WO2019071933A1 - 粉砂质海洋天然气水合物砾石吞吐开采方法及开采装置 - Google Patents

粉砂质海洋天然气水合物砾石吞吐开采方法及开采装置 Download PDF

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WO2019071933A1
WO2019071933A1 PCT/CN2018/083712 CN2018083712W WO2019071933A1 WO 2019071933 A1 WO2019071933 A1 WO 2019071933A1 CN 2018083712 W CN2018083712 W CN 2018083712W WO 2019071933 A1 WO2019071933 A1 WO 2019071933A1
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gravel
production
filling
hydrate
sand
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PCT/CN2018/083712
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English (en)
French (fr)
Inventor
刘昌岭
李彦龙
陈强
吴能友
孙建业
李承峰
胡高伟
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青岛海洋地质研究所
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Priority to US16/321,045 priority Critical patent/US10858914B2/en
Priority to JP2019507240A priority patent/JP6694549B2/ja
Publication of WO2019071933A1 publication Critical patent/WO2019071933A1/zh

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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
    • E21B41/00—Equipment or details not covered by groups E21B15/00 - E21B40/00
    • E21B41/0099—Equipment or details not covered by groups E21B15/00 - E21B40/00 specially adapted for drilling for or production of natural hydrate or clathrate gas reservoirs; Drilling through or monitoring of formations containing gas hydrates or clathrates
    • 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
    • E21B43/02—Subsoil filtering
    • E21B43/04—Gravelling of wells
    • 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
    • E21B43/35—Arrangements for separating materials produced by the well specially adapted for separating solids
    • 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
    • E21B43/38—Arrangements for separating materials produced by the well in the well
    • 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
    • E21B47/00—Survey of boreholes or wells
    • E21B47/06—Measuring temperature or pressure
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/01—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells specially adapted for obtaining from underwater installations

Definitions

  • the invention belongs to the field of high-efficiency exploitation of marine natural gas hydrate, and particularly relates to a silty marine natural gas hydrate gravel stimulation production device and a mining method.
  • Natural gas hydrates are widely distributed in high-latitude terrestrial permafrost and continental marginal sea sediments. It is an important potential energy source. How to mine and utilize it safely and efficiently has become a hot research topic in the world. In recent years, the research focus of countries around the world has gradually shifted from the original hydrate basic research and hydrate resource exploration to the gas hydrate test and mining stage. Especially in countries where conventional oil and gas resources are scarce, such as Japan, a large number of seawater gas hydrate trial mining research has been carried out and the industrialization target of medium and long-term hydrate exploitation has been formulated. From the point of view of mining methods, the current natural gas hydrate mining methods are mainly divided into pressure-reducing mining method, hydrothermal mining method, CO 2 displacement mining method and chemical injection mining method. From the 2002 Mallik5L-38 hydrate test The above-mentioned mining methods have been verified by some or all of the field tests.
  • the depressurization mining method is the most promising natural gas hydrate mining method.
  • it is China's first sea area gas hydrate test mining, or foreign hydrate test mining, are in the scientific experimental stage, there are still many key technologies to be solved from industrial mining.
  • the depressurization method still faces key problems such as unstable formation of the formation and difficulty in long-term exploitation and production due to large-scale sand production in the process of exploiting natural gas hydrates in the sea area.
  • the fluid extraction method based on the conventional anti-pressure method has achieved short-term test mining (60 days) success.
  • the CO 2 displacement mining method provides an idea for maintaining the stability of natural gas hydrate reservoirs.
  • this method forms CO 2 hydrate during the replacement process, the permeability of the near-well formation is reduced, which leads to difficulties in continuous mining in the later stage.
  • This method is still facing serious mining efficiency problems in large-diameter sandy reservoirs (IgnikSikumi-2012 test mining in the United States).
  • silty reservoirs the application effect can be imagined. Therefore, although the CO 2 replacement method can provide some reference for the long-term exploitation of hydrates, the replacement of hydrates by hydrates is obviously not available during the long-term exploitation of silty hydrates. If one can find a replacement of hydrates with other high-permeability substances (while replacing near-well shale or fine silt), it will have a revolutionary impact on the long-term exploitation of hydrates.
  • the CO 2 replacement method is a heat injection method in the usual sense. Although this method helps to maintain the formation pressure and slow down the formation instability to a certain extent, it can not solve the formation instability problem fundamentally, and it has been proved by the Mallik2L-38 hydrate test to mine the natural gas hydrate.
  • the applicability is very limited.
  • steam stimulation is commonly used to achieve single well production. At present, there is a very mature application, but for marine gas hydrate reservoirs, the efficiency of steam stimulation and the stability of reservoirs. The degree of improvement is not optimistic. Therefore, in terms of actual demand, hydrate mining needs to “swallow”, but the “throughput” substance must not be steam, but a substance that can promote the decomposition of hydrates and fill the formation deficit.
  • Japan's first marine gas hydrate test mining project used bare-hole extra-ceiling gravel to fill sand control technology, and achieved the effect of 6 days of 120,000 square meters of natural gas, which greatly encouraged the confidence of global marine gas hydrate research.
  • the extra-filled gravel layer played a very good role in improving productivity and sand control at the initial stage of production.
  • the “open-hole gravel pack” sand control completion technology was deducted for marine gas hydrate mining.
  • the depressurization method cannot solve the problem of formation deficit under long-term hydrate mining conditions, and the conventional sand control operation faces the challenge of sand control failure caused by formation deficit;
  • the steam stimulation method has been widely used in the exploitation of conventional heavy oil reservoirs, but the “steam” of steam stimulation can only promote the decomposition of hydrates and cannot fill the formation deficit;
  • One-time open-hole gravel filling sand control completion operation can play a good role in a short period of time, but because there is no follow-up source supply, the effective sand control period is short, which is insufficient to meet the long-term exploitation demand of marine gas hydrate.
  • the technical problem to be solved by the invention lies in the contradiction between the improvement of the production capacity, the sand control measures and the formation instability in the process of the large-area distribution of clayy silt marine gas hydrate depressurization or fluid extraction method in China.
  • Sand management concept proposed a silty marine natural gas hydrate gravel puff mining device and mining method.
  • a silty marine natural gas hydrate gravel throughput mining method comprising the following steps:
  • Step (3) and step (4) are switched and alternated according to the time node in time, so that the injected gravel is continuously filled with the replacement formation deficit, and the long-term production of the marine silty natural gas hydrate is maintained.
