CN114075951B - Natural gas hydrate exploitation shaft, system and method - Google Patents
Natural gas hydrate exploitation shaft, system and method Download PDFInfo
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- CN114075951B CN114075951B CN202010850039.8A CN202010850039A CN114075951B CN 114075951 B CN114075951 B CN 114075951B CN 202010850039 A CN202010850039 A CN 202010850039A CN 114075951 B CN114075951 B CN 114075951B
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- NMJORVOYSJLJGU-UHFFFAOYSA-N methane clathrate Chemical compound C.C.C.C.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O NMJORVOYSJLJGU-UHFFFAOYSA-N 0.000 title claims abstract description 90
- 238000000034 method Methods 0.000 title claims abstract description 28
- 238000004519 manufacturing process Methods 0.000 claims abstract description 97
- 239000004576 sand Substances 0.000 claims abstract description 79
- 238000000354 decomposition reaction Methods 0.000 claims abstract description 11
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 110
- 239000003345 natural gas Substances 0.000 claims description 55
- 238000010438 heat treatment Methods 0.000 claims description 37
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 19
- 238000005553 drilling Methods 0.000 claims description 15
- 238000000926 separation method Methods 0.000 claims description 10
- 238000005065 mining Methods 0.000 claims description 5
- 239000011148 porous material Substances 0.000 claims description 5
- 230000001154 acute effect Effects 0.000 claims description 3
- 238000011084 recovery Methods 0.000 claims description 2
- 230000002265 prevention Effects 0.000 abstract description 6
- 230000000903 blocking effect Effects 0.000 abstract description 3
- 239000007789 gas Substances 0.000 description 15
- 238000011161 development Methods 0.000 description 9
- 239000013049 sediment Substances 0.000 description 9
- 238000005516 engineering process Methods 0.000 description 6
- 238000012545 processing Methods 0.000 description 6
- 230000001105 regulatory effect Effects 0.000 description 6
- 238000002955 isolation Methods 0.000 description 4
- 239000003949 liquefied natural gas Substances 0.000 description 4
- 238000004062 sedimentation Methods 0.000 description 4
- 238000005243 fluidization Methods 0.000 description 3
- 230000005855 radiation Effects 0.000 description 3
- 239000013535 sea water Substances 0.000 description 3
- 239000007787 solid Substances 0.000 description 3
- 238000003860 storage Methods 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- 238000005520 cutting process Methods 0.000 description 2
- 239000003112 inhibitor Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000009825 accumulation Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 238000005056 compaction Methods 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005284 excitation Effects 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
- 239000003209 petroleum derivative Substances 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- -1 surface equipment Chemical compound 0.000 description 1
Classifications
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/01—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells specially adapted for obtaining from underwater installations
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
- E21B43/24—Enhanced recovery methods for obtaining hydrocarbons using heat, e.g. steam injection
- E21B43/2401—Enhanced recovery methods for obtaining hydrocarbons using heat, e.g. steam injection by means of electricity
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- Environmental & Geological Engineering (AREA)
- Fluid Mechanics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Filling Or Discharging Of Gas Storage Vessels (AREA)
Abstract
The invention discloses a well bore, a system and a method for exploiting natural gas hydrate, which fully consider the decomposition characteristics and reservoir characteristics of the natural gas hydrate, and adopt an open well completion production mode by utilizing an inclined well and a well completion pipe string, thereby avoiding a conventional complex sand prevention well completion pipe string, reducing sand blocking risks, improving production efficiency and greatly reducing exploitation cost.
Description
Technical Field
The invention relates to the technical field of natural gas hydrate development, in particular to a natural gas hydrate exploitation shaft, a natural gas hydrate exploitation system and a natural gas hydrate exploitation method.
Background
At present, the petroleum and natural gas resources are continuously reduced, and the natural gas hydrate resources are used as strategic reserve resources with huge resource quantity, and are developed and utilized to become hot spots pursued by various countries and large energy companies.
