A method for exploiting natural gas hydrates in the sea area by high-speed hydrothermal jet fragmentation

Abstract

The present invention discloses a method for exploiting natural gas hydrates in the sea area by high-speed hydrothermal jet fragmentation, which includes installing a cementing casing and a lifting platform on a sea surface platform, installing a riser pipe, a water jet self-advancing drill, a water pump, a gas pump and a gas storage tank on the lifting platform, horizontally drilling into the natural gas hydrate reservoir with a self-advancing rotary bit, shooting high-temperature water at high speed from the self-advancing rotary bit, using the high-speed hot water jet to fragment the natural gas hydrate reservoir to form a natural gas hydrate fragmented body, and at the same time using the hot water flow to thermally decompose the natural gas hydrate reservoir to form a gas-water mixture, and sucking the fragmented body and the gas-water mixture into the extraction casing by using negative pressure. The present invention adopts a method combining high-pressure water jet fragmentation, hot water heating decomposition and negative pressure reduction decomposition to exploit natural gas hydrates, with high exploitation efficiency, and can quickly suck the fragmented natural gas hydrates, the gas-water mixture generated by heating decomposition and pressure reduction decomposition into the extraction casing by negative pressure suction, improving the recovery rate.

Description

Technical Field

[0001] The present invention relates to the technical field of natural gas hydrate exploitation, and particularly to a method for exploiting natural gas hydrates in the sea area. Background Art

[0002] Natural gas hydrate is a clean energy source with low carbon, high energy density, wide distribution range and large reserves, and is recognized as the most potential alternative energy in the 21st century.

[0003] Different from traditional fossil fuels such as oil, natural gas and coal, due to the harsh occurrence conditions (high pressure and low temperature) of natural gas hydrates, conventional methods are not applicable to the exploitation of natural gas hydrates in the sea area. At present, the main methods for exploiting natural gas hydrates in the sea area include: pressure reduction method, thermal stimulation method, chemical reagent injection method and CO 2 replacement method, but each has its own deficiencies. The pressure reduction method has low exploitation efficiency, the thermal stimulation method consumes a large amount of heat and has low energy utilization rate, the injection of chemical inhibitors into the hydrate reservoir pollutes the environment, and the CO 2 replacement method has low replacement efficiency, and the produced gas is a mixed gas of natural gas and CO 2 and the mixed gas needs to be purified and separated. Moreover, when facing the situation where natural gas hydrates occur in muddy silt sediments, the above-mentioned exploitation methods cannot achieve high-efficiency exploitation effects. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for exploiting natural gas hydrates in the sea area by high-speed hydrothermal jet fragmentation, so as to solve the technical problems of exploiting natural gas hydrates in the sea area, and achieve the purposes of increasing exploitation efficiency and recovering high-concentration natural gas.

[0005] The method for exploiting natural gas hydrates in the sea area by high-speed hydrothermal jet fragmentation of the present invention includes the following steps:

[0006] 1) Drill vertical guide holes in the overlying layer and the natural gas hydrate reservoir on the seabed on the sea surface platform, install a cementing casing on the sea surface platform, and the lower end of the cementing casing extends into the overlying layer;

[0007] Install a lifting platform on the sea surface platform, install a riser on the lifting platform, the riser is located inside the cementing casing, the riser extends into the natural gas hydrate reservoir through the vertical guide hole, the lower end of the riser is closed, and side holes are provided on the side wall of the lower end of the riser;

[0008] Arrange a water jet self - advancing drill on the lifting platform. Set a extraction sleeve outside the high - pressure resistant water pipe that conveys high - pressure water to the self - advancing rotary bit of the water jet self - advancing drill. The inlet of the extraction sleeve is close to the self - advancing rotary bit. An electric heater is arranged on a section of the high - pressure resistant water pipe close to the self - advancing rotary bit. A power supply for the electric heater is arranged on the sea surface platform. A conveying channel for the extracted material is formed between the extraction sleeve and the high - pressure resistant water pipe. Lower the extraction assembly composed of the self - advancing rotary bit, the high - pressure resistant water pipe and the extraction sleeve into the casing pipe for water isolation;

[0009] Set a water pump on the lifting platform. The water extraction pipe connected to the inlet of the water pump extends into the lower part of the casing pipe for water isolation; Set an air extraction pump on the lifting platform. The air extraction pipe connected to the inlet of the air extraction pump extends into the upper part of the casing pipe for water isolation; Seal the upper port of the casing pipe for water isolation;

