Abstract:

In-situ sampling techniques are crucial to keep hydrate samples intact for characterizing the occurrence conditions and reserves of the gas hydrates in permafrost land. Having taken into account the thermophysical characteristic and the temperature-pressure dependence of gas hydrates, we have developed a borehole bottom freezing technique for gas hydrate sampling. This technique can significantly reduce the required sampling pressure and prevent decomposition of the hydrate samples by means of an external cold source which freezes the hydrate cores at the bottom of borehole. The gross structure of freezing sampler is consist of single action, control mechanism and freezing mechanism. The two elementary principles are freezing core by hole bottom and achieving the sample on the surface are analyzed, which analyses the required energy that freezing core for the sampler. The borehole bottom freezing sampling was tested by a trial of core drilling. Success in retaining freezing samples demonstrates that this technique can be applied to obtain freezing samples from the borehole bottom, creating a novel approach for development of in-situ hydrate corers.

Key words: gas hydrates, land exploration, hole bottom freezing, core drilling