However, the existing research is not known about the occurrence condition and the form of the natural gas hydrate, and the natural gas hydrate is only considered to be in soft mudstone underground based on the only few natural gas hydrate trial production in the current world, and sand is seriously produced in the exploitation process.
And the existing natural gas hydrate resource development engineering technology mainly depends on the oil gas resource development engineering technology which is continuously developed and improved. Aiming at the development of marine natural gas hydrate resources, current trial production utilizes a deepwater work platform, and a conventional drilling technology is used for drilling a reservoir. And then, by utilizing the characteristics of natural gas hydrate resources, hydrate resources are decomposed by means of reducing reservoir pressure, increasing reservoir temperature, injecting hydrate inhibitors and the like, so that the purpose of exploitation is achieved.
Traditional sand control completions are mostly adopted in the well completion aspect. The sediment is filtered by gravel packing, screen pipe completion, etc. But is terminated because of severe sand plugging during the test production. In the recent test production process in japan, geoform (expandable deformation sand control system) of harributon is adopted, and the sand control tool is based on the sand control principle of conventional oil and gas resource development, but is different from other sieve tubes in that the outer layer is covered with a layer of material capable of preventing extremely fine particle sediment, so that the sand control tool is suitable for hydrate reservoir resource development.
In terms of exploitation methods, a depressurization method, a thermal excitation method and an inhibitor method are proposed abroad. China Zhou Shou proposes a solid state fluidization method for academies. Based on the methods, two natural gas hydrate test production processes are continuously carried out in south China in 2017, a depressurization method and a solid fluidization method are respectively adopted, great progress in development and utilization of natural gas hydrate resources is obtained, and one step of setting is spanned.
Zhou Shou is a solid state fluidization method for a yard, which aims at marine shallow hydrate resources, utilizes conventional oil and gas drilling to slurry the hydrate resources on the sea floor and then decomposes and produces gas. However, due to insufficient compaction degree of the shallow layer of the seabed, great challenges are caused to the drilling engineering technology including well cementation, drilling, orientation and other processes, and the whole set of hydrate resource development and utilization engineering technology and equipment are further required to be perfected, so that the adaptability to the hydrate resource is improved.
At present, no effective matched engineering technology and exploitation system for the resource development and utilization of natural gas hydrate serving as a framework are proposed.
Disclosure of Invention
Aiming at the problems existing in the prior art, the invention provides a natural gas hydrate exploitation shaft, a natural gas hydrate exploitation system and a natural gas hydrate exploitation method, which effectively overcome the challenges caused by the specificity of a skeleton type natural gas hydrate resource deposit and effectively exploit ocean natural gas hydrate resources.
The invention provides a natural gas hydrate exploitation shaft, which comprises the following components: a well casing obliquely arranged in the natural gas hydrate layer, wherein a slit which is communicated with the outside is arranged on the well casing;
The inside of the well casing is provided with heating equipment for decomposing natural gas hydrate and a production string for collecting the decomposed natural gas entering the well casing from the slots.
Further, the heating device and the production string are installed at a position adjacent to the cutting seam, the production string is installed inside the heating device, or the production string and the heating device are installed in parallel.
Further, the slots are disposed on the sidewall of the wellbore casing, and the openings of the slots on the inner sidewall of the wellbore casing are smaller than the openings of the slots on the outer sidewall of the wellbore casing.
Further, the wellbore casing extends obliquely downward, and the slots extend obliquely upward from outside to inside in a radial direction of the wellbore casing.
Further, a sand setting pocket for settling the silt entering the well casing from the slit is connected to the bottom of the well casing.
Further, a lifting pump for lifting natural gas or a separating pump for separating mud and sand entering the well casing is arranged in the well casing.
Further, a shaft opening for collecting natural gas is arranged at the upper part of the natural gas hydrate layer, and the pressure of the shaft opening is smaller than that of the bottom of the shaft.
Further, a production line for conveying the collected natural gas downstream is connected to the wellhead.
