CN112483052A - Device and method for inhibiting generation of wellbore hydrate by circulating seawater - Google Patents
Device and method for inhibiting generation of wellbore hydrate by circulating seawater Download PDFInfo
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- CN112483052A CN112483052A CN202011517299.XA CN202011517299A CN112483052A CN 112483052 A CN112483052 A CN 112483052A CN 202011517299 A CN202011517299 A CN 202011517299A CN 112483052 A CN112483052 A CN 112483052A
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- 239000013535 sea water Substances 0.000 title claims abstract description 103
- 238000000034 method Methods 0.000 title claims abstract description 30
- 230000002401 inhibitory effect Effects 0.000 title claims abstract description 26
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 32
- 150000004677 hydrates Chemical class 0.000 claims abstract description 3
- 238000000576 coating method Methods 0.000 claims description 24
- 230000015572 biosynthetic process Effects 0.000 claims description 21
- 239000011248 coating agent Substances 0.000 claims description 21
- 238000009413 insulation Methods 0.000 claims description 13
- 239000004964 aerogel Substances 0.000 claims description 9
- 239000003365 glass fiber Substances 0.000 claims description 9
- 238000006073 displacement reaction Methods 0.000 claims description 7
- 238000005086 pumping Methods 0.000 claims description 7
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 6
- 239000011261 inert gas Substances 0.000 claims description 6
- 238000007599 discharging Methods 0.000 claims description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 3
- 229910052786 argon Inorganic materials 0.000 claims description 3
- 239000010425 asbestos Substances 0.000 claims description 3
- 239000000378 calcium silicate Substances 0.000 claims description 3
- 229910052918 calcium silicate Inorganic materials 0.000 claims description 3
- OYACROKNLOSFPA-UHFFFAOYSA-N calcium;dioxido(oxo)silane Chemical compound [Ca+2].[O-][Si]([O-])=O OYACROKNLOSFPA-UHFFFAOYSA-N 0.000 claims description 3
- 239000011381 foam concrete Substances 0.000 claims description 3
- 239000011810 insulating material Substances 0.000 claims description 3
- 239000012774 insulation material Substances 0.000 claims description 3
- 229910052743 krypton Inorganic materials 0.000 claims description 3
- DNNSSWSSYDEUBZ-UHFFFAOYSA-N krypton atom Chemical compound [Kr] DNNSSWSSYDEUBZ-UHFFFAOYSA-N 0.000 claims description 3
- 239000010451 perlite Substances 0.000 claims description 3
- 235000019362 perlite Nutrition 0.000 claims description 3
- 229910052895 riebeckite Inorganic materials 0.000 claims description 3
- 229910052724 xenon Inorganic materials 0.000 claims description 3
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 claims description 3
- 238000010438 heat treatment Methods 0.000 abstract description 6
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Natural products C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 abstract description 5
- 238000005265 energy consumption Methods 0.000 abstract description 3
- 230000007774 longterm Effects 0.000 abstract description 3
- 239000003345 natural gas Substances 0.000 abstract description 3
- -1 natural gas hydrates Chemical class 0.000 abstract 1
- 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 description 9
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- BRPQOXSCLDDYGP-UHFFFAOYSA-N calcium oxide Chemical compound [O-2].[Ca+2] BRPQOXSCLDDYGP-UHFFFAOYSA-N 0.000 description 1
- 239000000292 calcium oxide Substances 0.000 description 1
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Images
Classifications
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP 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
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
- E21B17/01—Risers
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
- E21B17/18—Pipes provided with plural fluid passages
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B34/00—Valve arrangements for boreholes or wells
- E21B34/06—Valve arrangements for boreholes or wells in wells
- E21B34/066—Valve arrangements for boreholes or wells in wells electrically actuated
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B36/00—Heating, cooling, insulating arrangements for boreholes or wells, e.g. for use in permafrost zones
- E21B36/003—Insulating arrangements
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B36/00—Heating, cooling, insulating arrangements for boreholes or wells, e.g. for use in permafrost zones
- E21B36/005—Heater surrounding production tube
Abstract
