CN110439529B - On-well three-phase separation device and method for solid fluidization exploitation of natural gas hydrate - Google Patents
On-well three-phase separation device and method for solid fluidization exploitation of natural gas hydrate Download PDFInfo
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- 239000007787 solid Substances 0.000 title claims abstract description 165
- 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 45
- 238000005191 phase separation Methods 0.000 title claims abstract description 37
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- 239000007788 liquid Substances 0.000 claims abstract description 109
- 238000000926 separation method Methods 0.000 claims abstract description 105
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims abstract description 51
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- 238000005553 drilling Methods 0.000 claims description 2
- 238000010008 shearing Methods 0.000 claims description 2
- -1 natural gas hydrates Chemical class 0.000 claims 7
- 238000011084 recovery Methods 0.000 claims 7
- 239000007789 gas Substances 0.000 abstract description 34
- 239000004576 sand Substances 0.000 abstract description 15
- 238000011044 inertial separation Methods 0.000 abstract description 8
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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
- E21B43/34—Arrangements for separating materials produced by the well
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- Geochemistry & Mineralogy (AREA)
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Abstract
The application relates to an uphole three-phase separation device and method for natural gas hydrate solid-state fluidization exploitation, and belongs to the field of natural gas hydrate exploitation. The invention provides an integrated design for realizing gas-liquid-solid three-phase separation of natural gas, water and silt and vaporization of natural gas hydrate by combining a cyclone separation and inertial separation mode, and the effective desorption and separation of natural gas in silt pores are enhanced by utilizing high-speed autorotation of particles in a cyclone field. The invention has high separation precision, can effectively separate the solid phase with the grain diameter less than or equal to 40um, and the content of liquid drops carried in the purified natural gas is less than 3% (w) of the gas. The method provides a reference for solving the problems of low gas, liquid and water treatment efficiency and low separation precision of micron-sized fine sand, natural gas and water of the existing separator.
Description
Technical Field
The invention relates to an uphole three-phase separation device and method for natural gas hydrate solid state fluidization exploitation, belonging to the technical field of natural gas hydrate exploitation.
Background
In the 21 st century, socioeconomic development has progressed rapidly, and energy consumption has increased increasingly, with accompanying increasing environmental problems. According to world energy statistics of the uk petroleum company (BP), fossil fuels are currently composed mainly of petroleum (35.8%), coal (28.4%) and natural gas (23.7%). The energy consumption increases at a rate of 1.8% per year, and according to the current level, it is globally ascertained that petroleum reserves can meet 40 years of consumption demand. With the development of economy and society, the limited resources are difficult to maintain the rapid development of national economy, and the great consumption of traditional fossil energy sources such as petroleum, coal and the like causes serious environmental pollution, so the pressure brought by the rapid development of economy is urgent to seek clean and efficient new energy sources.
Natural gas hydrate (Natural Gas Hydrate, abbreviated as NGH) is a cage-type crystalline compound formed by wrapping gas molecules such as methane and the like by water molecules in a low-temperature and high-pressure environment, and can be directly ignited, and is also called as natural gas hydrate. The natural gas hydrate gradually becomes an important future energy source with the advantages of large energy reserve, high energy density, small environmental pollution and the like, and causes extensive research in countries around the world. The natural gas hydrate is a new energy with huge reserves which is not yet developed at present, and the exploration and development of the new energy face huge challenges, on one hand, the decomposition of the natural gas hydrate on the sea floor can greatly influence global climate change; another aspect is exploration, production methods, drilling, and the like. Domestic Zhou Shou develops a deep water shallow natural gas hydrate solid state fluidization exploitation technology for institutions, namely deep water shallow uncontrollable non-diagenetic natural gas hydrate storage is changed into controllable natural gas hydrate resources through a submarine exploitation and airtight fluidization lifting system, so that production safety is ensured, environmental risks possibly brought by shallow hydrate decomposition are reduced, and the purpose of green controllable exploitation is achieved.
At present, the research of the foreign conventional three-phase separator is mature, and the production of the three-phase separator is standardized and serialized. Well-known three-phase separator manufacturers are the Expro company in the united kingdom, the united states camelron company, the Schlumberger company, the Baker Hughes company, and the like, which all have their own perfect technical support and can produce multiphase separation equipment according to the needs of users. The research on the oilfield ground equipment in China is started later, but the manufacturing level of the separators in China is greatly improved since the advanced technology is introduced abroad from the beginning of the 80 s, and particularly, in recent years, along with the increase of the demands at home and abroad, a plurality of new separator manufacturers with higher technical level are emerging. The separator has tens of strong separator production enterprises in China, partial product separation effects reach the world advanced level, and some products are even sold in North America, south America, middle east and other areas, but most three-phase separators produced in China are similar in structure, single in technology and poor in product adaptability, so that the enrichment and development of the separator technology also need more research and innovation.
Patent CN 104895546a provides a natural gas hydrate subsea separation process based on solid state fluidization exploitation, which is used for solid state fluidization exploitation of non-diagenetic natural gas hydrate on shallow surface layers of the seabed. The process comprises the following steps of (1) conveying hydrate primary pulp pumped after exploitation of a submarine excavator to a submarine screening device for screening treatment, (2) conveying large solid particles obtained after screening treatment to a submarine crushing device for crushing treatment, (3) screening the crushed hydrate mixture again, (4) separating the large solid particle mixture and the small solid particle mixture after screening treatment respectively, and (5) backfilling the seabed by the separated silt. The invention can realize the seabed separation of the hydrate in the solid state fluidization exploitation process of the non-diagenetic natural gas hydrate reservoir on the shallow surface layer of the seabed. The whole process is safe and efficient, and the content of hydrate in the separated sediment can be effectively controlled.
The patent CN207315341U provides a modularized submarine natural gas hydrate underground separation device, which comprises a final assembly column, a conical separator installation groove arranged in the final assembly column, a separator arranged in the separator installation groove, a first sealing disk arranged at the upper part of the conical separator installation groove, a liquid inlet runner, a sand discharge runner and a liquid outlet runner arranged in the final assembly column, a liquid inlet connecting pipe arranged at the upper end of the liquid inlet runner, a sand discharge connecting pipe arranged at the upper end of the sand discharge runner, a liquid inlet annulus arranged at the upper end of the final assembly column and communicated with the liquid inlet runner, a liquid inlet hole arranged on the inner wall of the liquid inlet annulus, a connecting ring arranged on the center of the connecting ring, a liquid outlet through hole arranged in the connecting ring, a connecting pipe installation hole arranged in the connecting ring, a sand settling tank arranged at the lower end of the final assembly column and a second sealing disk arranged under the sand settling tank. Through the scheme, the device is modularized, compact in structure, convenient to install and high in separation efficiency, and has great practical value and popularization value.
