阅读说明：本技术 一种天然气水合物储层冻结压裂增产改造方法及装置 (Method and device for increasing production and improving natural gas hydrate reservoir by freezing and fracturing ) 是由 周佳维 谢文卫 唐军 于彦江 寇贝贝 申凯翔 宁波 王英圣 欧芬兰 孙明远 于 2021-06-04 设计创作，主要内容包括：本发明公开了一种天然气水合物储层冻结压裂增产改造方法及装置,应用于水平井,其中,所述增产改造方法包括：初次冻结步骤：冻结管柱下入井筒内,通过冻结管柱向井筒内注入制冷剂进行第一次冻结,焖井第一时间后,在井筒外形成第一冻结区域,取出冻结管柱；射孔步骤：射孔枪下入井筒内,射孔枪在第一冻结区域内进行射孔,射孔操作完成后取出射孔枪；再次冻结步骤：冻结管柱再次下入井筒内,向井筒内注入制冷剂,制冷剂流入射孔内进行再次冻结,焖井第二时间后,在井筒外形成第二冻结区域,取出冻结管柱；压裂施工步骤：压裂工具连接压裂管柱下入井筒内,在第二冻结区域内进行分段压裂增产作业。(The invention discloses a method and a device for increasing production of a natural gas hydrate reservoir by freezing and fracturing, which are applied to a horizontal well, wherein the method for increasing production comprises the following steps: a primary freezing step: the freezing pipe column is put into the shaft, a refrigerant is injected into the shaft through the freezing pipe column for primary freezing, after the shaft is stewed for the first time, a first freezing area is formed outside the shaft, and the freezing pipe column is taken out; perforating: the perforating gun is put into the shaft, the perforating gun performs perforating in the first freezing area, and the perforating gun is taken out after the perforating operation is finished; and (3) freezing again: the freezing pipe column is put into the shaft again, a refrigerant is injected into the shaft, the refrigerant flow enters the hole to be frozen again, a second freezing area is formed outside the shaft after the shaft is stewed for a second time, and the freezing pipe column is taken out; fracturing construction: and the fracturing tool is connected with a fracturing pipe column and is put into the shaft, and staged fracturing stimulation operation is carried out in the second freezing area.)

1. A natural gas hydrate reservoir stratum freezing fracturing yield-increasing transformation method is applied to a horizontal well, and comprises the following steps:

a primary freezing step: the freezing pipe column is put into the shaft, a refrigerant is injected into the shaft through the freezing pipe column for primary freezing, after the shaft is stewed for the first time, a first freezing area is formed outside the shaft, and the freezing pipe column is taken out;

perforating: the perforating gun is put into the shaft, the perforating gun performs perforating in the first freezing area, and the perforating gun is taken out after the perforating operation is finished;

and (3) freezing again: the freezing pipe column is put into the shaft again, a refrigerant is injected into the shaft, the refrigerant flow enters the hole to be frozen again, a second freezing area is formed outside the shaft after the shaft is stewed for a second time, and the freezing pipe column is taken out;

fracturing construction: and the fracturing tool is connected with a fracturing pipe column and is put into the shaft, and staged fracturing stimulation operation is carried out in the second freezing area.

2. A gas hydrate reservoir freeze fracturing stimulation modification method according to claim 1, further comprising, after the fracturing construction step:

and repeating the re-freezing step and the fracturing construction step until the yield increasing transformation effect is completed.

3. A natural gas hydrate reservoir freezing fracturing stimulation and transformation method as claimed in claim 1, wherein the freezing pipe column comprises a heat insulation steel pipe located in a straight well section and a seamless steel pipe located in an inclined well section and a horizontal well section, the heat insulation steel pipe and the seamless steel pipe are connected through a conversion joint, and a heat insulation packer capable of being used for sealing an annular hollow area in a shaft is installed on the seamless steel pipe at a position close to the conversion joint.

4. A gas hydrate reservoir freeze fracturing stimulation program according to claim 1, further comprising, prior to the primary freezing step:

well cementation: injecting cement, and enabling the cement to return to a designed position;

a shaft cleaning step: cleaning the inside of the shaft.