A device and a method for inhibiting generation of well bore hydrates by circulating seawater belong to the technical field of exploitation of sea natural gas hydrates, and comprise an outer sleeve, a riser, an oil pipe, a water pump, a pulley, a cable and a motor, wherein the outer sleeve is sleeved outside the riser, the riser is of a hollow double-layer structure consisting of the outer wall of the riser and the inner wall of the riser, the outer wall of the riser is provided with an upper window and a lower window, and when one of the upper window and the lower window is opened, the other one is shielded; an annular space is formed between the oil pipe and the inner wall of the riser; the cable is wound on the pulley and forms a lifting system with the motor by connecting the outer sleeve; and a pump suction inlet of the water pump is positioned in an annular space formed between the inner wall of the riser and the oil pipe. The natural seawater is directly utilized to heat the pipe wall of the oil pipe, no extra heating energy is needed to be provided manually, the energy consumption is low, and the oil pipe is safe and environment-friendly; the upper windows and the lower windows are arranged at different positions of the outer wall of the marine riser, so that the efficient utilization of the seawater energy of the nodes at different times is realized, and the long-term effective operation of the system can be ensured.
Description
Technical Field
The invention belongs to the technical field of sea area natural gas hydrate exploitation, and particularly relates to a device and a method for inhibiting generation of wellbore hydrates by circulating seawater.
Background
During the sea natural gas hydrate exploitation process, natural gas generated by reservoir hydrate decomposition and water flow into the bottom of a well together, and the natural gas and the water move in a wellbore in a gas-water two-phase flow state. The temperature and pressure in the shaft are constantly changed along with the depth of the well under the influence of the temperature of seawater, throttling effect, pressure of the wellhead and the like. For a shaft above a mud line in a deep water low-temperature environment, secondary hydrate is easily generated on the inner wall of the shaft, a pipe column is blocked, and pressure building can be formed in severe cases to cause the pipe column to break, so that huge economic loss is caused.
At present, the commonly used methods for preventing the formation of gas hydrate in a gas well shaft mainly comprise a chemical inhibitor injection method and a downhole throttling method. The chemical inhibitor injection method is to inject chemical agents into a shaft from the ground regularly, breaks the continuity of production, and has the defects of high cost, insufficient safety, environmental protection and the like. The downhole throttling technology is to heat gas by means of formation heat energy to prevent hydrate from being generated, but in a low-temperature deep-water marine environment, the heat dissipation speed is high, and a heat source provided by the formation is not enough to inhibit the generation of secondary hydrate in a shaft.
Still other measures, see patent document, CN201910128714.3, disclose an electromagnetic heating device and method for exploiting seabed combustible ice, wherein a certain length of electromagnetic heating device is installed at the inlet end of an electric submersible pump to heat the bottom of the well, which is not suitable for a well bore above a deep cement line. The document number CN201810345979.4 discloses a method for exploiting natural gas hydrate by using a sleeve type heater, the sleeve type heater is placed in an exploitation interval, and for a low-temperature marine environment, the heat dissipation speed of a shaft is high, and the problem of secondary hydrate blockage of the shaft above a deepwater cement line cannot be solved. The publication No. CN201510183801.0 discloses a method for removing hydrate blockage of a gas recovery well shaft, which removes ice blockage by using reaction of an acidic solution and calcium oxide to release heat, but the method cannot be used for preventing secondary hydrate from generating. Document No. CN201110313048.4 discloses a spontaneous heating natural gas hydrate control device, which works by means of formation gas and is not suitable for gas-water co-production wells.
Therefore, an effective prevention method is urgently needed for the problem of secondary hydrate formation of the shaft above the mud line in the process of exploiting the sea natural gas hydrate.
