CN105625998B - A kind of reverse recovery method of sea bed gas hydrate stabilized zone and its winning apparatus - Google Patents

Abstract

The invention relates to a reverse mining method of a seabed natural gas hydrate stable layer, which includes the following steps: S1. Gas production by reducing pressure: firstly, the liquid in the production well is pumped out to reduce the bottom hole pressure, and the gas hydrate is exploited to free the bottom of the hydrate stable layer. At the same time, decompose the lower surface of the hydrate stable layer; S2, thermal injection decomposition: inject hot water or steam into the upper part of the production layer to decompose the natural gas hydrate stable layer from bottom to top, and extract it from the production well after decomposition; S3, carbon dioxide Consolidation: Inject carbon dioxide into the lower part of the production layer, so that the bottom of the production layer is gradually consolidated from bottom to top; S4, after the consolidation is completed, repeat steps S1, S2 and S3, and cycle mining until the gas hydrate stable layer is thinned to an appropriate level When the thickness is exceeded, stop production. The invention has the advantages of overcoming the problems of easy leakage of natural gas, easy pollution of the marine environment and easy occurrence of geological disasters during the exploitation of the seabed natural gas hydrate, and improving the safety and environmental protection of the exploitation.

Description

A reverse mining method and mining equipment for a seabed natural gas hydrate stable layer

technical field

The invention relates to the technical field of natural gas hydrate exploitation, in particular to a reverse exploitation method and exploitation equipment of a seabed natural gas hydrate stable layer.

Background technique

Natural gas hydrate (Natural Gas Hydrates, NGH) is a white solid crystalline substance formed during the interaction of small molecular gases such as light hydrocarbons, CO ₂ and H ₂ S with water under low temperature and high pressure conditions. It is called combustible ice. 1 cubic meter of natural gas hydrate can be converted into 164 cubic meters of natural gas and 0.8 cubic meters of water. It is an extremely efficient and clean energy source with much less pollution than coal and oil.

There are four main types of conventional mining methods for hydrates: depressurization method, heat injection method, chemical reagent injection method and carbon dioxide replacement method. The depressurization method is to reduce the pressure of the hydrate reservoir to below the phase equilibrium pressure of the hydrate by pumping water in the production well or in other ways, so as to decompose the hydrate. The main disadvantage of the depressurization method is that the heat required for hydrate decomposition and phase transition is very large, which may lead to secondary formation of hydrate or large-scale freezing, blockage of seepage paths, and affect long-term production efficiency.

The heat injection method is to inject heat energy into the hydrate at the bottom of the well to increase the temperature of the hydrate reservoir. When the reservoir pressure of the hydrate is lower than the phase equilibrium pressure of the hydrate at this temperature, the hydrate will decompose. The disadvantage of the heat injection mining method is that it not only needs to provide heat for hydrate decomposition and phase transition, but also heats sediments, pore gases and liquids. At the same time, there is a problem of heat dissipation in the upper and lower boundary layers, resulting in a large heat loss and high mining costs.

The chemical inhibitor injection method is to inject chemical reagents into the hydrate reservoir, such as brine, methanol, ethanol, ethylene glycol, glycerin, etc., to change the equilibrium conditions of the hydrate reservoir and move the phase equilibrium curve of the hydrate upward. Therefore, the hydrate cannot exist stably under the existing conditions, and thus decomposes. The disadvantages of the chemical reagent injection method are that the price of chemical reagents is high and the environment is seriously polluted. The influence of chemical reagents on the hydrate phase balance is not very obvious, and it is difficult to use this method alone to exploit the stable layer of seabed natural gas hydrate.

The carbon dioxide replacement method is mainly through introducing replacement carbon dioxide into the stable layer of natural gas hydrate. Since carbon dioxide can form hydrate at a higher temperature under the same conditions (such as the same pressure), carbon dioxide can hydrate natural gas. The natural gas in the material is replaced. The problem of the carbon dioxide replacement method is that the replacement process lasts for a long time, the replacement efficiency is low, the effect is not obvious, and it is not suitable for the exploitation of the seabed gas hydrate stable layer without a closed caprock. To sum up, if conventional methods are used to directly exploit this stable layer of marine gas hydrate along the bedding, it will easily lead to uncontrolled decomposition of gas hydrate reservoirs without sealed cap rocks, releasing a large amount of natural gas and causing environmental pollution. Therefore, exploring the development mode of seabed gas hydrate ore bodies without sealed cap rocks has become the focus of attention all over the world.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the prior art, provide a reverse mining method and mining equipment for the stable layer of seabed natural gas hydrate, overcome the difficult problem that the natural gas hydrate in the seabed is easy to leak during the mining process, and improve the production efficiency in the mining process. Safety and environmental protection.

