stopping injection of all mediums, this process can be called "well testing" with the purpose that the coal reservoir 40 outside the sleeve 38 goes through the crack forming reconstruction to be greatest extent; when it shows that the coal reservoir 40 has reached the limit for reconstruction, i.e., the bottom hole pressure is maintained to be below the fracturing pressure of the coal reservoir all the time after the spacer liquid is injected, stopping injection of any medium and waiting for a period of time, and when the thermo-pressure meter 42 shows that the bottom hole temperature is recovered to be higher than the phase change temperature of the phase change liquid, ending the construction.

In the present invention, the coal reservoir 40 is perforate, and spacer liquid, phase change liquid, spacer liquid and coolant liquid are injected successively into oillets 41 in the coal reservoir, so that the coolant liquid conducts the cold energy to the phase change liquid to produce the phase change and volumetric expansion, therefore netshaped crack is formed on the coal reservoir 40 around the oillets under a swelling stress due to low temperature and phase change liquid, the netshaped crack has many branches, which increases mining passages for the coal bed gas and thus better helps mining of the coal bed gas absorbed in the coal reservoir 40; moreover, the method causes the coal reservoir 40 to be expanded from the oillets 41 to produce the crack and to be free from washing by external objects, thereby reducing coal powder generated by coal rock and thus avoiding blocking of the crack, so that the crack formed by the present invention has a strong flow conductivity, which helps the drainage works after the coal reservoir 40 phase change reconstruction and improves mining efficiency of the coal bed gas.

As shown in Fig. 1, also with reference to Fig. 2, furthermore, in the step 1, perforating the coal reservoir 40 specifically comprises: perforating a plurality of oillets 41 having the diameter of 9-11mm in the sleeve 38 and the coal reservoir 40 outside the sleeve 38, the density of arrangement of the plurality of oillets 41 is 10-16/m, and all of the oillets 41 have the same phase angle of 60°-90°.

Wherein, the plurality of oillets 41 are deepened into the coal reservoir 40 and are aligned with the apertures on the sleeve 38, so that the phase change liquid can go through and enter each oillet 41 to be deepened into the coal reservoir 40, when the phase change liquid in the oillets 41 has phase change, i.e., volume expansion, it is possible to cause oppression to the coal reservoir 40 around the oillets 41, so that the coal reservoir 40 at the position form crack; the oillets 41 have the phase angle of preferably 60°, the density of arrangement of preferably 16/m, and the diameter of preferably 10mm.

As shown in Fig. 1, furthermore, the step 2: injecting a certain amount of spacer liquid into the thermal insulation oil pipe 39 by the ground cold exchange injection system specifically comprises: opening the top opening of the thermal insulation oil pipe 39 and the top opening of the sleeve 38; that is, by opening the second wellhead oil pipe gate 30 that is connected with the top opening of the thermal insulation oil pipe 39, the thermal insulation oil pipe 39 and the reconstruction liquid injection system 4 are communicated, and by opening the wellhead sleeve gate 27 that is connected with the top opening of the sleeve 38 as well as the throttle control valve 18 and the wellhead sleeve gate 27 between the sleeve 38 and the coolant liquid flowback tank 29, the annular gap and the coolant liquid flowback tank 29 between the sleeve 38 and the thermal insulation oil pipe 39 are communicated.

