WO2025232184A1 - 水合物储层压裂-开采-加固的多过程联合高效开采方法 - Google Patents

水合物储层压裂-开采-加固的多过程联合高效开采方法

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Publication number
WO2025232184A1
WO2025232184A1 PCT/CN2024/137985 CN2024137985W WO2025232184A1 WO 2025232184 A1 WO2025232184 A1 WO 2025232184A1 CN 2024137985 W CN2024137985 W CN 2024137985W WO 2025232184 A1 WO2025232184 A1 WO 2025232184A1
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Prior art keywords
reinforcement
fracturing
mining
hydrate
fracturing fluid
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Pending
Application number
PCT/CN2024/137985
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English (en)
French (fr)
Inventor
王路君
朱斌
孙传淇
王鹏
叶智刚
徐林方
宋昊奇
林伟岸
陈云敏
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Zhejiang University
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Zhejiang University
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Application filed by Zhejiang University filed Critical Zhejiang University
Publication of WO2025232184A1 publication Critical patent/WO2025232184A1/zh
Pending legal-status Critical Current
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Classifications

    • 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
    • E21B43/25—Methods for stimulating production
    • E21B43/26—Methods for stimulating production by forming crevices or fractures
    • 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

Definitions

  • This invention belongs to the fields of energy engineering and geotechnical engineering technology, and relates to a method for reinforcing and safely and efficiently exploiting natural gas hydrate reservoirs.
  • it relates to a multi-process combined efficient exploitation method of fracturing, exploitation and reinforcement of hydrate reservoirs, which is suitable for solving the problems of low gas production rate and easy instability of reservoirs during natural gas hydrate exploitation.
  • Natural gas hydrates are considered the most promising clean energy source to replace conventional oil and gas. It is estimated that the reserves of natural gas hydrates in the deep-sea sediments of the South my country Sea are approximately 80 billion tons of oil equivalent. In my country, natural gas hydrates are mainly found in deep-sea sediments under high pressure and low temperature conditions. Currently, depressurization extraction is widely recognized as the most economical and effective method for natural gas hydrate extraction. The sediments in the South my country Sea hydrate reservoirs are mainly silty mudstone with an average grain size of approximately 12 ⁇ m and low permeability, averaging millidarcy level. During depressurization extraction, pressure transmission is slow, hindering the expansion of the depressurization zone and resulting in low extraction efficiency.
  • Active hydraulic fracturing of the surrounding sediments to create fractures around the well is a common method for improving wellbore permeability in conventional underground energy extraction. If applied to natural gas hydrate extraction, it is expected to improve wellbore permeability while simultaneously expanding the depressurization zone, thereby increasing gas production efficiency.
  • natural gas hydrate extraction is a phase transition process in which the solid phase transforms into liquid water and gaseous methane.
  • the loss of solid phase in hydrate-bearing sediments weakens the cementation and support between soil skeletons.
  • the flow of liquid and gas two-phase flow in the pores often carries a large number of soil particles, increasing the risk of sand production and potentially causing well blockage.
  • Japan's two natural gas hydrate trial productions in the Nankai Trough were forced to stop due to sand production problems.
  • the decomposition of the solid phase can reduce the strength of the skeleton, causing reservoir deformation, and even leading to well tilting or reservoir collapse, resulting in serious engineering disasters.
  • the purpose of this invention is to address the shortcomings of existing technologies by providing a multi-process, efficient extraction method for hydrate reservoirs, encompassing fracturing, extraction, and reinforcement.
  • This invention utilizes a specific viscosity fracturing agent containing a high-permeability porous material proppant to hydraulically fracture the reservoir, followed by extraction methods such as depressurization and thermal injection. Simultaneously, the extracted area is reinforced using a cementing agent. Based on this, unexploited areas can be further fracturing as needed to expand the hydrate extraction range, thus filling the gap in the field of multi-process extraction of hydrate reservoirs, integrating fracturing, extraction, and reinforcement.
  • a multi-process combined efficient exploitation method for hydrate reservoirs including fracturing, extraction, and reinforcement, comprising the following steps:
  • Step 1 Install liquid injection pipelines inside the well.
  • pressure-resistant pipes are installed inside the production well to transport fracturing fluid and reinforcement agent, respectively.
  • the upper end of the pressure-resistant pipes is connected to the corresponding high-pressure liquid injection system on the offshore production platform.
  • Step 2 Install mining holes and nozzles on the mining shaft.
  • fracturing, reinforcement and production openings and nozzles are set at regular intervals.
  • the nozzles extend outward from the openings and the outer end of the nozzles is flush with the sand screen.
  • Step 3 Connect the nozzles to the corresponding high-pressure liquid injection systems.
  • the fracturing and reinforcement nozzles are connected to the lower end of the corresponding pressure-resistant pipes, so that the fracturing and reinforcement nozzles on the production well are connected to the corresponding high-pressure liquid injection system on the offshore production platform, so as to control the fracturing fluid and reinforcement agent to be injected into the hydrate reservoir independently through the nozzles.
  • Step 4 Prepare fracturing fluid and inject it into the hydrate reservoir
  • Fracturing fluid is prepared and injected into the hydrate reservoir through the fracturing fluid nozzle on the production well using the high-pressure liquid injection system on the offshore production platform to form fracturing fractures in the hydrate reservoir, and the porous material proppant in the fracturing fluid is deposited and fixed in the fractures.
  • the hydrate reservoir is depressurized or depressurization-thermal shock combined with the extraction well to enable the rapid decomposition and production of hydrates in the fracturing zone.
  • Step Six Prepare and inject the consolidating agent into the hydrate reservoir for reinforcement.
  • Step 7 Multi-process mining of hydrate reservoirs including fracturing, extraction, and reinforcement.
  • steps four to six Based on the required hydrate extraction range, repeat steps four to six. First, fracture the unexploited hydrate reservoir to form a fractured zone. Then, extract the hydrate in the fractured zone. After the hydrate in the fractured zone is decomposed and extracted, inject a reinforcing agent to transform the fractured zone into a reinforced zone. Then, continue to fracture the unexploited hydrate reservoir to expand the fractured zone. Perform multi-process combined efficient extraction of the hydrate reservoir, including fracturing, extraction, and reinforcement.
  • step one the pipelines transporting different liquids within the mining well are independent, and the pipelines are pressure-resistant pipelines capable of withstanding the pressure difference between the inside and outside.
  • step two the well is provided with several mining openings, which serve as transmission channels for the production of liquid gas during the extraction of natural gas hydrates; the outside of the well is wrapped with a sand-proof screen.
  • the nozzles have circular nozzle holes, and each set of nozzles consists of fracturing fluid nozzles and reinforcement agent nozzles.
  • the fracturing fluid nozzle has a nozzle hole for fracturing fluid spraying
  • the reinforcement agent nozzle has a reinforcement agent mother liquor nozzle and a reinforcement agent reactant nozzle.
  • Each set of nozzles surrounds a production well opening, and the nozzles extend outward from the well wall, pass through the sand control screen wrapped around the outside of the production well, and the outermost end of the nozzle is flush with the outermost end of the sand control screen.