5. A natural gas hydrate reservoir freezing fracturing stimulation modification method as claimed in claim 1, wherein the refrigerant is liquid nitrogen, liquid carbon dioxide or low temperature calcium chloride brine.

6. A natural gas hydrate reservoir freezing fracturing production-increasing transformation device is characterized by comprising a platform wellhead device arranged on a drilling platform, a seabed wellhead device arranged on the seabed, a shaft fixedly connected with the platform wellhead device and penetrating through the seabed wellhead device to extend into a natural gas hydrate reservoir, a fracturing system arranged on the drilling platform, a refrigerating system arranged on the drilling platform and a perforating gun;

the refrigerating system comprises refrigerating equipment and a freezing pipe column which is communicated with the refrigerating equipment and can be lowered into a shaft;

the fracturing system comprises a fracturing truck, a fracturing pipe column and a fracturing tool, wherein the fracturing pipe column is communicated with the fracturing truck and can be put into a shaft, and the fracturing tool is connected with the fracturing pipe column.

7. A natural gas hydrate reservoir freezing fracturing stimulation and transformation device as claimed in claim 6, wherein the freezing string comprises a heat insulation steel pipe located in the straight well section and a seamless steel pipe located in the inclined well section and the horizontal well section, the heat insulation steel pipe and the seamless steel pipe are connected through a crossover joint, and a heat insulation packer capable of being used for sealing an annular hollow area in the shaft is installed on the seamless steel pipe at a position close to the crossover joint.

8. The natural gas hydrate reservoir freezing fracturing stimulation modification device of claim 7, wherein the insulated steel tube is a vacuum insulated steel tube.

9. A natural gas hydrate reservoir freezing fracturing stimulation modification device as claimed in claim 6, wherein the fracturing tool comprises a fracturing sliding sleeve connected with the fracturing string, a first packer disposed at a first end of the fracturing sliding sleeve, and a second packer disposed at a second end of the fracturing sliding sleeve.

10. A natural gas hydrate reservoir freezing fracturing stimulation and transformation device as claimed in claim 6, wherein a temperature sensor and a pressure sensor for detecting temperature and pressure in the wellbore annulus region are arranged on the outer side wall of the freezing string.

Technical Field

The invention relates to the field of natural gas hydrate exploitation, in particular to a method and a device for increasing production and improving natural gas hydrate reservoir stratum freezing fracturing.

Background

The natural gas hydrate is clean energy with abundant resource quantity, the total carbon content of the natural gas hydrate is twice of the total carbon content of the traditional petrochemical energy at present, and more than 97 percent of the natural gas hydrate exists in the sea area. The natural gas hydrate in the south China sea is rich in resources and is a hot spot area for exploiting the natural gas hydrate in China. The natural gas hydrate reservoir sediment in the south sea area is muddy silt, has extremely low permeability, is in an unconsolidated or weakly consolidated state, and has soft stratum and low mechanical strength. At present, natural gas hydrate exploitation mainly comprises a depressurization method, a thermal excitation method, a replacement method, an inhibitor injection method and the like, but no matter what method is used, the low permeability of a natural gas hydrate reservoir stratum is an important factor for restricting the exploitation. Reservoirs that are not stimulated to produce industrial levels of gas flow are difficult to obtain.

The hydraulic fracturing of the horizontal well is a core technology for successfully and commercially developing unconventional oil and gas resources of low-permeability reservoirs such as shale gas, dense gas and dense oil. The hydraulic fracturing technology is utilized to perform yield increase transformation on a hydrate reservoir, a hydraulic fracture is formed, a natural gas flow channel with high flow conductivity can be established, the pressure relief range during depressurization exploitation is enlarged, the contact area between hot fluid of a thermal excitation method, replacement materials of a replacement method and an inhibitor injected by an inhibitor injection method and the natural gas hydrate is increased, damage to the reservoir during drilling and well completion is eliminated, the exploitation efficiency of various exploitation methods can be greatly improved, and the hydraulic fracturing technology has a good application prospect. However, the natural gas hydrate argillaceous silt reservoir is soft and is in a weakly cemented or unconsolidated state, so that the conventional hydraulic fracturing technology is difficult to be directly applied to natural gas hydrate development.