By use of the reconstruction liquid injection system 4 in the ground cold exchange injection system, spacer liquid is injected into the thermal insulation oil pipe 39 at a discharge rate of 0.5-3.0m3/min through the top opening of the thermal insulation oil pipe 39, the spacer liquid passes through a bottom opening of the thermal insulation oil pipe 39 to enter the annular gap between the thermal insulation oil pipe 39 and the sleeve 38; wherein, the spacer liquid passes through the spacer liquid tank 31, the fifth metering injection system 32, the fifth check valve 33, the reconstruction liquid three-way valve 34 and the second wellhead oil pipe gate 30 successively to be injected into the thermal insulation oil pipe 39, the fifth metering injection device 32 controls the discharge rate of the spacer liquid to be 0.5-3.0m3/min, preferably 1.0-2.0m3/min, the injection pressure is lower than the fracturing pressure of the coal bed, preferably injection pressure lower than 21Mpa; when a liquid surface position of the spacer liquid in the annular gap between the thermal insulation oil pipe 39 and the sleeve 38 is higher than a highest position of the plurality of oillets 41 in the coal reservoir 40, closing the top opening of the sleeve 38, i.e., the wellhead sleeve gate 27, so that the annular gap between the sleeve 38 and the thermal insulation oil pipe 39 is closed; the reconstruction liquid injection system 4 continues to inject a certain amount of spacer liquid at a discharge rate of 0.5-3.0m3/min into the thermal insulation oil pipe 39 through the top opening of the thermal insulation oil pipe 39, to cause the spacer liquid to enter the coal reservoir 40 through the oillets 41.

The spacer liquid is continued to be injected into the thermal insulation oil pipe 39 preferably at a discharge rate of 1 ,5m3/min and an injection pressure lower than 21Mpa, the annular gap between the sleeve 38 and the thermal insulation oil pipe 39 is closed, so that the continuously injected spacer liquid is forced to enter the oillets 41 in the coal reservoir 40.

As shown in Fig. 1, furthermore, the step 3: injecting a certain amount of phase change liquid into the thermal insulation oil pipe 39 by the ground cold exchange injection system specifically comprises: injecting a certain amount of phase change liquid at a discharge rate of 0.5-3.0m3/min into the thermal insulation oil pipe 39 by the reconstruction liquid injection system, and causing the phase change liquid to enter the coal reservoir 40 through the oillets 41.

Wherein, the phase change liquid passes through the phase change liquid tank 35, the sixth metering injection device 36, the sixth check valve 37, the reconstruction liquid three-way valve 34 and the second wellhead oil pipe gate 30 successively to be injected into the thermal insulation oil pipe 39, the sixth metering injection device 37 controls the discharge rate of the phase change liquid to be 0.5-3.0m3/min, and preferably 1.5m3/min, and the injection pressure is lower than 21Mpa; the spacer liquid in the oillets 41 is positioned between the phase change liquid and the coal reservoir 40, so as to prevent chemical reaction from occurring between the phase change liquid and the coal reservoir 40 to cause damage to the coal reservoir 40.

As shown in Fig. 1, furthermore, the step 4: continuing to inject a certain amount of spacer liquid into the thermal insulation oil pipe 39 specifically comprises: injecting a certain amount of spacer liquid at a discharge rate of 0.5-3.0m3/min into the thermal insulation oil pipe 39 by the reconstruction liquid injection system, and causing the spacer liquid to enter the coal reservoir 40 through the oillets 41.

Similarly, the spacer liquid passes through the spacer liquid tank 31, the fifth metering injection device 32, the fifth check valve 33, the reconstruction liquid three-way valve 34 and the second wellhead oil pipe gate 30 successively to be injected into the thermal insulation oil pipe 39, the fifth metering injection device 32 controls the discharge rate of the spacer liquid to be 0.5-3.0m3/min, and preferably 1.5m3/min, and the injection pressure is lower than 21Mpa; the spacer liquid injected into the oillets 41 this time is positioned between the phase change liquid and the coal reservoir, so as to prevent chemical reaction from occurring between the phase change liquid and the coolant liquid to influence the use effect.

