Method for exploiting natural gas hydrate in sea area through high-speed hydrothermal fluid jet breaking

Abstract

The invention discloses a method for exploiting natural gas hydrate in a sea area through high-speed hydrothermal fluid jet breaking, which comprises the following steps of: installing a well cementation sleeve and a lifting platform on a sea surface platform, installing a drill conductor, a water jet self-propelled drilling machine, a water suction pump, an air suction pump and a gas storage tank on the lifting platform, and horizontally drilling a natural gas hydrate reservoir by a self-propelled rotary drill bit, the self-propelled rotary drill bit ejects hot water at a high speed, the natural gas hydrate reservoir is broken through high-speed hot water jet flow to form a natural gas hydrate broken body, meanwhile, the natural gas hydrate reservoir is pyrolyzed through hot water flow to form a gas-water mixture, and the broken body and the gas-water mixture are sucked into the extraction sleeve through negative pressure. The natural gas hydrate is exploited by adopting a method of combining high-pressure water jet breaking, hot water heating decomposition and negative-pressure depressurization decomposition, the exploiting efficiency is high, the broken natural gas hydrate and a gas-water mixture generated by heating decomposition and depressurization decomposition can be quickly sucked into the extraction sleeve through negative-pressure suction, and the recovery rate is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of natural gas hydrate exploitation, and in particular to a method for exploiting natural gas hydrate in marine areas. Background Art

[0002] Natural gas hydrate is a clean energy with low carbon, high energy density, wide distribution range and large reserves. It is recognized as the most promising replacement energy in the 21st century. According to the assessment of the Ministry of Natural Resources, the total amount of natural gas hydrate resources in China is about 126×10 12 m 3 , of which marine reserves account for 70%.

[0003] Different from traditional fossil energy sources such as oil, natural gas, and coal, due to the harsh storage conditions (high pressure and low temperature) of natural gas hydrates, conventional methods are not suitable for offshore natural gas hydrate exploitation. At present, the offshore natural gas hydrate exploitation methods mainly include: depressurization method, thermal shock method, chemical reagent injection method and CO2 replacement method, but they all have shortcomings. The depressurization method has low exploitation efficiency, the thermal shock method consumes a lot of heat and has low energy utilization rate, the injection of chemical inhibitors into the hydrate reservoir pollutes the environment, the CO2 replacement method has low replacement efficiency, and the produced gas is a mixture of natural gas and CO2, which needs to be purified and separated. And when faced with the situation where natural gas hydrates are stored in muddy silt sand sediments, the above-mentioned exploitation methods cannot achieve efficient exploitation results. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a method for high-speed hydrothermal jet crushing and exploitation of natural gas hydrate in the sea area, so as to solve the technical problems of exploitation of natural gas hydrate in the sea area, increase the exploitation efficiency and the recovery of high-concentration natural gas, etc.

[0005] The method for high-speed hydrothermal jet crushing and exploitation of marine natural gas hydrates of the present invention comprises the following steps:

[0006] 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;

[0007] 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;

[0008] 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;

[0009] 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;

[0010] 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;

[0011] 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;

[0012] 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;

[0013] 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;

[0014] 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.

[0015] Furthermore, the method for high-speed hydrothermal jet crushing and exploitation of marine natural gas hydrates also includes installing an electric heater in the waterproof casing to pyrolyze the natural gas hydrates that float up into the negative pressure cavity.

[0016] Furthermore, the method for high-speed hydrothermal jet crushing and exploitation of marine natural gas hydrates also includes arranging a drying device on the sea surface platform to dry the gas before entering the gas storage tank.

[0017] Furthermore, the method for high-speed hydrothermal jet crushing and exploitation of marine natural gas hydrates also includes setting an L-shaped guide pipe 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.

[0018] Beneficial effects of the present invention:

[0019] 1. The high-speed hydrothermal jet crushing and exploitation of marine natural gas hydrates of the present invention adopts a method combining high-pressure water jet crushing, hot water heating decomposition, and negative pressure decomposition decomposition to exploit natural gas hydrates, with high mining efficiency. The crushed natural gas hydrates and the gas-water mixture produced by heating decomposition and decompression decomposition can be quickly sucked into the extraction casing through negative pressure suction, thereby improving the recovery rate.

[0020] 2. The high-speed hydrothermal jet crushing and exploitation of natural gas hydrates in the sea area of ​​the present invention can realize large-scale and efficient extraction of seabed natural gas hydrates through the lifting and lowering of the lifting platform and the translation of the sea surface platform. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the system structure for high-speed hydrothermal jet crushing and exploitation of marine natural gas hydrates. DETAILED DESCRIPTION

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

[0023] As shown in the figure, the method for high-speed hydrothermal jet crushing and exploitation of marine natural gas hydrate in this embodiment includes the following steps:

[0024] 1) Drill vertical guide holes on the sea surface platform 1 into the upper cover 2 and the natural gas hydrate reservoir 3 on the seabed, install a cementing casing 4 on the sea surface platform, and extend the lower end of the cementing casing into the upper cover.

