System for exploiting deep sea combustible ice by adopting decompression method

The utility model relates to a system for exploiting deep sea combustible ice by adopting a decompression method, and belongs to the technical field of ocean oil and gas resource exploitation. According to the technical key points, the device is composed of a mining platform, a wellhead device, a casing string, a mining string, an underground sand removal system, a monitoring system, an underwater conveying pipeline and an umbilical cable; and three-stage sand prevention and two-stage sand removal measures are adopted, so that sand can be effectively prevented and removed, and stable exploitation of combustible ice is ensured. The two gas-liquid separators, namely the tubular column cyclone gas-liquid separator and the filler gas-liquid separator, are arranged on the mining tubular column, so that efficient separation in a gas-liquid well is realized, and more thorough gas-liquid separation is ensured. The electric submersible pump is arranged below a mining layer, it is guaranteed that gas rapidly enters a m