As shown in Fig. 1, furthermore, the step 5: cooling the coolant liquid by the ground cold exchange injection system, and injecting the cooled coolant liquid into the thermal insulation oil pipe 39, wherein the coolant liquid conducts the cold energy to the phase change liquid to cause the phase change liquid to reach a phase change temperature and to produce volume expansion, when the thermo-pressure meter 42 shows that the bottom hole temperature is not decreased any more, stopping injection of the coolant liquid specifically comprises: transporting cold source to the cold exchange device 2 by the ultra-low temperature cold source circulation system 1 and transporting coolant liquid to the cold exchange device 2 by the coolant liquid circulation system 3 in the ground cold exchange injection system, and conducting cold energy by the cold source to the coolant liquid in the cold exchange device 2 to cause the temperature of the coolant liquid to be reduced to -10°C to -50°C; wherein opening all throttle control valves 18 in the ultra-low temperature cold source circulation system 1 to circulate the ultra-low temperature cold source, opening the throttle control valves 18 on the line from the first coolant liquid tank 19 to the cold exchange device 2 then to the second coolant liquid tank 23, and closing all of other throttle control valves 18, injecting the ultra-low temperature cold source and the coolant liquid into the cold source passage 16 and the coolant liquid passage 17 in the cold exchange device 2, performing cold exchange on the ultra-low temperature cold source and the coolant liquid by using the cold exchange device 2 to reduce the temperature of the coolant liquid to -10°C to -50°C, preferably -20~-40°C, and transporting the coolant liquid to the second coolant liquid tank 23 to be stored.

The top opening of the sleeve, i.e. the wellhead sleeve gate 27 is opened, so that the annular gap between the sleeve 38 and the thermal insulation oil pipe 39 is communicated with the coolant liquid flowback tank 29; by use of the coolant liquid circulation system, injecting temperature-lowered coolant liquid at a discharge rate of 0.5-3.0m3/min into the thermal insulation oil pipe 39 through the top opening of the thermal insulation oil pipe 39; wherein, injecting the coolant liquid into the thermal insulation oil pipe 39 in the well, firstly opening the top opening of the thermal insulation oil pipe 39, that is, opening the throttle control valves 18 and the first wellhead oil pipe gate 26 between the second coolant liquid tank 23 and the wellhead 5 successively, and meanwhile opening all of other throttle control valves 18 and the wellhead sleeve gate 27 in the coolant liquid circulation system 3, and the coolant liquid is injected at a discharge rate of 0.5-3.0m3/min, preferably 1.0m3/min, from the second coolant liquid tank 23 into the thermal insulation oil pipe 39 in the well under the control of the fourth metering injection device24; the coolant liquid conducts the cold energy to the phase change liquid in the oillets, the phase change liquid reaches the phase change temperature after receiving the cold energy and has volume expansion, so that the coal reservoir 40 around the oillets forms crack; the coolant liquid functions to transfer the cold energy carried by itself to the phase change liquid, so that the phase change liquid in the oillets 41 has phase change and its volume is expanded, so as to force the coal reservoir 40 around the oillets 41 to form crack to supply gas exploitation passages for exploitation of the coal bed gas.

The coolant liquid whose cold energy is conducted passes through the annular gas between the sleeve 38 and the thermal insulation oil pipe 39 to be drained to the coolant liquid circulation system 3 outside the coal bed gas to be recycled; wherein the coolant liquid whose cold energy is conducted is drained to the coolant liquid flowback tank 29 via the wellhead sleeve gate 27 from the annular gap between the sleeve 38 and the thermal insulation oil pipe 39, then flows to the cold exchange device 2 through the coolant liquid three-way valve 21, to go through the cold exchange again to be recycled.

When the thermo-pressure meter 42 shows that the bottom hole temperature is not decreased any more, injection of the coolant liquid is stopped.

As shown in Fig. 1, furthermore, the step 6: injecting once again a certain amount of spacer liquid into the thermal insulation oil pipe 39, if the thermo-pressure meter 42 shows that the bottom hole pressure rises to be higher than or equal to the fracturing pressure of the coal reservoir 40, then repeating the steps 3 to 6, continuing phase change reconstruction of the coal reservoir 40 outside the sleeve 38; if the thermo-pressure meter 42 shows that the bottom hole pressure is lower than the fracturing pressure of the coal reservoir all the time, then ending phase change reconstruction of the coal reservoir 40 outside the sleeve, specifically comprises: closing the top opening of the sleeve 38; injecting a certain amount of spacer liquid at a discharge rate of 0.5-3.0m3/min into the thermal insulation oil pipe 39 by the reconstruction liquid injection system 4, and the amount of the spacer liquid can be determined according to the actual demand of the coal bed gas.

