Geochemical characteristics of borehole cores and their indicative significance for gas hydrates in the permafrost area, Qinghai-Tibet Plateau

Abstract

The formation of gas hydrates in the permafrost zone of the Tibetan Plateau is complicated, so it is difficult to achieve significant breakthrough in gas hydrate exploration. In this paper, we compare the geochemical anomalies in different drill holes, with a view to elucidating their indicative roles in migration and accumulation of gas hydrate and hydrocarbon. The results demonstrate that the acidysis hydrocarbon and fluorescence spectra of the borehole in the discovered hydrate area show obvious enrichment characteristics, with significantly higher anomaly intensity than that in the borehole where no hydrate samples are found. The geochemical anomalies have obvious response characteristics with the cracks or fracture zones. The hydrocarbon genesis analysis indicates that the dominant cause is pyrolysis. The anomalies of acid hydrocarbon methane, methane carbon isotopes and fluorescence spectra can be used as indicators of natural gas hydrate and its transport and aggregation. The effective time and space configuration of the reservoir elements including gas source, migration and concentration, and permafrost conditions is crucial to the eventual formation of natural gas hydrate in the study region. The research can lay a foundation for future gas hydrate exploration in the Tibetan Plateau permafrost region.