  • step (1) is achieved by opening the hydrate reservoir, sealing the overlying stratum of the hydrate reservoir by using the production sleeve, and inserting the mechanical sieve to perform the naked-eye independent sieve on the hydrate reservoir.
  • the pipe is completed and the artificial bottom is laid; the gravel filling tool installation interface is reserved between the mechanical sieve and the upper production casing.
  • the installation method of the pipe string combination is: the gravel filling tool, the production oil pipe and the filling pipe column, the production oil pipe and the filling pipe column are located in the production casing, and the filling pipe column is separately produced.
  • the tubing is connected to the gravel packing tool, the gravel packing tool is located at the top boundary of the hydrate reservoir, and a control valve and a gas separator are installed at the inlet end of the production tubing, and a one-way control is also provided at the junction of the gravel packing tool and the production tubing.
  • the valve and gravel filling tool are also provided with a filling switching valve.
  • step (3) gravel filling process the one-way control valve on the lower side of the gravel filling tool is closed, the gravel filling switching valve is opened, the control valve at the lower end of the production tubing is closed, and the passage formed by the filling column and the gravel filling tool is used.
  • the outside of the mechanical sieve tube is filled with gravel to form a gravel filling layer.
  • the sand carrying liquid passes through the mechanical sieve tube and returns from the wellbore annulus to the platform wellhead.
  • the outer ring of the wellbore is the outer wall of the production tubing and the filling tubular string and the generating sleeve.
  • step (3) opening the one-way control valve on the lower side of the gravel filling tool, closing the gravel filling switching valve, opening the control valve at the lower end of the production tubing, and starting the lifting pump to extract the formation fluid , start depressurization production;
  • step (4) the gas-liquid solid three-phase produced from the hydrate reservoir flows into the wellbore, and after separation by the gas separator, the liquid-solid two-phase flows through the production tubing to the wellhead, and the gas is produced through the wellbore annulus. ;
  • step (4) the sand concentration parameter of the wellhead and the flow pressure of the bottom hole are monitored in real time. If there is a sudden increase in the concentration of sand or a sudden increase in the pressure difference at the bottom of the well, the further pressure reduction production is stopped. Go to step (3).
  • step (4) a process of continuously injecting water or a liquid containing a hydrate inhibitor into the inside of the production tubing by filling the column to ensure that the fine sand produced by the formation can be fully carried to the wellhead while preventing hydrate Secondary generation.
  • step (4) hydrate depressurization production process turns to step (3) the time node of the gravel injection is judged according to the abnormality of the wellbore sand production, or the sudden change of the bottom hole production pressure difference without artificial pressure regulation is judged;
  • Step (3) Gravel injection conversion step (4) The time node of hydrate depressurization production is that the grit injection pressure is rapidly increased and cannot be continuously injected; wherein the judgment of the sand outflow abnormality of the wellbore includes the fluctuation of the bottom hole pressure under steady production conditions, and the lifting Pump sanding temperature rise and wellhead monitoring sand concentration increase phenomenon.
  • the grain size of the grit used in the filling in the step (3) is larger than the level 1 to 2 in which the Saucier method is used in the same mining environment.
  • the grain size of the grit used in the filling in the step (3) is larger than the level 1 to 2 in the Saulier method under the same formation condition; the sand shielding precision of the mechanical screen in the step (1) is greater than that in the same formation
  • the accuracy of the mechanical screen used in the conventional oil and gas wells for unloading gravel is 2 to 3 grades.
  • the invention further provides a silty marine natural gas hydrate gravel stimulation production device, comprising a production casing, a production oil pipe and a filling pipe column disposed in the production casing, and a lifting pipe column is also arranged in the production oil pipe, and the lifting
  • the tubular string is connected to the lift pump, and the gap formed between the outer wall of the production tubing and the filling tubular string and the inner wall of the production casing is an annular hole of the wellbore;
  • a mechanical screen is connected to the lower end of the production sleeve, and a gravel filling tool is disposed between the production sleeve and the mechanical screen, and the production sleeve is placed below the hydrate reservoir, and the gravel filling tool is located
  • control valve
  • the outlet end of the filling pipe column is respectively connected with the gravel filling tool and the production oil pipe, and the one-way control valve is arranged at the communication place between the gravel filling tool and the production oil pipe, and the gravel filling tool is further provided with a filling switching valve, and the filling pipe column is The bottom of the gravel filling tool is connected with the production tubing.
  • the solution of the present invention replaces the solid phase (sludge, sandy fine particles and hydrate) by solid phase (large-diameter gravel) throughput, and adopts appropriate relaxation of the mechanical screen to ensure sand precision and select suitable filling gravel.
  • solid phase large-diameter gravel
  • This scheme is suitable for marine gas hydrate reservoirs that are not suitable for complete sand control and reservoir modification, such as high mud and silty, suitable for pore-filled reservoirs or natural gas hydration with thin massive hydrate interlayers.
  • the reservoir has solved the problem of low efficiency of CO 2 displacement mining of marine natural gas hydrates, difficulty in maintaining stable reservoirs by heat injection mining, and short-term effective period of pre-pipe gravel packing sand control operations, solving the problem of natural gas hydrate production capacity in China's seas. Improve the difficulty of reservoir and risk of reservoir instability, and promote the development of commercial hydrate mining technology.
  • FIG. 1 is a schematic view showing the gravel injection of a gravel stimulation production device according to an embodiment of the present invention
  • FIG. 2 is a schematic view showing the output of the gravel throughput mining device in the embodiment of the present invention.
  • FIG. 3 is a schematic view showing the progress of a gravel throughput cycle in the embodiment of the present invention.
  • 1 production casing
  • 2 production tubing
  • 3 filling pipe column
  • 4 gravel filling tool
  • 5 one-way control valve
  • 6 mechanical screen tube
  • 7 gravel filling layer
  • 8 grain filling layer
  • 8 grain filling layer
  • 9 - hydrate reservoir overburden
  • 10 gas separator
  • 11 control valve
  • 12 gravel filling switch valve
  • 13 well bore
  • P 0 gravel injection start pressure
  • P 1 gravel injection maximum pressure
  • the invention proposes a new idea of silty sand natural gas hydrate gravel puff and puff mining, by injecting a certain size of gravel into the mining stratum, realizing the "swallowing" of the gravel by the stratum, continuously filling up the hydrate decomposition and the muddy production of the stratum.
