WO2019114226A1 - 一种水流侵蚀法海洋天然气水合物开采方法 - Google Patents

一种水流侵蚀法海洋天然气水合物开采方法 Download PDF

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Publication number
WO2019114226A1
WO2019114226A1 PCT/CN2018/091092 CN2018091092W WO2019114226A1 WO 2019114226 A1 WO2019114226 A1 WO 2019114226A1 CN 2018091092 W CN2018091092 W CN 2018091092W WO 2019114226 A1 WO2019114226 A1 WO 2019114226A1
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natural gas
gas hydrate
hydrate
pressure
reservoir
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PCT/CN2018/091092
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English (en)
French (fr)
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宋永臣
陈兵兵
杨明军
王朋飞
孙慧茹
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大连理工大学
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Priority to US16/344,331 priority Critical patent/US20200063542A1/en
Publication of WO2019114226A1 publication Critical patent/WO2019114226A1/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
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
    • E21B43/20—Displacing by water
    • 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
    • E21B43/01—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 technical field of marine natural gas hydrate exploitation, and particularly relates to a method for extracting marine natural gas hydrate by water flow erosion method.
  • the natural gas hydrate mining technology mainly includes a pressure reduction mining method, a heat shock mining method, a chemical reagent injection mining method, a carbon dioxide displacement mining method, and a combination of various methods.
  • the depressurization method has special requirements for the nature of natural gas hydrate reservoirs. Only when the natural gas hydrate is located near the temperature-pressure equilibrium boundary, the depressurization mining method is economically feasible. Sex. The lack of mining power in the later stage of hydrate mining is also a defect, and the sudden drop in reservoir pressure during depressurization will destroy the reservoir and stabilize the marine environment.
  • the heat shock mining method has not yet solved the problem of low heat utilization efficiency, and only local heating can be performed, so the method needs to be further improved.
  • the chemical reagents required for chemical reagent injection are expensive, have a slow effect on the gas hydrate layer, and cause some environmental problems. Therefore, there are relatively few studies on this method.
  • the efficiency of carbon dioxide displacement mining is low, and it is impossible to achieve complete and efficient mining of natural gas hydrates. The mining takes a long time and there is a risk of leakage.
  • the present invention proposes a new hydrate mining method for the defects of current hydrate production methods. Meanwhile, in order to further improve the hydrate production efficiency and the stability of the reservoir structure, the present invention simultaneously proposes various combinations of the water flow erosion method, the pressure reduction mining method, and the heat injection mining method.
  • the invention aims at the shortcomings of the current natural gas hydrate mining technology, based on the influence of water flow on the stability of the hydrate, and utilizes the chemical potential between the hydrate phase and the environmental water phase caused by the water flow process over the hydrate phase equilibrium.
  • the decomposition of hydrate caused by the difference and the promotion of water flow to the heat and mass transfer in the reservoir provide a water flow erosion method for marine gas hydrate mining.
  • the method further controls the flow of marine water in the reservoir by controlling the pressure gradient of the production well and its surrounding reservoirs, and utilizes the water phase and the water molecules in the hydrate phase based on the high permeability around the production well.
  • the chemical potential difference drives the decomposition of the hydrate.
  • the reservoir salinity is increased, the phase equilibrium temperature of the system is increased, the heat and mass transfer inside the reservoir is accelerated, the hydrate is gradually stabilized and efficiently decomposed, and the hydrate mining is completely completed, and the displacement of the water flow process is utilized.
  • the stable and efficient mining process ensures the stability of the reservoir and eliminates the major natural disasters caused by the destruction of the reservoir structure caused by the large pressure drop and geological damage.
  • the method is easy to implement and is advantageous for large-scale commercial exploitation of hydrates.
  • the present invention simultaneously proposes various combinations of the water flow erosion method, the pressure reduction mining method, and the heat injection mining method.