Disclosure of Invention
The invention aims to provide a device and a method for inhibiting generation of a shaft hydrate by circulating seawater, which are used for solving the problem of formation of a shaft secondary hydrate above a mud line in the process of exploiting a natural gas hydrate in a sea area.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a device for inhibiting generation of a wellbore hydrate by circulating seawater, which is characterized by comprising the following components: the outer sleeve is sleeved outside the marine riser, the length of the outer sleeve is larger than the distance between the upper opening window and the lower opening window which are arranged on the outer wall of the marine riser, and the outer sleeve can axially move relative to the marine riser and is used for covering the upper opening window or the lower opening window; the marine riser is of a hollow double-layer structure consisting of an outer wall of the marine riser and an inner wall of the marine riser, an annulus is formed between the outer wall of the marine riser and the inner wall of the marine riser, an upper window and a lower window are arranged on the outer wall of the marine riser, wherein the upper window is located at a position 3-10 m below the sea level, the lower window is located at a position 10-100 m below the sea level, when the device for inhibiting the generation of the wellbore hydrate by circulating seawater works, when one of the upper window and the lower window is open, the other one is shielded, and the temperature of the seawater at the position of the open window is higher than 20 ℃; the oil pipe is positioned in the riser, and an annular space is formed between the oil pipe and the inner wall of the riser; the cable is wound on the pulley, one end of the cable is connected with the motor, and the other end of the cable is connected with the outer sleeve; and a pump suction inlet of the water pump is positioned in an annular space formed between the inner wall of the riser and the oil pipe.
As a preferable scheme of the present invention, the length of the outer sleeve is greater than the distance between the upper opening window and the lower opening window by 1m to 3 m.
Further, the inner surface and the outer surface of the outer wall of the marine riser are both provided with heat insulation coatings, or the outer wall of the marine riser adopts a double-layer concentric pipe wall, and an annular space of the double-layer concentric pipe wall is filled with heat insulation materials and inert gases or is vacuumized, so that the apparent heat conduction coefficient of the outer wall of the marine riser is kept below 0.04W/m.
Furthermore, the thermal insulation coating adopts an aerogel coating or a glass fiber coating.
Further, the heat insulating material is one of asbestos, diatomite, perlite, aerogel felt, glass fiber, foam concrete and calcium silicate; the inert gas is one of argon, krypton and xenon.
Further, the inner side of the oil pipe wall is provided with a heat insulation coating.
Furthermore, the thermal insulation coating adopts an aerogel coating or a glass fiber coating.
In a preferred embodiment of the present invention, the pump inlet is located at a position 5m to 20m below the sea water level in an annulus formed between the inner wall of the riser and the oil pipe.
The invention also provides a method for inhibiting the generation of the hydrate in the shaft by circulating seawater, which is characterized in that the method adopts the device for inhibiting the generation of the hydrate in the shaft by circulating seawater to circulate the seawater so as to inhibit the generation of the hydrate in the shaft, and comprises the following steps:
step S1, the temperature of the seawater at the position of the upper window is higher than that of the seawater at the position of the lower window, the temperature of the seawater at the position of the upper window is higher than 20 ℃, a motor is started, and the motor drives a cable to lower the outer sleeve through a pulley;
step S2, when the outer sleeve is lowered to a position for covering the lower opening window and opening the upper opening window, the motor is closed; the seawater sequentially flows into an annulus between the outer wall of the riser and the inner wall of the riser and an annulus between the inner wall of the riser and the oil pipe through the upper window;
step S3, starting a water pump, and pumping the seawater in the annulus between the inner wall of the riser and the oil pipe at the displacement of 10-60L/S;
step S4, directly discharging the seawater pumped by the water pump into the sea;
step S5, with the alternation of four seasons, the temperature of the seawater at the position of the lower windowing is higher than that of the seawater at the position of the upper windowing, the temperature of the seawater at the position of the upper windowing is higher than 20 ℃, a motor is started, and a motor drives a cable to lift the outer sleeve through a pulley;
step S6, when the outer sleeve is lifted to the position for covering the upper opening window and opening the lower opening window, the motor is closed; the seawater sequentially flows into an annulus between the outer wall of the riser and the inner wall of the riser and an annulus between the inner wall of the riser and the oil pipe through the upper window;
step S7, starting a water pump, and pumping the seawater in the annulus between the inner wall of the riser and the oil pipe at the displacement of 10-60L/S;
and step S8, directly discharging the seawater pumped by the water pump into the sea.