Patent CN107542431a discloses a method for gas-liquid-solid multiphase fluidization separation of natural gas hydrate seabed, which mainly comprises a fluidized bed, a feeding lock hopper, a cyclone separator, a sand lock hopper, a gas distribution plate, a heating plate, a control valve and the like. Firstly, mechanically crushing hydrate sediments into hydrate particles, mixing the hydrate particles with a proper amount of seawater to form hydrate slurry, storing the hydrate slurry in a feeding lock hopper, feeding the hydrate slurry into a fluidized bed through a feeding gate valve, enabling fluidized gas methane to enter the fluidized bed through a gas distribution plate at the bottom of the fluidized bed, forming stable gas-liquid-solid multiphase fluidized hydrate particles in the fluidized bed by the aid of the hydrate particles, the seawater and the fluidized gas, thermally decomposing the hydrate particles under the action of high-temperature seawater and an internal heating component, releasing methane gas, further separating crude methane gas through a cyclone separator, conveying the crude methane gas to an offshore platform, and backfilling decomposed residual silt to the sea bottom through a sand lock hopper.
The patent CN107543009A discloses a hydrate particle separating device of a gas pipeline, which is characterized by comprising a spiral flow generator, a primary pipeline, a secondary pipeline, a tertiary pipeline, a guide strip, a solar heat storage box, a photovoltaic solar panel and an air compressor, wherein the primary pipeline, the secondary pipeline and the tertiary pipeline are sequentially connected, the spiral flow generator is positioned in the primary pipeline and consists of a cylinder, a particle breaker, a spiral flow maintainer and a torsion belt, the particle breaker is welded at the front end of the cylinder, the torsion belt is welded around the cylinder, the spiral flow maintainer is welded at the rear end of the cylinder, the guide strip is positioned in the secondary pipeline and welded on the inner wall of the secondary pipeline, hydrate particles respectively flow into the solar heat storage box through a lower end connecting gap of the primary pipeline and the secondary pipeline and a lower end connecting gap of the tertiary pipeline, the photovoltaic solar panel is connected with the solar heat storage box and the two solar boxes are respectively connected with the rear end of the tertiary pipeline through the air compressor, and the primary pipeline and the tertiary pipeline are respectively connected with the gas pipeline through an inlet flange and an outlet flange.
Later in the 50 s of the 20 th century, the company Hydrocarbon Research Inc (HRI) and city service company first developed a commercial "H-Oil" ebullated bed technology and filed U.S. patent No. 25,770. On the basis of US 25,770, the problem of gas-liquid-solid separation around ebullated-bed reactors generally arises for 5 structural separations, respectively: (1) a hollow tower settling structure; (2) a cavity-separating sedimentation structure; (3) a circulation cup structure; (4) a cyclone separator structure; (5) inertial separation structure.
The empty tower sedimentation structure is that three-phase separation at the top of the reactor is realized by gravity sedimentation of a gas-liquid-solid three-phase mixture in the empty tower structure; the gas phase product is discharged from a gas phase outlet at the top of the reactor, and the liquid phase product is horizontally led out from the supernatant liquid at the upper layer of the free space area in the reactor or is horizontally led out. The cavity-separating sedimentation structure is characterized in that the gas-liquid-solid three-phase mixture is degassed preferentially in the reactor, and then the gas-phase-removed liquid-solid two-phase mixture enters a sedimentation area with a certain volume for sedimentation. The circulating cup structure is an improvement on the empty tower sedimentation structure, and a funnel-shaped space is arranged in the reactor and is specially used for gas-liquid two-phase retention separation so as to obtain a liquid-phase product with low gas content or without gas, and the liquid-phase product is sent to a circulating pump. The cyclone separator structure is that a cyclone separator is used in the reactor to replace the original separation structure, so that the gas-liquid separation is further enhanced, and the separation efficiency is improved. The inertial separation structure is characterized in that a buffer baffle is arranged at the top of the reactor to change the movement direction of fluid and particles, so that the catalyst is limited to expand upwards continuously and the particles are guided to settle downwards, the particles are separated from the fluid, and the obtained gas-liquid two-phase product without solid is discharged from the top of the reactor.
Compared with the conventional oil-gas reservoir, the natural gas hydrate reservoir has the advantages that the amount of the muddy sand is large, the muddy sand particle size is smaller than 40 mu m and is 83.25%, the muddy sand particle size is smaller than 10 mu m and is 40%, the median particle size is 20 mu m, and the conventional separation device for oil-gas field development is difficult to separate the trans-scale fine sand. Therefore, the development of the high-efficiency and low-consumption three-phase separation equipment aiming at the natural gas hydrate solid-state fluidization exploitation process has certain guiding significance for purifying natural gas, reducing the energy consumption in the gas conveying process and reducing the operation cost.
Disclosure of Invention
The invention aims at: the device has a compact structure, and can effectively strengthen the decomposition and vaporization of the hydrate and the separation precision of micron-sized fine sand, natural gas and water; thereby improving the natural gas yield; solves the problems of low gas, liquid and water treatment efficiency and low separation precision of fine sand, natural gas and water of the existing separator, and is used for the on-well three-phase separation device and method for the solid fluidization exploitation of natural gas hydrate.
The technical scheme of the invention is as follows:
an uphole three-phase separation device for solid fluidization exploitation of natural gas hydrate comprises a skirt, a separation tank body, a gas-liquid cyclone and a liquid-solid cyclone; the method is characterized in that: the separation tank body is fixedly arranged on the skirt seat, a top blind plate, a middle blind plate and a lower blind plate are arranged in the separation tank body from top to bottom at intervals, a plurality of gas-liquid cyclones are arranged between the top blind plate and the middle blind plate, a liquid-solid cyclone is arranged in the separation tank body below the lower blind plate, the top of the liquid-solid cyclone extends to above the middle blind plate, and a solid phase outlet pipe is arranged at the bottom of the liquid-solid cyclone; one end of the solid phase outlet pipe penetrates through the separation tank body to extend to the outer end of the skirt, a lower communicating pipe is arranged at the bottom of the separation tank body on one side of the liquid-solid separator, one end of the lower communicating pipe extends to the outer end of the skirt, and an upper communicating pipe is arranged at the top of the separation tank body.