  • the fracturing fluid is a liquid with viscosity, which can be a high-viscosity fracturing fluid or a low-viscosity fracturing fluid.
  • the high-viscosity fracturing fluid includes guar gum fracturing fluid and silicone oil fracturing fluid, while the low-viscosity fracturing fluid includes sodium chloride solution fracturing fluid.
  • the proppant includes one or more of porous ceramic particles, porous calcium carbonate particles, and polyester fiber materials; the proppant is uniformly mixed in the fracturing fluid to form a suspension.
  • the high-pressure fluid injection system includes constant-pressure injection and constant-flow injection.
  • the pressure or injection rate of the injected fracturing fluid is determined based on the mechanical parameters and pressure conditions of the hydrate reservoir obtained during pre-mining drilling.
  • the formula for calculating the minimum injection pressure pmin is:
  • K ⁇ sub>0 ⁇ /sub> is the static earth pressure coefficient at that location in the hydrate reservoir
  • ⁇ is the internal friction angle of the sediment in the hydrate reservoir
  • ⁇ ' is the average effective density of the hydrate reservoir and the overlying sediment layer
  • g is the gravitational acceleration
  • z is the burial depth of the hydrate reservoir at that location
  • NP is the hydrate cohesion coefficient
  • ch is the cohesive force of the hydrate.
  • the reinforcing agent consists of a reinforcing mother liquor and a reactant.
  • the ratio of the reinforcing mother liquor to the reactant is determined according to the required reaction time and reinforcement strength.
  • the reinforcing mother liquor is injected into the mined hydrated reservoir through the reinforcing mother liquor pipeline and the reinforcing mother liquor nozzle on the reinforcing agent nozzle for reinforcement.
  • the reactant is injected into the mined hydrated reservoir through the reinforcing reactant pipeline 209 and the reinforcing reactant nozzle on the reinforcing agent nozzle for reinforcement.
  • the reinforcement process is as follows: first, the reinforcing mother liquor is injected for a period of time, and then the reactant is injected to uniformly fill the pores of the soil skeleton. After standing for a period of time, the cement or crystals are generated, thus completing the reinforcement of the mined area.
  • the cement or crystals are porous and are formed at the contact points with the soil skeleton.
  • step six the pressure during reinforcement injection is less than or equal to the minimum injection pressure pmin of the fracturing fluid.
  • This invention is applicable to the field of offshore natural gas hydrate extraction. It can improve the permeability of the wellbore hydrate reservoir and form a dominant seepage path by using active fracturing. It can also reinforce the hydrate reservoir after fracturing by using chemical reaction or microbial induced crystallization reinforcement methods. Furthermore, through a multi-process combined method of fracturing-extraction-reinforcement, the fracturing area and hydrate decomposition area are repeatedly expanded to improve the efficiency of hydrate extraction and reservoir stability.
  • This invention presents a novel and clear approach, filling the gap in multi-process combined efficient extraction technology for natural gas hydrate reservoirs, including fracturing, extraction, and reinforcement. It provides new technology for the safe and efficient extraction of deep-sea natural gas hydrates, and solves the problems of low gas production rate due to low reservoir permeability and well blockage and reservoir instability caused by sand production during current natural gas hydrate extraction.
  • Figure 1 is a schematic diagram of the site layout and multi-process combined high-efficiency mining process of natural gas hydrate extraction in this invention, including fracturing, extraction and reinforcement.
  • (a) is a schematic diagram of the fracturing and extraction process; and (b) is a schematic diagram of the reinforcement and secondary fracturing process.
  • Figure 2 is a schematic diagram of the wellbore, nozzle arrangement, and internal pipeline structure in this invention; wherein, (a) in Figure 2 is a front view of the well; (b) in Figure 2 is a radial cross-sectional view of the well; (c) in Figure 2 is an axial cross-sectional view of the well; and (d) in Figure 2 is another axial cross-sectional view of the well.
  • Figure 3 is a flowchart of the multi-process combined high-efficiency mining method of hydrate reservoir fracturing-mining-consolidation in this invention.
  • the components are: reinforced zone 101, fracturing zone 102, hydrate reservoir 103, production well 104, overlying seawater 105, overlying soil layer 106, underlying layer 107, offshore production platform 108, production opening 201, fracturing fluid nozzle 202, reinforcer nozzle 203, production access channel 204, sand control screen 205, production well wall 206, fracturing fluid pipeline 207, reinforcer mother liquor pipeline 208, reinforcer reactant pipeline 209, reinforcer mother liquor nozzle 210, and reinforcer reactant nozzle 211.
  • first, second, third, etc. may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another.
  • first information may also be referred to as second information
  • second information may also be referred to as first information.
  • the word “if” as used herein may be interpreted as “when,” “in response to determination,” or “includes.”
  • the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process or method that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process or method.
  • an element defined by the phrase “comprising a" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.
  • the hydrate reservoir 103 described in this invention is located in deep-sea seabed sediments.
  • the hydrate reservoir 103 is covered from top to bottom by overlying seawater 105 and overlying soil 106, with an underlying layer 107 at the bottom.
  • the multi-process combined high-efficiency extraction method of the hydrate reservoir using fracturing, extraction, and reinforcement of this invention involves firstly, the extraction well 104 penetrating from the offshore extraction platform 108 through the overlying seawater 105 and overlying soil 106 into the unextracted hydrate reservoir 103.
  • the wellbore 206 is equipped with extraction openings 201, fracturing fluid nozzles 202, and reinforcement nozzles 203 at intervals.
  • the fracturing fluid nozzles 202 and reinforcement nozzles 203 form a group of nozzles surrounding the extraction openings 201.
  • the outer side of the wellbore 206 is covered with a sand-proof screen 205, and the outermost end of the nozzle is flush with the outermost end of the sand-proof screen 205.
  • Fracturing fluid pipeline 207, reinforcement agent mother fluid pipeline 208, and reinforcement agent reactant pipeline 209 are installed inside the wellbore 104 to connect the nozzle to the high-pressure liquid injection system on the offshore production platform 108.
  • the pipelines inside the well correspond to the nozzles and are arranged symmetrically in a central manner.
  • the produced liquid and gas are generated through the production channel 204 inside the well.
  • fracturing, mining and reinforcement are carried out in sequence.
  • the high-pressure pump of the high-pressure liquid injection system injects the fracturing fluid on the offshore mining platform 108 into the unmined hydrate reservoir 103 through the fracturing fluid pipeline 207 and the fracturing fluid nozzle 202, thereby generating fracturing fractures and forming a fracturing zone 102.
  • the proppant in the fracturing fluid can prevent the fractures from closing. Extraction can be carried out using the depressurization method.
  • CaCl2, urea, and water are uniformly mixed in proportion on the offshore extraction platform 108 to prepare the consolidation mother liquor of the consolidation agent.
  • DSM33 bacteria, urease, nutrient solution, and water are uniformly mixed in proportion to prepare the reaction agent of the consolidation agent.