The object of the present invention is achieved through the following technical solutions: a method for reverse mining of a seabed natural gas hydrate stable layer, which comprises the following steps:

S1. Reduced pressure gas production: drill a production well to pass through the seabed sediment layer and natural gas hydrate stable layer to reach the production layer, install a submersible pump at the bottom of the production well, open the regulating valve A, start the depressurized gas production module, and pass The submersible pump pumps the liquid in the production well to reduce the pressure in the production well. The free gas under the stable layer of natural gas hydrate and the natural gas decomposed on the lower surface of the stable layer of natural gas hydrate flow into the low-pressure production well under the action of the high pressure of the seabed hydrostatic water. After passing through the sand removal device, submersible pump and throttle valve, the mixed fluid passes through the gas-liquid-solid separator to separate the gas, water and sediment in the mixed fluid, and the separated mixed gas enters the gas separator to make The natural gas in the mixed gas is separated into the natural gas storage tank, and the carbon dioxide gas is separated into the carbon dioxide storage tank;

S2. Thermal injection decomposition: Open the regulating valve C, start the thermal injection decomposition module, the hot water or steam in the heat medium storage tank is injected into the production layer through the control well by the high-pressure pump, and the lower surface of the natural gas hydrate stable layer obtains heat Decomposition, the decomposed gas and injected hot water or steam are extracted from the production well through the submersible pump;

S3. Carbon dioxide consolidation: close regulating valve A and regulating valve C, close the decompression gas extraction module and thermal injection decomposition module, open regulating valve B, start the carbon dioxide consolidation module, and pressurize the carbon dioxide in the carbon dioxide storage tank through the high-pressure pump Afterwards, the control well is passed into the bottom of the production layer, and the injected carbon dioxide forms a solid carbon dioxide hydrate layer with the sediment and water in the production layer under the action of the formation high pressure and low temperature environment. The upper surface of the carbon dioxide hydrate layer moves upwards, and the thickness of the production layer gradually decreases. When the thickness decreases to the minimum thickness of the production layer, stop injecting carbon dioxide into the production layer;

S4. Stop injecting carbon dioxide. After the carbon dioxide, sediment and water in the production layer fully form a solid carbon dioxide hydrate layer, repeat steps S1, S2 and S3, and reversely exploit the gas hydrate stable layer in this way until the seabed gas hydrate When the stable layer is thinned to an appropriate thickness, stop production.

The production equipment used for the reverse mining method of the seabed natural gas hydrate stable layer includes a decompression gas production module, a thermal injection decomposition module and a carbon dioxide consolidation module. The depressurization gas production module includes a production well, a submersible pump, a liquid drainage gas production Pipelines, gas-liquid-solid separators and gas separators, the production well passes through the seabed sediment layer and the gas hydrate stable layer from the sea level, and extends into the production layer, and the submersible pump is installed at the bottom of the inner side of the production well to discharge liquid and gas The lower end of the pipeline is connected to the outlet of the submersible pump, the upper end is connected to the inlet of the gas-liquid-solid separator, the gas outlet of the gas-liquid-solid separator is connected to the inlet of the gas separator, and the natural gas outlet of the gas separator is connected to the inlet of the natural gas storage tank , the carbon dioxide outlet is connected to the inlet of the carbon dioxide storage tank, and a throttling valve and a regulating valve A are also installed on the pipeline of the liquid discharge gas production pipeline; the carbon dioxide consolidation module includes a control well, an injection pipeline and a high-pressure pump, and the control well is composed of The sea level passes through the seabed sediment layer and the gas hydrate stable layer in turn, and extends into the production layer. The injection pipeline is set in the control well, and the lower end is located at the bottom of the control well, and the upper end is connected to the outlet of the high-pressure pump. The inlet of the high-pressure pump is connected to the The outlet of the carbon dioxide storage tank is connected, and a regulating valve B is arranged on the pipeline between the high-pressure pump and the carbon dioxide storage tank; the thermal injection and decomposition module includes a heating device and a heat medium storage tank, the inlet of the heating device communicates with seawater, and the outlet connects with the The first inlet of the heat medium storage tank is connected, the outlet of the heat medium storage tank is connected with the inlet of the high-pressure pump, and a regulating valve C is arranged on the pipeline between the heat medium storage tank and the high-pressure pump.

