Pressure and temperature preservation techniques for gas-hydrate-bearing sediments sampling

Natural gas hydrates (NGH) can only exist under low temperature (generally below 10 °C) and high pressure (generally above 3.8 MPa). The prerequisite for investigations of NGH sediments is a sampling technique that prevents its volatiles during recovery. In this paper, some pressure and temperature preservation techniques for NGH sampling are investigated and analyzed intensively. The Chinese pressure and temperature corers including tight rock core sampler, pressure tight piston corer, wireline coring sampler and hydraulic pressure and temperature preservation (HPTP) corer are introduced in detail. Two pressure chambers (pressure chamber I and pressure chamber II) are designed with passive temperature preservation technique; using pressure accumulator (PA) cylinder pressure preservation technique, the pressure chamber was applied on the South China Sea at the water depth of 1352 m in 2006. Laboratory tests and the sea application show that the pressure preservation technique of the PA cylinder and the passive temperature preservation technique are successful for NGH sediments sampling. The main focus of future developments for NGH samplers in China is given, which offers the reference to the optimal design for the structure of NGH samplers and the new sampler development.