  • the consolidation mother liquor and the reaction agent of the consolidation agent are injected into the fracturing zone 102 through the consolidation agent mother liquor pipeline 208 and the consolidation agent reaction agent pipeline 209, respectively, via the consolidation agent nozzle 203.
  • the extracted fracturing zone 102 is transformed into the consolidation zone 101.
  • the high-pressure pump continues to inject fracturing fluid into the unextracted hydrate reservoir 103. Secondary fracturing transforms a portion of the unextracted hydrate reservoir 103 into the fracturing zone 102.
  • the subsequent multi-stage process of extraction, consolidation, and fracturing is repeated to continuously expand the hydrate extraction range.
  • the embodiments of the present invention and their implementation process include the following steps:
  • Step 1 Install liquid injection pipelines inside the well.
  • pressure-resistant pipes are installed in the production well 104 to transport fracturing fluid and reinforcement agent, respectively.
  • the upper end of the pressure-resistant pipes is connected to the corresponding high-pressure liquid injection system on the offshore production platform 108.
  • pipelines for transporting different liquids within the mining well 104 are independent to ensure that the independent injection of different liquids can be controlled.
  • the pipelines are pressure-resistant pipelines capable of withstanding internal and external pressure differences.
  • fracturing fluid pipelines 207 four consolidation agent mother liquor pipelines 208, and four consolidation agent reactant pipelines 209 are installed in the production well 104.
  • the three types of pressure-resistant pipelines are respectively connected to the consolidation agent mother liquor nozzle 210 and the consolidation agent reactant nozzle 211 of the fracturing fluid nozzle 202 and the consolidation agent nozzle 203.
  • the upper end of the pressure-resistant pipeline is connected to the corresponding high-pressure liquid injection system on the offshore production platform 108. They are used to transport fracturing fluid and consolidation agent, respectively.
  • the pipelines transporting different liquids are independent to achieve independent injection control of different liquids.
  • Step 2 Install mining holes and nozzles on the mining shaft.
  • fracturing, reinforcement and production openings and nozzles are set at regular intervals.
  • the nozzles extend outward from the openings and the outer end of the nozzles is flush with the sand screen 205.
  • the production well 104 is provided with several production openings 201, which serve as transmission channels for the production of liquid gas during the extraction of natural gas hydrates; the outside of the production well 104 is wrapped with a sand-proof screen 205, which can prevent sand from the hydrate reservoir 103 from clogging the production openings 201 on the production well 104 and the liquid gas production channels including the production well 104 during the extraction process.
  • each set of nozzles consists of a fracturing fluid nozzle 202 and a consolidation agent nozzle 203.
  • the fracturing fluid nozzle 202 has one nozzle hole for fracturing fluid ejection.
  • the consolidation agent nozzle 203 has two nozzle holes for the consolidation mother liquor and the consolidation agent reactant ejection, respectively.
  • Each set of nozzles surrounds a production well 201 to inject different liquids into the hydrate reservoir 103.
  • the nozzles extend outward from the well wall 206 of the production well and pass through the sand control screen 205 wrapped around the outside of the production well 104. The outermost end of the nozzle is flush with the outermost end of the sand control screen 205.
  • each production opening 201 is surrounded by one fracturing fluid nozzle 202 and one reinforcement nozzle 203.
  • the nozzles extend outward from the opening and out of the production well wall 206, with the outer end of the nozzle flush with the sand screen 205.
  • Step 3 Connect the nozzles to the corresponding high-pressure liquid injection systems.
  • the fracturing and reinforcement nozzles are connected to the lower ends of the corresponding pressure-resistant pipes, so that the fracturing and reinforcement nozzles on the production well 104 are connected to the corresponding high-pressure liquid injection systems on the offshore production platform 108, so as to control the fracturing fluid and reinforcement agent to be injected independently into the hydrate reservoir 103 through the nozzles.
  • the fracturing fluid nozzle 202 and the reinforcement agent nozzle 203 are respectively connected to the lower end of the corresponding pressure-resistant pipes, that is, the fracturing fluid nozzle 202 is connected to the lower end of the fracturing fluid pipe 207.
  • the two nozzles i.e., the reinforcement agent mother liquor nozzle 210 and the reinforcement agent reactant nozzle 211) provided on the reinforcement agent nozzle 203 are respectively connected to the lower end of the reinforcement agent mother liquor pipe 208 and the reinforcement agent reactant pipe 209.
  • This enables the fracturing fluid and the reinforcement agent to be injected independently into the hydrate reservoir 103 through the corresponding fracturing fluid nozzle 202 and the reinforcement agent nozzle 203.
  • Step 4 Prepare fracturing fluid and inject it into the hydrate reservoir
  • Fracturing fluid is prepared and injected into the hydrate reservoir 103 through the fracturing fluid nozzle 202 on the production well 104 using the high-pressure liquid injection system on the offshore production platform 108. This forms fracturing fractures in the hydrate reservoir 103, and the porous proppant in the fracturing fluid is deposited and fixed in the fractures to support them and prevent them from closing. This can improve the permeability of the fracturing zone 102 and form a dominant seepage channel.
  • the fracturing fluid is a liquid with a specific viscosity.
  • the fracturing fluid can be a high-viscosity fracturing fluid such as guar gum or silicone oil, or a low-viscosity fracturing fluid such as sodium chloride solution.
  • a low-viscosity fracturing fluid can be used, which facilitates the removal of the fracturing fluid during extraction; when the hydrate saturation of the hydrate reservoir 103 is low, a high-viscosity fracturing fluid can be used, which can reduce the loss of fracturing fluid in the hydrate reservoir 103 and successfully split the hydrate reservoir 103.
  • the components of the guar gum fracturing fluid are: 0.55% guar gum powder, 0.6% crosslinking agent, 0.2% ammonium persulfate, 0.2% soybean lecithin, and water; the components of the sodium chloride solution fracturing fluid are: 3.5% sodium chloride aqueous solution.
  • the proppant in the fracturing fluid can be one or more of the following materials: porous ceramic particles, porous calcium carbonate particles, polyester fibers, etc.
  • the proppant is uniformly mixed in the fracturing fluid to form a suspension, that is, the fracturing fluid is a suspension.
  • the high-pressure liquid injection system includes two injection methods: constant pressure injection and constant flow injection.
  • fracturing fluid is injected into the unmined hydrate reservoir 103 through the fracturing fluid nozzle 202 to form fracturing fractures, thus converting part of the unmined hydrate reservoir 103 into a fracturing zone 102.
  • the pressure or injection rate of the injected fracturing fluid is determined based on the mechanical parameters and pressure conditions of the hydrate reservoir 103 obtained by drilling before mining.
  • the specific calculation formula for the minimum injection pressure pmin is shown in formula (1):
  • K ⁇ sub>0 ⁇ /sub> is the static earth pressure coefficient at the hydrate reservoir 103
  • ⁇ is the internal friction angle of the sediment in the hydrate reservoir 103
  • ⁇ ' is the average effective density of the hydrate reservoir 103 and the overlying sediment layer
  • g is the gravitational acceleration
  • z is the burial depth of the hydrate reservoir 103
  • NP is the hydrate cohesion coefficient
  • ch is the cohesive force of the hydrate.