The natural gas hydrate and ice in the natural gas hydrate reservoir can improve the cementing strength of the stratum sediment, and the higher the proportion of the natural gas hydrate and ice, the higher the stratum strength and brittleness, and the better the stratum compressibility. The freezing method is widely applied to underground passage excavation projects such as coal mining and subway tunnels, and smooth implementation of the projects is ensured by freezing weak strata and strata water complex strata. The freezing method is applied to the natural gas hydrate development, and the fracturing yield-increasing technology can be applied to the natural gas hydrate development by artificially freezing a natural gas hydrate reservoir to improve the stratum strength and brittleness. The problem of fracturing yield increase of a horizontal well of a natural gas hydrate reservoir cannot be solved by the conventional yield increase transformation method, and the yield increase effect of the horizontal well matched with a fracturing yield increase technology on a low-permeability reservoir is better. Meanwhile, the conventional yield-increasing transformation method cannot control the initiation position of the hydraulic fracture, cannot control and guide the expansion of the hydraulic fracture, and cannot avoid the interference among different well fractures when the fracturing of a plurality of wells is implemented. And the influence of the freezing expansion effect on the pipeline strength when the large-range freezing is not considered in the conventional yield-increasing transformation method.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a method and a device for increasing production and improving natural gas hydrate reservoir stratum by freezing and fracturing.

The technical scheme adopted by the invention for solving the technical problems is as follows: a natural gas hydrate reservoir freezing fracturing yield-increasing transformation method is constructed and applied to a horizontal well, and the yield-increasing transformation method comprises the following steps:

a primary freezing step: the freezing pipe column is put into the shaft, a refrigerant is injected into the shaft through the freezing pipe column for primary freezing, after the shaft is stewed for the first time, a first freezing area is formed outside the shaft, and the freezing pipe column is taken out;

perforating: the perforating gun is put into the shaft, the perforating gun performs perforating in the first freezing area, and the perforating gun is taken out after the perforating operation is finished;

and (3) freezing again: the freezing pipe column is put into the shaft again, a refrigerant is injected into the shaft, the refrigerant flow enters the hole to be frozen again, a second freezing area is formed outside the shaft after the shaft is stewed for a second time, and the freezing pipe column is taken out;

fracturing construction: and the fracturing tool is connected with a fracturing pipe column and is put into the shaft, and staged fracturing stimulation operation is carried out in the second freezing area.

In the method for increasing production of natural gas hydrate reservoir by freezing and fracturing, after the fracturing construction step, the method further comprises the following steps:

and repeating the re-freezing step and the fracturing construction step until the yield increasing transformation effect is completed.

In the natural gas hydrate reservoir freezing fracturing production-increasing transformation method, the freezing pipe column comprises a heat-insulating steel pipe located in a straight well section and seamless steel pipes located in an inclined well section and a horizontal well section, the heat-insulating steel pipe and the seamless steel pipes are connected through a conversion joint, and a heat-insulating packer capable of being used for sealing an annular area in a shaft is installed on the seamless steel pipe close to the conversion joint.

In the method for increasing the yield of frozen fracturing of a natural gas hydrate reservoir, before the primary freezing step, the method for increasing the yield further comprises:

well cementation: injecting cement, and enabling the cement to return to a designed position;

a shaft cleaning step: cleaning the inside of the shaft.

In the method for increasing the production and improving the natural gas hydrate reservoir by freezing and fracturing, the refrigerant is liquid nitrogen, liquid carbon dioxide or low-temperature calcium chloride brine.

The other technical scheme adopted by the invention for solving the technical problem is as follows: constructing a natural gas hydrate reservoir freezing fracturing yield-increasing transformation device, wherein the yield-increasing transformation device comprises a platform wellhead device arranged on a drilling platform, a seabed wellhead device arranged on the seabed, a shaft fixedly connected with the platform wellhead device and penetrating through the seabed wellhead device to extend into a natural gas hydrate reservoir, a fracturing system arranged on the drilling platform, a refrigerating system arranged on the drilling platform and a perforating gun;

the refrigerating system comprises refrigerating equipment and a freezing pipe column which is communicated with the refrigerating equipment and can be lowered into a shaft;

the fracturing system comprises a fracturing truck, a fracturing pipe column and a fracturing tool, wherein the fracturing pipe column is communicated with the fracturing truck and can be put into a shaft, and the fracturing tool is connected with the fracturing pipe column.