  • the resulting formation deficit space applying the natural gas hydrate sand production management technology, appropriately widening the slit width of the mechanical sieve tube and the size of the swallowed gravel, so that the mud and fine particles of the near-well formation are discharged to the formation according to a certain ratio.
  • Embodiment 1 a silty marine natural gas hydrate gravel throughput mining method, referring to the structural principle described in FIG. 1 and FIG. 2, comprising the following steps:
  • Step (3) and step (4) are switched and alternated according to the time node in time, so that the injected gravel is continuously filled with the replacement formation deficit, and the long-term production of the marine silty natural gas hydrate is maintained.
  • the hydrate reservoir 8 is opened, the production sleeving layer 1 is used to seal the overlying stratum 9 of the hydrate reservoir, and the mechanical sieve 6 is driven down,
  • the hydrate reservoir 8 performs an independent screen completion completion under the naked eye, and an artificial bottom hole is disposed; a mechanical gravel pipe 6 is provided with a gravel filling tool 4 installation interface between the upper production casing 1 and the upper production casing 1.
  • the installation method of the pipe string combination is the gravel filling tool 4, the production oil pipe 2 and the filling pipe column 3, the production oil pipe 2 and the filling pipe column 3 are located in the production casing 1, and the filling pipe column 3 is respectively Connected with the production tubing 2 and the gravel packing tool 4, the gravel packing tool 4 is located at the top boundary of the hydrate reservoir 8, and at the inlet end of the production tubing 2 is installed a control valve 11 and a gas separator 10, a gravel packing tool 4 and production
  • the communication pipe 2 is also provided with a one-way control valve 5, and the gravel filling tool 4 is further provided with a gravel filling switching valve 12.
  • Step (3) During the gravel charging process, the one-way control valve 5 on the lower side of the gravel filling tool 4 is closed, the gravel filling switching valve 12 is opened, the control valve 11 at the lower end of the production tubing 2 is closed, and the gravel filling tool remaining at the bottom of the well is used.
  • the grit is filled into the outside of the mechanical screen 6 by filling the column 3 and the channel formed by the gravel filling tool 4 to form a gravel filling layer 7.
  • the annulus of the wellbore is an annulus formed by the outer wall of the production tubing and the filling tubular string and the inner wall of the generating casing; observe the change of the injection pressure during the gravel injection process, as shown in the progress of the gravel throughput cycle shown in FIG.
  • the grit injection pressure is gradually increased from P 0 to P 1 , the grit injection is stopped, that is, when the pressure is obviously increased, it is transferred to the next production stage, the P 0 is the grit injection start pressure, and P 1 is the maximum grit injection.
  • the maximum injection pressure P 1 on gravel determined according formation fracture pressure gradient in order to ensure the production throughput does not produce the formation pressure mud cracks or wear surface of the seabed, P 1 need to ensure the formation fracture pressure less than or equal Overlying soil surface or subsea pressure through pressure.
  • Step (3) During the conversion to step (4), the one-way control valve 5 on the lower side of the gravel filling tool 4 is opened, the gravel filling switching valve 12 is closed, the control valve 11 at the lower end of the production tubing 2 is opened, and the startup is located in the production tubing.
  • the lifting system extracts the formation fluid, starts the depressurization production, controls the bottom hole flow pressure, performs the natural gas hydrate depressurization method or the fluid extraction method under the condition of lower production pressure difference, and slowly increases the production pressure difference according to the actual situation; (4)
  • the gas-liquid-solid three-phase produced from the hydrate reservoir 8 in the process flows into the wellbore, and after separation by the gas separator 10, the liquid-solid two-phase flows through the production tubing 2 to the wellhead, and the gas passes through the wellbore annulus.
  • Step (4) During the implementation process, observe the working condition of the artificial lift system at the bottom of the well and the sand production at the wellhead, and monitor the sand concentration parameter of the wellhead and the flow pressure of the bottom hole in real time, when the wellhead or the bottom of the well appears. If the sand is abnormal, if there is a sudden increase in the concentration of sand or a sudden increase in the pressure difference at the bottom of the well, immediately stop the further production of the pressure drop, and then transfer to step (3), through the reciprocating cycle, the gravel is continuously filled. Replacing the formation loss, maintaining long-term production of marine silt gas hydrate.
  • the position of the gravel packing tool 4 at the bottom of the well is at the top boundary of the hydrate reservoir section 8, and The wellbore is depressurized without the gravel packing tool; in the process of step (4), the process of continuously injecting water or a liquid containing a hydrate inhibitor into the inside of the production tubing by the filling column is ensured.
  • the fine sand produced in the formation can be carried to the wellhead at the same time to prevent the secondary formation of the hydrate.
  • the filling column 3 is filled with the sand mortar separately to the outer layer of the pipe when the gravel is injected, and the water can be supplied to the production pipe 2 at the production stage. Used for carrying sand in the wellbore.
  • step (4) hydrate depressurization production process to step (3) the time node of grit injection is judged according to the abnormality of sand production in the wellbore, or the sudden change of the pressure difference of the bottom hole production without artificial pressure regulation; (3) Medium gravel injection step (4)
  • the time node of hydrate depressurization production is that the gravel injection pressure is rapidly rising and cannot be injected continuously, and the judgment basis of the wellbore sanding abnormality includes the bottom hole pressure fluctuation under steady production conditions, the lift pump
  • the phenomenon of sanding temperature rise and sand concentration increase at the wellhead is judged, and the specific production process is determined according to the choice of the actual lifting system.
  • the grain size of the grit used in the filling in the step (3) is larger than the level 1 to 2 in the Saulier method under the same formation condition; the sand shielding precision of the mechanical screen in the step (1) is greater than the same
  • the accuracy of the mechanical sieve tube used in the conventional oil and gas wells under the formation conditions is 2 to 3 grades, which helps to discharge the mud or fine particles in the near-well formation in time during the hydrate decomposition process, preventing the wellbore blockage and effectively
  • the pressure transmission efficiency of the hydrate wellbore and the decomposition efficiency of the hydrate are improved, and the particle size of the sand used in the gravel injection process is consistent with the grain size of the sand used in the completion of the open hole filling.