[0010] Arrange a gas storage tank on the sea surface platform. The gas storage tank is connected to the outlet of the air extraction pump through a pipeline;

[0011] 2) The water jet self - advancing drill works. Control the self - advancing rotary bit to penetrate through the side hole on the lower end side wall of the casing pipe for water isolation and horizontally drill into the natural gas hydrate reservoir, and supply power to the electric heater in front of the high - pressure resistant water pipe, so that the self - advancing rotary bit shoots out high - speed hot water. Use the high - speed hot water jet to break the natural gas hydrate reservoir to form a natural gas hydrate broken body. At the same time, use the hot water flow to thermally decompose the natural gas hydrate reservoir to form a gas - water mixture;

[0012] During the drilling process of the self - advancing rotary bit, the water pump works to drain water in the casing pipe for water isolation, so that a negative - pressure cavity is formed in the upper part of the casing pipe for water isolation. Then, the natural gas hydrate broken body and the gas - water mixture near the inlet of the extraction sleeve are sucked into the extraction sleeve by negative pressure and enter the casing pipe for water isolation along the extraction sleeve; The air extraction pump sends the gas entering the negative - pressure cavity into the gas storage tank;

[0013] 3) After the first - stage horizontal drilling and extraction are completed, adjust the height of the lifting platform, and then conduct the next - stage horizontal drilling and extraction. Repeat this way to complete the cyclic extraction of a vertical plane;

[0014] 4) After completing the cyclic extraction of a vertical cycle, adjust the position of the sea surface platform and conduct the cyclic extraction of the next vertical plane.

[0015] Furthermore, the method for fracturing and exploiting natural gas hydrates in the sea area by high - speed hydrothermal jet also includes installing an electric heater in the casing pipe for water isolation to thermally decompose the natural gas hydrates floating into the negative - pressure cavity.

[0016] Furthermore, the method for fracturing and exploiting natural gas hydrates in the sea area by high - speed hydrothermal jet also includes setting a drying device on the sea surface platform to dry the gas before it enters the gas storage tank.

[0017] Further, the method for exploiting natural gas hydrate in the sea area by high-speed hydrothermal jet fragmentation further includes arranging an L-shaped guiding pipe at the bottom of the water isolation casing to guide the self-advancing rotary drill bit to penetrate through the side hole on the lower end side wall of the water isolation casing.

[0018] Advantages of the present invention:

[0019] 1. The present invention exploits natural gas hydrate in the sea area by high-speed hydrothermal jet fragmentation, and adopts a method combining high-pressure water jet fragmentation, hot water heating decomposition and negative pressure decompression decomposition to exploit natural gas hydrate, with high exploitation efficiency. Moreover, through negative pressure suction, the fragmented natural gas hydrate and the gas-water mixture generated by heating decomposition and decompression decomposition can be quickly sucked into the extraction casing, improving the recovery rate.

[0020] 2. The present invention exploits natural gas hydrate in the sea area by high-speed hydrothermal jet fragmentation. Through the lifting of the lifting platform and the translation of the sea surface platform, large-area and high-efficiency extraction of submarine natural gas hydrate can be realized. Description of the drawings

[0021] Figure 1 It is a schematic structural diagram of the system for exploiting natural gas hydrate in the sea area by high-speed hydrothermal jet fragmentation. Specific embodiments

[0022] The present invention will be further described below in conjunction with the drawings and embodiments.

[0023] As shown in the figure, the method for exploiting natural gas hydrate in the sea area by high-speed hydrothermal jet fragmentation in this embodiment includes the following steps:

[0024] 1) Drill vertical guiding holes in the overlying layer 2 and the natural gas hydrate reservoir 3 on the seabed from the sea surface platform 1, install a cementing casing 4 on the sea surface platform, and the lower end of the cementing casing extends into the overlying layer.

[0025] Install a lifting platform 5 on the sea surface platform, install a water isolation casing 6 on the lifting platform. The water isolation casing is located inside the cementing casing 4 and extends into the natural gas hydrate reservoir through the vertical guiding hole. The lower end of the water isolation casing is closed, and side holes are provided on the lower end side wall of the water isolation casing.

