Device and method for solid-state fluidized mining of natural gas hydrates in shallow seabed

A device for solid-state fluidized mining of natural gas hydrates in a shallow seabed, comprising:

• a sea surface support system;
• a pipeline delivery system;
• and
• an undersea drilling system;
• wherein the sea surface support system comprises a hydrate drilling vessel floating on seawater, a hydrate storage tank, a high-pressure pump set and a continuous double-layer oil pipe storage device arranged on the hydrate drilling vessel;
• the pipeline delivery system comprises 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 continuous double-layer oil pipe penetrates the recyclable conduit;
• a head end of the continuous double-layer oil pipe is fixed on the continuous double-layer oil pipe storage device, wherein an inner channel of the continuous double-layer oil pipe is connected to the hydrate storage tank, and an outer channel of the continuous double-layer oil pipe is connected to an outlet port of the high-pressure pump set;
• and a tail end of the continuous double-layer oil pipe is connected to the undersea drilling system in a hydrate reservoir in the shallow seabed;
• the undersea drilling system comprises a hydrate slurry separator, a first three-layer tube, an internal and external fluid exchange joint of double-layer tube and a second three-layer tube, connected successively;
• via the hydrate slurry separator, the outer channel of the continuous double-layer oil pipe communicates with a middle channel of the first three-layer tube, while the inner channel of the continuous double-layer oil pipe communicates with an inner channel of the first three-layer tube;
• a channel of the hydrate slurry separator is in communication with an outer channel of the first three-layer tube;
• through the internal and external fluid exchange joint of double-layer tube, the middle channel of the first three-layer tube communicates with an inner channel of the second three-layer tube, while the inner channel of the first three-layer tube communicates with a middle channel of the second three-layer tube;
• the outer channel of the first three-layer tube communicates with an outer channel of the second three-layer tube;
• a jet head is arranged in an end of the inner channel of the second three-layer tube;
• the jet head communicates with the second three-layer tube, and is equipped with a pressure differential sliding sleeve;
• a hydrate drill bit is fixed at an end of the jet head, and is provided with a seawater ejecting-drilling channel along an axial direction of the hydrate drill bit;
• and the seawater ejecting-drilling channel communicates with the jet head;
• a single screw pump is fixed in the inner channel of the first three-layer tube, and a hydraulic motor is fixed in the inner channel of the second three-layer tube;
• via a coupling penetrating the internal and external fluid exchange joint of double-layer tube, one end of an output shaft of the hydraulic motor connects to an input shaft of the single screw pump, and the other end of the output shaft is fixedly connected to the jet head;
• a sediment backfilling casing is equipped outside the undersea drilling system, the sediment backfilling casing is defined as an outer portion of the first three-layer tube, the internal and external fluid exchange joint of double-layer tube and the second three-layer tube;
• one end of the sediment backfilling casing is connected to a sediment outlet of the channel of the hydrate slurry separator, and the other end of the sediment backfilling casing is arranged with a sediment backfilling channel;
• a plurality of jet holes communicating with the jet head are provided on a cylindrical surface of the sediment backfilling casing along a circumferential direction of the sediment backfilling casing, and a return port communicating with the outer channel of the second three-layer tube is further provided on the cylindrical surface of the sediment backfilling casing.