The gas-liquid cyclone is annularly arranged on the top blind plate 5 and the middle blind plate, and the number of the gas-liquid cyclone is 2-8.
The top of the gas-liquid cyclone is communicated with the inner cavity of the separation tank above the top blind plate; the bottom of the gas-liquid cyclone is communicated with the inner cavity of the separation tank body between the middle blind plate and the lower blind plate.
And a middle communicating pipe is arranged on the corresponding separation tank body between the middle blind plate and the lower blind plate.
The gas-liquid cyclone consists of a cyclone tube and an overflow tube, wherein the cyclone tube is a conical body, the top end of the cyclone tube is provided with the overflow tube, and a gas-liquid cyclone inlet is arranged on the cyclone tube at one side of the overflow tube; the gas-liquid cyclone inlet is communicated with the cyclone tube, and flanges are respectively arranged on the circumferences of the top of the overflow tube and the bottom of the cyclone tube.
The liquid-solid cyclone consists of a cyclone shell, a liquid-solid overflow pipe and cyclone blades, wherein the cyclone shell is funnel-shaped, the liquid-solid overflow pipe is arranged at the central part of the cyclone shell, a plurality of cyclone blades are uniformly distributed between the liquid-solid overflow pipe and the inner wall of an upper port of the cyclone shell, and a solid phase outlet pipe is fixedly arranged at the bottom of the cyclone shell.
The separation method of the natural gas hydrate three-phase separation device comprises the following steps:
1) Under certain pressure, natural gas hydrate (comprising gas, liquid and solid three-state) enters the inner cavity of the separation tank body below the lower blind plate 7 from a feed port (lower communicating pipe 8) at the bottom of the three-phase separator;
2) The natural gas hydrate entering the bottom of the separation tank body is continuously lifted along with the continuous entering of the liquid level, the lifted liquid level gradually floods the cyclone shell of the liquid-solid cyclone, and enters the cyclone shell through the gaps among the cyclone blades and enters the cyclone shell;
3) The natural gas hydrate enters the cyclone shell through the cyclone blade; because the cyclone blades are obliquely arranged, natural gas hydrate performs three-dimensional spiral rotation flow in an annular flow space formed between a shell of the liquid-solid cyclone and the liquid-solid overflow pipe under the drainage effect of the cyclone blades, wherein the radial force applied to solid particles in the cyclone separation process of the liquid-solid cyclone is mainly inertial centrifugal force, centripetal buoyancy and fluid drag force and is different in size, the solid particles are subjected to centrifugal sedimentation, coarse particles (heavy phase) with relatively large diameters and part of liquid are discharged from a solid phase outlet pipe at the bottom, and relatively fine particles (light phase) and part of liquid are discharged from the liquid-solid overflow pipe into a separation tank between a top blind plate and a middle blind plate; the purpose of fractionation is achieved. Meanwhile, the solid particles rotate at a high speed of 1000rad/s to 3000rad/s in the liquid-solid cyclone field, so that the cementation breaking and decomposition of the hydrate can be further enhanced;
4) After a certain amount of hydrate entering the separating tank body between the top blind plate and the middle blind plate is collected, the hydrate tangentially enters a cyclone tube of the conical body through a gas-liquid cyclone inlet at a certain pressure; and generates strong three-dimensional elliptic strong rotary shearing turbulence motion;
5) In the process, because the particle size difference (or density difference) exists between coarse particles (or heavy phase) and fine particles (or light phase) in the hydrate, the size of the coarse particles (or heavy phase) and the fine particles (or light phase) is different in centrifugal force, centripetal buoyancy force, fluid drag force and the like, and most of the coarse particles (or heavy phase) and liquid are discharged through a bottom flow port of the gas-liquid cyclone under the action of centrifugal sedimentation, enter a separation tank body between a middle blind plate and a lower blind plate and are discharged through a middle communicating pipe;
6) The fine particles (or heavy phase) and the liquid are discharged through the bottom flow port of the gas-liquid cyclone, and the gas (or light phase) is discharged and collected through the upper communicating pipe, so that the purpose of separating the gas and the liquid is achieved, and one working cycle is completed.
To demonstrate the separation effect of the three-phase separation device: the inventors of the present application conducted three-phase separation experiments of natural gas hydrate under conditions that the gas flow rates Ug were 6mm/s,8mm/s,10mm/s,15mm/s, respectively, and the solid contents of the inertial separation inlet (i.e., the concave conical surface formed by the cone section of the cyclone separator and the reactor wall), the cyclone separator inlet, and the overflow port during the experiments. Experiments show that the overflow port of the cyclone separator meets the requirement of no solid particles entrainment under the conditions of gas speed lower than 15mm/s and liquid speed lower than 8 mm/s. The specific results are shown in FIGS. 4-7.
According to experimental results, the three-phase separation device aims at three-phase separation of the natural gas hydrate extracted from the well, the concentration of solid particles carried in seawater can be reduced to 10ppm, and the content of liquid drops carried in the natural gas is less than 3% (w) of the gas content.
Drawings
FIG. 1 is a schematic diagram of the structure of the present invention;
FIG. 2 is a schematic cross-sectional view of a gas-liquid cyclone of the present invention;
FIG. 3 is a schematic cross-sectional view of a liquid-solid cyclone of the present invention;
FIG. 4 is a graph showing the results of three-phase separation experiments at a gas velocity Ug of 6mm/s in accordance with the present invention;
FIG. 5 is a graph showing the results of three-phase separation experiments at a gas velocity Ug of 8mm/s in accordance with the present invention;
FIG. 6 is a graph showing the results of three-phase separation experiments at a gas velocity Ug of 10mm/s in accordance with the present invention;
FIG. 7 is a graph showing the results of three-phase separation experiments at a gas velocity Ug of 15mm/s according to the present invention.