A natural gas hydrate exploitation system which is installed on the sea and comprises water surface equipment, underwater equipment and output equipment;
The water surface equipment comprises a drilling platform and platform equipment arranged on the drilling platform;
the underwater equipment comprises the exploitation shaft and a water isolation pipe positioned between the sea level and the natural gas hydrate layer;
One end of the production pipeline is connected with the shaft opening, and the other end of the production pipeline is connected with the output equipment and used for purifying, liquefying and storing the produced natural gas.
A natural gas exploitation method implemented by adopting the natural gas hydrate exploitation system comprises the following steps:
1) Logging in a well through a drilling platform, and setting a well casing in a production well;
2) Running a production string and heating equipment in a wellbore casing;
3) The power supply equipment is used for supplying power to the heating equipment, natural gas hydrate in the reservoir is heated, the decomposition rate of the natural gas hydrate is controlled at a constant speed, and the pressure of the shaft is controlled to be smaller than the pressure at the bottom of the shaft by adjusting the collection amount of the natural gas in the shaft opening;
4) And conveying the produced natural gas to integrated treatment equipment through a production pipeline connected to a shaft hole, so as to finish exploitation.
According to the well bore, the system and the method for exploiting the natural gas hydrate, the decomposition characteristics and the reservoir characteristics of the natural gas hydrate are fully considered, and an open well completion production mode is adopted by utilizing the inclined well and the well completion pipe string, so that the conventional complex sand prevention well completion pipe string is avoided, the sand blocking risk is reduced, the production efficiency is improved, and the exploitation cost is greatly reduced.
Drawings
The invention will be described in more detail hereinafter on the basis of embodiments and with reference to the accompanying drawings. Wherein:
FIG. 1 is a schematic diagram of a natural gas hydrate recovery system according to the present invention;
FIG. 2 is a schematic illustration of a slot in a wellbore casing;
Fig. 3 is an enlarged view of the slit structure.
In the figure: 1-a sea water layer; 2-mud line; a 3-hydrate layer; 4-derrick; 5-a power supply device; 6-a power supply line; 7-a production line; 8-a riser; 9-a production string; 10-a wellhead; 11-wellbore casing; 12-heating equipment; 13-slotting the sleeve; 14-slotting; 15-sand setting pocket; 16-sleeve sidewall; 17-slotting openings; 18-a separation device; 19-a liquefaction plant; 20-a small liquefied storage device; 21-a mobile integrated treatment device; 22-gas line; 23-LNG liquefaction plant; 24-lifting pump.
Detailed Description
In order to clearly illustrate the inventive concept, the present invention will be described below with reference to examples.
In the description of the present invention, it should be noted that the positional or positional relationship indicated by the terms such as "upper", "lower", "horizontal", "top", "bottom", etc. are based on the positional or positional relationship shown in the drawings, are merely for convenience of describing the present invention and simplifying the description, and do not indicate or imply that the apparatus or element in question must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
The invention aims at exploiting skeleton type natural gas hydrate resources based on two types of natural gas hydrate resources, namely skeleton type resources taking natural gas hydrate as a skeleton and hydrate resources taking natural gas hydrate as pore contents.
Because natural gas hydrate is taken as a framework, water, sediment and the like are taken as pore contents, after the hydrate is mined, non-cemented sediment, water and the like can be settled along with the mining of the natural gas hydrate, and sand can be mined along with the hydrate resource, so that the later mining efficiency of the hydrate is affected.
Example 1
As shown in fig. 1, the invention provides a natural gas hydrate exploitation shaft, which comprises a shaft sleeve 11 obliquely arranged in a natural gas hydrate layer 3, wherein a slit 14 which is communicated with the outside is arranged on the shaft sleeve 11;
The interior of the wellbore casing 11 is provided with a heating device 12 for decomposing natural gas hydrate and a production string 9 for collecting the decomposed natural gas entering the wellbore casing 11 from the slots 14.
The invention discloses a natural gas hydrate exploitation shaft, which abandons a traditional oil gas sand control system and provides an open sand production exploitation system according to stratum characteristics of skeleton type natural gas hydrate exploitation.