The bottom of the production well is provided with a sand control device.

The liquid outlet of the gas-liquid-solid separator communicates with the second inlet of the heat medium storage tank.

The present invention has the following advantages:

1. During the production process, the method of reverse mining the lower part of the gas hydrate stable layer was adopted by combining the pressure reduction method and the heat injection method, and the gas hydrate stable layer itself was used as a closed cap rock. Since the upper part of the production layer is a gas hydrate stable layer , the lower part is the solid layer of carbon dioxide hydrate, which forms an upper cover layer and a lower cover layer, which ensures the safety of the production layer mining process. In theory, there is no problem of natural gas leakage and environmental pollution.

2. Utilizing the characteristics that carbon dioxide is easy to form solid hydrate, the sediment and remaining water after hydrate decomposition are consolidated to ensure the stability of the seabed geological structure after natural gas hydrate mining. It has a supporting function, and will not cause cavities in the lower part of the natural gas hydrate stable layer due to excessive exploitation, which will lead to submarine geological disasters, such as submarine collapse and landslides, and even tsunamis.

3. Due to the rational use of carbon dioxide waste gas, direct emission into the atmosphere is avoided, the carbon dioxide content in the atmosphere is reduced, and the atmospheric greenhouse effect is reduced. When the required carbon dioxide is insufficient, it can be collected from some factories and enterprises that produce more carbon dioxide to ensure the supply of carbon dioxide.

Description of drawings

Fig. 1 is a structural schematic diagram of reverse mining of a seabed gas hydrate stable layer;

In the figure: 1-production well, 2-sand control device, 3-submersible pump, 4-discharging gas production pipeline, 5-throttle valve, 6-regulating valve A, 7-gas-liquid-solid separator, 8-gas Separator, 9-natural gas storage tank, 10-carbon dioxide storage tank, 11-regulating valve B, 12-high pressure pump, 13-control well, 14-injection pipeline, 15-heating device, 16-heat medium storage tank, 17- Control valve C, 18-seabed sediment layer, 19-gas hydrate stable layer, 20-production layer, 21-carbon dioxide hydrate layer, 22-formation.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following description.

A method for reverse mining of a seabed natural gas hydrate stable layer, comprising the following steps:

S1. Depressurization gas production: drill a production well 1 to pass through the seabed sediment layer 18, the natural gas hydrate stable layer 19, and reach the production layer 20. Install a submersible pump 3 at the bottom of the production well 1, open the regulating valve A6, and start the descending process. The pressure gas recovery module uses the submersible pump 3 to extract the liquid in the production well 1, so that the pressure in the production well 1 is reduced, and the free gas under the natural gas hydrate stable layer 19 and the natural gas decomposed on the lower surface of the natural gas hydrate stable layer 19 are released on the seabed Under the action of hydrostatic high pressure, it flows into the low-pressure production well 1, and the produced mixed fluid passes through the sand removal device 2, submersible pump 3 and throttle valve 5, and then passes through the gas-liquid-solid separator 7 to separate the gas in the mixed fluid. , water and silt are separated, and the separated mixed gas enters the gas separator 8, the natural gas in the mixed gas is separated into the natural gas storage tank 9, and the carbon dioxide gas is separated into the carbon dioxide storage tank 10;

S2. Thermal injection decomposition: open the regulating valve C17, start the thermal injection decomposition module, the hot water or steam in the heat medium storage tank 16 is injected into the production layer 20 through the control well 13 by the high-pressure pump 12, and the natural gas hydrate stable layer 19 The lower surface is decomposed after gaining heat, and the decomposed natural gas and part of the formation fluid are extracted from the production well 1 through the submersible pump 3, and most of the decomposed sand remains in the production layer 20 due to the blocking effect of the sand control device 2, and sinks into the bottom of the production layer 20, and with the advancement of the production process of the gas hydrate stable layer 19, the lower surface of the gas hydrate stable layer 19 moves upwards, and the thickness of the production layer 20 gradually increases. When the maximum thickness of the production layer 20 is reached , stop injecting heat into the production layer 20;

S3. Carbon dioxide consolidation: close the regulating valve A6 and regulating valve C17, close the pressure-reducing gas extraction module and the thermal injection decomposition module, open the regulating valve B11, start the carbon dioxide consolidation module, and pass the carbon dioxide in the carbon dioxide storage tank 10 through the high-pressure pump 12 After pressurization, the control well 13 is passed into the bottom of the production layer 20, and the introduced carbon dioxide forms a solid carbon dioxide hydrate layer 21 with the sediment and water in the production layer 20 under the action of the high-pressure and low-temperature environment of the formation 22. As the formation process of the carbon dioxide hydrate layer 21 progresses, the upper surface of the carbon dioxide hydrate layer 21 moves upwards, and the thickness of the production layer 20 gradually decreases. When the thickness of the production layer 20 is reduced to the minimum, stop injecting carbon dioxide into the production layer 20.