  • the fracturing fluid creates splitting fractures in the hydrate reservoir 103. Subsequently, the porous proppant material in the fracturing fluid is deposited and fixed in the fractures, supporting the fractures, preventing the fractures from closing during the mining process, and improving the permeability of the fracturing zone 102.
  • the hydrate reservoir 103 is exploited by depressurization or depressurization-thermal shock combined methods through the production opening 201 on the production well 104, so that the hydrate in the fracturing zone 102 can be rapidly decomposed and produced.
  • the gas production duration is determined according to the gas production rate characteristics.
  • Step Six Prepare and inject the consolidating agent into the hydrate reservoir for reinforcement.
  • the reinforcing agent consists of a reinforcing mother liquor and a reactant.
  • the ratio of the reinforcing mother liquor to the reactant is determined according to the required reaction time and reinforcement strength.
  • the reinforcing mother liquor and the reactant are injected into the mined hydrate reservoir 103 through their respective independent pressure-resistant pipes (i.e., the reinforcing mother liquor pipe 208 and the reinforcing reactant pipe 209) and the corresponding reinforcing mother liquor nozzle 210 and reinforcing reactant nozzle 211 on the reinforcing agent nozzle 203 for reinforcement.
  • a cement or crystal is formed in the pores of the hydrate reservoir 103, which can play a supporting and cementing role.
  • the reaction between the two can be a chemical reaction or a biological reaction.
  • the formation principle of the cement or crystal is shown in formula (2):
  • the reinforcing mother liquor is first injected into the fractured zone 102 after mining through the reinforcing mother liquor nozzle 210 of the reinforcing agent nozzle 203 on the mining well 104. Then, the reactant is injected into the fractured zone 102 after mining through the reinforcing agent reactant nozzle 211 of the reinforcing agent nozzle 203 to fill the pores of the soil skeleton.
  • the volume ratio of the reinforcing mother liquor and reactant injected into the hydrate reservoir 103 is 1:1. After standing for a period of time, calcium carbonate crystallizes and deposits, thus reinforcing the mined area.
  • the pressure during reinforcement agent injection should be less than or equal to the minimum injection pressure pmin of the fracturing fluid to ensure that the reinforcement agent can fully fill the pores between the soil skeletons without disturbing the soil skeletons.
  • the injection rate of the reinforcement agent should be increased as much as possible to improve the reinforcement efficiency.
  • the range of the fracture zone 102 and the reinforced zone 101 is continuously expanded, the extraction range is increased, the permeability of the hydrate reservoir 103 and the stability of the soil skeleton around the extraction well 104 are improved, the extraction efficiency of depressurization and other methods is increased, and the risk of instability of the soil skeleton around the extraction well 104 is reduced.