Considering the subsidence that can appear in the skeleton type natural gas hydrate exploitation process, through the well casing 11 of slope installation, the pressure-bearing that increases the tubular column is reduced to minimum with upper portion silt subsidence causes, and the well casing 11 of slope setting has increased the area of contact of exploitation pit shaft and natural gas hydrate layer 3 maximize simultaneously.
By means of the heating device 12 arranged in the well casing 11, the natural gas hydrate layer 3 near the well can be continuously heated, and after the natural gas hydrate is heated and decomposed, the natural gas hydrate which is subsequently settled from the upper part can be continuously heated, so that a continuous and stable exploitation process is maintained.
The invention fully considers the subsidence of hydrate in the exploitation process, and on the basis of early test-produced sand, by arranging the slots 14 which are communicated with the outside on the shaft sleeve 11, an open sand prevention exploitation mode which allows sand to be produced in the natural gas production process (namely, a small part of silt to enter the shaft sleeve 11) is formed, and by inclining the shaft sleeve 11, most of the silt which uniformly subsides at a certain exploitation speed slides down along the outer wall of the shaft sleeve 11 in an inclined way, and is combined with the slots 14 arranged on the shaft sleeve 11, so that the natural gas after heating decomposition enters the shaft sleeve 11 from the slots 14, and at the same time, a small part of sand bodies are allowed to enter the shaft from the slots 14 of the shaft sleeve 11 along with the exploitation of the natural gas hydrate.
According to the natural gas hydrate exploitation shaft, the decomposition rate of the hydrate in the reservoir is controlled at a constant speed, the collection amount of natural gas at the shaft mouth is regulated, and the pressure of the shaft is controlled to be smaller than the bottom hole pressure, so that the depressurization production process of the natural gas hydrate is formed.
The production pipe column 9 for collecting the natural gas is arranged in the well casing 11, so that the natural gas entering the well casing 11 from the slots 14 after being continuously heated and decomposed in the natural gas hydrate layer 3 can be effectively collected, and the consistency of natural gas exploitation is maintained.
Example 2
The heating device 12 and the production string 9 in the present embodiment are installed inside the wellbore casing 11 adjacent to the slots 14, and the production string 9 is concentrically installed in the heating device 12 with a hollow structure, so that the decomposed natural gas is heated more conveniently and quickly from the hydrate layer 3 to the wellbore casing 11 through the slots 14, so that the production string 9 can collect the decomposed natural gas quickly and timely.
The heating device 12 in this embodiment is installed close to the side wall of the wellbore casing 11 provided with the slots 14, and this arrangement mode can effectively and continuously heat the hydrate reservoir, after the hydrate supported by the lower part as the framework is decomposed, the upper reservoir is inclined and settled, and continuously contacts the casing wall, so that the continuously settled natural gas hydrate is always in the heat radiation range of the heating device 12, and can continuously assist the exploitation of natural gas, thereby realizing the low-cost and high-efficiency production of the natural gas hydrate.
The production string 9 and the heating device 12 in this embodiment may also be installed in parallel inside the wellbore casing 11 according to the specific structure of the heating device 12, so as to meet the requirements in actual production.
The bottom end of the production string 9 in this embodiment is an open structure, and the decomposed natural gas enters the production string 9 through the opening at the bottom end thereof, and finally enters the wellbore orifice 10 communicated with the production string 9.
Besides adopting the bottom end opening structure, the natural gas collecting technical purpose can be achieved by uniformly distributing holes on the side wall of the production tubular column 9.
Example 3
Referring to fig. 2-3, the slots 14 in this embodiment are provided in the casing side wall 16 of the wellbore casing 11, the slots 14 being provided with slot openings 17 in the casing side 16, wherein the openings of the slots 14 in the inner side wall of the wellbore casing 11 are smaller than the openings of the slots 14 in the outer side wall of the wellbore casing 11. In addition, the wellbore casing 11 extends obliquely downward along a horizontal plane, and the slots 14 extend obliquely upward from outside to inside in a radial direction of the wellbore casing 11.