  • the gravel When the gravel is gravel, there is a smooth mortar flow channel to ensure that the mortar is intermittently squeezed into the outer layer of the pipe; the gravel packing tool is placed at the top of the hydrate reservoir, because the gravel layer injected in the early stage will occur during the hydrate production process. Creeping and sinking, the formation deficit space is mainly in the upper part of the hydrate reservoir, so this design helps to intermittently carry out gravel injection in the later stage to ensure the smooth progress of the gravel throughput process;
  • the filling column is also used as a wellbore replenishing pipe column in the post-sludge tunneling column and hydrate depressurization/fluid extraction and mining process.
  • the three-way design realizes the switching of the wellbore hydration and mortar injection, simplifying the design of the wellbore string.
  • part of the shale and fine components that are produced into the wellbore during the hydrate depressurization/fluid extraction process can be smoothly carried to the wellhead with the help of the water supply line to prevent the wellbore from blocking.
  • the pipeline can also be injected into the pipeline as a hydrate inhibitor to ensure the safe flow of the wellbore and ensure the continuous advancement of the gravel throughput process.
  • Embodiment 2 discloses a silty marine natural gas hydrate gravel throughput mining device, referring to FIG. 1 and FIG. 2, including a production casing 1, a production oil pipe 2 and a filling pipe column disposed in the production casing 1. 3.
  • the production tubing 2 is further provided with a lifting pipe column (not shown), and the lifting pipe column is connected with the lifting pump to form a gap between the oil pipe 2 and the outer wall of the filling pipe string 3 and the inner wall of the production casing 1.
  • a wellbore annulus 13; a mechanical screen 6 is connected to the lower end of the production casing 1, and a gravel packing tool 4 is further disposed between the production casing 1 and the mechanical screen 6, and the production casing 1 is inserted into the hydrate.
  • the gravel packing tool 4 can be left unrecognizable
  • the wellbore is subjected to pressure reduction production, and a gas separator 10 and a control valve are further disposed at the lower end of the production oil pipe.
  • the outlet end of the filling column 3 is respectively connected with the gravel filling tool 4 and the production tubing 2.
  • the communication between the gravel filling tool 4 and the production tubing 2 is provided with a one-way control valve 5, and the gravel filling tool 4 is also provided with gravel packing.
  • the switching valve 12 is connected, and the filling pipe string 3 is connected to the production oil pipe 2 under the gravel filling tool 4.
  • the filling pipe string 3 is separately filled with the sand mortar in the outer layer of the production casing 2 when the gravel (gravel) is injected, and is produced in the production. In the stage, water can be supplied to the production tubing for sand carrying in the wellbore.