In a preferred embodiment of the present invention, the displacement of the water pump is 30L/s to 60L/s.
Through the design scheme, the invention can bring the following beneficial effects: the invention provides a device and a method for inhibiting the generation of a shaft hydrate by circulating seawater, wherein the wall of an oil pipe is directly heated by utilizing natural seawater without artificially additionally providing heating energy, so that the device is low in energy consumption, safe and environment-friendly; the upper windows and the lower windows are arranged at different positions of the outer wall of the marine riser, so that the efficient utilization of the seawater energy of the nodes at different times is realized, and the long-term effective operation of the system can be ensured.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limitation and are not intended to limit the invention in any way, and in which:
FIG. 1 is a diagram of the working state of the device for inhibiting the formation of hydrate in a shaft by circulating seawater in spring and summer.
Fig. 2 is a diagram of the working state of the device for inhibiting the formation of the hydrate in the shaft by circulating seawater in autumn and winter.
The respective symbols in the figure are as follows: 1-an outer sleeve; 2-outer wall of riser; 3-inner wall of the riser; 4-windowing on the upper part; 5-windowing down; 6-oil pipe; 7-a water pump; 8-pump suction inlet; 9-a pulley; 10-a cable; 11-motor.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the present invention.
As shown in fig. 1 and 2, arrow a indicates the seawater circulation direction, and arrow b indicates the hydrate reservoir.
As shown in fig. 1 and 2, the device for inhibiting the generation of the hydrate in the shaft by circulating seawater comprises an outer sleeve 1, a marine riser, an oil pipe 6, a water pump 7, a pulley 9, a cable 10 and a motor 11.
The outer sleeve 1 is movably sleeved outside the riser, and the length of the outer sleeve 1 is larger than the distance between the upper opening window 4 and the lower opening window 5 which are arranged on the outer wall 2 of the riser. In order to take account of the window closing effect of the windowing and the pipe consumption, the length of the outer sleeve 1 is larger than the distance between the upper windowing 4 and the lower windowing 5 by 1 m-3 m, and the outer sleeve 1 can axially move relative to the marine riser under the drive of the cable 10 and is used for covering the upper windowing 4 or the lower windowing 5.
The riser is a hollow double-layer structure consisting of a riser outer wall 2 and a riser inner wall 3, and an annulus is formed between the riser outer wall 2 and the riser inner wall 3; the marine riser is a heat-insulation marine riser, specifically, heat-insulation coatings are arranged on the inner surface and the outer surface of the outer wall 2 of the marine riser or the outer wall 2 of the marine riser adopts a double-layer concentric pipe wall, and an annular space of the double-layer concentric pipe wall is filled with heat-insulation materials and inert gases or vacuumized, so that the apparent heat conduction coefficient of the outer wall 2 of the marine riser is kept below 0.04W/m DEG C, and heat is prevented from being transferred to low-temperature seawater at the lower part in the seawater circulation process; the heat insulation coating adopts an aerogel coating or a glass fiber coating. The heat insulating material is one of asbestos, diatomite, perlite, aerogel felt, glass fiber, foam concrete and calcium silicate; the inert gas is one of argon, krypton and xenon. An upper windowing part and a lower windowing part are arranged on the outer wall 2 of the marine riser, wherein the upper windowing part 4 is positioned in a high-temperature region of seawater in spring and summer and is positioned 3-10 m below the sea level; the lower window 5 is positioned in a high-temperature area of seawater in autumn and winter and is positioned 10-100 m below the sea level. The specific position of the window is determined by the vertical temperature distribution of the seawater in the mined sea area because the seawater in different sea areas is vertically distributed in four seasons. When the device for inhibiting the generation of the hydrate in the shaft by circulating seawater works, one of the upper open window 4 and the lower open window 5 is opened, and the other one is shielded, so that the hydrate is prevented from being generated on the inner wall of the oil pipe 6, the opened open window is used as an inlet for seawater to enter the whole device, and the temperature of the seawater at the position of the open window is higher than 20 ℃.