If the thermo-pressure meter 42 shows that the bottom hole pressure rises to be higher than or equal to the fracturing pressure of the coal reservoir 40, it shows that the phase change reconstruction of the coal reservoir 40 outside the sleeve 38 is not completed, repeating the steps 3 to 6, i.e., repeating the process of injecting successively the phase change liquid, the spacer liquid, the coolant liquid and the spacer liquid, so that the coal reservoir 40 around the sleeve 38 at the bottom hole receives crack forming reconstruction to the greatest extend, if the thermo-pressure meter 42 shows that the bottom hole pressure is lower than the fracturing pressure of the coal reservoir 40 all the time, then the coal reservoir 40 outside the sleeve 38 has reached the limit of phase change reconstruction to generate crack, at this time, opening the top opening of the sleeve 38, temperature in the bottom hole rises slowly and pressure decreases slowly, waiting until the thermo-pressure meter 42 shows that the bottom hole temperature is recovered and is higher than the phase change temperature of the phase change liquid, ending phase change reconstruction of the coal reservoir 40.

Preferably, the coolant liquid is saturated salt water, the phase change liquid is clean water, and the spacer liquid is kerosene.

Wherein the cold source is used for preserving cold energy and can be in the manner of liquid nitrogen, liquid C02, low-temperature nitrogen gas, low temperature compressor 13-group refrigeration and the like; the phase change liquid can have phase state change i.e. volume expansion after absorbing the cold energy, crack forming of the coal reservoir 40 is reconstructed by freezing and expansion of the phase change liquid which is preferably clean water or low concentration salt water and also can be other low-concentration liquid which easily has phase change due to low temperature; the coolant liquid is used for carrying cold energy of the low-temperature cold source and transferring it to the phase change liquid which has phase change after absorbing the cold energy, so as to perform reconstruction of the coal reservoir 40, and is preferably saturated salt water; the spacer liquid is used for spacing the fluids or solids, so that chemical reaction and ion exchange do not occur between the coolant liquid and the phase change liquid and between the coal reservoir 40 and the phase change liquid, and the spacer liquid itself will not have reaction with the fluids and the solids, and is preferably kerosene. Embodiment 2

Another embodiment of the present invention provides a coal reservoir phase change reconstructing method, comprising: drilling depth of the coal bed gas is 690m, burial depth of the coal bed is 650-656m, thickness of the coal bed is 6m, temperature of the coal bed is 30°C, a roof of the coal bed is sandy mudstone of 8.8m, a floor of the coal bed is siltstone of 6.7m, the fracturing pressure of the coal bed is 21MPa; liquid nitrogen is used as the low-temperature cold source, calcium chloride solution having concentration of 28% is used as the coolant liquid, clean water is used as the phase change liquid, and kerosene is used as the spacer liquid, step 1, mineshaft preparation: lowering a sleeve 38 having the diameter of 139.7mm into the coal bed gas well, then perforating the coal reservoir 40 having the depth of 650-656m, the perforated oillets 41 have phase angle of 60°, diameter of 10mm and density of arrangement of 16/m; lowering a thermal insulation oil pipe 39 having the diameter of 88.9mm into the sleeve 38 to the depth of 665m, meanwhile, the thermo-pressure meter 42 which has a temperature measurement range of -50-100°C and a pressure measurement range of 0-70MPa is installed at the bottom of the thermal insulation oil pipe 39; the bottom of the thermal insulation oil pipe 39 is connected to the thermo-pressure meter 42 by screw threads, and the thermo-pressure meter 42 is communicated to the ground with a low temperature resistant cable, for collecting bottom hole temperature and pressure value.

Step 2, ground preparation: arranging the ground cold exchange injection system at a position close to the wellhead 5, testing pressure and temperature of the coolant liquid circulation system 3 with calcium chloride solution having concentration of 28% at the injection pressure of 35MPa and at the temperature of -40°C; testing pressure of the reconstruction liquid injection system 4 with clean water and kerosene at the pressure of 35MPa; starting construction in the coal bed gas well after the devices are debugged to be qualified.