  • the fine particles and muddy of the formation are allowed to be produced into the wellbore during the hydrate mining process, and the effective wellbore is filled with water to the wellhead by filling the pipe string; the gravel is filled with large particles to fill the fine particles and mud of the formation.
  • the deficit caused by the quality output the effect of improving the productivity of silty reservoirs, preventing large-scale deficits in the stratum, and extending the effective period of sand control for wellbore, providing new ideas for the exploitation of silty hydrates in China's sea areas and promoting The development of hydrate commercial mining technology.

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Abstract

公开了一种粉砂质海洋天然气水合物砾石吞吐开采方法及开采装置，开采方法通过砂砾注入与降压生产的交替进行，填补置换地层亏空，并配合适度出砂，维持长效生产，实现粗粒径砂砾与地层泥质、砂质细颗粒和水合物分解空间的间歇性吞吐置换，促进粉砂质天然气水合物储层的高效降压开采，并降低海洋天然气水合物长期开采过程中的地层失稳坍塌风险。

Description

粉砂质海洋天然气水合物砾石吞吐开采方法及开采装置 技术领域
本发明属于海洋天然气水合物高效开采领域，具体涉及一种粉砂质海洋天然气水合物砾石吞吐开采装置及开采方法。
背景技术
天然气水合物广泛分布于高纬度陆地永久冻土带与大陆边缘海沉积物中，是一种重要的潜在能源，如何安全高效地对其进行开采利用已经成为当前国际上的研究热点。近年来，世界各国的研究重点已经由原来的水合物基础研究、水合物资源勘查逐步转入天然气水合物试采阶段。尤其是常规油气资源较为紧缺的国家，如日本，已经展开了大量的海域天然气水合物试开采研究并制定了中长期水合物开采产业化目标。从开采方法的角度，目前天然气水合物开采方法从机理上主要分为降压开采法、注热开采法、CO 2置换开采法和注化学剂开采法等，从2002年Mallik5L-38水合物试采到2017年中国南海水合物试采，上述开采方法均已进行了部分或全部现场试验验证。
历次试采实践均表明，降压开采法是最具有应用前景的天然气水合物开采方法。然而，无论是我国首次海域天然气水合物试采，还是国外历次水合物试采，均处于科学实验阶段，离产业化开采还有很多关键技术需要解决。降压法在开采海域天然气水合物过程中仍然面临着地层失稳、大面积出砂导致的长期开采提产难度大等关键问题。尤其是对我国海域大面积分布的粉砂质水合物储层而言，在常规降压法基础上改良的流体抽取法取得了短期试采的(60天)成功。但是由于该类储层沉积物粒径小、粘土含量高，属于极弱固结的低渗或超低渗储层，开采过程中如果按照常规油气储层防砂的思路进行严防死堵，则必然会对生产井产能产生严重影响；反之，稍微放大井筒挡砂精度，则近井地层的细颗粒或泥质颗粒会很容易流入井筒，久而久之，必然会导致近井地层的亏空。由于地层细组分产出造成的亏空与由于水合物分解造成的亏空叠加，将会使储层面临严重的稳定性问题，因此，从降压法开采粉砂质储层水合物的需求而言，需要对降压法进行进一步的改进和优化——降压开采中需要向储层中注 入其他物质，从而解决上述问题。
CO 2置换开采法为维持天然气水合物储层稳定性提供了思路，但是由于该方法在置换过程中会形成CO 2水合物，降低近井地层渗透率，导致后期持续开采困难。该方法在大粒径砂质储层(美国IgnikSikumi-2012试采)中尚且面临严重的开采效率问题，对粉砂质储层而言，其应用效果可想而知。因此，虽然CO 2置换法能为水合物长期开采提供一定的借鉴思路，但是以水合物置换水合物的做法，在粉砂质水合物长期开采过程中显然是不可用的。如果能找到一种用其他高渗透物质置换水合物(同时置换近井泥质或细粉砂)，则会对水合物的长期开采产生革命性的影响。
如果将上述CO 2换成热蒸汽注入，则CO 2置换法即为通常意义上的注热法开采。该方法虽然有助于维持地层压力，从一定程度上减缓地层失稳，但是也无法从根本上解决地层失稳问题，而且已经被Mallik2L-38水合物试采证明其对海洋天然气水合物的开采适用性非常有限。常规稠油油藏开发过程中常用蒸汽吞吐来实现单井提产，目前已经有了非常成熟的应用，但对海洋天然气水合物储层而言，蒸汽吞吐的效率问题和对储层稳定性的改善程度却不容乐观。因此，从实际需求上讲，水合物开采需要“吞吐”，但“吞吐”的物质一定不是蒸汽，而是一种即能促进水合物分解，又能填充地层亏空的物质。
2013年日本首次海洋天然气水合物试采工程采用裸眼管外砾石充填防砂工艺，取得了6天12万方天然气的效果，极大地鼓舞了全球海洋天然气水合物研究的信心。管外充填砾石层在生产初期起到了非常好的提高产能和防砂双重作用，但随着试采终止，“裸眼管外砾石充填”防砂完井工艺则被扣上了不适合海洋天然气水合物开采井的“冤枉帽子”：因为水合物分解过程中，管外地层空间逐渐变大，砾石充填层发生蠕动和亏空，导致产出流体直接冲击筛网，很快产生冲蚀破坏，导致防砂有效期急剧下降(6d)，水合物试开采被迫终止。
综上所述，目前的天然气水合物开采方法与现场实际需求之间还存在如下关键问题需要解决：
1.降压法无法解决水合物长期开采条件下的地层亏空问题，常规防砂作业 面临着因为地层亏空造成的防砂失效的挑战；
2.长期稳定的水合物生产迫切需要对地层亏空量进行及时的填充或置换，但是CO 2置换法只能解决水合物产出造成的亏空却无法解决由于地层泥砂产出造成的亏空，而且还会对天然气水合物的进一步生产产生影响；
3.蒸汽吞吐法在常规稠油储层的开采中已经有了非常广阔的应用，但是蒸汽吞吐法吞吐的“蒸汽”只能促进水合物分解，无法填补地层亏空；
4.一次性裸眼砾石充填防砂完井作业虽然能在短期内起到良好的作用，但由于没有后续物源补给，造成防砂有效期短，不足以满足海洋天然气水合物长期开采的需求。