  • a method for mining marine gas hydrate by water flow erosion method comprising the following steps:
  • Each group of natural gas hydrate production channels includes three production channels, which are two pressure-control channels and one pressure-control and gas-out channel; A plurality of water storage channels are drilled between adjacent mining channels in the layer, so that the pressure control channels and the pressure control and outlet channels are connected in the natural gas hydrate reservoir for accessing an appropriate amount of seawater;
  • the middle mining channel is selected as the pressure control and outlet channel in each gas hydrate production channel, and the gas hydrate reservoir pressure is controlled by the pressure control and outlet channels and the natural gas hydrate production channel in the natural gas hydrate reservoir
  • the pressure difference promotes the flow of seawater.
  • the flow of water drives the decomposition of hydrates by changing the chemical potential difference between the hydrate phase and the water phase inside the reservoir.
  • the seawater flow process inside the gas hydrate reservoir increases natural gas hydration.
  • the salinity of the reservoir increases the phase equilibrium temperature of the system and accelerates the heat and mass transfer inside the natural gas hydrate reservoir, further promoting the decomposition of the hydrate;
  • the gas hydrate reservoir partial hydrate is decomposed by the pressure reduction method or the injection method in the early stage of natural gas hydrate production; the mining method of the invention is used in the later stage of natural gas hydrate mining;
  • Safe and efficient mining to solve the problem of insufficient power in the late stage of the depressurization mining method and the inefficient efficiency of the hydrothermal mining method.
  • the invention has the beneficial effects of providing a seawater gas hydrate mining technology by water flow erosion method, and realizing the effective combination of water flow erosion method, pressure reduction mining and heat injection mining method, and solving the defects of other hydrate mining methods.
  • it provides a feasible method for large-scale exploitation of natural gas hydrates, eliminating reservoir structural damage, geological damage and major natural disasters caused by large pressure drop.
  • it is of great significance for the subsequent experiments and practical research of natural gas hydrate mining methods.
  • FIG. 1 is a schematic illustration of the principles of the present invention.
  • FIG. 2 is a schematic view of a mining method of the present invention.
  • Figure 3 is a schematic illustration of the combination of the present invention and a reduced pressure production method.
  • Fig. 4 is a schematic view showing the combination of the present invention and the heat injection production method.
  • the principle of the seawater gas hydrate mining method of the water flow erosion method of the present invention is shown in Fig. 1.
  • the hydrogen bond breaks due to the chemical potential difference existing between the hydrate phase and the water phase, the hydrate decomposes, and the gas molecules overflow.
  • the water erosion method accelerates the heat and mass transfer process inside the reservoir, which promotes the decomposition of hydrates in many aspects.
  • the water flow erosion method of the present invention uses a low-density mud drilling technology to drill a series of natural gas hydrate production channels in the natural gas hydrate region, and utilizes these production channels to conduct water flow erosion mining of natural gas hydrates.
  • a group of mining channels includes three channels: a pressure control and an outlet channel in the middle, and a pressure control channel on both sides.
  • three suitable drilling locations are selected in the middle of the reservoir, and three production channels are drilled in the natural gas hydrate occurrence area using low-density mud drilling technology, and adjacent production channels in the hydrate reservoir Drilling a number of horizontal water storage channels for accessing an appropriate amount of seawater to facilitate the flow of seawater;
  • the middle natural gas hydrate production channel is selected as the natural gas pressure control and outlet passage.
  • the adjacent production passage is only used as the pressure control passage.
  • the natural gas hydrate reservoir pressure is regulated by the natural gas pressure control and the outlet passage, thereby controlling the natural gas hydrate in the reservoir.
  • the pressure difference between the production channels, the pressure difference is used to promote the flow of seawater in the horizontal water storage channel, thereby controlling the collection and collection speed of the natural gas hydrate;
  • the hydrate reservoir pressure has been maintained above and below the pressure of the unmined reservoir, ensuring the stability of the reservoir, eliminating the structural damage of the reservoir due to the large pressure drop, and geological damage. And the occurrence of major natural disasters.
  • Adjusting the natural gas pressure control and outlet passage pressure stabilizing the pressure difference between adjacent production passages as the optimal pressure difference, promoting the stable flow of seawater in the storage passage, and controlling the seawater flow velocity as the optimum flow rate for promoting hydrate decomposition.