Step 3, ground cold exchange: starting the coolant liquid circulation system 3, the ultra-low temperature cold source circulation system 1 and the cold exchange device 2 in the ground cold exchange injection system to perform cooling process of the coolant liquid, that is, cooling the calcium chloride solution having concentration of 28% i.e. the coolant liquid to -30—35°C in the cold exchange device 2.

Step 4, starting the reconstruction liquid injection system 4 of the ground cold exchange injection system to inject spacer liquid to the thermal insulation oil pipe 39: opening the second wellhead oil pipe gate 30 and the wellhead sleeve gate 27, passing kerosene i.e. the spacer liquid through the spacer liquid tank 31, the fifth metering injection device 32, the fifth check valve 33, the reconstruction liquid three-way valve 34 and the second wellhead oil pipe gate 30 successively to inject into the thermal insulation oil pipe 39, the fifth metering injection device 32 controls the discharge rate of the kerosene to be 1.0~2.0m Vmin and the injection pressure to be lower than 21MPa, when a liquid surface position of the kerosene in the annular gap between the thermal insulation oil pipe 39 and the sleeve 38 is higher than a highest position of the plurality of oillets 41 in the coal reservoir 40, closing the top opening of the sleeve 38.

Step 5, continuing to inject the kerosene at the injection pressure lower than 21MPa and the discharge rate of 1.5m3/min into the thermal insulation oil pipe 39 in the well through the second wellhead oil pipe gate 30, to force the kerosene to enter the coal reservoir 40 via the oillets 41.

Step 6, injecting phase change liquid into the thermal insulation oil pipe 39: stopping injection of the kerosene, injecting clean water i.e. the phase change liquid at the injection pressure lower than 21MPa and the discharge rate of 1.5m3/min into the oillets 41 of the coal reservoir 40 through the second wellhead oil pipe gate 30 and the thermal insulation oil pipe 39.

Step 7, injecting the spacer liquid for the second time: repeating the step 5 in this embodiment.

Step 8, coolant liquid circulation, cooling the coal bed: stopping injection of kerosene i.e. the spacer liquid, opening the wellhead sleeve gate 27, starting the coolant liquid circulation system 3, injecting the calcium chloride solution having concentration of 28% i.e. the coolant liquid having the temperature of -30-35°C at the discharge rate of lm3/min into the thermal insulation oil pipe 39 in the well through the first wellhead oil pipe gate 26, lowering temperature of the coal reservoir 40 in the well, and meanwhile the coolant liquid has cold exchange with the phase change liquid so that the phase change liquid in the oillets 41 have phase change and volume expansion, to oppress the coal reservoir 40 around the oillets 41 to form crack. The coolant liquid after the cold exchange flows back to be drained out of the coal bed gas well along the annular gap between the thermal insulation oil pipe 39 and the sleeve 38, then enters the coolant liquid circulation system 3 to be refrigerated for recycling.

Step 9, when the thermo-pressure meter 42 monitors that the bottom hole temperature is not decreased any more, repeating the steps 5 to 8 in this embodiment, repeatedly performing phase change reconstruction on the coal reservoir 40, increasing crack generated by the coal reservoir 40 around the oillets 41, and enlarging the range of phase change reconstruction of the coal reservoir 40; step 10: closing the wellhead sleeve gate 27, injecting again kerosene i.e. the spacer liquid at the injection pressure of 22MPa and the discharge rate of 1.2~1.5m3/min into the thermal insulation oil pipe 39, and monitoring bottom hole pressure change by the thermo-pressure meter 42 at the bottom, when the bottom hole pressure rises to be higher than or equal to 21 MPa, it shows that the coal reservoir 40 around the sleeve 38 at the bottom hole still can continue to form crack, then repeating the steps 4 to 10 in this embodiment, but when the bottom hole pressure is lower than 21MPa all the time, stopping injection of the kerosene.

Step 11, temperature recovery after reconstruction: opening the wellhead sleeve 38 gate, squeezing the kerosene into the coal reservoir 40 at the discharge rate of 1.2-1.5m3/min, and monitoring bottom hole temperature and pressure change by the thermo-pressure meter 42, when the bottom hole temperature is recovered to 0°C, stopping injection of the kerosene, and completing the construction.