In the natural gas hydrate reservoir freezing fracturing production-increasing transformation device, the freezing pipe column comprises a heat-insulating steel pipe located in a straight well section and seamless steel pipes located in an inclined well section and a horizontal well section, the heat-insulating steel pipe and the seamless steel pipes are connected through a conversion joint, and a heat-insulating packer capable of being used for sealing an annular area in a shaft is installed on the seamless steel pipe close to the conversion joint.

In the natural gas hydrate reservoir freezing fracturing production-increasing transformation device, the heat-insulating steel pipe is a vacuum heat-insulating steel pipe.

In the natural gas hydrate reservoir freezing fracturing production-increasing transformation device, the fracturing tool comprises a fracturing sliding sleeve connected with a fracturing string, a first packer arranged at the first end of the fracturing sliding sleeve and a second packer arranged at the second end of the fracturing sliding sleeve.

In the natural gas hydrate reservoir freezing fracturing production-increasing transformation device, the outer side wall of the freezing pipe column is provided with a temperature sensor and a pressure sensor for detecting the temperature and the pressure in the well casing annular area.

The implementation of the method and the device for increasing the production of the natural gas hydrate reservoir by freezing and fracturing has the following beneficial effects: when the method and the device for improving the natural gas hydrate reservoir stratum freezing fracturing yield increase are implemented, the reservoir stratum is firstly frozen for the first time before fracturing yield increase operation is carried out, the first freezing area is perforated after the first freezing is finished, freezing is carried out again after the perforation is finished to form a second freezing area, and finally, a fracturing tool is put in to carry out staged fracturing yield increase operation. By artificially freezing the reservoir, the consolidation strength of the stratum is improved, the brittleness of the stratum is enhanced, and the conditions for hydraulic fracturing yield-increasing transformation of the hydrate reservoir are created. Furthermore, the hydraulic fracture initiation pressure is reduced through perforation, the approximate fracture initiation position is determined, the fracture expansion is guided, the unpredictable and uncontrollable conditions of the fracture initiation position are avoided, the reservoir is effectively cut along the transverse cutting seam initiated at the perforation position, and the higher reservoir modification volume can be obtained. Meanwhile, through manual freezing again, the refrigerant can be diffused to the perforation holes, the efficiency of manually freezing the reservoir can be improved, and the freezing range of the reservoir is enlarged. When the stratum is frozen, the volume can expand due to the freeze-expansion effect, the perforation holes provide a certain space for the volume expansion of the sediment, and the possibility of damage to a shaft caused by the freeze-expansion effect is reduced.

Drawings

The invention will be further described with reference to the accompanying drawings and examples, in which:

FIG. 1 is a schematic flow diagram of a first embodiment of a gas hydrate reservoir freeze fracturing stimulation modification method of the present invention;

FIG. 2 is a schematic structural diagram of primary freezing in a first embodiment of a gas hydrate reservoir freeze fracturing stimulation apparatus of the present invention;

FIG. 3 is a schematic structural diagram of a perforating step in a first embodiment of a gas hydrate reservoir freeze fracturing stimulation apparatus of the present invention;

fig. 4 is a schematic structural diagram of a fracturing construction step in a first embodiment of the natural gas hydrate reservoir freezing fracturing stimulation and modification device of the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As shown in fig. 1, in a first embodiment of the gas hydrate reservoir freezing fracturing stimulation method of the present invention, the stimulation method is applied to a horizontal well, and the stimulation method includes:

a primary freezing step S101: the freezing pipe column is put into the shaft, a refrigerant is injected into the shaft through the freezing pipe column for primary freezing, after the shaft is stewed for the first time, a first freezing area is formed outside the shaft, and the freezing pipe column is taken out.

Specifically, the freezing pipe column combination is designed according to the conditions of a well body structure, stratum thickness and the like, and the freezing pipe column is lowered into the well to set the depth. The heat insulation pipe is selected above the top of the natural gas hydrate reservoir, the vacuum heat insulation type oil pipe is preferably selected as the heat insulation pipe, the seamless steel pipe is connected below the adapter, the adapter is preferentially arranged at the boundary position of the reservoir and the overlying stratum, the heat insulation packer is arranged at the lower part of the adapter, and by arranging the heat insulation packer, the freezing pipe column combination can effectively reduce heat transfer between the refrigerant and the environment when the refrigerant is conveyed to the stratum through the freezing pipe column, so that the influence of low temperature on the environment can be reduced, and the reservoir can be refrigerated in a centralized manner.

