Abstract:

In this paper a case was set in the gas hydrate drilling hole of DK-2 in the Qilian Mountain permafrost. Oil and gas indication-bearing core samples were analyzed with reservoir pyrolysis, and in combination with field observation of oil and gas indications, the nature of oil and gas indications and their possible indicative implication to gas hydrate were discussed. The field-observed oil and gas indication phenomena such as various kinds of oil trace, oil patch, oil immersion and oil staining, mostly occurred within fine sandstone, medium sandstone, and partly on interfaces between silt mudstone and carbonate lamina or within their fissures, which were proven by indoor reservoir pyrolysis results. The nature of oil and gas indications showed that the crude oil was mainly composed of medium-weighted oil or heavy-weighted oil with minor over-heavy-weighted oil and even with asphalt. In the drilling hole, the oil and gas indications were closely associated with gas hydrate, and especially those characterized by medium-weighted oil within or just below gas hydrate occurrence interval could be a sign for gas hydrate occurrence.

Key words: oil and gas indication, gas hydrate, Qilian Mountain permafrost, Qinghai