  • Adjusting the natural gas pressure control and outlet passage pressure stabilizing the pressure difference between adjacent production passages as the optimal pressure difference, promoting the stable flow of seawater in the storage passage, and controlling the seawater flow velocity as the optimum flow rate for promoting hydrate decomposition.
  • the CH 4 gas generated by the decomposition of natural gas hydrate is collected at the gas pressure control and outlet of the gas outlet, and the collected gas is stored and transported.
  • the seawater separated by the natural gas pressure control and the outlet passage is discharged back to the reservoir through the pressure control passages on both sides for secondary flow utilization.
  • the marine gas hydrate mining technology combining the water flow erosion method and the pressure reduction mining method of the invention adopts low-density mud drilling technology to drill a series of natural gas hydrate production channels in the natural gas hydrate reservoir, and the part is reduced by pressure reduction.
  • the hydrate decomposes first, increasing the fluidity of the seawater inside the reservoir.
  • the natural gas hydrate is further extracted by a water flow erosion method.
  • a group of mining channels includes two channels: pressure control and gas collection channels, pressure control and return channels.
  • two suitable drilling locations and appropriate pressure-pressure ports are selected in the natural gas hydrate reservoir, and two mining channels are drilled in the gas hydrate formation area using low-density mud drilling technology, and in two A number of horizontal water storage channels are drilled between the channels and near the channels for accessing an appropriate amount of seawater to facilitate the flow of seawater between the reservoirs.
  • One production well is selected as the pressure control and gas collection passage, and the other well is used as the pressure control and return passage.
  • the hydrate is extracted by the pressure reduction method in the early stage of hydrate production.
  • the pressure control and the pressure of the gas gathering channel By reducing the pressure control and the pressure of the gas gathering channel, the hydrate of the gas hydrate reservoir is decomposed, and the water flow channel inside the reservoir is opened to improve the permeability of the hydrate production channel and the water storage channel and the interior of the reservoir, thereby promoting the seawater in The increased mobility within the reservoir promotes the exploitation of water erosion.
  • the pressure difference between the pressure control and the return passage is controlled by a large amount of decomposition gas generated by the decomposition, and the pressure difference between the pressure control and the return passage is promoted to the seawater in the two production wells.
  • the flow between the reservoirs realizes the decomposition of the reservoir hydrate by controlling the flow velocity of the seawater, thereby achieving further sufficient exploitation of the residual hydrate by the seawater erosion method.
  • the natural gas is collected at the outlet of the natural gas discharge collection channel and stored and transported; the water generated after the gas-liquid separation at the natural gas collection port is backfilled from the adjacent pressure-control and return channels.
  • the marine gas hydrate mining technology combining the water flow erosion method and the heat injection mining method of the invention adopts low-density mud drilling technology to drill a series of natural gas hydrate production channels in the natural gas hydrate reservoir, and the part is heated by the heat injection method.
  • the hydrate decomposes first, increasing the fluidity of the seawater inside the reservoir.
  • the natural gas hydrate is further extracted by a water flow erosion method.
  • a group of mining channels includes two channels: a marine water injection well and a natural gas collection well.
  • a suitable drilling position is selected, and two production wells are drilled into the natural gas hydrate reservoir using low-density mud drilling technology, one as a marine water injection well and one as a natural gas collection well;
  • the water injection pump is injected into the ocean water injection well.
  • the ocean water flows from the wellbore to the surrounding reservoir in the natural gas hydrate reservoir. Due to the temperature difference between the ocean water and the natural gas hydrate reservoir, in the process of flow
  • the heat of the ocean water is transferred to the surrounding hydrate reservoir through heat conduction and heat convection, promotes partial decomposition of the hydrate, opens the void passage, and forms a high-permeability area around the wellbore.
  • the formation of the high-permeability region is beneficial to the storage of the ocean water.
  • the flow in the layer The amount of initial injection of ocean water can be determined according to parameters such as ocean water temperature, reservoir temperature, saturation of natural gas hydrate, formation permeability, heat transfer coefficient, and water injection pump characteristics;
  • the decomposition of natural gas hydrate When injecting ocean water, the decomposition of natural gas hydrate will generate a large amount of natural gas.