[0025] A lifting platform 5 is installed on the sea surface platform, and a waterproof casing 6 is installed on the lifting platform. The waterproof casing is located inside the cementing casing 4, and the waterproof casing extends into the natural gas hydrate reservoir through the vertical guide hole. The lower end of the waterproof casing is closed, and a side hole is provided on the side wall of the lower end of the waterproof casing.

[0026] A water jet self-propelled drilling rig 7 is arranged on the lifting platform, and an extraction casing 10 is arranged outside a high-pressure resistant water pipe 9 for conveying high-pressure water to a self-propelled rotary drill bit 8 of the water jet self-propelled drilling rig. The inlet of the extraction casing is close to the self-propelled rotary drill bit, and an electric heater 11 is arranged at a section of the high-pressure resistant water pipe close to the self-propelled rotary drill bit. A power supply 12 for supplying power to the electric heater is arranged on the sea surface platform, and an extraction material conveying channel 13 is formed between the extraction casing and the high-pressure resistant water pipe. The 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.

[0027] A water pump 14 is arranged on the lifting platform, and a water pump pipe 15 connected to the inlet of the water pump extends into the lower part of the waterproof casing; the lower end of the water pump pipe 15 is close to the bottom of the waterproof casing 6, which can pump out the mud and sand in the lower layer, and avoid the accumulation of mud and sand at the bottom of the waterproof casing 6; the inlet of the water pump 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 pump pipe. An air pump 16 is arranged on the lifting platform, and an air pump pipe 17 connected to the inlet of the air pump extends into the upper part of the waterproof casing; the upper end of the waterproof casing is closed.

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

[0029] 2) The water jet self-propelled drilling rig is operated, and the self-propelled rotary drill bit is controlled to penetrate the side hole on the side wall of the lower end of the waterproof casing and drill horizontally into the natural gas hydrate reservoir, and the electric heater at the front of the high-pressure water pipe is powered to make the self-propelled rotary drill bit eject hot water at high speed, and the high-speed hot water jet is used to crush the natural gas hydrate reservoir to form a natural gas hydrate crushed body, and the hot water flow is used to pyrolyze the natural gas hydrate reservoir to form a gas-water mixture. In the specific implementation, a crushing tool can also be installed on the rotating head of the self-propelled rotary drill bit to improve the crushing effect.

[0030] During the drilling process of the self-propelled rotary drill bit, the water pump works to drain the water from the waterproof casing, forming a negative pressure cavity 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 enter the waterproof casing along the extraction casing; the air pump sends the gas entering the negative pressure cavity into the gas storage tank. The negative pressure formed near the extraction casing inlet can also promote the decomposition of natural gas hydrate and matter.

[0031] 3) After one horizontal drilling and extraction is completed, adjust the height of the lifting platform and then carry out the next horizontal drilling and extraction, and repeat this process to complete the cyclic extraction of a vertical surface.

[0032] 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.

[0033] In this embodiment, high-speed hydrothermal jet crushing and exploitation of marine natural gas hydrates adopts a method combining high-pressure water jet crushing, hot water heating decomposition, and negative pressure decomposition decomposition to exploit seabed natural gas hydrates. The exploitation efficiency is high, and the crushed natural gas hydrates, the gas-water mixture produced by heating decomposition and decompression decomposition can be quickly sucked into the extraction casing through negative pressure suction, thereby improving the recovery rate.

[0034] In this embodiment, high-speed hydrothermal jets are used to crush and exploit natural gas hydrates in the sea area. By raising and lowering the lifting platform and translating the sea surface platform, large-scale and efficient extraction of seabed natural gas hydrates can be achieved.

[0035] As an improvement to the above-mentioned embodiment, the method for crushing and exploiting natural gas hydrate in the sea area by high-speed hydrothermal jet also includes installing an electric heater 19 in the waterproof casing to pyrolyze the natural gas hydrate that floats up to the negative pressure cavity. Since the solubility of natural gas in seawater is very small, the natural gas that enters the waterproof casing can automatically float up into the negative pressure cavity. At the same time, the density of natural gas hydrate is also smaller than that of seawater, so the crushed natural gas hydrate can also automatically float up to the negative pressure cavity in the waterproof casing. Heating the solid natural gas hydrate in the negative pressure cavity by the electric heater 19 can accelerate its decomposition.

[0036] As an improvement to the above embodiment, the method for high-speed hydrothermal jet crushing and exploitation of marine natural gas hydrates further includes setting a drying device 20 on the sea surface platform to dry the gas before entering the gas storage tank. The drying process can improve the quality of the natural gas.

[0037] As an improvement to the above embodiment, the method for high-speed hydrothermal jet crushing and exploiting marine natural gas hydrates further includes setting an L-shaped guide tube 21 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. This improvement allows the self-propelled 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 solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in 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 thermally decompose 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 high-speed hydrothermal jet crushing and exploitation of marine natural gas hydrate 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.

Images