The invention provides a method and system for extracting stranded gas (such as natural gas or hydrogen) or a mixture of oil and natural gas from a subterranean environment such as beneath the ocean floor and converting it into a solid hydrate such as a clathrate featuring a) extracting stranded gas (such as natural gas or hydrogen) or a mixture of oil and natural gas; b) optionally separating the natural gas from the mixture of oil and natural gas in a first tank or vessel; c) transporting the stranded gas to a second tank or vessel; d) introducing sea water into the second tank or vessel; e) mixing the stranded gas and water to form a clathrate hydrate/water slurry; f) removing excess water from the clathrate hydrate slurry to form a solid comprising a clathrate hydrate; and g) processing the solid comprising a clathrate hydrate into a transportable form; and h) optionally collecting the gas into a transportable vessel.

A method for recovering gas in natural gas hydrate exploitation is disclosed, in which a gas-water mixture at a bottom of a exploitation well is delivered to an ocean surface platform through a marine riser, by adopting the gas-lift effect of methane gas derived from the dissociation of natural gas hydrate, so as to achieve a controllable flowing production of marine natural gas hydrate. In the startup stage, the pressure in the bottom of the well is decreased by the gas-lift effect of the injected gas to allow dissociation of the hydrate. In the flowing production stage, the flowing production is achieved by the gas-lift effect of the gas derived from the dissociation of the natural gas hydrate, wherein a seafloor gas tank is employed to control the flowing rate and replenish the consumed gas.

A submarine shallow hydrate exploitation device, including an exploitation unit and a collection unit. The exploitation unit includes: a submarine ship working on a seabed; a drain chamber arranged on the submarine ship, wherein a pressure valve is arranged at a top of the drain chamber, one-way drain holes are formed in a bottom of the drain chamber, and water from massive hydrates is controlled to be discharged out of the drain chamber; a high-speed spiral bit configured to mine and convey sediments; a rotary ring arranged at an inlet end of the drain chamber and configured to connect the drain chamber with the high-speed spiral bit to provide rotation power for the high-speed spiral bit; a steering arm arranged on the submarine ship and configured to realize a rotation of the high-speed spiral bit; a crusher arranged on the submarine ship and configured to crush dried massive hydrates.

The present invention discloses a device for solid-state fluidization mining of seabed shallow layer non-diagenetic natural gas hydrates. The device comprises a hydraulic jet nozzle set, a coiled tubing, a hydrate collecting ship arranged on the sea surface, a transfer station arranged in sea water and a riser arranged in a seabed surface layer. A guide seat is arranged in the riser. The hydraulic jet nozzle set is arranged in the guide seat. A delivery pipe connected with the transfer station sleeves a nozzle body. An opening is formed in a position where the delivery pipe is in contact with the nozzle body. The transfer station is connected with the hydrate collecting ship. The present invention further discloses a method for collecting seabed shallow layer non-diagenetic hydrates.

A comprehensive three-dimensional exploitation experimental system for large-scale and full-sized exploitation wells includes a reactor, configured to prepare a natural gas hydrate sample, for simulating an environment for forming a natural gas hydrate reservoir in seafloor sediments. The reactor includes a reactor body, an upper cover disposed at an upper surface of the reactor body, and a lower cover disposed at a lower surface of the reactor body; a gas introducing module, configured to introduce gas to the reactor during hydrate formation; a liquid introducing module, configured to introduce liquid to the reactor during hydrate formation; a temperature regulating module, configured to regulate a temperature in the reactor; a data collecting-processing-displaying module, configured to collect, store, process and display data of the comprehensive three-dimensional exploitation experimental system during an experiment.

The present invention discloses a device for solid-state fluidization mining of seabed shallow layer non-diagenetic natural gas hydrates. The device comprises a hydraulic jet nozzle set, a coiled tubing, a hydrate collecting ship arranged on the sea surface, a transfer station arranged in sea water and a riser arranged in a seabed surface layer. A guide seat is arranged in the riser. The hydraulic jet nozzle set is arranged in the guide seat. A delivery pipe connected with the transfer station sleeves a nozzle body. An opening is formed in a position where the delivery pipe is in contact with the nozzle body. The transfer station is connected with the hydrate collecting ship. The present invention further discloses a method for collecting seabed shallow layer non-diagenetic hydrates.

The present invention provides a method of water flow erosion for marine gas hydrate exploitation. Based on the characteristics of higher permeability around gas hydrate exploitation well, controlling the seawater flow process by the pressure difference between hydrate reservoir and gas hydrate exploitation well. And the chemical potential difference between hydrate phase and water phase is the main driving factor for promoting the hydrate decomposition. Meanwhile, the salinity will increase and then the phase equilibrium temperature of hydrate will increase during seawater flow process. The water flow erosion accelerates the heat and mass transfer in hydrate reservoir to promote the efficient and complete decomposition and collection of hydrate. And the method of water flow erosion can decrease the risk of the geographical destruction caused by the large pressure drop. The present invention also provides the combination modes of water flow erosion with depressurization, thermal injection and other methods.

Disclosed is a device for solid-state fluidized mining of natural gas hydrates in a shallow seabed, including: a sea surface support system, a pipeline delivery system, and an undersea drilling system. The sea surface support system includes a hydrate drilling vessel floating on seawater. The pipeline delivery system includes a continuous double-layer oil pipe, a recyclable conduit installed in a sediment cover, an open-hole steering packer installed outside the recyclable conduit. The undersea drilling system includes a hydrate slurry separator, a single screw pump, a hydraulic motor, a jet head and a differential pressure sliding sleeve close to the hydrate drill bit. The present invention has the following beneficial effects. The device achieves a multi-directionally horizontal drilling and production in the hydrate reservoir with a single well head, improving the drilling efficiency and single well production.

A high-efficiency yield-increasing exploitation method for natural gas hydrates includes steps of drilling of natural gas hydrate reservoirs along horizontal wells, seepage increasing by fracturing for fracture forming and stability improvement by grouting in the natural gas hydrate reservoirs, and yield improvement by combined exploitation of depressurization of the horizontal wells and heat injection; according to the present invention, drilling time is shortened by rapid drilling along the horizontal wells, the permeability of the reservoirs can be effectively improved by fracturing for fracture forming, the stability of the reservoirs can be improved by injecting by the combined exploitation method of depressurization of the horizontal wells and heat injection.

An apparatus for preventing and controlling secondary generation of hydrates in a wellbore during depressurization exploitation of offshore natural gas hydrates includes a gas recovery pipe column, a water recovery pipe column, a gas-liquid mixed transportation pipe section, a data collecting and processing unit, and a reaction control apparatus; according to characteristics of different exploitation pipe columns, three injection pipelines and three monitoring points are arranged to predict dynamic changes in a secondary generation risk of the hydrates throughout the wellbore; measures for preventing and controlling the secondary generation of the hydrates are taken at different pipe column positions by the integrated utilization of inhibitor injection, heating for pipe columns, the additional arrangement of electric submersible pumps, and other methods.