  • the pressure difference between the ocean water injection well and the natural gas collection well is adjusted, and the pressure difference is used to promote the ocean water in two.
  • the flow velocity of the ocean water is controlled by controlling the stability of the pressure difference between the two production wells, thereby realizing the control of the stable decomposition rate of the hydrate;
  • the natural gas and water obtained by hydrate decomposition are driven by pressure through a flow path formed by decomposition of hydrate or a horizontal channel drilled between two production wells by low-density mud drilling technology to collect gas from a lower pressure natural gas collection well.
  • the collected natural gas is stored and transported, and the collected water is reinjected into the marine water injection well for recycling.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Geology (AREA)
  • Mining & Mineral Resources (AREA)
  • Physics & Mathematics (AREA)
  • Environmental & Geological Engineering (AREA)
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  • General Life Sciences & Earth Sciences (AREA)
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Abstract

本发明属于海洋天然气水合物开采技术领域，提供了一种水流侵蚀法海洋天然气水合物开采方法，基于开采井周边渗透性较高的特点，通过井与储层间的压力梯度，进而控制海洋水在储层内的流动。利用流动水相与水合物相之间产生的化学势差驱动水合物分解。同时增加了储层盐度，提高体系相平衡温度，加快储层内部传热传质，实现水合物高效稳定分解，并保证了开采的完全化。利用水的驱替作用，实现对开采天然气的高效收集。同时降低因较大压降导致的储层结构破坏而引起的重大自然灾害的概率。为进一步提高水合物的开采效率，本发明同时提出了水流侵蚀法与降压开采法及注热开采法等的各种组合方法。本发明易于实现，有利于实现水合物的大规模商业化开采。

Description

一种水流侵蚀法海洋天然气水合物开采方法 技术领域
本发明属于海洋天然气水合物开采技术领域，具体涉及一种水流侵蚀法海洋天然气水合物开采方法。
 背景技术
在当今传统化石燃料日益缺乏的条件下，开发利用新能源已经成为了世界各国的重点研究内容。天然气水合物作为一种新型能源，具有高效、高能量聚集、储量大、环境友好等特点，开采前景广阔，并得到了世界范围内的重视。目前天然气水合物的开采技术主要包括降压开采法、热激开采法、化学试剂注入开采法和二氧化碳置换开采法以及各种方法的组合。