  • this invention innovatively adopts a multi-process combined high-efficiency mining method of fracturing-production-reinforcement, which has the advantages of novel method, simple operation and clear process. It fills the gap in the multi-process combined high-efficiency mining technology of fracturing-production-reinforcement of natural gas hydrate reservoirs, provides new technology for the safe and efficient mining of deep-sea natural gas hydrates, can solve the problems of low gas production rate and easy instability of reservoirs during natural gas hydrate mining, and can achieve the goal of safe, stable and long-term sustainable mining of natural gas hydrates in the field.

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Abstract

一种水合物储层压裂-开采-加固的多过程联合高效开采方法包括：在开采井（104）内设置各自独立的液体注入耐压管道；在开采井上设置用于压裂、加固和开采的开孔（201）及喷嘴；在井内利用管道将压裂和加固的喷嘴分别与对应的注入系统连接；将制备的压裂液注入水合物储层（103），形成压裂裂缝；通过开采井对储层进行降压等方式的开采；将制备的加固剂注入开采后的储层中进行加固；重复上述步骤对储层进行压裂-开采-加固的多过程联合高效开采。该方法通过压裂过程提高开采井周储层渗透性，通过加固过程提高储层稳定性，多过程联合开采强化了开采过程的高效性和安全性，为深海天然气水合物安全高效开采提供了新的多过程联合高效开采方法。

Description

水合物储层压裂-开采-加固的多过程联合高效开采方法 技术领域
本发明属于能源工程和岩土工程技术领域，涉及一种天然气水合物储层加固及安全高效开采方法，尤其涉及一种水合物储层压裂-开采-加固的多过程联合高效开采方法，适用于解决天然气水合物开采时的产气速率低及储层易失稳的问题。
背景技术
天然气水合物被认为是目前最有潜力替代常规油气的清洁能源，据估计我国南海深海沉积物中的天然气水合物储量约为800亿吨油当量。我国天然气水合物主要赋存于高压低温环境的深海沉积物中，目前降压开采被公认为是天然气水合物开采最经济和有效的方法。我国南海水合物储层沉积物主要为泥质粉砂，平均粒度约为12μm，渗透率低，平均渗透率为毫达西级，降压开采时压力传递慢、不利于降压区扩大，导致开采效率低。采用主动注液压裂井周沉积物在井周形成裂隙，是常规地下能源开采时提高井周渗透性的常用方法，如果用于天然气水合物的开采，可望提高井周渗透性同时扩大降压分解区，提高开采产气效率。
与传统油气开采不同，天然气水合物开采是一个固相转化为液相水和气相甲烷气的相变过程，含水合物沉积物固相的损失会减弱土骨架之间的胶结及支撑作用，孔隙间液气二相流的流动往往携带大量土颗粒运移，开采出砂的风险将增加，进而可能导致堵塞开采井，日本在南开海槽进行的两次天然气水合物试采均因出砂问题被迫中止；同时固相的分解会造成骨架强度降低而造成储层变形，甚至导致开采井倾斜或储层塌陷，引起严重的工程灾变。
目前，我国南海水合物储层渗透性低导致有效开采范围小、产气效率低，同时存在开采出砂、储层失稳坍塌等工程灾变风险，是制约天然气水合物商业化开采的瓶颈难题。因此，探索一种能在低渗透沉积物储层中进行高效和持续开采、同时保证储层变形在安全可控范围内的开采方法，是实现天然气水合物能源高效、安全、长期开采目标首要解决的关键难题。
发明内容
本发明的目的在于针对现有技术的不足，提供一种水合物储层压裂-开采-加固的多过程联合高效开采方法。本发明利用包含高渗性多孔材料支撑剂的特定粘度压裂液压裂储层，之后进行降压、注热等形式的开采，同时利用加固剂的胶结加固作用对已开采区进行加固；在上述基础上根据开采范围需要继续压裂未开采区，扩大水合物开采范围，可填补水合物储层压裂、开采和加固的多过程开采这一领域的空白。
本发明的目的是通过以下技术方案来实现的：一种水合物储层压裂-开采-加固的多过程联合高效开采方法，包括以下步骤：
步骤一：开采井内设置液体注入管道
在开采井内设置若干耐压管道，分别用于输送压裂液和加固剂，耐压管道上端与海上开采平台上对应的高压液体注入系统连接；
步骤二：开采井上设置开采孔及喷嘴
在开采井与天然气水合物储层接触的部分，每间隔一定距离设置压裂、加固和开采的开孔及喷嘴，喷嘴向外侧从开孔中伸出，喷嘴外端与防砂筛网平齐；
步骤三：喷嘴分别与对应的高压液体注入系统连接
将压裂和加固的喷嘴分别与对应的耐压管道下端连接，以使开采井上压裂和加固的喷嘴分别与海上开采平台上对应的高压液体注入系统连接，以控制压裂液和加固剂通过喷嘴独立地注入水合物储层；
步骤四：制备压裂液并注入水合物储层
制备压裂液，并利用海上开采平台上的高压液体注入系统，通过开采井上的压裂液喷嘴将压裂液注入水合物储层，以在水合物储层中形成压裂裂缝，且压裂液中的多孔材料支撑剂沉积固定于裂缝中；
步骤五：水合物开采
通过开采井上的开采开孔对水合物储层进行降压或降压-热激联合方式的开采，以使压裂区水合物快速分解产出；
步骤六：制备加固剂并注入水合物储层加固
制备加固剂，并利用海上开采平台上的高压液体注入系统，通过开采井上的加固剂喷嘴将加固剂由压裂产生的裂缝注入开采后的水合物储层，静置一段时间，对已开采区进行加固；
步骤七：水合物储层压裂-开采-加固多过程开采
根据水合物开采范围需求，重复步骤四至步骤六，先压裂未开采水合物储层形成压裂区，然后对压裂区的水合物进行开采，压裂区水合物分解开采完毕后注入加固剂将压裂区转化为加固区，而后继续压裂未开采水合物储层扩大压裂区，对水合物储层进行压裂-开采-加固的多过程联合高效开采。
进一步地，所述步骤一中，开采井内输送不同液体的管道各自独立，管道为能够承受内外压力差的耐压管道。
进一步地，所述步骤二中，开采井上设有若干开采开孔，为天然气水合物开采时液气产出的传输通道；开采井外侧包裹有防砂筛网。
进一步地，所述步骤二中，喷嘴上的喷孔为圆形喷孔，每组喷嘴由压裂液喷嘴和加固剂喷嘴组成，其中，压裂液喷嘴上设有一个用于压裂液喷出的喷孔，加固剂喷嘴上设有加固剂加固母液喷孔和加固剂反应剂喷孔；每组喷嘴围绕在一个开采开孔周围，喷嘴从开采井井壁向外伸出，穿过包裹在开采井外侧的防砂筛网，喷嘴最外端与防砂筛网最外端平齐。
进一步地，所述步骤四中，压裂液为具有粘度的液体，压裂液为高粘度压裂液或低粘度压裂液，高粘度压裂液包括胍胶压裂液和硅油压裂液，低粘度压裂液包括氯化钠溶液压裂液。
进一步地，所述步骤四中，支撑剂包括多孔陶瓷颗粒、多孔碳酸钙颗粒、聚酯纤维材料中的一种或多种混合；支撑剂均匀混合在压裂液中，形成悬浊液。
