Well drilling device for undersea in-situ exploitation of natural gas hydrate

A well drilling device for undersea in-situ exploitation of a natural gas hydrate, comprising:

• a well drilling module, wherein the well drilling module comprises a frame, wherein a portal framed lead rail and a manipulator are mounted in the frame, a lower hydraulic tong is mounted at a bottom of the frame, an upper hydraulic tong is arranged coaxially above the lower hydraulic tong, and a coaxial space between the upper hydraulic tong and the lower hydraulic tong is a drilling column placement position;
• the upper hydraulic tong is mounted in a top drive, and the top drive is assembled in the portal framed lead rail to move vertically in a vertical direction of the portal framed lead rail;
• and a pipe rack is arranged in a rotation range of the manipulator, the pipe rack is configured to store and place a drilling column, and the manipulator is configured to grab the drilling column to a position between the upper hydraulic tong and the lower hydraulic tong;
• wherein when the drilling column with a drilling bit is transferred to the drilling column placement position by the manipulator, the upper hydraulic tong tightly clamps, and the lower hydraulic tong opens;
• and the top drive moves down, the lower hydraulic tong tightly clamps, the upper hydraulic tong opens, the top drive moves down and is buckled in a rotating manner, and the lower hydraulic tong opens to complete drilling-in of a first drilling column;
• wherein after the drilling-in of the first drilling column is completed, the lower hydraulic tong tightly clamps, the top drive is unbuckled and moves up, after a subsequent drilling column is transferred to the drilling column placement position by the manipulator, the upper hydraulic tong tightly clamps, the top drive moves down, and rotating connection buckled at a top of a well, the upper hydraulic tong opens, the top drive moves down and is buckled in the rotating manner, and the lower hydraulic tong opens to complete continuous drilling-in of the drilling columns;
• wherein the drilling column adopts well drilling with a casing, and a down-hole drilling column combination of the well drilling with the casing comprises a drilling bit having a diameter smaller than an inner diameter of the casing and a reamer configured for passing through the inner diameter of the casing and enlarging a size of a borehole to be equal to a size of the casing;
• and
• wherein four legs are further mounted at bottom four sides of the frame, and are all driven by independent hydraulic motors to extend outwards.