因此，亟待提出一种新型的、能够防止地层大面积亏空的开发方法，配合目前常用的降压法，从根本上解决目前海域天然气水合物试采过程中遇到的地层严重出砂、地层失稳等工程地质灾害，对于延长天然气水合物的开采生命周期至关重要，也有助于有效推进我国的海域天然气水合物产业化进程。
发明内容
本发明所要解决的技术问题在于针对我国大面积分布的粘土质粉砂海洋天然气水合物降压或流体抽取法开采过程中，所面临的提高产能、防砂措施和地层失稳之间的矛盾，基于出砂管理理念，提出一种粉砂质海洋天然气水合物砾石吞吐开采装置及开采方法。
本发明是采用以下的技术方案实现的：粉砂质海洋天然气水合物砾石吞吐开采方法，包括以下步骤：
(1)钻井至目标层位，对水合物储层进行裸眼筛管完井；
(2)安装并下入井筒管柱组合；
(3)进行筛管外砾石循环充填，观察充填压力变化，并及停止充填；
(4)不起出原有管柱组合，调整阀门流程，开井生产，并实时观察地层出砂情况及井底生产压差变化；
步骤(3)和步骤(4)根据时间节点及时切换、交替进行，使注入的砾石不断填充置换地层亏空，维持海洋粉砂质天然气水合物的长效生产。
进一步的，所述步骤(1)通过以下方式实现：打开水合物储层，利用生产套管封固水合物储层上覆地层，下入机械筛管，对水合物储层进行裸眼下独立筛管完井，打人工井底；机械筛管与其上部生产套管之间预留砾石充填工具安装接口。
进一步的，所述步骤(2)中，管柱组合的安装方式为：下入砾石充填工具、生产油管和充填管柱，生产油管和充填管柱位于生产套管内，且充填管柱分别与生产油管和砾石充填工具连通，砾石充填工具位于水合物储层的顶界，且在生产油管的入口端安装有控制阀及气体分离器，砾石充填工具与生产油管的连通处还设置有单向控制阀，砾石充填工具上还设置有充填转换阀。
进一步的，步骤(3)砾石充填过程中，关闭砾石充填工具下侧的单向控制阀，打开砂砾充填转换阀，关闭生产油管下端的控制阀，通过充填管柱和砾石充填工具形成的通道向机械筛管外部注入砂砾，形成砂砾充填层，砂砾注入过程中携砂液透过机械筛管，由井筒环空上返至平台井口，井筒环空为生产油管和充填管柱的外壁与生成套管的内壁形成的环空；观察砂砾注入过程中的砂浆注入泵出口压力变化，当砂砾注入压力由P 0逐渐增大到P 1，停止砂砾注入，转入下一个生产阶段，所述P 0为砂砾注入启动压力，P 1为砂砾注入最大压力。
进一步的，步骤(3)向步骤(4)转换的过程中：打开砾石充填工具下侧的单向控制阀，关闭砂砾充填转换阀，打开生产油管下端的控制阀，启动举升泵抽取地层流体，开始降压生产；
步骤(4)过程中从水合物储层产出的气液固三相，流入井筒后，经过气体分离器的分离，液固两相通过生产油管流至井口，气体则通过井筒环空产出；
步骤(4)实施过程中，实时监测井口含砂浓度参数、井底流动压力变化情况，若出现含砂浓度突然增大或者井底流动压差的突然增大，则停止进一步降压生产，转入步骤(3)。
进一步的，步骤(4)过程中，还包括由充填管柱不断向生产油管内部注入水或含有水合物抑制剂的液体的过程，保证地层产出细砂能全部携带至井口的同时防止水合物二次生成。
进一步的，由步骤(4)水合物降压生产过程转步骤(3)砂砾注入的时间节点根据井筒出砂异常进行判断，或者在没有人为调压情况下井底生产压差的突变进行判断；由步骤(3)砂砾注入转步骤(4)水合物降压生产的时间节点是砂砾注入压力迅速抬升，无法继续注入；其中，井筒出砂异常的判断依据包括平稳生产条件下井底压力波动、举升泵砂磨升温和井口监测砂浓度增大现象出现。
进一步的，所述步骤(3)中充填所用的砂砾粒径大于在同样开采环境下采用Saucier法设计结果的1级-2级。
进一步的，所述步骤(3)中充填所用的砂砾粒径大于在相同地层条件下采用Saucier法设计结果的1级-2级；步骤(1)中机械筛管的挡砂精度大于在相同地层条件下所采用的常规油气井裸眼砾石充填所用机械筛管精度的2级-3级。
本发明另外还提出一种粉砂质海洋天然气水合物砾石吞吐开采装置，包括生产套管，设置在生产套管内的生产油管和充填管柱，生产油管内还设置有举升管柱，举升管柱与举升泵相连，生产油管和充填管柱的外壁与生产套管的内壁之间形成的空隙为井筒环空；
所述生产套管下端连接有机械筛管，且在生产套管和机械筛管之间还设置有砾石充填工具，生产套管下入至水合物储层的上方位置处，且砾石充填工具位于水合物储层的顶界，而机械筛管位于其下方水合物储层段，砾石充填工具可以在不起出的情况下对井筒进行降压生产，另外在生产油管的下端还设置有气体分离器及控制阀；
所述充填管柱的出口端分别与砾石充填工具及生产油管连通，砾石充填工具与生产油管的连通处设置有单向控制阀，砾石充填工具上还设置有充填转换阀，且充填管柱在砾石充填工具的下方与生产油管连通，充填管柱在注入砾石时单独向生产套管管外地层充填混砂砂浆，而在生产阶段可以向生产油管补水，用于井筒携砂。
与现有技术相比，本发明的优点和积极效果在于：
(1)本发明方案通过固相(大直径砂砾)吞吐来置换固相(泥质、砂质细 颗粒及水合物)，并采用适当放宽机械筛管挡砂精度、选择合适的填充砾石等操作，帮助水合物分解过程中及时排出近井地层的泥质或细颗粒，防止井筒堵塞，有效克服海洋粉砂质水合物储层泥质含量高、渗透率低、胶结疏通不适合压裂改造等不足，并有效提高井筒及近井地层的压力传递效率，为水合物降压/流体抽取生产井提产保驾护航；
(2)采用间歇性停止降压/流体抽取生产并向管外地层中挤注砂砾，及时补充地层亏空量，有效延长防砂有效期和降压开采周期，有效解决了因为长期的水合物开采导致的地层亏空和地层失稳问题、延长降压/流体抽取开采周期，并为水合物的产业化开采提供依据；
(3)本方案适合于高泥质、粉砂质等不适合进行完全防砂和储层改造的海洋天然气水合物储层，适合于孔隙充填型储层或具有薄块状水合物夹层的天然气水合物储层，解决了海洋天然气水合物CO 2置换开采的低效率、注热开采维持储层稳定难的问题和先期管外砾石充填防砂作业有效期短的问题，解决了我国海域天然气水合物开采产能提高难和储层失稳风险大的难题，促进水合物商业化开采技术的发展。
附图说明
图1为本发明实施例中砾石吞吐开采装置砂砾注入示意图；
图2为本发明实施例中砾石吞吐开采装置地层产出物流出示意图；
图3为本发明实施例中砾石吞吐开采周期进度示意图；
其中，1—生产套管；2—生产油管；3—充填管柱；4—砾石充填工具；5—单向控制阀；6—机械筛管；7—砂砾充填层；8—水合物储层；9—水合物储层上覆地层；10—气体分离器；11—控制阀；12—砂砾充填转换阀；13-井筒环空；P 0—砂砾注入启动压力；P 1—砂砾注入最大压力。
具体实施方式
为了能够更加清楚地理解本发明的上述目的、特征和优点，下面结合附图及实施例对本发明做进一步说明。需要说明的是，在不冲突的情况下，本申请的实施例及实施例中的特征可以相互组合。