The above descriptions are merely preferred embodiments of the present invention, but not for limiting the present invention, and any modification, equivalent replacement, improvement and the like within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A ground cold exchange injection system, comprising: an ultra-low temperature cold source circulation system, a cold exchange device, a coolant liquid circulation system and a reconstruction liquid injection system, wherein, the ultra-low temperature cold source circulation system is used for transporting a cold source and is connected to the cold exchange device, the coolant liquid circulation system and the cold exchange device are connected in succession to a wellhead through an oil pipe in the wellhead, the oil pipe is further connected to the reconstruction liquid injection system, and a sleeve outside the oil pipe is connected to the coolant liquid circulation system; the ultra-low temperature cold source circulation system transfers cold energy of the cold source through the cold exchange device to the coolant liquid transported from the coolant liquid circulation system to the cold exchange device; the coolant liquid that obtains the cold energy enters the coal reservoir via the oil pipe; phase change liquid that is transported from the reconstruction liquid injection system to the coal reservoir receives the cold energy, and reconstructs the stratum; and the coolant liquid flows from the sleeve outside the oil pipe into the coolant liquid circulation system.
2. The ground cold exchange injection system according to claim 1, characterized in that, the cold exchange device is provided with a cold source passage and a coolant liquid passage, the ultra-low temperature cold source circulation system is connected to the cold source passage, the coolant liquid circulation system is connected to the coolant liquid passage, and the cold energy of the cold source is transferred to the coolant liquid in the coolant liquid passage through the cold source passage.
3. The ground cold exchange injection system according to claim 2, characterized in that, the ultra-low temperature cold source circulation system comprises: a cold source tank, a first metering injection device, a first check valve, a cold source three-way valve, an evaporator, a second metering injection device, the cold source passage, a condenser and a compressor which are connected in succession, wherein an outlet of the cold source tank is connected to an inlet of the first metering injection device, an outlet of the first metering injection device is connected to an inlet of the first check valve, an outlet of the first check valve is connected to an inlet of the evaporator and an outlet of the compressor respectively through the cold source three-way valve, an outlet of the evaporator is connected to an inlet of the second metering injection device, an outlet of the second metering injection device is connected to an inlet of the cold source passage of the cold exchange device, an outlet of the cold source passage is connected to an inlet of the condenser, an outlet of the condenser is connected to an inlet of the compressor, an outlet of the compressor is connected to the cold source three-way valve to form a loop, and the compressor is further connected to the cold source three-way valve.
4. The ground cold exchange injection system according to claim 3, characterized in that, the coolant liquid circulation system comprises a first coolant liquid tank, a second check valve, a coolant liquid three-way valve, a third metering injection device, the coolant liquid passage, a second coolant liquid tank, a fourth metering injection device and a third check valve which are connected in succession, wherein the third check valve is connected to the oil pipe in the wellhead; the coolant liquid circulation system further comprises a fourth check valve and a coolant liquid flowback tank that are connected to each other, the fourth check valve is further connected to the sleeve outside the oil pipe, and the coolant liquid flowback tank is further connected to the coolant liquid three-way valve; an outlet of the first coolant liquid tank is connected to an inlet of the second check valve, an outlet of the second check valve is connected to an inlet of the third metering injection device and an outlet of the coolant liquid flowback tank respectively through the coolant liquid three-way valve, an outlet of the third metering injection device is connected to an inlet of the coolant liquid passage, an outlet of the coolant liquid passage is connected to an inlet of the second coolant liquid tank, an outlet of the second coolant liquid tank is connected to an inlet of the fourth metering injection device, the fourth metering injection device is connected to an inlet of the third check valve, an outlet of the third check valve is connected to the oil pipe in the well through a first wellhead oil pipe gate, a sleeve is provided outside the oil pipe, a wellhead sleeve gate is provided on the sleeve at a position of the wellhead, an outlet of the wellhead sleeve gate is connected to an inlet of the fourth check valve, an outlet of the fourth check valve is connected to an inlet of the coolant liquid flowback tank, and an outlet of the coolant liquid flowback tank is connected to the coolant liquid three-way valve.