[0026] Arrange a water jet self-advancing drill rig 7 on the lifting platform. A extraction casing 10 is arranged outside the high-pressure resistant water pipe 9 that conveys high-pressure water to the self-advancing rotary drill bit 8 of the water jet self-advancing drill rig. The inlet of the extraction casing is close to the self-advancing rotary drill bit. An electric heater 11 is arranged on a section of the high-pressure resistant water pipe close to the self-advancing rotary drill bit. A power supply 12 for supplying power to the electric heater is arranged on the sea surface platform. A extraction material conveying channel 13 is formed between the extraction casing and the high-pressure resistant water pipe. The extraction assembly composed of the self-advancing rotary drill bit, the high-pressure resistant water pipe and the extraction casing is lowered into the water isolation casing.

[0027] A water pump 14 is installed on the lifting platform, and a water suction pipe 15 connected to the inlet of the water pump extends into the lower part of the water isolation casing; the lower end of the water suction pipe 15 is close to the bottom of the water isolation casing 6, which can pump out the sediment at the lower layer, and can prevent the sediment from accumulating at the bottom of the water isolation casing 6; the inlet of the water suction pipe 15 is lower than the outlet of the extraction casing, so that the natural gas hydrate and natural gas discharged from the extraction casing will not be sucked into the water suction pipe. An air extraction pump 16 is installed on the lifting platform, and an air extraction pipe 17 connected to the inlet of the air extraction pump extends into the upper part of the water isolation casing; the upper port of the water isolation casing is closed.

[0028] A gas storage tank 18 is arranged on the sea surface platform, and the gas storage tank is connected to the outlet of the air extraction pump through a pipeline.

[0029] 2) The water jet self-advancing drill works, and the self-advancing rotary drill bit is controlled to penetrate through the side hole on the lower side wall of the water isolation casing and horizontally drill into the natural gas hydrate reservoir, and the electric heater in front of the high-pressure water pipe is powered, so that the self-advancing rotary drill bit shoots out high-temperature water at high speed, and the high-speed hot water jet is used to break the natural gas hydrate reservoir to form a natural gas hydrate broken body. At the same time, the natural gas hydrate reservoir is pyrolyzed by the hot water flow to form a gas-water mixture. In a specific implementation, a crushing tool can also be installed on the rotating head of the self-advancing rotary drill bit to improve the crushing effect.

[0030] During the drilling process of the self-advancing rotary drill bit, the water pump works to drain the water in the water isolation casing, so that a negative pressure cavity is formed in the upper part of the water isolation casing. Furthermore, the natural gas hydrate broken body and the gas-water mixture near the inlet of the extraction casing are sucked into the extraction casing under negative pressure and enter the water isolation casing along the extraction casing; the air extraction pump sends the gas entering the negative pressure cavity into the gas storage tank. The negative pressure formed near the inlet of the extraction casing can also promote the decomposition of natural gas hydrates.

[0031] 3) After the first horizontal drilling and extraction are completed, adjust the height of the lifting platform, and then perform the next horizontal drilling and extraction. Repeat this process to complete the cyclic extraction of a vertical plane.

[0032] 4) After completing the cyclic extraction of a vertical cycle, adjust the position of the sea surface platform and perform the cyclic extraction of the next vertical plane.

[0033] In this embodiment, high-speed hydrothermal jet fragmentation is used to exploit natural gas hydrates in the sea area. A method combining high-pressure water jet fragmentation, hot water heating decomposition, and negative pressure reduction decomposition is adopted to exploit submarine natural gas hydrates. The exploitation efficiency is high, and through negative pressure suction, the broken natural gas hydrates, the gas-water mixture generated by heating decomposition and pressure reduction decomposition can be quickly sucked into the extraction casing, improving the recovery rate.

[0034] In this embodiment, high-speed hydrothermal jet fragmentation is used to exploit natural gas hydrates in the sea area. By lifting the lifting platform and translating the sea surface platform, large-area and high-efficiency extraction of submarine natural gas hydrates can be achieved.

[0035] As an improvement to the above embodiments, the method for exploiting marine natural gas hydrates by high-speed hydrothermal jet fragmentation further includes installing an electric heater 19 in the water isolation casing to thermally decompose the natural gas hydrates floating into the negative pressure cavity. Since the solubility of natural gas in seawater is very small, the natural gas entering the water isolation casing can automatically float into the negative pressure cavity. At the same time, the density of natural gas hydrates is also smaller than that of seawater. Therefore, the fragmented natural gas hydrates can also automatically float into the negative pressure cavity in the water isolation casing. By heating the solid natural gas hydrates in the negative pressure cavity with the electric heater 19, the decomposition can be accelerated.