降压开采法作为目前被公认的最有效的水合物开采方法，对天然气水合物藏的性质有特殊的要求，只有当天然气水合物位于温压平衡边界附近时，降压开采法才具有经济可行性。降压法在水合物开采后期的开采动力不足也是其存在的缺陷，且降压开采过程储层压力骤降会破坏储层及稳定的海洋环境。热激开采法至今尚未很好地解决热利用效率较低的问题，而且只能进行局部加热，因此该方法尚有待进一步完善。化学试剂注入开采法所需的化学试剂费用昂贵，对天然气水合物层的作用缓慢，而且还会带来一些环境问题，所以，目前对这种方法投入的研究相对较少。二氧化碳置换开采效率低下，不能实现天然气水合物的完全高效开采，开采耗时较长，且存在泄漏危险。
本发明针对目前水合物开采方法所存在的缺陷，提出了一种新的水合物开采方法。同时，为了进一步提高水合物的开采效率以及储层结构的稳定性，本发明同时提出了水流侵蚀法与降压开采法以及注热开采法等的各种组合方法。
 技术问题
本发明针对目前天然气水合物开采技术的不足，基于水流动对水合物稳定存在的影响，在水合物相平衡之上，利用水流动过程中引起的水合物相与环境水相之间的化学势差所导致的水合物的分解，以及水流动对储层内传热传质的促进作用，提供了一种水流侵蚀法海洋天然气水合物开采技术。本方法通过控制开采井与其周边储层的压力梯度，进一步控制海洋水在储层内部的流动，基于开采井周边渗透率较高的特点，利用水相与水合物相内水分子之间产生的化学势差驱动水合物的分解。同时增加了储层盐度，提高了体系相平衡温度，加快储层内部传热传质，实现水合物的逐步稳定高效分解，并且保证了水合物开采的完全化，利用水流动过程的驱替作用，实现对开采天然气的高效收集。稳定高效的开采过程同时保证了储层存在的稳定性，排除了因为较大压降导致的储层结构破坏，地质破坏而引起的重大自然灾害。本方法易于实现，有利于实现水合物的大规模商业化开采。为了进一步提高水合物的开采效率以及储层结构的稳定性，本发明同时提出了水流侵蚀法与降压开采法以及注热开采法等的各种组合方法。
 技术解决方案
本发明的技术方案：
一种水流侵蚀法海洋天然气水合物开采方法，包括以下步骤：
（1）选取钻井位置，钻取多组天然气水合物开采通道，每组天然气水合物开采通道包括三个开采通道，分别为两个控压通道和一个控压与出气通道；在天然气水合物储层中相邻的开采通道之间钻取多个存水通道，实现控压通道与控压与出气通道在天然气水合物储层是相通的，用于存取适量的海水；
（2）每组天然气水合物开采通道中选取中间的开采通道作为控压与出气通道，通过控压与出气通道控制天然气水合物储层压力和天然气水合物储层中天然气水合物开采通道之间的压力差，促使海水的流动，水的流动会通过改变储层内部水合物相与水相的化学势差来驱动水合物的分解；同时天然气水合物储层内部的海水流动过程增加了天然气水合物储层盐度，提高了体系相平衡温度，并且加快了天然气水合物储层内部传热传质，进一步促进了水合物的分解；
（3）改变控压与出气通道的压力，提高相邻控压通道之间的压力差，促使海水在存水通道中的流动速度变大，促进天然气水合物储层中水合物的部分分解，增大天然气水合物储层内部渗透率；
（4）调节控压与出气通道压力，稳定相邻控压通道之间的压力差，促使海水在存水通道中的稳定流动，海水流动速度选取为促进水合物分解的最佳流速，从而促进天然气水合物储层中水合物高效、安全持续分解；
（5）在控压与出气通道出口收集CH 4气体，通过对CH 4气体的收集来控制控压与出气通道内部压力，并对收集的气体进行储藏与运输；由控压与出气通道分离出的海水通过两侧的控压通道排回天然气水合物储层，进行二次流动利用。
为了实现水合物的高效安全开采，在天然气水合物开采前期先通过降压法或注热法使天然气水合物储层部分水合物分解；在天然气水合物开采后期再采用本发明的开采方法；二者结合，有助于提高天然气水合物开采通道、存水通道周边以及天然气水合物储层内部的渗透率，增加海水在天然气水合物储层内部的流动性，进一步通过水流侵蚀法实现水合物的安全高效开采，解决降压开采法后期动力不足以及注热开采法效率不高的问题。
 有益效果
本发明的有益效果是：提供了一种水流侵蚀法海洋天然气水合物开采技术，并实现了水流侵蚀法与降压开采以及注热开采法的有效结合，解决了其他水合物开采方法存在的缺陷以及目前天然气水合物开采过程中的难题，为实现天然气水合物的大规模开采提供了可行的方法，排除了因为较大压降导致的储层结构破坏，地质破坏以及重大自然灾害的发生。同时，对于天然气水合物开采方法的后续实验和实际研究具有重要的意义。