5. The ground cold exchange injection system according to claim 4, characterized in that, the reconstruction liquid injection system comprises a spacer liquid tank, a fifth metering injection device, a fifth check valve and a reconstruction liquid three-way valve which are connected in succession, wherein the reconstruction liquid three way valve is further connected to the oil pipe in the wellhead; the reconstruction liquid injection system further comprises a phase change liquid tank, a sixth metering injection device and a sixth check valve in succession, and the sixth check valve is further connected to the reconstruction liquid three-way valve.
6. The ground cold exchange injection system according to claim 5, characterized in that, the ground cold exchange injection system further comprises a pressure meter and a thermometer, wherein the pressure meter and the thermometer are provided between the first metering injection device and the first check valve, between the second metering injection device and the cold source passage, between the compressor and the cold source three-way valve, between the third metering injection device and the coolant liquid passage, between the third check valve and the oil pipe, between the fourth check valve and the coolant liquid flowback tank, and between the reconstruction liquid three way valve and the oil pipe; and the thermometer is provided between the coolant liquid passage and the second coolant liquid tank.
7. A coal reservoir phase change reconstructing method, comprising: step 1: lowering the sleeve into a coal bed gas well, perforating the coal reservoir, lowering a thermal insulation oil pipe and a thermo-pressure meter into the sleeve, and providing an annular space between the sleeve and the thermal insulation oil pipe; step 2: injecting a certain amount of spacer liquid into the thermal insulation oil pipe by the ground cold exchange injection system; step 3: injecting a certain amount of phase change liquid into the thermal insulation oil pipe by the ground cold exchange injection system; step 4: continuing to inject a certain amount of spacer liquid into the thermal insulation oil pipe; step 5: cooling the coolant liquid by the ground cold exchange injection system, and injecting the cooled coolant liquid into the thermal insulation oil pipe, wherein the coolant liquid conducts the cold energy to the phase change liquid to cause the phase change liquid to reach a phase change temperature and to produce volume expansion; when the thermo-pressure meter shows that the bottom hole temperature is not decreased any more, stopping injection of the coolant liquid; step 6: injecting once again a certain amount of spacer liquid into the thermal insulation oil pipe, if the thermo-pressure meter shows that the bottom hole pressure is higher than or equal to the fracturing pressure of the coal reservoir, then repeating the steps 3 to 6, continuing phase change reconstruction of the coal reservoir outside the sleeve; if the thermo-pressure meter shows that the bottom hole pressure is lower than the fracturing pressure of the coal reservoir, then ending phase change reconstruction of the coal reservoir outside the sleeve.
8. The coal reservoir phase change reconstructing method according to claim 7, characterized in that, in the step 1, perforating the coal reservoir specifically comprises: perforating a plurality of oillets having diameters of 9mm-llmm in the sleeve and the coal reservoir outside the sleeve, the density of arrangement of the plurality of oillets is 10/m-16/m, and all of the oillets having the same phase angle of 60°-90°.
9. The coal reservoir phase change reconstructing method according to claim 8, characterized in that, the step 2: injecting a certain amount of spacer liquid into the thermal insulation oil pipe by the ground cold exchange injection system specifically comprises: opening the top opening of the thermal insulation oil pipe and the top opening of the sleeve; by use of the reconstruction liquid injection system in the ground cold exchange injection system, spacer liquid is injected into the thermal insulation oil pipe at a discharge rate of 0.5m3/min-3.0m3/min through the top opening of the thermal insulation oil pipe, the spacer liquid passes through a bottom opening of the thermal insulation oil pipe to enter the annular gap between the thermal insulation oil pipe and the sleeve; when a liquid surface position of the spacer liquid in the annular gap between the thermal insulation oil pipe and the sleeve is higher than a highest position of the plurality of oillets in the coal reservoir, closing the top opening of the sleeve; the reconstruction liquid injection system continues to inject a certain amount of spacer liquid at a discharge rate of 0.5m3/min-3.0m3/min into the thermal insulation oil pipe through the top opening of the thermal insulation oil pipe, to cause the spacer liquid to enter the coal reservoir through the oillets.
