Apparatus for preventing and controlling secondary generation of hydrates in wellbore during depressurization exploitation of offshore natural gas hydrates and prevention and control method

An apparatus for preventing and controlling secondary generation of hydrates in a wellbore during depressurization exploitation of offshore natural gas hydrates, wherein the apparatus comprises 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;

• tail ends of the gas recovery pipe column and the water recovery pipe column are connected with a top of the gas-liquid mixed transportation pipe section;
• the gas-liquid mixed transportation pipe section is positioned in hydrate reservoirs;
• and the gas recovery pipe column and the water recovery pipe column recover gases and water decomposed by the natural gas hydrates in the reservoirs respectively, a joint of the water recovery pipe column and the gas-liquid mixed transportation pipe section and a joint of the gas recovery pipe column and the gas-liquid mixed transportation pipe section are provided with a casing pipe, the first electric submersible pump is positioned in the casing pipe, and a blowout preventer is arranged on a tail end of the gas recovery pipe column;
• the data collecting and processing unit comprises a first data monitoring point, a second data monitoring point, a third data monitoring point, and a computer terminal;
• the first data monitoring point is positioned on a top of the gas recovery pipe column, and collects a temperature, pressure and gas flow of the top of the gas recovery pipe column;
• the second data monitoring point is positioned on a top of the water recovery pipe column, and collects a temperature, pressure and gas flow of the top of the water recovery pipe column;
• the third data monitoring point is positioned on a tail end of the gas-liquid mixed transportation pipe section, and collects a temperature and pressure of a well bottom;
• and the computer terminal receives and processes temperature, pressure, and flow data collected from the first data monitoring point, the second data monitoring point, and the third data monitoring point;
• the reaction control apparatus comprises a signal actuator, a hydrate inhibitor storage tank, a hydrate inhibitor injection pump, a first inhibitor injection point, a second inhibitor injection point, a third inhibitor injection point, a first electric submersible pump, a second electric submersible pump, and a heater;
• one end of the signal actuator is connected with the computer terminal, and the other end of the signal actuator is connected with the hydrate inhibitor injection pump;
• the hydrate inhibitor injection pump is respectively connected with the first inhibitor injection point, the second inhibitor injection point, and the third inhibitor injection point via injection pipelines, and a control valve is arranged on each of the injection pipelines;
• the first inhibitor injection point is positioned on the top of the gas recovery pipe column, the second inhibitor injection point is positioned at a bottom of the gas recovery pipe column, and the third inhibitor injection point is positioned on the tail end of the gas-liquid mixed transportation pipe section;
• the first electric submersible pump is positioned at a bottom of the water recovery pipe column, and the second electric submersible pump is positioned in the middle of the water recovery pipe column;
• and the heater is positioned at the bottom of the gas recovery pipe column;
• and
• the apparatus collecting, by the three data collection points installed on the top of the gas recovery pipe column, the top of the water recovery pipe column, and the tail end of the gas-liquid mixed transportation pipe section, temperature, pressure and flow data at different positions, the different data collection points being connected with the computer terminal for transmitting the collected data to the computer terminal in real time;
• performing, by the computer terminal, analysis and processing on the data collected from the different data collection points, sending instructions to the signal actuator to control inhibitor injection rates of different hydrate inhibitor injection points, and to control power of the heater in the gas recovery pipe column and power of the different electric submersible pumps in the water recovery pipe column to prevent and control the secondary generation of the hydrates in the gas recovery pipe column and the water recovery pipe column.