 附图说明
图1是本发明的原理示意图。
图2是本发明的开采方法示意图。
图3是本发明与降压开采方法相互结合的示意图。
图4是本发明与注热开采方法相互结合的示意图。
 本发明的实施方式
本发明的水流侵蚀法海洋天然气水合物开采方法的原理如图1所示，是由于水合物相与水相之间存在的化学势差导致的氢键断裂，水合物分解，气体分子溢出。同时水流侵蚀法加速了储层内部传热传质过程，从多个方面促进了水合物的分解。
以下结合技术方案和附图进一步详细说明本发明的实施例。
实施例一
本发明的水流侵蚀法海洋天然气水合物开采方法采用低密度泥浆钻井技术，在天然气水合物区域钻取一系列天然气水合物开采通道，利用这些开采通道对天然气水合物进行水流侵蚀开采。以其中一组开采通道为例进行说明，一组开采通道包括三个通道：中间的控压与出气通道，两侧的控压通道。
如图2所示，在储层中部选取3个合适的钻井位置，采用低密度泥浆钻井技术在天然气水合物赋存区域钻取三个开采通道，并在水合物储层中相邻的开采通道之间钻取若干个水平存水通道，用于存取适量的海水，便于海水的流动；
选取中间的天然气水合物开采通道作为天然气控压与出气通道，相邻的开采通道仅作为压力控制通道，通过天然气控压与出气通道调节天然气水合物储层压力，进而控制储层中天然气水合物开采通道之间的压力差，利用压力差促进海水在水平存水通道中的流动，从而控制天然气水合物的开采收集速度；
改变天然气控压与出气通道出口处的天然气收集速度，进而改变天然气控压与出气通道压力，提高相邻开采通道之间的压力差，促使海水在水平存水通道中的流动速度变大，促进储层部分水合物的快速分解，打开空隙通道，增大储层内部渗透率，有利于海水在存水通道中流动速度的控制；
天然气水合物在开采过程中，水合物储层压力一直维持在未开采储层的压力上下浮动，保证了储层存在的稳定性，排除了因为较大压降导致的储层结构破坏，地质破坏以及重大自然灾害的发生。
调节天然气控压与出气通道压力，稳定相邻开采通道之间的压力差为最佳压力差，促使海水在存水通道中的稳定流动，海水流动速度控制为促进水合物分解的最佳流速，从而促进天然气水合物储层高效、安全的持续分解；
在天然气控压与出气通道出口收集天然气水合物分解产生的CH 4气体，并对收集的气体进行储藏与运输。由天然气控压与出气通道分离出的海水通过两侧的控压通道排回储层进行二次流动利用。
实施例二
以下结合图3和实施例二进行详细叙述。
本发明的水流侵蚀法与降压开采法相互结合的海洋天然气水合物开采技术，采用低密度泥浆钻井技术，在天然气水合物储层钻取一系列天然气水合物开采通道，通过降压开采使部分水合物首先分解，增加海水在储层内部的流动性。进而通过水流侵蚀法对天然气水合物进行开采。以其中一组开采通道为例进行说明，一组开采通道包括两个通道：控压与集气通道，控压与回流通道。
如图3所示，在天然气水合物储层选取两个合适的钻井位置以及合适的降压口，采用低密度泥浆钻井技术在天然气水合物赋存区域钻取两个开采通道，并在两个通道之间及通道附近钻取若干个水平存水通道，用于存取适量的海水，便于海水在储层间的流动。
选取一口开采井作为控压与集气通道，另一口井作为控压与回流通道，在水合物开采初期通过降压法进行水合物的开采。通过降低控压与集气通道压力使天然气水合物储层部分水合物分解，打开储层内部水流动通道，提高水合物开采通道及存水通道周边及储层内部的渗透率，从而促使海水在储层内部的流动性增加，推动水流侵蚀法开采的进行。
当储层部分水合物在降压过程中分解后，通过分解瞬间产生的大量分解气来控制控压与集气通道，控压与回流通道之间的压力差，促使海水在两个开采井之间的流动，通过控制海水的流动速度实现储层水合物的分解，从而实现通过海水侵蚀法对残余水合物进行进一步充分的开采。
在储层水合物开采过程中，为了避免水合物短时间内大量分解导致的地质失稳以及在水合物开采后期出现的开采效率低下等问题，可以在水合物开采中期及开采后期，结合降压开采，通过控制储层两开采通道之间的稳定压差来实现对水流速度的控制，进而控制水合物的分解速度。
在在天然气排出收集通道出口收集天然气，并对其进行储藏与运输；在天然气收集口进行气液分离后产生的水从旁边的控压与回流通道回填再利用。
