Abstract:

Presently there is no systematic helium (He) resource evaluation method, nor evaluation parameter standard. This study, by comparing the accumulation controlling factors of natural gas and crustal helium, identifies eight key controlling factors of crustal helium accumulation and three co-occurrence styles between carrier-gas and helium, namely, different sources in one reservoir, same source in one reservoir, and same source in different reservoirs. For preliminary quantitative evaluation of helium resource, four classification and evaluation methods using ten different algorithms are established—with percentage method using five; statistical method, one; analogy method, three; and genetic method, one. Helium-rich gas reservoirs are generally characterized by normal to low pressure. The helium content is positively correlated with three parameters—source type, U/Th contents, and source rock volume, and negatively correlated with three parameters—distance from the main fault, burial depth, and hydrocarbon-generating intensity; while moderate basal tectonic activity is conducive to helium release and enrichment. Analogy method is established based on the quantitative relationships between the eight key factors and helium content. Scale sequence method is based on the principle that gases from different sources in one reservoir have different scale sequences. And genetic method is based on the radioactive decay model of helium release and accumulation. The evaluation methods are used widely both at home and abroad, and their application shall effectively contribute to the discovery of large-scale helium reserves in China.

Key words: carrier gas, co-occurrence relationships, helium content, genetic method, scale sequence, resource evaluation