The present invention relates to the technical field of
natural gas hydrate extraction, and specifically to a device and method for depressurizing and extracting marine
natural gas hydrates. The device comprises an
offshore drilling platform, a
drill string, a casing, and a conduit. The drilling platform can lift or lower the
drill string, the casing, and the conduit. A first
pipe is provided inside the
drill string, and a
drill bit is fixedly connected to the bottom. The casing is sleeved on the outer
peripheral side of the
drill string and forms an annular
accommodation space between the casing and the
drill string, and an annular sealing device is provided on the side wall. The conduit is arranged in the annular
accommodation space and is provided with a pressure regulating device. The side wall is provided with a slit and is connected to the casing and the
hydrate layer through a circulation device.
Fracturing fluid is introduced into the
hydrate layer, and the pressure in the conduit is adjusted until the hydrate reaches the
phase equilibrium point and decomposes, and then the
natural gas is collected to the
offshore drilling platform through the conduit. After the extraction is completed, the
drill string, the
drill bit, the casing, and the conduit can be lifted and recovered by controlling the
offshore drilling platform, and then recycled after disassembly and cleaning, which not only improves the extraction efficiency but also reduces the extraction cost.