实施例三
以下结合图4和实施例三进行详细叙述。
本发明的水流侵蚀法与注热采法相互结合的海洋天然气水合物开采技术，采用低密度泥浆钻井技术，在天然气水合物储层钻取一系列天然气水合物开采通道，通过注热法使部分水合物首先分解，增加海水在储层内部的流动性。进而通过水流侵蚀法对天然气水合物进行开采。以其中一组开采通道为例进行说明，一组开采通道包括两个通道：海洋水注入井，天然气收集井。
如图4所示，选取合适的钻井位置，采用低密度泥浆钻井技术钻取两口开采井至天然气水合物储层内部，一口作为海洋水注入井，一口作为天然气收集井；
启动注水泵将海洋水注入到海洋水注入井中，海洋水在天然气水合物储层中会由井筒开始向周围储层流动，由于海洋水与天然气水合物储层存在温度差，在流动的过程中，海洋水的热量会通过热传导和热对流传递给周围的水合物储层，促进水合物的部分分解，打开空隙通道，在井筒周围形成高渗透区域，高渗透区域的形成有利于海洋水在储层中的流动。初始注入海洋水的量可以根据海洋水温度、储层温度、天然气水合物的饱和度、地层渗透率、热传导系数及注水泵特性等参数来确定；
在注入海洋水时，天然气水合物的分解会产生大量天然气，通过控制天然气收集井的天然气收集速度来调节海洋水注入井与天然气收集井之间的压力差，利用压力差促进海洋水在两个开采井之间的流动；
为了实现储层水合物高效、安全的持续分解，通过控制两开采井之间压力差的稳定来控制海洋水的流动速度，进而实现对水合物稳定分解速度的控制；
水合物分解得到的天然气和水在压力的驱动下通过水合物分解后形成的流道或利用低密度泥浆钻井技术在两开采井之间钻取的水平通道流向压力较低的天然气收集井进行收集，并对收集的天然气进行储藏与运输，对收集的水重新注入到海洋水注入井中进行循环利用。
以上实施例是本发明具体实施方式的三种，本领域技术人员在本技术方案范围内进行的通常变化和替换应包含在本发明的保护范围内。

Claims (2)

  1. 一种水流侵蚀法海洋天然气水合物开采方法，其特征在于，包括以下步骤：
    （1）选取钻井位置，钻取多组天然气水合物开采通道，每组天然气水合物开采通道包括三个开采通道，分别为两个控压通道和一个控压与出气通道；在天然气水合物储层中相邻的开采通道之间钻取多个存水通道，实现控压通道与控压与出气通道在天然气水合物储层是相通的，用于存取适量的海水；
    （2）每组天然气水合物开采通道中选取中间的开采通道作为控压与出气通道，通过控压与出气通道控制天然气水合物储层压力和天然气水合物储层中天然气水合物开采通道之间的压力差，促使海水的流动，水的流动会通过改变天然气水合物储层内部水合物相与水相的化学势差来驱动水合物的分解；同时天然气水合物储层内部的海水流动过程增加了天然气水合物储层盐度，提高了体系相平衡温度，并且加快了天然气水合物储层内部传热传质，进一步促进了水合物的分解；
    （3）改变控压与出气通道的压力，提高相邻控压通道之间的压力差，促使海水在存水通道中的流动速度变大，促进天然气水合物储层中水合物的部分分解，增大天然气水合物储层内部渗透率；
    （4）调节控压与出气通道压力，稳定相邻控压通道之间的压力差，促使海水在存水通道中的稳定流动，海水流动速度选取为促进水合物分解的最佳流速，从而促进天然气水合物储层中水合物高效、安全持续分解；
    （5）在控压与出气通道出口收集CH 4气体，通过对CH 4气体的收集来控制控压与出气通道内部压力，并对收集的气体进行储藏与运输；由控压与出气通道分离出的海水通过两侧的控压通道排回天然气水合物储层，进行二次流动利用。
  2. 根据权利要求1所述的水流侵蚀法海洋天然气水合物开采方法，其特征在于，
    为了实现水合物的高效安全开采，在天然气水合物开采前期先通过降压法或注热法使天然气水合物储层部分水合物分解，增加天然气水合物储层的局部渗透性；在天然气水合物开采后期再采用权利要求1所述的开采方法；二者结合，有助于提高天然气水合物开采通道、存水通道周边以及天然气水合物储层内部的渗透率，增加海水在天然气水合物储层内部的流动性，进一步通过水流侵蚀法实现水合物的安全高效开采。
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