In the figure: 1. skirt, 2, separating tank, 3, gas-liquid cyclone, 4, liquid-solid cyclone, 5, top blind plate, 6, middle blind plate, 7, lower blind plate, 8, lower communicating pipe, 9, upper communicating pipe, 10, cyclone tube, 11, overflow pipe, 12, gas-liquid cyclone inlet, 13, middle communicating pipe, 14, cyclone shell, 15, liquid-solid overflow pipe, 16, cyclone blade, 17, solid phase outlet pipe.
Detailed Description
The on-well three-phase separation device for the solid fluidization exploitation of the natural gas hydrate comprises a skirt (1), a separation tank body (2), a gas-liquid cyclone (3) and a liquid-solid cyclone (4); the separation tank body (2) is fixedly arranged on the skirt (1), a top blind plate (5), a middle blind plate (6) and a lower blind plate (7) are arranged in the separation tank body (2) from top to bottom at intervals, a plurality of gas-liquid swirlers (3) are arranged between the top blind plate (5) and the middle blind plate (6), and the gas-liquid swirlers (3) are annularly arranged on the top blind plate (5) and the middle blind plate (6) and are (6) in number. The gas-liquid cyclone (3) consists of a cyclone tube (10) and an overflow tube (11), wherein the cyclone tube (10) is a conical body, the top end of the cyclone tube (10) is provided with the overflow tube (11), and a gas-liquid cyclone inlet 12 is arranged on the cyclone tube (10) at one side of the overflow tube (11); the gas-liquid cyclone inlet 12 is communicated with the cyclone tube (10), and flanges are respectively arranged on the top of the overflow tube (11) and the circumference of the bottom of the cyclone tube (10). The top of the gas-liquid cyclone (3) is communicated with the inner cavity of the separation tank above the top blind plate (5); the bottom of the gas-liquid cyclone (3) is communicated with the inner cavity of the separation tank between the middle blind plate (6) and the lower blind plate (7). A middle communicating pipe (13) is arranged on the separating tank body (2) corresponding to the middle blind plate (6) and the lower blind plate (7).
Install liquid-solid swirler (4) in separation jar body (2) of lower part blind plate (7) below, liquid-solid swirler (4) comprises swirler shell (14), liquid-solid overflow pipe (15) and whirl blade (16), and swirler shell (14) are the funnel form, and the central point of swirler shell (14) is provided with liquid-solid overflow pipe (15), and the equipartition has a plurality of whirl blades (16) between liquid-solid overflow pipe (15) and swirler shell (14), and solid phase outlet pipe (17) are equipped with admittedly to the bottom of swirler shell (14). A liquid-solid overflow pipe (15) of the liquid-solid cyclone (4) extends to the upper part of the middle blind plate (6), and a solid phase outlet pipe (17) is arranged at the bottom of the liquid-solid cyclone (4); one end of a solid phase outlet pipe (17) penetrates through the separation tank body (2) to extend to the outer end of the skirt (1), a lower communicating pipe (8) is arranged at the bottom of the separation tank body (2) at one side of the liquid-solid separator (4), one end of the lower communicating pipe (8) extends to the outer end of the skirt (1), and an upper communicating pipe (9) is arranged at the top of the separation tank body (2) (see figures 1-3).
The separation method of the natural gas hydrate three-phase separation device comprises the following steps:
under a certain pressure, natural gas hydrate (including gas, liquid and solid tri-states) enters the inner cavity of the separation tank body (2) below the lower blind plate (7) from the lower communicating pipe (8) at the bottom of the three-phase separator, the natural gas hydrate entering the bottom of the separation tank body (2) is continuously lifted along with the continuous entering of the natural gas hydrate into the liquid level, the lifted liquid level gradually floods the cyclone shell (14) of the liquid-solid cyclone (4), and enters the cyclone shell (1) through the gaps among the cyclone blades (16) to enter the cyclone shell (14); the natural gas hydrate enters the cyclone shell through the cyclone blades; because the cyclone blades (16) are obliquely arranged, natural gas hydrate performs three-dimensional spiral rotation flow in an annular flow space formed between a shell of the liquid-solid cyclone (4) and the liquid-solid overflow pipe (15) under the drainage effect of the cyclone blades (16), wherein radial forces applied to solid particles in the cyclone separation process of the liquid-solid cyclone (4) are mainly inertial centrifugal force, centripetal buoyancy and fluid drag force and are different in size, coarse particles (heavy phase) with relatively larger diameters and part of liquid are discharged from a solid phase outlet pipe (17) at the bottom under the centrifugal sedimentation effect, and relatively fine particles (light phase) and part of liquid are discharged from the liquid-solid overflow pipe (15) into a separation tank (2) between the top blind plate 5 and the middle blind plate 6; the purpose of fractionation is realized; meanwhile, the solid particles rotate at a high speed of 1000rad/s to 3000rad/s in the liquid-solid cyclone field, so that the cementation breaking and decomposition of the hydrate can be further enhanced;
natural gas, liquid and a small amount of fine silt which enter the separation tank body 2 between the top blind plate 5 and the middle blind plate 6 are dragged by the air flow, and enter the cyclone tube 14 of the conical body tangentially by the air-liquid cyclone inlet 12 at a certain pressure; in the process, fine particles and liquid are discharged through a bottom flow port of a gas-liquid cyclone due to the action of a three-dimensional cyclone field, enter a separation tank body 2 between a middle blind plate 6 and a lower blind plate 7 and are discharged through a middle communicating pipe 13, and meanwhile, solid particles are rotated at a high speed of more than 10000rad/s in the gas-solid cyclone field, so that the effective desorption and separation of natural gas in silt pores can be further enhanced; while fine particles (or heavy phase) and liquid are discharged through the bottom flow port of the gas-liquid cyclone, gas (or light phase) is discharged and collected by the upper communicating pipe 9, so that the purpose of separating gas and liquid is achieved, and one working cycle is completed.
The process of separating natural gas hydrate by the three-phase separation device is analyzed as follows:
the separation process of the three-phase separation device consists of three processes, namely: (a) inertial separation: realizing the coalescence and growth of bubbles and the coarse separation of solid particles; (B) cyclone separation: realizing the fine separation of solid particles; (C) gravity separation: avoiding the secondary entrainment of solid particles.