进一步地，所述步骤四中，高压液体注入系统包括恒压注入和恒流注入，注入压裂液的压力或注入速率根据开采前钻探获得的水合物储层力学参数和压力条件确定，最小注入压力pmin的计算公式为：
式中，K0为水合物储层该处的静止土压力系数，Φ为水合物储层沉积物内摩擦角，ρ'为水合物储层及上覆沉积物层的平均有效密度，g为重力加速度，z为水合物储层该处的埋深，NP为水合物粘聚作用系数，ch为水合物的粘聚力。
进一步地，所述步骤六中，加固剂由加固母液和反应剂组成，加固母液和反应剂的比例根据所需反应时间和加固强度确定；加固母液由加固剂加固母液管道和加固剂喷嘴上的加固剂加固母液喷孔注入开采后的水合物储层进行加固，反应剂由加固剂反应剂管道209和加固剂喷嘴上的加固剂反应剂喷孔注入开采后的水合物储层进行加固；加固流程为：先注入加固母液一段时间后，再注入反应剂，使其均匀填充土骨架孔隙，静置一段时间等待胶结体或结晶体生成，完成对已开采区域的加固。
进一步地，所述加固母液和反应剂反应时在水合物储层孔隙中形成胶结体或结晶体，其形成原理如下式所示：
所述胶结体或结晶体具有多孔特征，所述胶结体或结晶体在土骨架接触处生成。
进一步地，所述步骤六中，加固剂注入时压力小于等于压裂液的最小注入压力pmin。
与现有技术相比，本发明的有益效果为：
本发明适用于海域天然气水合物开采领域，能够采用主动劈裂的方法提高井周水合物储层渗透性和形成优势渗流路径，采用化学反应或微生物诱导结晶加固的方法加固压裂后的水合物储层，并且通过压裂-开采-加固的多过程联合方法，多次重复不断扩大压裂区域及水合物分解区域，提高水合物开采的效率和储层稳定性。
本发明方法新颖，思路清晰，填补了天然气水合物储层压裂-开采-加固的多过程联合高效开采技术的空白，为深海天然气水合物安全高效开采提供新的技术，解决目前天然气水合物开采时由于储层渗透性低导致的产气速率低及由于储层出砂导致的开采井堵塞及储层失稳的问题。
附图说明
图1是本发明中天然气水合物开采现场布置及压裂-开采-加固的多过程联合高效开采过程示意图；其中，图1中的(a)为压裂及开采过程示意图；图1中的(b)为加固及二次压裂过程示意图；
图2是本发明中开采井孔、喷嘴布置及内部管道结构示意图；其中，图2中的(a)为开采井前视图；图2中的(b)为开采井径向剖面图；图2中的(c)为开采井的一种轴向剖面图；图2中的(d)为开采井的另一种轴向剖面图；
图3是本发明中水合物储层压裂-开采-加固的多过程联合高效开采方法的流程图。
图中，加固区101、压裂区102、水合物储层103、开采井104、上覆海水105、上覆盖土层106、下伏层107、海上开采平台108、开采开孔201、压裂液喷嘴202、加固剂喷嘴203、井内开采通道204、防砂筛网205、开采井井壁206、压裂液管道207、加固剂加固母液管道208、加固剂反应剂管道209、加固剂加固母液喷孔210、加固剂反应剂喷孔211。
具体实施方式
这里将详细地对示例性实施例进行说明，其示例表示在附图中。下面的描述涉及附图时，除非另有表示，不同附图中的相同数字表示相同或相似的要素。以下示例性实施例中所描述的实施方式并不代表与本申请相一致的所有实施方式。相反，它们仅是与如所附权利要求书中所详述的、本申请的一些方面相一致的装置和方法的例子。应当理解的是，以上的一般描述和后文的细节描述仅是示例性和解释性的，并不能限制本申请。
在本申请使用的术语是仅仅出于描述特定实施例的目的，而非旨在限制本申请。在本申请和所附权利要求书中所使用的单数形式的“一种”、“所述”和“该”也旨在包括多数形式，除非上下文清楚地表示其他含义。还应当理解，本文中使用的术语“和/或”是指并包含一个或多个相关联的列出项目的任何或所有可能组合。
应当理解，尽管在本申请可能采用术语第一、第二、第三等来描述各种信息，但这些信息不应限于这些术语。这些术语仅用来将同一类型的信息彼此区分开。例如，在不脱离本申请范围的情况下，第一信息也可以被称为第二信息，类似地，第二信息也可以被称为第一信息。取决于语境，如在此所使用的词语“如果”可以被解释成为“在……时”或“当……时”或“响应于确定”。而且，术语“包括”、“包含”或者其任何其他变体意在涵盖非排他性的包含，从而使得包括一系列要素的过程、方法不仅包括那些要素，而且还包括没有明确列出的其他要素，或者是还包括为这种过程、方法所固有的要素。在没有更多限制的情况下，由语句“包括一个……”限定的要素，并不排除在包括所述要素的过程、方法、物品或者设备中还存在另外的相同要素。
下面结合附图，对本发明的技术方案进行详细说明。在不冲突的情况下，下述的实施例及实施方式中的特征可以相互组合。
如图1-图2所示，本发明中所述的水合物储层103位于深海海底沉积物中，水合物储层103从上到下覆盖有上覆海水105和上覆盖土层106，水合物储层103下部为下伏层107。本发明的水合物储层压裂-开采-加固的多过程联合高效开采方法，首先开采井104从海上开采平台108穿过上覆海水105和上覆盖土层106插入未开采水合物储层103中，开采井井壁206上每隔一段距离设有开采开孔201、压裂液喷嘴202和加固剂喷嘴203，图中所示的开采开孔201环向中心对称布置四个，当然，也可根据需求改变布置密度。压裂液喷嘴202和加固剂喷嘴203这两种喷嘴组成一组喷嘴围绕在开采开孔201周围。开采井井壁206外侧包裹有防砂筛网205，喷嘴最外端与防砂筛网205最外端平齐。在开采井104内设置压裂液管道207、加固剂加固母液管道208和加固剂反应剂管道209，用于连接喷嘴与海上开采平台108上的高压液体注入系统，井内管道同喷嘴对应，中心对称布置，开采产出的液气通过井内开采通道204产出。
本发明中压裂、开采与加固先后重复进行，使用高压液体注入系统的高压泵将海上开采平台108上的压裂液通过压裂液管道207和压裂液喷嘴202注入未开采水合物储层103中，产生压裂裂缝形成压裂区102，压裂液中的支撑剂可阻止裂缝闭合。开采可通过降压法开采，待压裂区102中的水合物分解完成后，在海上开采平台108上将CaCl2、尿素和水按比例均匀混合调配制成加固剂的加固母液，将DSM33细菌、尿素酶、营养液和水按比例均匀混合调配制成加固剂的反应剂，使用高压液体注入系统的高压泵将加固剂的加固母液和反应剂分别通过加固剂加固母液管道208和加固剂反应剂管道209，经由加固剂喷嘴203注入到压裂区102中，静置一段时间等待结晶加固，将开采后的压裂区102转化为加固区101。待加固区101加固完成后，继续使用高压泵将压裂液注入未开采水合物储层103中，二次压裂将一部分未开采水合物储层103转化为压裂区102，后续重复开采、加固及压裂的多阶段过程，不断扩大水合物开采范围。
如图3所示，本发明实施例及其实施过程，包括以下步骤：
步骤一：开采井内设置液体注入管道
在开采井104内设置若干耐压管道，分别用于输送压裂液和加固剂，耐压管道上端与海上开采平台108上对应的高压液体注入系统连接。
进一步地，开采井104内输送不同液体的管道各自独立，以保证能够控制不同的液体的独立注入，管道为能够承受内外压力差的耐压管道。
具体地，在开采井104内设置压裂液管道207、加固剂加固母液管道208和加固剂反应剂管道209各4个，将3种耐压管道分别与压裂液喷嘴202、加固剂喷嘴203的加固剂加固母液喷孔210和加固剂反应剂喷孔211连接，耐压管道上端与海上开采平台108上对应的高压液体注入系统连接，分别用于输送压裂液和加固剂，输送不同液体的管道各自独立以实现不同液体的独立注入控制。
步骤二：开采井上设置开采孔及喷嘴