The oil pipe 6 is positioned inside the riser, an annular space is formed between the oil pipe 6 and the inner wall 3 of the riser, and a heat insulation coating is arranged on the inner side of the pipe wall of the oil pipe 6 to prevent heat of the oil pipe 6 from dissipating, so that the temperature of the pipe wall of the oil pipe 6 can be approximately equal to the temperature of circulating seawater, and hydrate can be prevented from being generated on the inner wall of the oil pipe 6. The thermal insulation coating can be selected from an aerogel coating or a glass fiber coating.
The mooring rope 10 is wound on the pulley 9, one end of the mooring rope 10 is connected with the motor 11, the other end of the mooring rope 10 is connected with the sleeve 4, the motor 11 rotates and simultaneously drives the mooring rope 10 to run on the pulley 9, and the outer sleeve 1 is lifted and lowered by changing the rotation direction of the motor 11.
And a pump suction inlet 8 of the water pump 7 is positioned in an annular space formed between the inner wall 3 of the marine riser and the oil pipe 6, and in order to ensure the suction effect, the position of the pump suction inlet 8 is positioned at a position 5-20 m below the sea water level in the annular space formed between the inner wall 3 of the marine riser and the oil pipe 6.
The following describes in detail the specific operation process of the device for inhibiting the formation of wellbore hydrate by circulating seawater in spring and summer with reference to fig. 1, and specifically includes the following implementation steps:
A. in spring and summer, the temperature of the seawater at the position of the upper window 4 is higher than that of the seawater at the position of the lower window 5, the motor 11 is started, and the motor 11 drives the mooring rope 10 to lower the outer sleeve 1 through the pulley 9;
B. when the outer sleeve 1 is lowered to the position for covering the lower windowing 5 and opening the upper windowing 4, the motor 11 is closed;
C. according to the principle of a U-shaped pipe, seawater sequentially flows into an annular space between the outer wall 2 and the inner wall 3 of the riser and an annular space between the inner wall 3 of the riser and the oil pipe 6 through the upper opening window 4, and a pressure balance system is established;
D. starting a water pump 7, and pumping seawater in the annular space between the inner wall 3 of the marine riser and the oil pipe 6 at a displacement of 45L/s to realize seawater circulation in the marine riser;
E. the seawater pumped by the water pump 7 is directly discharged into the sea.
The following describes in detail the specific operation process of the device for inhibiting the formation of wellbore hydrate by circulating seawater in autumn and winter, which is provided by the invention, with reference to fig. 2, and specifically includes the following implementation steps:
A. in autumn and winter, the temperature of the seawater at the position of the lower window 5 is higher than that of the seawater at the position of the upper window 4, the motor 11 is started, the motor 11 drives the cable 10 to lift the outer sleeve 1 through the pulley 9;
B. when the outer sleeve 1 is lifted to the position for covering the upper open window 4 and opening the lower open window 5, the motor 11 is closed;
C. according to the principle of a U-shaped pipe, seawater sequentially flows into an annular space between the outer wall 2 and the inner wall 3 of the riser and an annular space between the inner wall 3 of the riser and the oil pipe 6 through the lower opening window 5, and a pressure balance system is established;
D. starting a water pump 7, and pumping seawater in the annular space between the inner wall 3 of the marine riser and the oil pipe 6 at a discharge capacity of 50L/s to realize seawater circulation in the marine riser;
