A suction cylinder exploitation device for marine natural gas hydrates, comprising an exploitation cylinder capable of sinking into a stratum below a seabed, a water pump, a sand control device and a gas-liquid lifting system, wherein:
- the exploitation cylinder is a cylindrical structure with an upper side sealed and a lower side not sealed, and comprises a top plate and a vertical cylinder wall;
- the water pump is communicated with an inner cavity of a cylinder body and is able to discharge liquid out of the exploitation cylinder to reduce a pressure in the exploitation cylinder to control the exploitation cylinder to sink in the stratum to enter, together with the sand control device and the gas-liquid lifting system, a natural gas hydrate reservoir and/or a natural gas hydrate and free gas mixture reservoir and/or a free natural gas reservoir below the seabed;
- at least one cavity is enclosed by the combination between the exploitation cylinder and the sand control device, and the sand control device allows liquid and/or gas to pass through to enter the cavity and is able to tilter out silt;
- the cavity is communicated with at least one channel;
- the gas-liquid lifting system comprises at least one lifting power device, which has an end connected to the cavity and an end connected to an offshore processing system, and is used to lift the liquid and/or gas in the cavity;
- when the liquid and/or gas is lifted, a pressure in the cavity is reduced to reduce a pressure of the stratum around to promote natural gas hydrates to be decomposed into water and natural gas, which enter the cavity through the sand control device under the effect of a pressure difference, so that exploitation of the natural gas hydrates is realized;
- the channel includes a water pipe and a gas pipe;
- the water pipe has an end connected to the lifting power device and an end connected to an upper portion of the exploitation cylinder;
- the gas pipe has an end connected to the cavity and an end connected to an upper portion of the exploitation cylinder to collect gas;
- under the effect of formation pressure and gravity, formation fluid enters the cavity, the liquid in the cavity flows downward and is pressed into the water pipe to be lifted by the lifting power device;
- the gas in the cavity flows upwards through the gas pipe;
- the lifting power device is an electric pump and the electric pump is an electric immersible centrifugal pump, an electric immersible screw pump, a mud pump, or a combination of these three pumps;
- the cavity is formed in an outer side of the vertical cylinder wall of the exploitation cylinder or in an internal space of the exploitation cylinder;
- when the cavity is formed in an outer side of the vertical cylinder wall of the exploitation cylinder;
- the exploitation cylinder has a perforated pipe wall, and a hole is formed in the perforated pipe wall;
- the sand control device is arranged in the hole and/or covers the bole;
- the perforated pipe wall has a permeable and protective function, allows liquid and gas to pass through, and protects the sand control device against erosion damage from the formation pressure and fluid;
- and the gas and liquid enter the cavity in the outer side of the vertical cylinder wall through the perforated pipe wall and the sand control device;
- when the cavity is formed in an internal space of the exploitation cylinder, the stratum in the internal space is cleared out of the cylinder through a jet drilling system, and the cavity is defined by the top plate, the vertical cylinder wall and a sealing bottom of the exploitation cylinder;
- a hole is formed in a lower portion of the vertical cylinder wall, and the sand control device is arranged in the hole and/or covers the hole;
- a vertical well wall at this position has a permeable and protective function, allows liquid and gas to pass through, and protects the sand control device against erosion damage from the formation pressure and fluid;
- and the gas and liquid enter the cavity in the internal space of the exploitation cylinder through the vertical well wall and the sand control device.