在开采井104与天然气水合物储层103接触的部分，每间隔一定距离设置压裂、加固和开采的开孔及喷嘴，喷嘴向外侧从开孔中伸出，喷嘴外端与防砂筛网205平齐。
进一步地，开采井104上设有若干开采开孔201，为天然气水合物开采时液气产出的传输通道；开采井104外侧包裹有防砂筛网205，可以防止开采过程中水合物储层103出砂堵塞开采井104上的开采开孔201以及包含开采井104在内的液气产出通道。
进一步地，喷嘴上的喷孔为圆形喷孔，每组喷嘴由压裂液喷嘴202和加固剂喷嘴203组成，其中，压裂液喷嘴202上设有一个喷孔，用于压裂液喷出；加固剂喷嘴203上设有两个喷孔，分别用于加固剂的加固母液和加固剂的反应剂喷出；每组喷嘴围绕在一个开采开孔201周围，实现水合物储层103中不同液体的注入，喷嘴从开采井井壁206向外伸出，穿过包裹在开采井104外侧的防砂筛网205，喷嘴最外端与防砂筛网205最外端平齐。
具体地，在开采井104与未开采天然气水合物储层103接触的部分，轴向每间隔2米设置4个环向中心对称的开采开孔201，每个开采开孔201周围环绕有压裂液喷嘴202和加固剂喷嘴203各1个，喷嘴向外侧从开孔中伸出，伸出开采井井壁206，喷嘴外端与防砂筛网205平齐。
步骤三：喷嘴分别与对应的高压液体注入系统连接
将压裂和加固的喷嘴分别与对应的耐压管道下端连接，以使开采井104上压裂和加固的喷嘴分别与海上开采平台108上对应的高压液体注入系统连接，以控制压裂液和加固剂通过喷嘴独立地注入水合物储层103。
具体地，将压裂液喷嘴202和加固剂喷嘴203分别与对应的耐压管道下端连接，即压裂液喷嘴202和压裂液管道207下端连接，加固剂喷嘴203上设置的两个喷孔(即加固剂加固母液喷孔210和加固剂反应剂喷孔211)分别和加固剂加固母液管道208以及加固剂反应剂管道209下端连接，使得压裂液喷嘴202和加固剂喷嘴203通过对应的耐压管道分别与海上开采平台108上对应的高压液体注入系统连接，能够控制压裂液和加固剂分别通过对应的压裂液喷嘴202和加固剂喷嘴203独立地注入水合物储层103。
步骤四：制备压裂液并注入水合物储层
制备压裂液，并利用海上开采平台108上的高压液体注入系统，通过开采井104上的压裂液喷嘴202将压裂液注入水合物储层103，以在水合物储层103中形成压裂裂缝，且压裂液中的多孔材料支撑剂沉积固定于裂缝中，用于支撑裂缝阻止裂缝闭合，可以提高压裂区102渗透性同时形成渗流优势通道。
进一步地，压裂液为具有特定粘度的液体，注入水合物储层103时利用液体的压力劈裂水合物储层103，形成压裂裂缝。压裂液可以为胍胶、硅油等高粘度压裂液，也可以为氯化钠溶液等低粘度压裂液。当水合物储层103的水合物饱和度较高时可采用低粘度压裂液，便于开采时压裂液的排除；当水合物储层103的水合物饱和度较低时可采用高粘度压裂液，可以减少压裂液在水合物储层103中的损失，顺利劈裂水合物储层103。
其中，胍胶压裂液的组成成分为：质量分数为0.55％的胍胶粉、质量分数为0.6％的交联剂、质量分数为0.2％的过硫酸铵、质量分数为0.2％的大豆卵磷脂以及水；氯化钠溶液压裂液的组成成分为：质量分数为3.5％的氯化钠水溶液。
进一步地，压裂液中的支撑剂可以为多孔陶瓷颗粒、多孔碳酸钙颗粒、聚酯纤维等材料中的一种或多种材料混合，支撑剂均匀地混合在压裂液中，形成悬浊液，即压裂液为悬浊液。
进一步地，高压液体注入系统包括恒压注入和恒流注入这两种注入方式，利用海上开采平台108上的高压液体注入系统，通过压裂液喷嘴202将压裂液注入未开采水合物储层103中形成压裂裂缝，将部分未开采水合物储层103转化为压裂区102，注入压裂液的压力或注入速率根据开采前钻探获得的水合物储层103力学参数和压力条件确定，最小注入压力pmin的具体计算公式如公式(1)所示：
式中，K0为水合物储层103该处的静止土压力系数，Φ为水合物储层103沉积物内摩擦角，ρ'为水合物储层103及上覆沉积物层的平均有效密度，g为重力加速度，z为水合物储层103该处的埋深，NP为水合物粘聚作用系数，ch为水合物的粘聚力。
压裂液在水合物储层103中产生劈裂裂缝，随后，压裂液中的多孔材料支撑剂沉积固定于裂缝中，支撑裂缝，阻止开采过程中裂缝闭合，提高压裂区102的渗透性。
步骤五：水合物开采
通过开采井104上的开采开孔201对水合物储层103进行降压或降压-热激联合等方式的开采，以使压裂区102水合物快速分解产出，其中，根据产气速率特征确定该次产气时长。
步骤六：制备加固剂并注入水合物储层加固
制备加固剂，并利用海上开采平台108上的高压液体注入系统，通过开采井104上的加固剂喷嘴203将加固剂由压裂产生的裂缝注入开采后的水合物储层103，静置一段时间，对已开采区进行加固。
进一步地，加固剂由加固母液和反应剂组成，加固母液和反应剂的比例根据所需反应时间和加固强度确定；加固母液和反应剂分别由各自独立的耐压管道(即加固剂加固母液管道208和加固剂反应剂管道209)和加固剂喷嘴203上对应的加固剂加固母液喷孔210和加固剂反应剂喷孔211注入开采后的水合物储层103进行加固；加固流程为：先注入加固母液一段时间后，再注入反应剂，使其均匀填充土骨架孔隙，静置一段时间等待胶结体或结晶体生成，完成对已开采区域的加固，达到加固的效果。
进一步地，加固母液和反应剂反应时在水合物储层103孔隙中形成胶结体或结晶体，可以起到支撑和胶结加固的作用，二者之间的反应可以是化学反应，也可以是生物反应，胶结体或结晶体形成原理如公式(2)所示：
进一步地，产生的胶结体或结晶体具有较高强度，且具有多孔特征，胶结体或结晶体主要在土骨架接触处生成，对土骨架起到胶结固定和加固支撑作用，且保持其孔隙通道，不影响储层渗透性。
具体地，加固剂的加固母液中各成分的浓度配比为：CaCl2浓度2mol/L、尿素浓度3mol/L及充足的水；加固剂的反应剂中各成分的浓度配比为：营养液6g/L、尿素酶2g/L、冻干DSM33细菌1g/L及充足的水。细菌诱导生成碳酸钙结晶的化学反应方程式如公式(3)和公式(4)所示：
具体地，利用海上开采平台108上的高压液体注入系统，先通过开采井104上的加固剂喷嘴203的加固剂加固母液喷孔210将加固母液由压裂产生的裂缝注入开采后的压裂区102，然后通过加固剂喷嘴203的加固剂反应剂喷孔211将反应剂注入开采后的压裂区102，使其填充土骨架孔隙，注入水合物储层103的加固母液和反应剂体积比例为1:1，静置一段时间使碳酸钙结晶沉积，对已开采区域进行加固。
进一步地，加固剂注入时压力应小于等于压裂液的最小注入压力pmin，以保证加固剂可以充分填充土骨架间的孔隙，且不会对土骨架产生扰动，在不大于最小注入压力pmin的前提下尽量提高加固剂注入速率，以提高加固效率。
步骤七：水合物储层压裂-开采-加固多过程开采
根据水合物开采范围需求，重复步骤四至步骤六，先压裂未开采水合物储层103形成压裂区102，然后对压裂区102的水合物进行开采，压裂区102水合物分解开采完毕后注入加固剂将压裂区102转化为加固区101，而后继续压裂未开采水合物储层103扩大压裂区102，对水合物储层103进行压裂-开采-加固的多过程联合高效开采，不断扩展压裂区102及加固区101范围，扩大开采范围，提高水合物储层103渗透性及开采井104周土骨架稳定性，提升降压等方式的开采效率，降低开采井104周土骨架的失稳风险。
进一步地，根据水合物储层103厚度、水合物储层103水合物饱和度、渗透性等参数和水合物储层103开采范围等需求，可重复步骤四至步骤六的操作进行多次压裂-开采-加固；对扩展区进行上述操作时可根据需求对压裂液、加固剂进行重新配制，同时注入速率和注入压力根据需求进行调整。