10. The coal reservoir phase change reconstructing method according to claim 9, characterized in that, the step 3: injecting a certain amount of phase change liquid into the thermal insulation oil pipe by the ground cold exchange injection system specifically comprises: injecting a certain amount of phase change liquid at a discharge rate of 0.5m3/min-3.0m3/min into the thermal insulation oil pipe by the reconstruction liquid injection system, and causing the phase change liquid to enter the coal reservoir through the oillets.
11. The coal reservoir phase change reconstructing method according to claim 10, characterized in that, the step 4: continuing to inject a certain amount of spacer liquid into the thermal insulation oil pipe specifically comprises: injecting a certain amount of spacer liquid at a discharge rate of 0.5m3/min-3.0m3/min into the thermal insulation oil pipe by the reconstruction liquid injection system, and causing the spacer liquid to enter the coal reservoir through the oillets.
12. The coal reservoir phase change reconstructing method according to claim 11, characterized in that, the step 5: cooling the coolant liquid by the ground cold exchange injection system, and injecting the cooled coolant liquid into the thermal insulation oil pipe, wherein the coolant liquid conducts the cold energy to the phase change liquid to cause the phase change liquid to reach a phase change temperature and to produce volume expansion, when the thermo-pressure meter shows that the bottom hole temperature is not decreased any more, stopping injection of the coolant liquid specifically comprises: transporting a cold source to the cold exchange device by the ultra-low temperature cold source circulation system and transporting coolant liquid to the cold exchange device by the coolant liquid circulation system in the ground cold exchange injection system, and conducting cold energy by the cold source to the coolant liquid in the cold exchange device to cause the temperature of the coolant liquid to be reduced to -10°C to -50°C; opening the top opening of the sleeve; by use of the coolant liquid circulation system, injecting temperature-lowered coolant liquid at a discharge rate of 0.5m3/min-3.0m3/min into the thermal insulation oil pipe through the top opening of the thermal insulation oil pipe; the coolant liquid conducts the cold energy to the phase change liquid in the oillets, the phase change liquid reaches the phase change temperature after receiving the cold energy and has volume expansion, so that the coal reservoir around the oillets forms crack; the coolant liquid whose cold energy is conducted passes through the annular gas between the sleeve and the thermal insulation oil pipe to be drained to the coolant liquid circulation system outside the coal bed gas to be recycled; when the thermo-pressure meter shows that the bottom hole temperature is not decreased any more, injection of the coolant liquid is stopped.
13. The coal reservoir phase change reconstructing method according to claim 12, characterized in that, the step 6: injecting once again a certain amount of spacer liquid into the thermal insulation oil pipe, if the thermo-pressure meter shows that the bottom hole pressure is higher than or equal to the fracturing pressure of the coal reservoir, then repeating the steps 3 to 6, continuing phase change reconstruction of the coal reservoir outside the sleeve; if the thermo-pressure meter shows that the bottom hole pressure is lower than the fracturing pressure of the coal reservoir, then ending the coal reservoir phase change reconstructing outside the sleeve, specifically comprising: closing the top opening of the sleeve; injecting a certain amount of spacer liquid at a discharge rate of 0.5m3/min-3.0m3/min into the thermal insulation oil pipe by the reconstruction liquid injection system, if the thermo-pressure meter shows that the bottom hole pressure is higher than or equal to the fracturing pressure of the coal reservoir, then continuing phase change reconstruction of the coal reservoir outside the sleeve, repeating the steps 3 to 6, if the thermo-pressure meter shows that the bottom hole pressure is lower than the fracturing pressure of the coal reservoir, then opening the top opening of the sleeve, waiting until the thermo-pressure meter shows that the bottom hole temperature is recovered and is higher than the phase change temperature of the phase change liquid, ending the phase change reconstruction of the coal reservoir outside the sleeve.
14. The coal reservoir phase change reconstructing method according to any of claims 7 to 13, characterized in that, the coolant liquid is saturated salt water, the phase change liquid is clean water, and the spacer liquid is kerosene.