Title : Helium accumulation regulations and prediction of favorable areas in the Qaidam Basin
Abstract:
Helium is an important strategic scarce resource, and several helium-rich gas reservoirs have been discovered in the Qaidam Basin. However, the research on the main controlling factors of helium enrichment and the regulation of helium accumulation are still relatively weak, and there is a lack of research on the accumulation mode of helium-rich gas reservoirs in the basin. Based on the helium content testing of natural gas in the Qaidam Basin, in combination with the geological background data such as the distribution of basement lithology and tectonic features, we analyse the helium distribution characteristics, sources and main controlling factors of helium enrichment in the Qaidam Basin, and establish the helium reservoir formation model. The results show that the gas reservoirs in the Dongping 3 block, Jianbei and Mabei are rich-medium helium reservoirs, while the gas reservoirs in the Dongping 1 block, Niuzhong, Niudong, Kuntai and Nanbaxian are low-depleted helium reservoirs. The rich-medium helium reservoirs are distributed in the middle and shallow parts of the premontane uplift zone at the edge of the basin. The helium gas belongs to the typical shell-source genesis, which is mainly derived from the ancient basement rocks such as granite, granodiorite, granodiorite gneiss, etc., supplemented by the sedimentary rock systems such as mud shale and shale. The enrichment of helium is mainly controlled by ancient basement rocks, active groundwater, moderate natural gas injection and tectonic uplift movements. The widely distributed basement granite, granodiorite, and granodiorite gneiss provide sufficient helium sources. Active groundwater is favourable for helium preservation and enrichment. Adequate natural gas injection controls the helium content. The multi-phase tectonic uplift movements not only provide efficient channels and power for helium transport, but also provide favourable zones for helium aggregation. Combined with the geological and tectonic background of the Qaidam Basin and the controlling factors of helium enrichment, the enrichment model of helium captured by natural gas in the context of ancient uplift at the basin margin is established. It is predicted that the three major pre-mountain palaeo-rise/palaeo-slope zones of Qilian Mountains, Kunlun Mountains and Arjinshan Mountains at the basin margin are favourable zones for helium resource enrichment.