The refrigerant may be liquid nitrogen, liquid carbon dioxide or other refrigerant substance, and liquid nitrogen is preferred as one embodiment of the present invention. And (3) delivering liquid nitrogen to the reservoir through the freezing pipe column by refrigeration equipment, wherein the liquid nitrogen flows out from the tail end of the freezing pipe column, is gasified to absorb heat, and flows and diffuses to the freezing pipe column and the shaft annulus. Under the standard atmospheric pressure, the liquid nitrogen temperature can reach-196 ℃, the reservoir temperature can be effectively reduced to realize artificial freezing, the reservoir cementation strength and brittleness are improved, and the shaft and well wall consolidation strength is improved. The annular space temperature and pressure can be monitored through a bottom hole pressure sensor and a temperature sensor, liquid nitrogen is injected into a stratum, soaking is carried out for a period of time, the frozen stratum range around the horizontal well can be predicted for a period of soaking according to the bottom hole temperature, soaking time, reservoir physical properties and other data, and the first artificially frozen reservoir range is recorded as a first freezing area. After the initial freezing is complete, the freezing string is removed from the wellbore.

A perforation step S102: and (4) putting the perforating gun into the shaft, perforating the perforating gun in the first freezing area, and taking out the perforating gun after the perforating operation is finished.

The perforating gun is lowered into the horizontal well, and the perforating gun can be lowered into the well through a coiled tubing, a drill string or a cable and the like. The invention takes a coiled tubing conveyed perforating gun as an example, the perforating gun is sent to the designed position of the horizontal well section to carry out perforation with optimized perforation parameters, and the selected perforation depth is larger than the range of a shaft (comprising a production casing and a cement sheath) and smaller than the reservoir range of the first freezing zone.

Perforations can reduce the mechanical strength of the formation, and thus, hydraulic fractures are generally initiated along the perforations. The formation fracture initiation pressure can be reduced through perforation, and the fracture initiation position and the fracture propagation direction of the hydraulic fracture are controlled. When the second manual freezing is carried out, the liquid nitrogen can be diffused to the perforation holes, and the efficiency of manually freezing the reservoir can be improved. When the stratum is frozen, the volume can expand due to the freeze-expansion effect, the perforation holes provide a certain space for the volume expansion of the sediment, and the possibility of damage to a shaft caused by the freeze-expansion effect is reduced. During formation freeze-swelling, the redistribution of stresses around the perforations may cause some fracture propagation.

Re-freezing step S103: and the freezing pipe column is put into the shaft again, the refrigerant is injected into the shaft, the refrigerant flow enters the hole to be frozen again, after the well is stewed for a second time, a second freezing area is formed outside the shaft, and the freezing pipe column is taken out.

And after the perforation step is finished, taking out the perforating gun, the coiled tubing and the like, and putting the freezing pipe column into the shaft again for second manual freezing, wherein the freezing is mainly used for forming a larger manual freezing range of the reservoir, and improving the strength and the brittleness of the reservoir creates favorable conditions for fracturing yield-increasing transformation.

And (3) dredging a well before the freezing pipe column is put into the well, cleaning reservoir sediments falling into the shaft during perforation construction, injecting a refrigerant into the shaft through the freezing pipe column again, injecting a refrigerant flow into the hole for refreezing, stewing for a second time, forming a second freezing area inside and outside the shaft, and taking out the freezing pipe column. The second freeze zone is larger than the first freeze zone.

A fracturing construction step S104: and the fracturing tool is connected with a fracturing pipe column and is put into the shaft, and staged fracturing stimulation operation is carried out in the second freezing area.