由此实施可见，本发明创新性地采用压裂-开采-加固的多过程联合高效开采方法，具有方法新颖、操作简单、流程清晰等优势，填补了天然气水合物储层压裂-开采-加固的多过程联合高效开采技术的空白，为深海天然气水合物安全高效开采提供新的技术，能够解决天然气水合物开采时的产气速率低及储层易失稳的问题，可以实现天然气水合物现场安全稳定、长期可持续开采的目的。
需要说明的是，本申请的实施例有较佳的实施性，并非是对本申请任何形式的限定。本申请实施例中描述的技术特征或者技术特征的组合不应当被认为是孤立的，它们可以被相互组合从而达到更好的技术效果。本申请优选实施方式的范围也可以包括另外的实现，且这应被本申请实施例所属技术领域的技术人员所理解。
对于相关领域普通技术人员已知的技术、方法和设备可能不作详细讨论，但在适当情况下，所述技术、方法和设备应当被视为授权说明书的一部分。在这里示出和讨论的所有示例中，任何具体值应被解释为仅仅是示例性的，而不是作为限定。因此，示例性实施例的其它示例可以具有不同的值。
本申请的附图均采用非常简化的形式且均使用非精准的比例，仅用以方便、明晰地辅助说明本申请实施例的目的，并非是限定本申请可实施的限定条件。任何结构的修饰、比例关系的改变或大小的调整，在不影响本申请所能产生的效果及所能达成的目的下，均应在本申请所揭示的技术内容所能涵盖的范围内。
上述描述仅为本申请的较佳实施例的描述，并非是对本申请范围的任何限定。任何熟悉该领域的普通技术人员根据上述揭示的技术内容做出的任何变更或修饰均应当视为等同的有效实施例，均属于本申请技术方案保护的范围。

Claims (10)

  1. 一种水合物储层压裂-开采-加固的多过程联合高效开采方法，其特征在于，包括以下步骤：
    步骤一：开采井内设置液体注入管道
    在开采井(104)内设置若干耐压管道，分别用于输送压裂液和加固剂，耐压管道上端与海上开采平台(108)上对应的高压液体注入系统连接；
    步骤二：开采井上设置开采孔及喷嘴
    在开采井(104)与天然气水合物储层(103)接触的部分，每间隔一定距离设置压裂、加固和开采的开孔及喷嘴，喷嘴向外侧从开孔中伸出，喷嘴外端与防砂筛网(205)平齐；
    步骤三：喷嘴分别与对应的高压液体注入系统连接
    将压裂和加固的喷嘴分别与对应的耐压管道下端连接，以使开采井(104)上压裂和加固的喷嘴分别与海上开采平台(108)上对应的高压液体注入系统连接，以控制压裂液和加固剂通过喷嘴独立地注入水合物储层(103)；
    步骤四：制备压裂液并注入水合物储层
    制备压裂液，并利用海上开采平台(108)上的高压液体注入系统，通过开采井(104)上的压裂液喷嘴(202)将压裂液注入水合物储层(103)，以在水合物储层(103)中形成压裂裂缝，且压裂液中的多孔材料支撑剂沉积固定于裂缝中；
    步骤五：水合物开采
    通过开采井(104)上的开采开孔(201)对水合物储层(103)进行降压或降压-热激联合方式的开采，以使压裂区(102)水合物快速分解产出；
    步骤六：制备加固剂并注入水合物储层加固
    制备加固剂，并利用海上开采平台(108)上的高压液体注入系统，通过开采井(104)上的加固剂喷嘴(203)将加固剂由压裂产生的裂缝注入开采后的水合物储层(103)，静置一段时间，对已开采区进行加固；
    步骤七：水合物储层压裂-开采-加固多过程开采
    根据水合物开采范围需求，重复步骤四至步骤六，先压裂未开采水合物储层(103)形成压裂区(102)，然后对压裂区(102)的水合物进行开采，压裂区(102)水合物分解开采完毕后注入加固剂将压裂区(102)转化为加固区(101)，而后继续压裂未开采水合物储层(103)扩大压裂区(102)，对水合物储层(103)进行压裂-开采-加固的多过程联合高效开采。
  2. 根据权利要求1所述的水合物储层压裂-开采-加固的多过程联合高效开采方法，其特征在于，所述步骤一中，开采井(104)内输送不同液体的管道各自独立，管道为能够承受内外压力差的耐压管道。
  3. 根据权利要求1所述的水合物储层压裂-开采-加固的多过程联合高效开采方法，其特征在于，所述步骤二中，开采井(104)上设有若干开采开孔(201)，为天然气水合物开采时液气产出的传输通道；开采井(104)外侧包裹有防砂筛网(205)。
  4. 根据权利要求1所述的水合物储层压裂-开采-加固的多过程联合高效开采方法，其特征在于，所述步骤二中，喷嘴上的喷孔为圆形喷孔，每组喷嘴由压裂液喷嘴(202)和加固剂喷嘴(203)组成，其中，压裂液喷嘴(202)上设有一个用于压裂液喷出的喷孔，加固剂喷嘴(203)上设有加固剂加固母液喷孔(210)和加固剂反应剂喷孔(211)；每组喷嘴围绕在一个开采开孔(201)周围，喷嘴从开采井井壁(206)向外伸出，穿过包裹在开采井(104)外侧的防砂筛网(205)，喷嘴最外端与防砂筛网(205)最外端平齐。
  5. 根据权利要求1所述的水合物储层压裂-开采-加固的多过程联合高效开采方法，其特征在于，所述步骤四中，压裂液为具有粘度的液体，压裂液为高粘度压裂液或低粘度压裂液，高粘度压裂液包括胍胶压裂液和硅油压裂液，低粘度压裂液包括氯化钠溶液压裂液。
  6. 根据权利要求1所述的水合物储层压裂-开采-加固的多过程联合高效开采方法，其特征在于，所述步骤四中，支撑剂包括多孔陶瓷颗粒、多孔碳酸钙颗粒、聚酯纤维材料中的一种或多种混合；支撑剂均匀混合在压裂液中，形成悬浊液。
  7. 根据权利要求1所述的水合物储层压裂-开采-加固的多过程联合高效开采方法，其特征在于，所述步骤四中，高压液体注入系统包括恒压注入和恒流注入，注入压裂液的压力或注入速率根据开采前钻探获得的水合物储层(103)力学参数和压力条件确定，最小注入压力pmin的计算公式为：
    式中，K0为水合物储层(103)该处的静止土压力系数，Φ为水合物储层(103)沉积物内摩擦角，ρ'为水合物储层(103)及上覆沉积物层的平均有效密度，g为重力加速度，z为水合物储层(103)该处的埋深，NP为水合物粘聚作用系数，ch为水合物的粘聚力。
  8. 根据权利要求1所述的水合物储层压裂-开采-加固的多过程联合高效开采方法，其特征在于，所述步骤六中，加固剂由加固母液和反应剂组成，加固母液和反应剂的比例根据所需反应时间和加固强度确定；加固母液由加固剂加固母液管道(208)和加固剂喷嘴(203)上的加固剂加固母液喷孔(210)注入开采后的水合物储层(103)进行加固，反应剂由加固剂反应剂管道209和加固剂喷嘴(203)上的加固剂反应剂喷孔(211)注入开采后的水合物储层(103)进行加固；加固流程为：先注入加固母液一段时间后，再注入反应剂，使其均匀填充土骨架孔隙，静置一段时间等待胶结体或结晶体生成，完成对已开采区域的加固。
  9. 根据权利要求8所述的水合物储层压裂-开采-加固的多过程联合高效开采方法，其特征在于，所述加固母液和反应剂反应时在水合物储层(103)孔隙中形成胶结体或结晶体，其形成原理如下式所示：
    所述胶结体或结晶体具有多孔特征，所述胶结体或结晶体在土骨架接触处生成。
  10. 根据权利要求1所述的水合物储层压裂-开采-加固的多过程联合高效开采方法，其特征在于，所述步骤六中，加固剂注入时压力小于等于压裂液的最小注入压力pmin。
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