(A) Inertial separation is the separation by inertia of solid particles dispersed in a liquid-solid two-phase mixture. In the three-phase separation device, the densities of the liquid phase and the gas phase are smaller than those of the solid phase, and the liquid phase in which small bubbles are uniformly dispersed can be used as a quasi-homogeneous fluid. When the quasi-homogeneous fluid impinges on the outer wall surface of the cone section of the liquid-solid separator 4, the flow direction of the gas-liquid quasi-homogeneous fluid changes rapidly, and solid particles cannot be separated along with the movement of the gas-liquid quasi-homogeneous fluid under the action of inertia. The stress analysis of the solid particles is as follows:
(a) Drag force of fluid
The three-phase mixture entering the down-connection pipe (8) of the three-phase separation device is regarded as a two-phase mixture with solid particles and a gas-liquid quasi-homogeneous fluid, and the particles can be regarded as being uniformly distributed in the gas-liquid quasi-homogeneous fluid. And the particles have the same flow velocity with the gas-liquid quasi-homogeneous fluid, and because of the density difference of the particles and the gas-liquid quasi-homogeneous fluid, in the gas-liquid quasi-homogeneous fluid dynamic process, the velocity slip exists between the particles and the gas-liquid quasi-homogeneous fluid to generate momentum transfer, and the gas-liquid quasi-homogeneous fluid generates drag force on the particles：
In the formula (1), the components are as follows,is the drag coefficient;
is the diameter of solid particles, m;
density of quasi-homogeneous fluid of gas-liquid, kg/m 3 ；
Is the relative velocity, m/s, between the solid particles and the gas-liquid quasi-homogeneous fluid.
The drag force of the fluid is caused by the viscosity of the liquid phase, including pressure differential drag and frictional drag, the magnitude of the drag being related to the particle size, shape, surface area of the solid particles, and the distribution of the velocity of the liquid on the surface (i.e., the flow state of the liquid near the object plane). The drag coefficient can be summarized as:
in the formula (2), the Reynolds number of the particles is：
In the formula (3), the amino acid sequence of the compound,dynamic viscosity of quasi-homogeneous gas-liquid fluid, +.>；
(b) Additional mass force
The two-phase mixture of solid particles and gas-liquid quasi-homogeneous fluid enters an annular space formed by the outer wall surface of the cone section of the liquid-solid separator 4 from the three-phase mixture inlet (lower communicating pipe) of the three-phase separation device, and the solid particles do accelerated motion due to the reduced flow area, so that the surrounding gas-liquid quasi-homogeneous fluid correspondingly generates acceleration, and under the inertia effect, the reaction force, namely the additional mass force, to the solid particles is expressed
(c) Basset acceleration force
When the solid particles move in the gas-liquid quasi-homogeneous phase fluid in an accelerating way, the solid particles are subjected to an unsteady fluid acting force, namely Basset acceleration force, due to the instability of a boundary layer on the surfaces of the particles. The Basset acceleration force delays the velocity change of the solid particles and is related to the acceleration of the solid particles:
s is the current time;
t is the time of action of force, s;
(d) Pressure gradient force
In the annular space formed by the wall surface of the three-phase separator and the outer wall surface of the cone section of the liquid-solid separator 4, the gas-liquid quasi-homogeneous fluid changes along the axial flow direction of the three-phase separator, the generated centrifugal force changes the pressure field in the flow field, the gas-liquid quasi-homogeneous fluid flows in a reverse pressure gradient, and the force caused by the pressure gradient received by the solid particles in the flow field is：
In the formula (6), the amino acid sequence of the compound,。
(e) Magnus force
The pressure gradient in the flow field causes the solid particles to rotate during movement. Under the condition of low particle Reynolds number, the rotation motion of the solid particles can drive the surrounding gas-liquid quasi-homogeneous fluid to move. In combination with the bernoulli equation, it has been found that this results in an increase in dynamic pressure and a decrease in static pressure of the gas-liquid quasi-homogenous fluid on one side of the solid particles, while the dynamic pressure and the static pressure of the gas-liquid quasi-homogenous fluid on the other side are decreased, such that the solid particles tend to one side of the decrease in static pressure, which is referred to as the Magnus effect. The force that urges the solid particles toward the static pressure reducing side is referred to as Magnus force.
。
In the formula (7), the amino acid sequence of the compound,is the rotational angular velocity of the solid particles;
representing higher order remainders.
In addition to the above forces, forces that may act on the solid particles include Staffman lift in the shear flow perpendicular to the direction of fluid flow, thermophoretic forces caused by temperature gradients, brownian forces of turbulent diffusion, and the like.
Particle motion analysis
The following basic assumptions are made for the motion analysis of particles during inertial separation:
(1) Speed slippage exists between the solid particles and the gas-liquid quasi-homogeneous phase;
(2) The solid particles are used as a disperse phase and are uniformly distributed at the inlet of the separator;
(3) Collisions between particles are not considered.
In the annular space formed by the wall surface of the three-phase separator and the outer wall surface of the cone section of the separator, solid particles are deflected to the wall surface due to the fact that the motion track of the solid particles is inconsistent with the main flow direction of the gas-liquid quasi-homogeneous fluid under the action of inertia due to the fact that the gas-liquid quasi-homogeneous fluid is rapidly deflected, and therefore the solid particles are separated.
When the flow in the annular space formed by the wall surface of the three-phase separator and the outer wall surface of the cone section of the three-phase separator is similar to laminar flow and the pressure loss when the gas-liquid quasi-homogeneous fluid flows through the corner is ignored, the separation model for simplifying the inertial separation process of the three-phase separator is annular like the inlet section of FIG. 4 and gradually tapers upwardsIs small. Setting the flow rate of the gas-liquid quasi-homogeneous phase fluid containing solid particles at an inlet asDue to inertia, the solid particles start to thicken towards the wall of the three-phase separator after entering this annular space.