And taking out the freezing pipe column, cleaning the shaft, and putting the freezing pipe column into the fracturing pipe column for fracturing yield-increasing transformation. In order to obtain larger reservoir reconstruction volume, the invention selects a horizontal well subsection multi-cluster fracturing technology as an embodiment, a fracturing pipe column is connected with a fracturing tool, the fracturing tool comprises a fracturing sliding sleeve and a packer, in the fracturing action process, the packer is used for setting, the horizontal well is sectioned, the fracturing sliding sleeve in each section is a fracturing fluid outlet, fracturing fluid is injected, the fracturing fluid enters the stratum along a perforation, the stratum is fractured, the fracturing tool packer is used for setting at a preset position to divide the horizontal section of the horizontal well into a plurality of sections, and fracturing production-increasing operation is carried out according to a preferable fracturing scheme.

Because the formation temperature is low after artificial freezing, the selected fracturing fluid should meet the performance requirements of the fracturing process on the fracturing fluid under the low-temperature condition.

When the natural gas hydrate reservoir freezing fracturing production-increasing transformation method is implemented, storage is firstly frozen for the first time before fracturing production-increasing operation is carried out, after the freezing for the first time is finished, a first freezing area is perforated, after the perforation is finished, the freezing is carried out again to form a second freezing area, and finally, a fracturing tool is put in to carry out staged fracturing production-increasing operation. By artificially freezing the reservoir, the consolidation strength of the stratum is improved, the brittleness of the stratum is enhanced, and the conditions for hydraulic fracturing yield-increasing transformation of the hydrate reservoir are created. Furthermore, the hydraulic fracture initiation pressure is reduced through perforation, the approximate fracture initiation position is determined, the fracture expansion is guided, the unpredictable and uncontrollable conditions of the fracture initiation position are avoided, the reservoir is effectively cut along the transverse cutting seam initiated at the perforation position, and the higher reservoir modification volume can be obtained. Meanwhile, through manual freezing again, the refrigerant can be diffused to the perforation holes, and the efficiency of manually freezing the reservoir can be improved. When the stratum is frozen, the volume can expand due to the freeze-expansion effect, the perforation holes provide a certain space for the volume expansion of the sediment, and the possibility of damage to a shaft caused by the freeze-expansion effect is reduced.

Further, after the fracturing construction step, the stimulation modification method further comprises the following steps:

and repeating the refreezing step and the fracturing construction step until the yield-increasing transformation effect is completed.

After the fracturing production increasing operation is completed, the refreezing step and the fracturing construction step can be repeatedly carried out so as to realize continuous exploitation and improve the exploitation efficiency.

In order to prevent heat transfer between the refrigerant and the marine environment, the influence of low temperature on the marine environment is reduced. The freezing pipe column comprises a heat insulation steel pipe positioned in a straight well section and seamless steel pipes positioned in an inclined well section and a horizontal well section, wherein the heat insulation steel pipe and the seamless steel pipes are connected through a conversion joint, and a heat insulation packer which can be used for sealing an annular space area in a shaft is arranged on the seamless steel pipe close to the conversion joint.

When the refrigerant flows through the heat insulation steel pipe, the heat insulation is carried out through the heat insulation steel pipe, and the heat transfer between the refrigerant and the marine environment can be reduced or avoided. Furthermore, by arranging the heat insulation packer, the refrigerant is limited to flow in the reservoir, heat transfer between the refrigerant and the marine environment can be reduced or avoided, and the reservoir is refrigerated in a centralized manner. The insulated pipe is preferably a vacuum insulated oil pipe.

Further, before the primary freezing step, the stimulation modification method further comprises:

well cementation: injecting cement, and enabling the cement to return to a designed position;

a shaft cleaning step: cleaning the inside of the shaft.

During the completion process, cement injection is required to complete the well. And injecting cement, and enabling the cement to return to the designed position. And (3) after the cement is solidified, dredging the well to ensure that the inside of the shaft is smooth when the pipe column is put into the well, ensuring that the position of the shaft where the heat-insulating separator is located is clean, and ensuring that the heat-insulating packer is smoothly set.

And injecting cement for cementing before the first freezing, and consolidating the well bore and the formation annulus. Conventional cementing and well cementation can cause partial decomposition of reservoir hydrate due to cement hydration and heat release, and the consolidation effect is poor. In the application, effective consolidation between the stratum and the shaft can be guaranteed through primary freezing, and fracturing of the stratum and the shaft annulus by fracturing fluid is avoided, so that fracturing is not carried out along perforation holes.