[0036] As an improvement to the above embodiments, the method for exploiting marine natural gas hydrates by high-speed hydrothermal jet fragmentation further includes setting up a drying device 20 on the sea surface platform to dry the gas before it enters the gas storage tank. Through the drying treatment, the quality of natural gas can be improved.

[0037] As an improvement to the above embodiments, the method for exploiting marine natural gas hydrates by high-speed hydrothermal jet fragmentation further includes setting an L-shaped guiding pipe 21 at the bottom of the water isolation casing to guide the self-advancing rotary drill bit to pass through the side hole on the lower side wall of the water isolation casing. This improvement can enable the self-advancing rotary drill bit 8 to smoothly drill horizontally into the natural gas hydrate reservoir.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for high-speed hydrothermal jet crushing and exploitation of marine natural gas hydrates, characterized in that: The following steps are involved: 1) Drilling vertical guide holes into the upper cover and natural gas hydrate reservoir on the seabed on the offshore platform, installing cementing casing on the offshore platform, and extending the lower end of the cementing casing into the upper cover; A lifting platform is installed on the sea surface platform, and a watertight casing is installed on the lifting platform. The watertight casing is located inside the cementing casing, and the watertight casing extends into the natural gas hydrate reservoir through a vertical guide hole. The lower end of the watertight casing is closed, and a side hole is provided on the side wall of the lower end of the watertight casing; A water jet self-propelled drilling rig is arranged on the lifting platform, and an extraction casing is arranged outside a high-pressure resistant water pipe for conveying high-pressure water to a self-propelled rotary drill bit of the water jet self-propelled drilling rig, the inlet of the extraction casing is close to the self-propelled rotary drill bit, an electric heater is arranged at a section of the high-pressure resistant water pipe close to the self-propelled rotary drill bit, a power supply for supplying power to the electric heater is arranged on the sea surface platform, an extraction material conveying channel is formed between the extraction casing and the high-pressure resistant water pipe, and an extraction assembly consisting of the self-propelled rotary drill bit, the high-pressure resistant water pipe and the extraction casing is lowered into the waterproof casing; A water pump is arranged on the lifting platform, and a water pump pipe connected to the water pump inlet is extended into the lower part of the waterproof casing; an air pump is arranged on the lifting platform, and an air pump pipe connected to the air pump inlet is extended into the upper part of the waterproof casing; the upper port of the waterproof casing is sealed; An air storage tank is arranged on the offshore platform, and the air storage tank is connected to the outlet of the air pump through a pipeline; 2) The water jet self-propelled drilling rig is operated to control the self-propelled rotary drill bit to penetrate through the side hole on the side wall of the lower end of the waterproof casing to horizontally drill into the natural gas hydrate reservoir, and power is supplied to the electric heater at the front of the high-pressure resistant water pipe to make the self-propelled rotary drill bit eject hot water at high speed, and use the high-speed hot water jet to break the natural gas hydrate reservoir to form a natural gas hydrate broken body, and at the same time use the hot water flow to pyrolyze the natural gas hydrate reservoir to form a gas-water mixture; During the drilling process of the self-propelled rotary drill bit, the water pump works to drain the water from the waterproof casing, so that a negative pressure cavity is formed on the upper part of the waterproof casing, and then the natural gas hydrate fragments and gas-water mixture near the extraction casing inlet are sucked into the extraction casing by negative pressure, and then enter the waterproof casing along the extraction casing; the air pump sends the gas entering the negative pressure cavity into the gas storage tank; 3) After one horizontal drilling and extraction is completed, the height of the lifting platform is adjusted, and the next horizontal drilling and extraction is carried out, and the cycle of extraction on a vertical surface is repeated in this way; 4) After completing one vertical cycle of extraction, adjust the position of the sea surface platform to carry out the next vertical cycle of extraction.

2. The method for crushing and exploiting marine natural gas hydrate by high-speed hydrothermal jet according to claim 1 is characterized in that: The method also includes installing an electric heater in the watertight casing to pyrolyze the natural gas hydrate that floats up into the negative pressure cavity.

3. The method for crushing and exploiting marine natural gas hydrate by high-speed hydrothermal jet according to claim 1 is characterized in that: It also includes installing a drying device on the sea surface platform to dry the gas before entering the gas storage tank.

4. The method for crushing and exploiting marine natural gas hydrate by high-speed hydrothermal jet according to claim 1 is characterized in that: It also includes setting an L-shaped guide tube at the bottom of the waterproof casing to guide the self-propelled rotary drill bit to pass through the side hole on the side wall of the lower end of the waterproof casing.

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