本发明提出一种粉砂质海洋天然气水合物砾石吞吐开采新思路，通过向开采地层中注入一定粒径的砂砾，实现地层对砂砾的“吞”，不断填补由于水合物分解和地层泥质产出造成的地层亏空空间；应用海洋天然气水合物出砂管理技术，适当放宽机械筛管的缝宽尺寸及吞入砂砾的粒径，使近井地层的泥质及细颗粒按照一定的比例排出地层，实现地层细组分的“吐”，通过上述物质交换，实现地层细组分与粗粒径砂砾的吞吐置换，有效填补地层亏空防止地层失稳的同时提高近井渗透率，促进水合物的有效分解，为我国海域粉砂质水合物开采提供新思路，具体的通过以下方案实现：
实施例1，粉砂质海洋天然气水合物砾石吞吐开采方法，参考图1和图2所述结构原理，包括以下步骤：
(1)钻井至目标层位，对水合物储层进行裸眼筛管完井；
(2)安装并下入井筒管柱组合；
(3)进行筛管外砾石循环充填，观察充填压力变化，并及停止充填；
(4)不起出原有管柱组合，调整阀门流程，开井生产，并实时观察地层出砂情况及井底生产压差变化；
步骤(3)和步骤(4)根据时间节点及时切换、交替进行，使注入的砾石不断填充置换地层亏空，维持海洋粉砂质天然气水合物的长效生产。
具体的，步骤(1)中，按照常规海洋浅部地层钻井作业措施，打开水合物储层8，利用生产套管1封固水合物储层上覆地层9，下入机械筛管6，对水合物储层8进行裸眼下独立筛管完井，打人工井底；机械筛管6与其上部生产套管1之间预留砾石充填工具4安装接口。步骤(2)中，管柱组合的安装方式为下入砾石充填工具4、生产油管2和充填管柱3，生产油管2和充填管柱3位于生产套管1内，且充填管柱3分别与生产油管2和砾石充填工具4连通，砾石充填工具4位于水合物储层8的顶界，且在生产油管2的入口端安装有控制阀11及气体分离器10，砾石充填工具4与生产油管2的连通处还设置有单向控制阀5，砾石充填工具4上还设置有砂砾充填转换阀12。
步骤(3)砾石充填过程中，关闭砾石充填工具4下侧的单向控制阀5，打 开砂砾充填转换阀12，关闭生产油管2下端的控制阀11，利用留在井底的砾石充填工具4，通过充填管柱3和砾石充填工具4形成的通道向机械筛管6外部注入砂砾，形成砂砾充填层7，砂砾注入过程中携砂液透过机械筛管6，由井筒环空13上返至平台井口，井筒环空为生产油管和充填管柱的外壁与生成套管的内壁形成的环空；观察砂砾注入过程中的注入压力变化，如图3所示的砂砾吞吐开采周期进度示意图，当砂砾注入压力由P 0逐渐增大到P 1，停止砂砾注入，即观察到压力明显增大时，转入下一个生产阶段，所述P 0为砂砾注入启动压力，P 1为砂砾注入最大压力，砂砾注入最大压力P 1根据地层破裂压力梯度确定，为保证吞吐生产中不产生地层裂隙或压穿海底泥面，需保证P 1小于等于地层破裂压力或上覆海底泥面压穿压力。
步骤(3)向步骤(4)转换的过程中，打开砾石充填工具4下侧的单向控制阀5，关闭砂砾充填转换阀12，打开生产油管2下端的控制阀11，启动位于生产油管内的举升系统抽取地层流体，开始降压生产，控制井底流压，在较低生产压差条件下进行天然气水合物降压法或流体抽取法开采，并根据实际情况缓慢提高生产压差；步骤(4)过程中从水合物储层8产出的气液固三相，流入井筒后，经过气体分离器10的分离，液固两相通过生产油管2流至井口，气体则通过井筒环空13产出；步骤(4)实施过程中，观察井底人工举升系统的工作状况和井口产砂情况，实时监测井口含砂浓度参数、井底流动压力变化情况，当井口或井底出现出砂异常，如果出现含砂浓度突然增大或者井底流动压差的突然增大，则马上停止进一步降压生产，转入步骤(3)，通过往复循环，使注入砂砾不断填充置换地层亏空，维持海洋粉砂质天然气水合物的长效生产。
为了实现提高粉砂质储层产能、防止地层大面积亏空、延长井筒防砂有效期的三重目标，本实施例中，砾石充填工具4在井底的位置在水合物储层段8的顶界，且在不起出砾石充填工具的情况下对井筒进行降压生产；在步骤(4)过程中，还包括由充填管柱不断向生产油管内部注入水或含有水合物抑制剂的液体的过程，保证地层产出细砂能全部携带至井口的同时防止水合物二次生成，实际情况下，充填管柱3在注入砂砾时单独向管外地层充填混砂砂浆，在生产 阶段可以向生产油管2补水，用于井筒携砂。
另外，由步骤(4)水合物降压生产过程转步骤(3)砂砾注入的时间节点根据井筒出砂异常进行判断，或者在没有人为调压情况下井底生产压差的突变进行判断；由步骤(3)中砂砾注入转步骤(4)水合物降压生产的时间节点是砂砾注入压力迅速抬升，无法继续注入，而井筒出砂异常的判断依据包括平稳生产条件下井底压力波动、举升泵砂磨升温、井口监测砂浓度增大等现象进行判断，具体生产过程中根据实际举升系统的选择而决定。
更重要的是，所述步骤(3)中充填所用的砂砾粒径大于在相同地层条件下采用Saucier法设计结果的1级-2级；步骤(1)中机械筛管的挡砂精度大于相同地层条件下所采用的常规油气井裸眼砾石充填所用机械筛管精度的2级-3级，有助于在水合物分解过程中及时排出近井地层的泥质或细颗粒，防止井筒堵塞，有效提高水合物井筒的压力传递效率和水合物的分解效率，且在砂砾注入过程中使用的砂粒粒径，与完井阶段裸眼充填所使用的砂粒粒径一致。
由于水合物长期开采过程中，随着地层水合物的不断分解和部分泥质、细颗粒的产出，地层总会发生一定程度的亏空，前期充填的砂砾会发生一定的蠕动，采用间歇性停止降压/流体抽取生产并向管外地层中挤注砂砾，将有效填充这部分亏空，防止地层的大面积亏空；如果不及时补充地层的亏空，前期充填砂砾将发生蠕动下沉，导致井底防砂筛管直接面对地层产出流体的正面冲蚀，会降低防砂作业有效期，基于本方案及时补充地层亏空量，则将有效延长防砂有效期。
经过多轮次的水合物降压/流体抽取开采-砂砾挤注过程，实现近井泥质和细粉砂与大粒径砂砾的物质交换，使近井附加压降明显减小，与砂砾粒径设计及机械筛管的挡砂精度设计产生协同效应，共同促进水合物的进一步分解，提高粉砂质水合物储层产能；而且，选择裸眼充填防砂完井作业，方便后期向井筒管外注入砂砾时，能有顺利的砂浆流动通道，保证砂浆间歇性顺利挤注到管外地层；砾石充填工具设置在水合物储层顶界，因为在水合物生产过程中，前期注入的砾石层将发生蠕动、下沉，地层亏空空间主要在水合物储层上部，因 此这种设计有助于在后期间歇性进行砂砾注入，保证砂砾吞吐开采进程的顺利进行；
充填管柱同时作为后期砂砾吞吐管柱和水合物降压/流体抽取开采过程中的井筒补水管柱，通过三通设计实现井筒补水与砂浆注入的切换，简化井筒管柱设计。同时，水合物降压/流体抽取过程中产出到井筒的部分泥质和细组分能够通过补水管线补水的帮助下，顺利携带至井口，防止井筒砂堵。同时该管线还可以作为水合物抑制剂注入管线，保证井筒流动安全，同时保证砂砾吞吐过程的持续推进。
实施例2，本实施例公开一种粉砂质海洋天然气水合物砾石吞吐开采装置，参考图1和图2，包括生产套管1，设置在生产套管1内的生产油管2和充填管柱3，生产油管2内还设置有举升管柱(未示意)，举升管柱与举升泵相连，生产油管2和充填管柱3的外壁与生产套管1的内壁之间形成的空隙为井筒环空13；所述生产套管1下端连接有机械筛管6，且在生产套管1和机械筛管6之间还设置有砾石充填工具4，生产套管1下入至水合物储层8的上方位置处，且砾石充填工具4位于水合物储层8的顶界，而机械筛管6位于其下方水合物储层段，砾石充填工具4可以在不起出的情况下对井筒进行降压生产，另外在生产油管的下端还设置有气体分离器10及控制阀11.