In the invention, the refrigerant is liquid nitrogen, liquid carbon dioxide or low-temperature calcium chloride brine. Preferably, the refrigerant is liquid nitrogen.

As shown in fig. 2 to 4, in the first embodiment of the natural gas hydrate reservoir freezing and fracturing stimulation apparatus of the present invention, the stimulation apparatus 1 includes a platform wellhead device 3 disposed on a drilling platform 2, a subsea wellhead device 4 disposed on the seabed, a wellbore 5 fixedly connected to the platform wellhead device 3 and extending into the natural gas hydrate reservoir through the subsea wellhead device 4, a fracturing system 6 disposed on the drilling platform 2, a refrigeration system 7 disposed on the drilling platform 2, and a perforating gun 15; the refrigerating system 7 comprises refrigerating equipment and a freezing pipe column 8 which is communicated with the refrigerating equipment and can be put into the shaft 5; the fracturing system 6 includes a fracturing truck, a fracturing string 16 in communication with the fracturing truck and positionable in the wellbore 5, and a fracturing tool connected to the fracturing string 16.

When the natural gas hydrate reservoir freezing, fracturing and yield-increasing transformation device 1 is used, the freezing pipe column 8 is connected with refrigeration equipment, then the freezing pipe column 8 is put into a preset position in the shaft 5, and a refrigerant is injected for primary freezing to form a first freezing area 13. The freeze string 8 is removed and a perforating gun 15 is lowered through coiled tubing 14 into the first freeze zone 13 in the wellbore 5 for perforating operations. After perforating is completed, the perforating gun 15 is removed, the freeze string 8 is lowered into the first freeze zone 13 in the wellbore 5 again, the refrigerant is injected and refrozen occurs, and the refrigerant flow enters the perforations and freezes to form a second freeze zone 17. And (3) taking out the freezing pipe column 8, connecting the fracturing tool with a fracturing truck through the fracturing pipe column 16, and then putting the fracturing pipe column 16 and the fracturing tool into a second freezing area 17 of the shaft 5 to perform staged fracturing stimulation.

Preferably, the freezing pipe string 8 comprises an insulated steel pipe 11 positioned in a straight well section and a seamless steel pipe 12 positioned in a slant well section and a horizontal well section, the insulated steel pipe 11 and the seamless steel pipe 12 are connected through a conversion joint 9, and an insulated packer 10 which can be used for sealing an annular area in the shaft 5 is arranged on the seamless steel pipe 12 at a position close to the conversion joint 9.

When the refrigerant flows through the heat insulation steel pipe 11, heat transfer between the refrigerant and the marine environment can be reduced or avoided by performing heat insulation through the heat insulation steel pipe 11. Furthermore, by arranging the heat insulation packer 10, the refrigerant is limited to flow in the reservoir, so that heat transfer between the refrigerant and the marine environment can be reduced or avoided, and the reservoir can be refrigerated in a centralized manner.

In the present embodiment, the heat-insulating steel pipe 11 is a vacuum heat-insulating steel pipe 11, and is preferably a vacuum heat-insulating oil pipe.

Specifically, for better staged fracturing stimulation, the fracturing tool comprises a fracturing sliding sleeve 18 connected with the fracturing string 16, a first packer 19 arranged at a first end of the fracturing sliding sleeve 18, and a second packer 20 arranged at a second end of the fracturing sliding sleeve 18. During the fracturing action, the two ends of the fracturing sliding sleeve 18 can be set through the first packer 19 and the second packer 20, and then the fracturing construction action is carried out.

In order to facilitate the operator to know the freezing condition in the shaft 5, the outer side wall of the freezing pipe column 8 is provided with a temperature sensor and a pressure sensor for detecting the temperature and the pressure in the annular area of the shaft 5. The temperature sensor and the pressure sensor are electrically connected with a monitoring display device on the drilling platform 2, and the temperature and pressure information of the annular area in the shaft 5 is fed back in real time.

In addition, in the present invention, unless otherwise expressly specified or limited, the terms "connected," "stacked," and the like are to be construed broadly, e.g., as meaning permanently connected, detachably connected, or integrally formed; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.