The above arrangement forms, on the one hand, a counter-extension of the slots 14 relative to the wellbore casing 11 and, on the other hand, a large outside and a small inside opening of the slots 14 on the wellbore casing 11.
The special reverse extension structure of the slit 14 is more beneficial to the fact that the natural gas outside the well casing 11 after being heated and decomposed passes through the slit 14 from bottom to top and enters the well casing 11, so that a channel is provided for the natural gas after being decomposed; simultaneously, the slots 14 with large outer parts and small inner parts can better prevent sand bodies from entering the well casing 11, so that the sand prevention performance of the well is further optimized.
The slot 14 extends in a direction that is not perpendicular to the direction of settlement of the sand body and that is at an acute angle to the downward sliding direction of the sand body on the outer wall of the wellbore casing 11, further reducing the likelihood of the sand body actively entering the wellbore casing 11 from the slot 14.
Example 4
This embodiment fully considers that during the natural gas production process, a small portion of the silt enters the interior of the well casing 11 through the slots 14, and a sand settling pocket 15 is connected to the bottom of the well casing 11 to settle the small portion of the silt allowed to enter the well casing 11 with the natural gas from the slots 14.
According to the open sand production system, by means of the sand setting pocket 15 connected to the bottom of the shaft sleeve 11, a small part of sediment entering the shaft sleeve 11 is effectively settled along the shaft sleeve 11 which is obliquely downward extended, the load of subsequent separation of natural gas is reduced, and the shaft depth and the depth of the sand setting pocket 15 in the embodiment can be reasonably calculated according to specific production, so that the technical requirement that the sand accumulation top of the sand setting pocket 15 is positioned below the production pipe column 9 and the heating equipment 12 is met.
In this embodiment, the wellbore casing 11 and the sand setting pocket 15 are preferably arranged in an integral structure, so that the integral structure can be more conveniently lowered in the well after the well is formed.
Example 5
Based on the production process of the depressurization method and the combined adoption of the open sand-out exploitation mode, a small amount of sand enters the shaft sleeve 11 from the slit 14 due to the internal and external pressure difference effect of the shaft sleeve 11, the natural gas is lifted by the lifting pump 24 arranged in the shaft sleeve 11, and according to the lifting force of the lifting pump 24 on the sand and water entering the shaft sleeve 11, the lifting pump 24 is regulated to lift only the natural gas, so that the sand and the water are automatically settled into the sand pocket 15.
In addition, from the perspective of separating the sand and water from the casing 11, in this embodiment, the sand may be separated by a separator pump, and finally discharged into the sand pocket 15.
The provision of the lift pump 24 or the separation pump can be reasonably performed with reference to technical information such as the reserves of the natural gas hydrate layer 3 and the production period.
In calculating the length and size of the sand pocket 15, the sand pocket can be calculated comprehensively according to the production speed of gas, the sedimentation speed of the sand body after separation treatment and the sliding speed of the sand body on the outer wall of the shaft sleeve 11.
Example 6
The upper part of the natural gas hydrate layer 3 is provided with a shaft mouth 10 for collecting natural gas, the pressure of the shaft mouth 10 is controlled to be smaller than the pressure of the bottom of the shaft by uniformly controlling the decomposition rate of the hydrate and adjusting the collection amount of the natural gas at the shaft mouth 10, and the decomposed natural gas is continuously introduced into the shaft mouth 10 through the production pipe column 9, so that the continuous exploitation of the natural gas is maintained.
A production line 7 for delivering natural gas downstream is connected to the wellbore orifice 10, and the collected natural gas can be continuously delivered downstream through the production line 7, so that the continuity of the whole production process is maintained.
Example 7
Referring to fig. 1, the embodiment provides a production system including the above-mentioned natural gas hydrate production wellbore, which is installed at sea and mainly used for producing skeleton-type natural gas hydrate, including surface equipment, underwater equipment and natural gas output equipment.
