Fault Control of Gas Hydrate Accumulation in Qilian Mountain Permafrost

Gas hydrate was successfully sampled again in the DK-9 hole in Qilian Mountain permafrost since it was first discovered in 2008. However, gas hydrate occurrences are heterogeneous both in horizon and in profile, which are restricted just within a limited area. The geological controlling factors that affect gas hydrate occurrences are not yet known in Qilian Mountain permafrost. Since the features of gas hydrate and other related geological information were well recorded in DK-9, on the basis of analyses of geochemical and geological data in this hole, a possible geological pattern is put forward for a gas hydrate reservoir in this area. In this paper, the features of hydrocarbon in headspace gases from cores at various depths are compared with the occurrences of gas hydrate, faults, or fractures in DK-9 in Qilian Mountain permafrost. The results show that gas hydrate and its related anomalies fall into intervals with higher hydrocarbon contents in headspace gases. In the meantime, faults or fracture zones serve as migration paths for gases in the deep and provide accumulation space for gas hydrate in the shallow in Qilian Mountain permafrost. Specifically, the F-1 and F-2 faults mainly control gas hydrate accumulation in Qilian Mountain permafrost.