E. the seawater pumped by the water pump 7 is directly discharged into the sea.
A method of circulating seawater to inhibit wellbore hydrate formation, the method comprising the steps of:
(a) when the temperature of the shallow sea water is higher than that of the middle sea water, the motor 11 drives the mooring rope 10 to lower the outer sleeve 1 through the pulley 9, wherein the shallow sea water is the sea water which is 3-10 m below the sea level, and the middle sea water is the sea water which is 10-100 m below the sea level;
(b) when the outer sleeve 1 is lowered to the position for covering the lower windowing 5 and opening the upper windowing 4, the motor 11 is closed;
(c) according to the principle of a U-shaped pipe, shallow high-temperature seawater sequentially flows into an annular space between the outer wall 2 of the marine riser and the inner wall 3 of the marine riser and an annular space between the inner wall 3 of the marine riser and the oil pipe 6 through the upper opening window 4, and a pressure balance system is established;
(d) starting a water pump 7, pumping seawater in an annular space between the inner wall 3 of the riser and the oil pipe 6 at a discharge capacity of 10L/s-60L/s, and realizing seawater circulation in the riser;
(e) the heat-exchanged seawater pumped by the water pump 7 is directly discharged into the sea;
(f) with the alternation of four seasons, when the temperature of the shallow layer seawater is lower than that of the middle layer seawater, the water pump 7 is closed;
(g) turning on the motor 11, the motor 11 drives the cable 10 to lift the outer sleeve 1 up through the pulley 9;
(h) when the outer sleeve 1 is lifted to the position for covering the upper open window 4 and opening the lower open window 5, the motor 11 is closed;
(i) according to the principle of a U-shaped pipe, the middle-layer seawater flows into the riser through the lower opening window 5;
(j) starting a water pump 7, and extracting seawater in an annular space between the inner wall 3 of the riser and the oil pipe 6 to realize seawater circulation in the riser;
further, in order to ensure that the temperature of the oil pipe 6 is always higher than the generation temperature of the natural gas hydrate, the discharge capacity of the pump can be increased to increase the circulation speed of the seawater, and preferably, the discharge capacity of the pump is more than 30L/s.
In conclusion, aiming at the problem of formation of secondary hydrate of the shaft above a mud line in the process of exploiting the natural gas hydrate in the sea area, the invention provides the device and the method for inhibiting generation of the shaft hydrate by circulating seawater, the natural seawater is directly utilized to heat the pipe wall of the oil pipe 6, artificial additional heating energy is not needed, the energy consumption is low, and the device is safe and environment-friendly; the upper opening window 4 and the lower opening window 5 are arranged at different positions of the outer wall 2 of the marine riser, so that the efficient utilization of seawater energy at different time nodes is realized, and the long-term effective operation of the system can be ensured.
Claims (10)
1. An apparatus for circulating seawater to inhibit hydrate formation in a wellbore, comprising: the marine riser comprises an outer sleeve (1), a riser, an oil pipe (6), a water pump (7), a pulley (9), a cable (10) and a motor (11), wherein the outer sleeve (1) is sleeved outside the riser, the length of the outer sleeve (1) is greater than the distance between an upper window (4) and a lower window (5) which are arranged on the outer wall (2) of the riser, and the outer sleeve (1) can axially move relative to the riser and is used for covering the upper window (4) or the lower window (5); the marine riser is of a hollow double-layer structure consisting of a marine riser outer wall (2) and a marine riser inner wall (3), an annulus is formed between the marine riser outer wall (2) and the marine riser inner wall (3), an upper window and a lower window are arranged on the marine riser outer wall (2), wherein the upper window (4) is located at a position 3 m-10 m below the sea level, the lower window (5) is located at a position 10 m-100 m below the sea level, when the device for inhibiting the generation of the wellbore hydrate by circulating seawater works, one of the upper window (4) and the lower window (5) is open, the other one is shielded, and the temperature of the seawater at the position of the open window is higher than 20 ℃; the oil pipe (6) is positioned inside the riser, and an annulus is formed between the oil pipe (6) and the inner wall (3) of the riser; the cable (10) is wound on the pulley (9), one end of the cable (10) is connected with the motor (11), and the other end of the cable is connected with the outer sleeve (1); and a pump suction inlet (8) of the water pump (7) is positioned in an annular space formed between the inner wall (3) of the water-resisting pipe and the oil pipe (6).