The water surface equipment comprises a drilling platform and platform equipment arranged on the drilling platform, wherein the platform equipment comprises a derrick, power supply equipment 5 for providing power for heating equipment 12 and a production pipeline 7, and the power supply equipment 5 is connected with the heating equipment 12 through the power supply pipeline 6.
The underwater equipment comprises the exploitation shaft and a water isolation pipe 8 vertically arranged in the sea water layer 1, wherein the top of the water isolation pipe 8 protrudes out of the sea water layer 1, and the bottom of the water isolation pipe is connected with a mud line 2 of a subsurface stratum. The well casing 11 is connected with the riser 8, the production pipeline 7 and the power supply pipeline 6 are respectively connected with the well mouth 10 and the heating equipment 12 after passing through the riser 8, the well mouth 10 is arranged at the upper part of the natural gas hydrate layer 3 in the riser 8, and the well casing 8 and the production pipeline 7 are mainly supported by utilizing a derrick, and the well is formed (well drilling, well casing 11 and well completion are put in) and the heating pipeline is put in.
The output equipment of the natural gas comprises an integrated treatment equipment 21, one end of the production pipeline 7 is connected with the shaft mouth 10, and the other end of the production pipeline is connected with the integrated treatment equipment 21 and is used for purifying, liquefying and storing the extracted natural gas.
According to the natural gas hydrate exploitation system, the production pressure difference is reasonably regulated through the wellhead 10 mainly according to the decomposition characteristics of the hydrate, and meanwhile, the natural gas hydrate layer 3 close to the well wall is heated and decomposed by combining the underground heating equipment 12, so that the natural gas hydrate is produced through the production tubular column 9.
During the production process, after the skeleton natural gas hydrate is decomposed, the non-cemented sediment, water and other pore contents in the pores can be settled to the vicinity of the well casing 11 along with the output of the natural gas hydrate. Accordingly, open sand production is performed by providing a well casing 11 that is inclined and cutting a slot 14 in the casing wall.
The inclined arrangement of the wellbore casing 11 allows a large part of the settled sand to slide down the casing outer wall without entering the production string 9 with the natural gas. Meanwhile, the slits 14 are utilized to provide a channel for the decomposed natural gas to enter, and the special slits 14 with reverse directions and large outside and small inside can better prevent sand bodies from entering the production pipe column 9, so that the sand prevention performance is further optimized. Meanwhile, considering that part of sand enters the production pipe column 9 through the slots 14 in the depressurization production process, a sand settling pocket 15 is arranged at the lower part of the shaft sleeve 11, and the sand separated by the lifting pump 24 or the separating pump is settled into the sand settling pocket 15. The depths of the shaft sleeve 11 and the sand setting pocket 15 are designed according to reasonable calculation based on the production speed of gas, the sedimentation speed of the sand after separation treatment and the sliding speed of the sand on the outer wall of the shaft sleeve 11 and combined with the reserves and the mining period of the natural gas hydrate layer 3, and the production pipe column 9 can be built in the underground heating equipment 12 or arranged in the shaft sleeve 11 in parallel with the heating equipment 12.
Natural gas output devices, including small, mobile integrated processing devices 21, and remote access, etc. The integrated processing equipment 21 is mainly used for processing and storing the extracted natural gas, and comprises a separation equipment 18, a liquefying equipment 19, a small-sized liquefying storage equipment 20 and the like, and is remotely connected with a gas pipeline 22, an LNG liquefying station 23 and the like.
The invention also provides a natural gas exploitation method implemented by adopting the natural gas hydrate exploitation system, and the exploitation method is explained below by combining the specific structure of the natural gas hydrate exploitation system shown in fig. 1-3.
The well is completed through a drilling platform, a well casing 11 with slots 14 on the side wall is put into a production well, then a production string 9 is put into the well casing 11, a downhole heating device 12 can be put into the well casing 11 in two ways in the production process, the production string 9 can be arranged in the well casing 11 side by side, or the production string 9 can be arranged in a heating device 12 with a hollow structure (the selection mode depends on the structure of the heating device 12), and a lifting pump 24 or a separation pump is put into the well before the production is started.