所述充填管柱3的出口端分别与砾石充填工具4及生产油管2连通，砾石充填工具4与生产油管2的连通处设置有单向控制阀5，砾石充填工具4上还设置有砂砾充填转换阀12，且充填管柱3在砾石充填工具4的下方与生产油管2连通，充填管柱3在注入砾石(砂砾)时单独向生产套管2管外地层充填混砂砂浆，而在生产阶段可以向生产油管补水，用于井筒携砂。
通过上述开采装置的设计，在水合物开采过程中允许地层细颗粒和泥质产出到井筒，并通过充填管柱有效的井筒补水携带至井口；用大颗粒的砂砾填补由于地层细颗粒和泥质产出造成的亏空，实现提高粉砂质储层产能、防止地层大面积亏空、延长井筒防砂有效期的“一箭三雕”效果，为我国海域粉砂质水合物开采提供新思路，并促进了水合物商业化开采技术的发展。
以上所述，仅是本发明的较佳实施例而已，并非是对本发明作其它形式的限制，任何熟悉本专业的技术人员可能利用上述揭示的技术内容加以变更或改型为等同变化的等效实施例应用于其它领域，但是凡是未脱离本发明技术方案内容，依据本发明的技术实质对以上实施例所作的任何简单修改、等同变化与改型，仍属于本发明技术方案的保护范围。

Claims (9)

  1. 粉砂质海洋天然气水合物砾石吞吐开采方法，其特征在于，包括以下步骤：
    (1)钻井至目标层位，对水合物储层进行裸眼筛管完井；
    (2)安装并下入井筒管柱组合；
    (3)进行筛管外砾石循环充填，观察充填压力变化，并及停止充填；
    (4)不起出原有管柱组合，调整阀门流程，开井生产，并实时观察地层出砂情况及井底生产压差变化；
    步骤(3)和步骤(4)根据时间节点及时切换、交替进行，使注入的砾石不断填充置换地层亏空，维持海洋粉砂质天然气水合物的长效生产。
  2. 根据权利要求1所述的开采方法，其特征在于：所述步骤(1)通过以下方式实现：打开水合物储层，利用生产套管封固水合物储层上覆地层，下入机械筛管，对水合物储层进行裸眼下独立筛管完井，打人工井底；机械筛管与其上部生产套管之间预留砾石充填工具安装接口。
  3. 根据权利要求1所述的开采方法，其特征在于：所述步骤(2)中，管柱组合的安装方式为：下入砾石充填工具、生产油管和充填管柱，生产油管和充填管柱位于生产套管内，且充填管柱分别与生产油管和砾石充填工具连通，砾石充填工具位于水合物储层的顶界，且在生产油管的入口端安装有控制阀及气体分离器，砾石充填工具与生产油管的连通处还设置有单向控制阀，砾石充填工具上还设置有充填转换阀。
  4. 根据权利要求1所述的开采方法，其特征在于：步骤(3)砾石充填过程中，关闭砾石充填工具下侧的单向控制阀，打开砂砾充填转换阀，关闭生产油管下端的控制阀，通过充填管柱和砾石充填工具形成的通道向机械筛管外部注入砂砾，形成砂砾充填层，砂砾注入过程中携砂液透过机械筛管，由井筒环空上返至平台井口，井筒环空为生产油管和充填管柱的外壁与生成套管的内壁形成的环空；观察砂砾注入过程中的砂浆注入泵出口压力变化，当砂砾注入压力由P 0逐渐增大到P 1，停止砂砾注入，转入下一个生产阶段，所述P 0为砂砾注入启动压力，P 1为砂砾注入最大压力。
  5. 根据权利要求1所述的开采方法，其特征在于：
    步骤(3)向步骤(4)转换的过程中：打开砾石充填工具下侧的单向控制阀，关闭砂砾充填转换阀，打开生产油管下端的控制阀，启动举升泵抽取地层流体，开始降压生产；
    步骤(4)过程中从水合物储层产出的气液固三相，流入井筒后，经过气体分离器的分离，液固两相通过生产油管流至井口，气体则通过井筒环空产出；
    步骤(4)实施过程中，实时监测井口含砂浓度参数、井底流动压力变化情况，若出现含砂浓度突然增大或者井底流动压差的突然增大，则停止进一步降压生产，转入步骤(3)。
  6. 根据权利要求5所述的开采方法，其特征在于：步骤(4)过程中，还包括由充填管柱不断向生产油管内部注入水或含有水合物抑制剂的液体的过程。
  7. 根据权利要求1所述的开采方法，其特征在于：由步骤(4)水合物降压生产过程转步骤(3)砂砾注入的时间节点根据井筒出砂异常进行判断；由步骤(3)砂砾注入转步骤(4)水合物降压生产的时间节点是砂砾注入压力迅速抬升，无法继续注入；其中，井筒出砂异常的判断依据包括平稳生产条件下井底压力波动、举升泵砂磨升温和井口监测砂浓度增大现象出现。
  8. 根据权利要求2所述的开采方法，其特征在于：所述步骤(3)中充填所用的砂砾粒径大于在相同地层条件下采用Saucier法设计结果的1级-2级；步骤(1)中机械筛管的挡砂精度大于在相同地层条件下所采用的常规油气井裸眼砾石充填所用机械筛管精度的2级-3级。
  9. 粉砂质海洋天然气水合物砾石吞吐开采装置，其特征在于，包括生产套管，设置在生产套管内的生产油管和充填管柱，生产油管内还设置有举升管柱，举升管柱与举升泵相连，生产油管和充填管柱的外壁与生产套管的内壁之间形成的空隙为井筒环空；
    所述生产套管下端连接有机械筛管，且在生产套管和机械筛管之间还设置有砾石充填工具，生产套管下入至水合物储层的上方位置处，且砾石充填工具位于水合物储层的顶界，而机械筛管位于其下方水合物储层段，另外在生产油管的下端还设置有气体分离器及控制阀；
    所述充填管柱的出口端分别与砾石充填工具及生产油管连通，砾石充填工具与生产油管的连通处设置有单向控制阀，砾石充填工具上还设置有充填转换阀，且充填管柱在砾石充填工具的下方与生产油管连通。
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