2. The apparatus for inhibiting hydrate formation in a wellbore using circulating seawater of claim 1, wherein: the length of the outer sleeve (1) is larger than the distance between the upper windowing (4) and the lower windowing (5) by 1-3 m.
3. The apparatus for inhibiting hydrate formation in a wellbore using circulating seawater of claim 1, wherein: and the inner surface and the outer surface of the outer wall (2) of the marine riser are both provided with heat insulation coatings, or the outer wall (2) of the marine riser adopts a double-layer concentric pipe wall, and an annular space of the double-layer concentric pipe wall is filled with heat insulation materials and inert gases or vacuumized, so that the apparent heat conduction coefficient of the outer wall (2) of the marine riser is kept below 0.04W/m.
4. The apparatus for inhibiting hydrate formation in a wellbore using circulating seawater of claim 3, wherein: the heat insulation coating adopts an aerogel coating or a glass fiber coating.
5. The apparatus for inhibiting hydrate formation in a wellbore using circulating seawater of claim 3, wherein: the heat insulating material is one of asbestos, diatomite, perlite, aerogel felt, glass fiber, foam concrete and calcium silicate; the inert gas is one of argon, krypton and xenon.
6. The apparatus for inhibiting hydrate formation in a wellbore using circulating seawater of claim 1, wherein: and a heat insulation coating is arranged on the inner side of the pipe wall of the oil pipe (6).
7. The apparatus for inhibiting hydrate formation in a wellbore using circulating seawater of claim 6, wherein: the heat insulation coating adopts an aerogel coating or a glass fiber coating.
8. The apparatus for inhibiting hydrate formation in a wellbore using circulating seawater of claim 1, wherein: the position of the pump suction inlet (8) is located at a position 5-20 m below the sea water level in an annulus formed between the inner wall (3) of the water-resisting pipe and the oil pipe (6).
9. A method of circulating seawater to inhibit hydrate formation in a wellbore, the method using the apparatus of any one of claims 1 to 8, comprising the steps of:
step S1, the temperature of the seawater at the position of the upper window (4) is higher than that of the seawater at the position of the lower window (5), the temperature of the seawater at the position of the upper window (4) is higher than 20 ℃, a motor (11) is started, and the motor (11) drives a cable (10) to lower the outer sleeve (1) through a pulley (9);
step S2, when the outer sleeve (1) is lowered to the position for covering the lower windowing (5) and opening the upper windowing (4), the motor (11) is closed; seawater sequentially flows into an annulus between the outer wall (2) and the inner wall (3) of the marine riser and an annulus between the inner wall (3) and the oil pipe (6) of the marine riser through the upper window (4);
step S3, starting a water pump (7), and pumping seawater in the annular space between the inner wall (3) of the marine riser and the oil pipe (6) at a displacement of 10-60L/S;
step S4, directly discharging the seawater pumped by the water pump (7) into the sea;
step S5, with the alternation of four seasons, the temperature of the seawater at the position of the lower window (5) is higher than that of the seawater at the position of the upper window (4), the temperature of the seawater at the position of the upper window (4) is higher than 20 ℃, a motor (11) is started, and the motor (11) drives a cable (10) to lift the outer sleeve (1) through a pulley (9);
step S6, when the outer sleeve (1) is lifted to the position covering the upper window (4) and opening the lower window (5), the motor (11) is closed; seawater sequentially flows into an annulus between the outer wall (2) and the inner wall (3) of the marine riser and an annulus between the inner wall (3) and the oil pipe (6) of the marine riser through the upper window (4);
step S7, starting a water pump (7), and pumping seawater in the annular space between the inner wall (3) of the marine riser and the oil pipe (6) at a displacement of 10-60L/S;
and step S8, directly discharging the seawater pumped by the water pump (7) into the sea.
10. The method for inhibiting the generation of wellbore hydrates according to claim 9, wherein the displacement of the water pump (7) is 30L/s to 60L/s.
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