Anywhere within the annular spaceThe two velocity components of the solid particles of (2) are tangential velocity +.>And radial speed->. When a gas-liquid pseudo-homogeneous fluid carrying solid particles is diverted in an annular space, a differential equation can be established:
combining formula (8) and formula (9)
For solid particles passing through the inertial separator zone
Assuming a laminar flow regime, the drag coefficient is the following:
obtainable from formula (11):
taking formula (13) into formula (10), there are:
theoretical derivation of separation efficiency
As shown in FIG. 4, the solid particles entering the annular space formed by the outer wall of the conical section of the separator and the wall of the three-phase separator and entering the polar coordinate system (r 0, 0) into the annular space are obtained by integrating the formula (13) and are rotated by pi-beta angle θ ：
The function of formula (15) is an archimedes curve, which is the boundary between the solid particles after separation and the gas-liquid quasi-homogenous fluid, thus forThe separation efficiency of solid particles of particle size can be expressed as:
as is evident from equation (16), whenAlong->Is increased by (1)>A trend of increasing and then decreasing is presented. />Will also affect the separation efficiency.
(B) Cyclone separation
The liquid-solid two-phase mixture is subjected to three-dimensional spiral rotation flow in an annular flow space formed between a column cone structure and an overflow pipe structure of the separator under the drainage effect of the cyclone guide vane, the flow state is extremely complex, and the stress condition of solid particles is also extremely complex.
During centrifugation of solid particles, radial forces acting on the solid particles play a key role. The radial forces to which the solid particles are subjected during the cyclonic separation of the three-phase separator are mainly inertial centrifugal forces, centripetal buoyancy forces and fluid drag forces, and are subjected to additional forces such as Magnus forces and Staffman forces, which affect the movement of the droplets in the cyclonic field.
Theory of vortex motion
The vortex motion is the rotation motion of fluid and can be divided into free vortex motion, forced vortex motion and combined vortex motion, and the vortex motion with three different characteristics.
As shown in FIG. 5, when the fluid is rotated about the vertical axis Z, the total energy on each concentric surface in the direction of the radius of rotationThe value is pressure energy->Kinetic energy->Potential energy->I.e.:
in the formula (17), the amino acid sequence of the compound,
under laminar flow, the fluid rotates around the vertical axis, and the speed of the fluid is the tangential speed of the fluid rotating around the vertical axisAnd the potential change of the fluid can be ignored, so the formula (17) can be simplified as:
in the formula (18), the amino acid sequence of the compound,
differentiating r from formula (18) to obtain:
for the fluid infinitesimal in FIG. 5In other words, the pressure difference acting on both sides of the fluid element in the radial direction is sufficient to provide the centripetal force required for the rotation of the fluid element about the vertical axis>When the fluid is in a slight conditionIn the equilibrium state, namely:
namely:
dividing both sides of formula (20) byObtaining:
bringing formula (21) into (3-19), to obtain:
equation (22) is a basic equation of the rotating fluid, and reflects the energy change law of the rotating fluid during the motion process. By the equation (22), the tangential velocity distribution of the fluid in the rotating flow field can be studied.
(a) Fluid tangential velocity distribution model in free vortex
The fluid particles revolve around the main shaft only and do not have a motion called free vortex motion for rotation about their own instantaneous axis. Free vortex is characterized by an angular velocity vector of 0, i.e. Free vortex is potential vortex without external energy supplement, i.e.>. Thus, from the basic equation of the rotating moving fluid of formula (22), it is possible to obtain:
namely:
due toThus, from equation (23):
integrating equation (24) yields:
in the formula (24), the amino acid sequence of the compound,
namely:
in the formula (25), the amino acid sequence of the amino acid,
equation (25) is the distribution law of tangential velocity of fluid in free vortex. In free vortex motion, the tangential velocity of a fluid particle is inversely proportional to its radius of rotation, according to equation (25). When (when)When, i.e. at infinity from the vortex coreThere is->The method comprises the steps of carrying out a first treatment on the surface of the When (when)At the vortex core, there is +.>As shown in fig. 5. However, is->There is no physical meaning, and obviously no existence is possible. In fact, when r is reduced to some extent, the tangential velocity will no longer follow the distribution of the tangential velocity of the fluid as in equation (25).
(b) Fluid tangential velocity distribution model in forced vortex
The fluid having a rotation about its own instantaneous axis is called forced vortex motion, the forced vortex being characterised by an angular velocity vector other than zero, i.e. When incompressible fluid performs forced vortex motion, the rotation of the incompressible fluid is similar to that of a rigid body, and the tangential velocity distribution rule of the fluid is as shown in fig. 7, namely:
/>
in the formula (26), the amino acid sequence of the compound,
and due to angular velocityConstant, it can be expressed as:
in the formula (27), the amino acid sequence of the compound,
(c) Fluid tangential velocity distribution model in combined vortex
The combined vortex is a combined motion of free vortex and forced vortex. The periphery of the combined vortex belongs to free vortex motion, and the vortex core of the combined vortex belongs to forced vortex motion. The general formula of tangential velocity of free vortex motion can be unified according to the formula (25) and the formula (27):
when n=1, free vortex motion, i.eThe method comprises the steps of carrying out a first treatment on the surface of the When n= -1, a forced vortex movement is given, i.e. +.>。
At the junction of free and forced vortices, there is a maximum tangential velocityThere are:
i.e. whenAnd belongs to free vortex; when->And belongs to the forced vortex.
Particle stress analysis:
inertial centrifugal force:
inertial centrifugal force to which the particles are subjected：
In the formula (30), the amino acid sequence of the compound,water density of solid particles, kg/m 3 ;
Is the diameter of solid particles, m;
tangential velocity, m/s, of solid particles;
r is the radial position radius of the solid particles, m;
centripetal buoyancy:
centripetal buoyancy experienced by the particles；
In the formula (31),is of liquid phase density of kg/m 3 ；
Tangential velocity, m/s, of solid particles;
from the above, it can be seen that the magnitude of centripetal buoyancy is related to the inlet velocity of the three-phase separator, the diameter of the solid particles and the density of the liquid phase.
Fluid drag force:
the particles are subjected to fluid drag forces：
/>
In the formula (32), the amino acid sequence of the compound,in order for the coefficient of drag to be the same,
is the radial relative velocity, m/s, between the solid particles and the liquid phase.