S4. Stop injecting carbon dioxide. After the carbon dioxide, sediment and water in the production layer 20 fully form a solid carbon dioxide hydrate layer 21, repeat steps S1, S2 and S3, and reversely exploit the natural gas hydrate stable layer 19 in this way until the bottom of the sea. When the gas hydrate stable layer 19 is thinned to an appropriate thickness, the production is stopped.

As shown in Figure 1, the production equipment used for the reverse mining method of the seabed natural gas hydrate stable layer includes a decompression gas production module, a thermal injection decomposition module and a carbon dioxide consolidation module, and the depressurization gas production module includes a production well 1, Submersible pump 3, liquid drainage and gas production pipeline 4, gas-liquid-solid separator 7 and gas separator 8, production well 1 passes through seabed sediment layer 18 and natural gas hydrate stable layer 19 sequentially from sea level, and extends into the production layer 20. The bottom of the production well 1 is provided with a sand prevention device 2 to prevent a large amount of sediment from mixing into the liquid drainage gas production pipeline 4 and causing blockage. The lower end of the pump is connected to the outlet of the submersible pump 3, the upper end is connected to the inlet of the gas-liquid-solid separator 7, the gas outlet of the gas-liquid-solid separator 7 is connected to the inlet of the gas separator 8, and the natural gas outlet of the gas separator 8 is connected to the natural gas storage The inlet of the tank 9 is connected, and the carbon dioxide outlet is connected with the inlet of the carbon dioxide storage tank 10. Due to the rational use of the carbon dioxide waste gas, direct emission into the atmosphere is avoided, the carbon dioxide content in the atmosphere is reduced, and the greenhouse effect is reduced. A throttle valve 5 and a regulating valve A6 are also installed on the pipeline of the liquid discharge gas production pipeline 4, and the throttle valve 5 prevents a blowout during the gas production process; the carbon dioxide consolidation module includes a control well 13, an injection pipeline 14 and a The high-pressure pump 12 and the control well 13 pass through the seabed sediment layer 18 and the gas hydrate stable layer 19 sequentially from the sea level, and extend into the production layer 20. The injection pipeline 14 is arranged in the control well 13, and the lower end is located at the bottom of the control well 13 The bottom and the upper end are connected to the outlet of the high-pressure pump 12, the inlet of the high-pressure pump 12 is connected to the outlet of the carbon dioxide storage tank 10, and a regulating valve B11 is arranged on the pipeline between the high-pressure pump 12 and the carbon dioxide storage tank 10; The module includes a heating device 15 and a heat medium storage tank 16, the inlet of the heating device 15 communicates with seawater, the outlet communicates with the first inlet of the heat medium storage tank 16, the outlet of the heat medium storage tank 16 communicates with the inlet of the high-pressure pump 12, and the heat A regulating valve C17 is provided on the pipeline between the medium storage tank 16 and the high-pressure pump 12 , and the liquid outlet of the gas-liquid-solid separator 7 communicates with the second inlet of the heat medium storage tank 16 .

Claims (4)

1. a kind of reverse recovery method of sea bed gas hydrate stabilized zone, it is characterised in that：It comprises the following steps：

S1, decompression gas production：Beat a bite producing well（1）Pass through sea-bottom deposit nitride layer（18）, gas hydrates stabilized zone（19）, arrive Up to production layer（20）, in producing well（1）Shaft bottom installing submersible pump（3）, open regulating valve A（6）, start decompression gas production module, Pass through immersible pump（3）Extract producing well（1）Interior liquid, makes producing well（1）Interior pressure reduction, gas hydrates stabilized zone （19）Following free state mixed gas and gas hydrates stabilized zone（19）The natural gas that lower surface is decomposed is in seabed hydrostatic In the presence of high pressure, the producing well of low pressure is flowed to（1）Interior, the fluid-mixing of extraction passes through immersible pump（3）And choke valve（5）Afterwards, Pass through gas-liquid-solid separator again（7）, the mixed gas in fluid-mixing, water and silt are separated, the gaseous mixture isolated Body enters gas separator（8）, the natural gas in mixed gas is segregated into natural gas storage tank（9）, carbon dioxide point From entering carbon dioxide storage tank（10）；

