Characteristics of rare gas isotopes and main controlling factors of helium enrichment in the northern margin of the Qaidam Basin, China

Abstract

Based on the study of the geological background, it is considered that the main factors affecting helium enrichment in the northern margin of the Qaidam Basin (NMQB) are widely distributed rock masses, developed fractures, groundwater system, and more. Among these factors, the rock masses provide sufficient helium gas source, while the fractures and the groundwater system provide good natural gas migration channels and carriers. 4He, 20Ne, and other rare gas isotopes have a good linear relationship, which proves that the groundwater system plays a vital role in the helium enrichment process, and helium flux is high. Based on the theoretical understanding of helium reservoir formation formed by helium investigation in the Weihe Basin and its adjacent areas, it is predicted that the NMQB has the prospect of crustal helium resources. Through the analysis of natural gas wellhead samples in the helium prospective areas of the Mabei and Dongping gas fields in this area, it is found that the helium content is generally high. Isotope analysis shows that helium in this area is typically crust sourced. Furthermore, 21 out of the 22 source helium samples analyzed in this paper meet or exceed the industrial standard. According to the average helium gas volume fraction of sixteen samples in the Mabei area of 0.28%, Mabei area alone can become an extensive helium resource prospective area. Through further investigation and evaluation, it is expected to obtain super large helium reserves in the study area.