Particle motion analysis:
the Newton's second law is applied to the movement of solid particles in the centrifugal separation process of a three-phase separator, namely the resultant force acting on the solid particles is equal to the product of the mass of the solid particles and the acceleration. The general equation for solid particle motion is therefore:
(mass x acceleration) = (volumetric force) + (fluid resistance) + (unsteady force)
Wherein the volume force is a non-contact force acting on the object through the space, such as gravity, inertial force, electromagnetic force, etc.; the fluid resistance is the resistance of the fluid to the particles as the particles move relative to the fluid. The unsteady forces are those that take into account the effects of particles having acceleration relative to the fluid, such as Magnus forces, basset forces, etc.
Since the centrifugal separation process of the separator is extremely short, the flow state of the fluid is not adjusted in time due to the effect of inertia, and the unstable force can be ignored, which can be referred to as the Clift study. Therefore, only the inertial centrifugal force, centripetal buoyancy force and fluid drag force of the solid particles in the cyclone separation process of the three-phase separator can be considered in a simplified way:
liquid phase residence time
The residence time T of the liquid phase in the three-phase separator is:
wherein,
in the formula (35), the amino acid sequence of the compound,s is the residence time of the liquid phase in the annular space from the outlet of the cyclone guide vane to the tail end of the overflow pipe; />The time s required for the liquid phase to return after possibly reaching the natural rotational flow length;
for the volume of the annular region from the swirl vane outlet to the overflow pipe end, m 3 ；
For the volume of the area below the end of the overflow pipe, m 3 ；
For the volume flow of the liquid phase, m 3 /s
Theoretical derivation of separation efficiency:
according to the boundary layer separation theory, a thin layer exists near the inner wall surface of the three-phase separator, and the thin layer is in a laminar flow state. The solid particles are separated as they move into this laminar thin layer. Based on this theory, the theoretical separation efficiency of the three-phase separator is deduced, and the following assumptions are made:
(1) Outside the laminar flow thin layer, the particle particles are uniformly distributed;
(2) Neglecting liquid phase radial velocity；
(3) No tangential relative slippage between the particles and the liquid phase, i.e.(the tangential velocity of the solid particles is consistent with that of the liquid phase);
(4) The concentration of the solid particles in the liquid-solid phase is insufficient to influence the flow structure of the three-dimensional spiral swirl field;
(5) The tangential velocity in the three-phase separator corresponds to the combined vortex motion as described by equation (28), namely:
in the formula (37), the amino acid sequence of the compound,is the tangential velocity of the inlet liquid phase, m/s;
is the diameter of the three-phase separator, m.
Thereby the processing time of the product is reduced,the approach velocity of the wall-treated solid particles obtainable by formula (33)
Assuming a particle number per unit volume of C S The number of particles per unit area in the three-phase separator per unit time is. In axial length->In the inner, the number of particles separated is +.>These particles are from volume +.>Is separated in the liquid phase volume of (a), so that:
assuming that the initial particle number concentration of the liquid-solid two-phase mixture isAfter a separation residence time T in the three-phase separator, the particle number concentration at the overflow pipe inlet of the three-phase separator is +.>Therefore, the equation (40) can be integrated with:
namely:
for particle size of particles ofParticle separation efficiency>Can be expressed as:
substituting the formula (38) into the formula (43) to obtain the particle size of the particlesParticle separation efficiency>：
(C) Gravity separation
The clarified liquid phase of the centrifugal separation process in the separator overflows the separator through a liquid-solid overflow pipe 15, and when the clarified liquid phase passes through the overflow pipe, the liquid velocity is too high, which results in that part of the particles in the downcomer of the separator are entrained upwards. In order to avoid this back mixing entrainment, gravity separation design is required for the overflow tube structure.
Free sedimentation of particles:
the settling process in which solid particles are only affected by their own weight, buoyancy and fluid drag forces generated when the two are relatively moved in a fluid, and are not disturbed by other mechanical forces, is called free settling.
The solid particles being subjected to gravity in a stationary fluidThe method comprises the following steps:
the particles being subjected to buoyancy in a stationary fluidThe method comprises the following steps:
drag force of particles in stationary fluidThe method comprises the following steps:
at the final speed of the particles in the liquid phase, the stress of the particles is balanced
It is known that the end velocity of the settling terminal of the particles in a stationary fluidIs that
It can be deduced that:
(1) Stokes region
(2) Alembic area）
Interference sedimentation of particles
When the particle concentration in the liquid-phase two-phase mixture is increased, the interference among particles and the influence of the wall on the particle movement are obviously increased, so that the particle sedimentation process is influenced. And wake vortices formed by sedimentation of individual particles will also affect the sedimentation movement of subsequent particles. The sedimentation of the particles in this case is known as interference sedimentation.
(1) Low concentration particle interference sedimentation
The sedimentation theory formula affected by the concentration is obtained as follows:
-the final speed of sedimentation of the particles, m/s;
the end speed of sedimentation in the concentration Cs, m/s;
-solid volume concentration, m 3 /m 3 ；
The formula is shown inUnder the condition, the method is more accurate.