S2, heat injection are decomposed：Open regulating valve C（17）, start heat injection decomposing module, thermal medium storage tank（16）In hot water or steam By high-pressure pump（12）By controlling well（13）To production layer（20）Interior injection, gas hydrates stabilized zone（19）Lower surface obtain Obtain and decomposed after heat, natural gas and formation fluid after decomposition pass through immersible pump（3）By producing well（1）Extraction；

S3, carbon dioxide consolidation：Close regulating valve A（6）With regulating valve C（17）, close decompression gas production module and mould decomposed in heat injection Block, opens regulating valve B（11）, start carbon dioxide consolidation module, by carbon dioxide storage tank（10）In carbon dioxide pass through height Press pump（12）By control well after pressurization（13）It is passed through production layer（20）Bottom, the carbon dioxide being passed through is on stratum（22）High pressure, In the presence of low temperature environment, with production layer（20）In silt and water formation solid-state carbon dioxide hydrate layer（21）, with Carbon dioxide hydrate layer（21）The propulsion of forming process, carbon dioxide hydrate layer（21）Upper surface is elapsed upwards, produces layer （20）Thickness gradually decrease, when being reduced to production layer（20）Minimum thickness when, stop to production layer（20）Carbon dioxide injection；

S4, stopping injection carbon dioxide, payzone to be generated（20）Interior carbon dioxide is sufficiently formed the titanium dioxide of solid-state with silt, water Kohlenhydrate layer（21）Afterwards, repeat step S1, S2 and S3, so circulates reverse exploitation of gas hydrate stabilized zone（19）, directly To sea bed gas hydrate stabilized zone（19）When being thinned to suitable depth, stop production.

2. a kind of winning apparatus of the reverse recovery method of sea bed gas hydrate stabilized zone as claimed in claim 1, it is special Levy and be：The described reverse winning apparatus of sea bed gas hydrate stabilized zone includes decompression gas production module, heat injection decomposing module Module is consolidated with carbon dioxide, described decompression gas production module includes producing well（1）, immersible pump（3）, liquid discharging gas producing pipeline（4）、 Gas-liquid-solid separator（7）And gas separator（8）, producing well（1）Sea-bottom deposit nitride layer is sequentially passed through by sea level（18）And day Right gas hydrate stabilized zone（19）, and stretch into production layer（20）Top, immersible pump（3）It is arranged at producing well（1）Inside bottom, Liquid discharging gas producing pipeline（4）Lower end and immersible pump（3）Outlet connection, upper end and gas-liquid-solid separator（7）Entrance connection, gas Liquid-solid separator（7）Gas vent and gas separator（8）Entrance connection, gas separator（8）Gas outlet with Natural gas storage tank（9）Entrance connection, carbon dioxide outlet and carbon dioxide storage tank（10）Entrance connection, liquid discharging gas producing pipeline （4）Pipeline on be also equipped with choke valve（5）With regulating valve A（6）；Described carbon dioxide consolidation module includes control well （13）, flow in pipes（14）And high-pressure pump（12）, control well（13）Sea-bottom deposit nitride layer is sequentially passed through by sea level（18）And day Right gas hydrate stabilized zone（19）, and stretch into production layer（20）Bottom, flow in pipes（14）It is arranged at control well（13）It is interior, and Lower end is located at control well（13）Bottom, upper end and high-pressure pump（12）Outlet connection, high-pressure pump（12）Entrance and titanium dioxide Carbon storage tank（10）Outlet connection, high-pressure pump（12）With carbon dioxide storage tank（10）Between pipeline on be provided with regulating valve B （11）；Described heat injection decomposing module includes heater（15）With thermal medium storage tank（16）, heater（15）Entrance with Seawater is connected, outlet and thermal medium storage tank（16）First entrance connection, thermal medium storage tank（16）Outlet and high-pressure pump（12） Entrance connection, thermal medium storage tank（16）With high-pressure pump（12）Between pipeline on be provided with regulating valve C（17）.

3. winning apparatus according to claim 2, it is characterised in that：Described producing well（1）Bottom be provided with sand prevention Device（2）.

4. winning apparatus according to claim 2, it is characterised in that：Described gas-liquid-solid separator（7）Liquid outlet With thermal medium storage tank（16）Second entrance connection.