After production is started, the decomposition rate of the hydrate in the reservoir is controlled at a constant speed, the collection amount of the natural gas at the well head 10 is regulated, the pressure in the well head 10 and the well casing 11 communicated with the well head 10 is controlled to be smaller than the pressure at the bottom of the well, meanwhile, the power supply equipment 5 is used for supplying power to the underground heating equipment 12, the natural gas hydrate in the reservoir is heated, the decomposition rate of the natural gas hydrate is controlled at a constant speed, and the well pressure is controlled to be smaller than the pressure at the bottom of the well through regulating the collection amount of the natural gas at the well head 10.
The reservoir layer contacted with the slotted casing 13 (the well casing section provided with slots) is decomposed after being heated, so that natural gas, sediment, water and other contents in the hydrate layer 3 can rapidly fill the space before the hydrate is not decomposed, and the hydrate reservoir layer continuously contacts the slotted casing 13, so that the hydrate reservoir layer continuously plays a role in continuous heating in the heat radiation range of the heating equipment 12.
The inclined well casing 11 can avoid the strong pressure on the well caused by the sedimentation of the upper reservoir, and the problem of bearing pressure cannot be caused. Meanwhile, in the sediment settling process, the sediment cannot vertically enter the shaft like a horizontal well, so that serious sand blockage is caused. The inclined shaft can enable most sand bodies to subside and slide to other parts of the shaft sleeve 11 along the outer wall of the sleeve, so that the sand production degree in the extraction process is greatly reduced. Meanwhile, the extending direction of the slots 14 arranged on the shaft sleeve 11 is opposite to the extending direction of the shaft sleeve 11, the extending direction of the slots is not perpendicular to the settling direction of the sand bodies, and the downward sliding direction of the sand bodies on the outer wall of the shaft sleeve 11 is acute with the extending direction of the slots 14, so that the possibility that the sand bodies actively enter the shaft sleeve 11 from the slots 14 is further reduced.
In the depressurization production process of the present invention, open sand production is employed, with a small amount of sand being introduced into the wellbore casing 11 from the slots 14 as a result of the pressure differential. After entering, the lifting pump 24 can be effectively controlled, the underground lifting pump 24 is regulated to only lift gas according to the lifting force of sand bodies and water entering the shaft sleeve 11, the sand bodies and the water are automatically settled into the sand setting pocket 15, or the mixed materials enter the separating pump for separation treatment, and finally the sand bodies are discharged into the sand setting pocket 15.
The length and size of the sand pocket 15 can be calculated according to the gas production speed, the sand sedimentation speed and the slip speed of the sand on the outer wall of the sleeve.
The exploitation method can effectively and continuously heat the hydrate reservoir, after the hydrate supported by the framework at the lower part is decomposed, the upper reservoir is settled and continuously contacts the wall of the well casing 11, and is always in the heat radiation range of the heating equipment 12, and the production by the depressurization method can be continuously assisted, so that the low-cost and high-efficiency production of the natural gas hydrate is realized.
After the gas is produced, the gas is connected into the production pipeline 7 through the underwater wellhead 10, and the movable integrated treatment equipment 21, the gas transmission pipeline 22 or the LNG liquefying station 23 is selectively utilized according to the production and the conditions of nearby facilities. If the movable integrated processing equipment 21 is directly connected, the integrated processing is directly carried out on the small tug or movable equipment through the separation equipment 18, the liquefaction equipment 19, the small liquefaction storage equipment 20 and the like, and then the integrated processing is carried to ground gathering and transportation sites such as a liquefied gas station and the like; if the natural gas pipeline is convenient nearby, the natural gas pipeline can be directly connected to a natural gas pipe network, and can also be directly connected to a nearby liquefied natural gas station for further utilization.