(2) High concentration particle interference sedimentation
Hawksley obtains a sedimentation formula under high concentration based on the assumption of particle stress balance in sedimentation process
Shape factor (for sphere->For non-sphere->）
The coefficient of interaction between solid particles, for spheres, +.>Dimensionless
(mud and sand do not flocculate) and +.>(the shape of the silt is similar to that of a sphere, flocculation phenomenon exists), and no factor exists
Experimental formula for obtaining high-concentration particle interference sedimentation
Void fraction
Overflow pipe structure design
The design principle for the overflow pipe is as follows: the safety coefficient of 1.0 is got to the rising liquid speed in the cyclone overflow pipe, and the maximum rising liquid speed of cyclone overflow pipe is not more than particle interference sedimentation terminal end speed, satisfies:
cross-sectional area of overflow pipe of cyclone, m 2 ，/>
Cross-sectional area of three-phase separator, m 2 ，/>。/>
Claims (10)
1. A separation method of an uphole three-phase separation device for solid fluidization exploitation of natural gas hydrate, which is characterized by comprising the following steps: it comprises the following steps:
1) Under a certain wellhead pressure, drilling fluid carries natural gas hydrate and silt into an inner cavity of a separation tank body (2) below a lower blind plate (7) from a lower communicating pipe (8) at the bottom of an uphole three-phase separation device to perform preliminary gravity sedimentation;
2) The natural gas hydrate entering the inner cavity of the bottom of the separation tank body is broken, glued and decomposed under the turbulent flow effect, when the liquid level rises to and floods the upper port of the liquid-solid cyclone (4), the three-phase mixture enters the cyclone shell (14) at a certain speed under the cyclone diversion effect;
3) The three-phase mixture enters the cyclone shell (14) through the cyclone blades (16); because the cyclone blades (16) are obliquely arranged, the three-phase mixture is subjected to three-dimensional spiral rotation flow in an annular flow space formed between the shell of the liquid-solid cyclone (4) and the liquid-solid overflow pipe (15) under the drainage effect of the cyclone blades (16), wherein the radial force of solid particles in the cyclone separation process of the liquid-solid cyclone (4) is mainly inertial centrifugal force, centripetal buoyancy force and fluid drag force and is different in size, most of silt is discharged from a solid phase outlet pipe (17) at the bottom along with liquid under the centrifugal sedimentation effect, and liquid and a small amount of fine silt are discharged into a separation tank body (2) between a top blind plate (5) and a middle blind plate (6) along with natural gas by the liquid-solid overflow pipe (15); the purpose of fractionation is realized; meanwhile, the solid particles rotate at a high speed of 1000rad/s to 3000rad/s in the liquid-solid cyclone field, so that the cementation breaking and decomposition of the hydrate can be further enhanced;
4) Natural gas, liquid and a small amount of fine silt which enter a separation tank body between the top blind plate (5) and the middle blind plate (6) are dragged by air flow, and tangentially enter a cyclone tube (10) of the conical body through a gas-liquid cyclone inlet (12) at a certain pressure; and generates strong three-dimensional elliptic strong rotary shearing turbulence motion;
5) In the process, due to the action of the three-dimensional cyclone field, fine particles and liquid are discharged through a bottom flow port of the gas-liquid cyclone, enter a separation tank body (2) between a middle blind plate (6) and a lower blind plate (7), and are discharged through a middle communicating pipe (13), and meanwhile, solid particles rotate at a high speed of more than 10000rad/s in the gas-solid cyclone field, so that the effective desorption and separation of natural gas in silt pores can be further enhanced;
6) The natural gas is discharged and collected by the upper communicating pipe (9), thereby achieving the purpose of purifying the natural gas, and one working cycle is completed.
2. A separation method of an uphole three-phase separation device for solid state fluidization recovery of natural gas hydrates as claimed in claim 1, wherein: the on-well three-phase separation device of the step 1) comprises a skirt (1), a separation tank body (2), a gas-liquid cyclone (3) and a liquid-solid cyclone (4); the separation tank body (2) is fixedly arranged on the skirt (1), a top blind plate (5), a middle blind plate (6) and a lower blind plate (7) are arranged in the separation tank body (2) from top to bottom at intervals, a plurality of gas-liquid cyclones (3) are arranged between the top blind plate (5) and the middle blind plate (6), a liquid-solid cyclone (4) is arranged in the separation tank body (2) below the lower blind plate (7), the top of the liquid-solid cyclone (4) extends to the position above the middle blind plate (6), and a solid phase outlet pipe (17) is arranged at the bottom of the liquid-solid cyclone (4); one end of a solid phase outlet pipe (17) penetrates through the separation tank body (2) to extend to the outer end of the skirt (1), a lower communicating pipe (8) is arranged at the bottom of the separation tank body (2) on one side of the liquid-solid separator (4), one end of the lower communicating pipe (8) extends to the outer end of the skirt (1), and an upper communicating pipe (9) is arranged at the top of the separation tank body (2).
3. A separation method of an uphole three-phase separation device for solid state fluidization exploitation of natural gas hydrate according to claim 2, wherein: the gas-liquid cyclone (3) is annularly arranged on the top blind plate (5) and the middle blind plate (6), and the number of the gas-liquid cyclone is 2-8.
4. A separation method of an uphole three-phase separation device for solid state fluidization recovery of natural gas hydrates as claimed in claim 3, wherein: the top of the gas-liquid cyclone (3) is communicated with the inner cavity of the separation tank above the top blind plate (5); the bottom of the gas-liquid cyclone (3) is communicated with the inner cavity of the separation tank between the middle blind plate (6) and the lower blind plate (7).
5. A separation method of an uphole three-phase separation device for solid state fluidization recovery of natural gas hydrates as claimed in claim 4, wherein: the separating tank body (2) corresponding to the middle blind plate (6) and the lower blind plate (7) is provided with a middle communicating pipe (13).
6. A separation method of an uphole three-phase separation device for solid state fluidization recovery of natural gas hydrates as claimed in claim 4, wherein: the gas-liquid cyclone (3) is composed of a cyclone tube (10) and an overflow tube (11), wherein the cyclone tube (10) is a cone, and the overflow tube (11) is arranged at the top end of the cyclone tube (10).
7. A separation method of an uphole three-phase separation device for solid state fluidization recovery of natural gas hydrates as claimed in claim 6, wherein: a gas-liquid rotational flow inlet (12) is arranged on the rotational flow pipe (10) at one side of the overflow pipe (11); the gas-liquid cyclone inlet (12) is communicated with the cyclone tube (10).
8. A separation method of an uphole three phase separation device for solid state fluidization recovery of natural gas hydrates as claimed in claim 7, wherein: flanges are respectively arranged on the top of the overflow pipe (11) and the circumference of the bottom of the cyclone pipe (10).
9. A separation method of an uphole three-phase separation device for solid state fluidization exploitation of natural gas hydrate according to claim 2, wherein: the liquid-solid cyclone (4) is composed of a cyclone shell (14), a liquid-solid overflow pipe (15) and cyclone blades (16), wherein the cyclone shell (14) is funnel-shaped.
10. A separation method of an uphole three-phase separation device for solid state fluidization recovery of natural gas hydrates as claimed in claim 9, wherein: the central part of the cyclone shell (14) is provided with a liquid-solid overflow pipe (15), a plurality of cyclone blades (16) are uniformly distributed between the liquid-solid overflow pipe (15) and the inner wall of the upper port of the cyclone shell (14), and a solid phase outlet pipe (17) is fixedly arranged at the bottom of the cyclone shell (14).
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| CN112642248B (en) * | 2020-12-18 | 2022-08-02 | 四川宏华石油设备有限公司 | Efficient shale gas desanding device, desanding system and desanding method |
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