It is pointed out that the invention considers the decomposition characteristics and reservoir characteristics of natural gas hydrate, adopts an open well completion production mode by utilizing the inclined shaft sleeve, avoids the conventional complex sand prevention well completion pipe string, reduces the sand blocking risk, improves the production phase ratio and greatly reduces the exploitation cost.
Besides the mode of arranging the slots on the sleeve of the shaft, the invention can also adopt the structure of the slotted screen pipe, and the sleeve, the slotted screen pipe and the sand setting pocket can be directly connected into the well after being connected into an integral structure, so that the technical purposes of open exploitation and effective sand setting in the invention can be achieved, and the invention is not repeated.
Finally, it is to be understood that the above embodiments are merely exemplary embodiments employed for the purpose of illustrating the principles of the present invention, however, the present invention is not limited thereto. Various modifications and improvements may be made by those skilled in the art without departing from the principles and spirit of the invention, and such modifications and improvements are also considered within the scope of the invention.
Claims (7)
1. A natural gas hydrate recovery wellbore for recovering a natural gas hydrate resource having a natural gas hydrate as a framework, wherein the pore contents of the natural gas hydrate resource comprise water and silt, comprising: a well casing obliquely arranged in the natural gas hydrate layer, wherein a slit which is communicated with the outside is arranged on the well casing;
the inside of the well casing is provided with heating equipment for decomposing natural gas hydrate and a production string for collecting the decomposed natural gas entering the well casing from the slit;
the shaft sleeve obliquely extends downwards, the slots extend upwards from outside to inside in the radial direction of the shaft sleeve, and the extending direction of the slots and the downward sliding direction of the sand body on the outer wall of the shaft sleeve form an acute angle;
the bottom of the shaft sleeve is connected with a sand setting pocket for settling mud and sand entering the shaft sleeve from the slit;
The slots are arranged on the side wall of the shaft sleeve, and the openings of the slots on the inner side wall of the shaft sleeve are smaller than the openings of the slots on the outer side wall of the shaft sleeve.
2. The natural gas hydrate production wellbore of claim 1, wherein the heating apparatus and production tubing string are installed adjacent the slots, the production tubing string is installed inside the heating apparatus, or the production tubing string is installed in parallel with the heating apparatus.
3. A natural gas hydrate production wellbore according to claim 1, wherein a lifting pump for lifting natural gas or a separation pump for separating sand into the wellbore casing is provided inside the wellbore casing.
4. A natural gas hydrate production wellbore according to any of claims 1-3, characterized in that an upper part of the natural gas hydrate layer is provided with a wellbore opening for collecting natural gas, the wellbore opening having a pressure which is less than the pressure of the bottom of the production wellbore.
5. A natural gas hydrate production wellbore as claimed in claim 4 wherein a production line for delivering the collected natural gas downstream is connected to the wellhead.
6. A natural gas hydrate exploitation system which is installed on the sea and is characterized by comprising water surface equipment, underwater equipment and output equipment;
The water surface equipment comprises a drilling platform and platform equipment arranged on the drilling platform;
The subsea equipment comprising a natural gas hydrate production wellbore according to any of claims 1-5 and a riser between sea level and a natural gas hydrate layer;
One end of the production pipeline is connected with the shaft opening, and the other end of the production pipeline is connected with the output equipment and used for purifying, liquefying and storing the produced natural gas.
7. A mining method implemented using the mining system of claim 6, comprising the steps of:
1) Logging in a well through a drilling platform, and setting a well casing in a production well;
2) Running a production string and heating equipment in a wellbore casing;
3) The power supply equipment is used for supplying power to the heating equipment, natural gas hydrate in the reservoir is heated, the decomposition rate of the natural gas hydrate is controlled at a constant speed, and the pressure of the shaft is controlled to be smaller than the pressure at the bottom of the shaft by adjusting the collection amount of the natural gas in the shaft opening;
4) And conveying the produced natural gas to integrated treatment equipment through a production pipeline connected to a shaft hole, so as to finish exploitation.
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