关键词: 氦气, 源控论, 氦源岩, 氦气生气强度, 金秋气田, 大探1井, 安岳气田, 四川盆地

Abstract: Because helium has long been overlooked as an independent resource, research on its accumulation mechanisms remains limited, and a comprehensive theoretical framework for helium accumulation has yet to be established. Although previous studies have provided valuable insights into the accumulation conditions and enrichment patterns of crustal helium, their theoretical guidance has been substantially limited by the difficulty of effectively predicting favorable areas for helium-rich gas reservoirs. To theoretically clarify the main controlling factors and predictability of the distribution of medium- to large-sized helium gas fields, this study identifies the major sources of helium in gas reservoirs through an analysis of typical helium-bearing and helium-rich gas reservoirs in Sichuan Basin and systematically discusses the theoretical basis and predictive indexes for the accumulation, distribution, and enrichment of crustal helium in petroliferous basins. The research results show as follows. (1) The helium in gas fields/reservoirs from different structural levels of Sichuan Basin (the Jurassic Jinqiu gas field in the upper structural level, the Permian-Triassic multi-layer gas fields of southern Sichuan Basin in the middle structural level, and the helium-rich Well Datan1 gas reservoir and helium-poor Anyue gas field within Dengying Formation in the lower structural level) is mainly sourced from the strata where the gas reservoirs are located. This feature is widely manifested in Sichuan Basin. Based on the age-accumulation effect of ⁴⁰Ar/³⁶Ar ratio of natural gas in different strata of typical oil and gas fields in Sichuan Basin, Tarim Basin and Ordos Basin, the possibility that helium in the gas reservoir of each stratum is predominantly derived from the bedrocks is further ruled out. (2) The theoretical basis for the understanding that crustal helium mainly originates from reservoir strata depends on the fact that the hydrocarbon lateral migration distance is generally much greater than its vertical migration distance. Under this condition, the accumulation of crustal helium also follows the “Source Control Theory”, and the reservoir strata generally serve as the dominant helium source rocks. Accordingly, that the main helium sources of some helium-bearing and helium-rich gas fields/reservoirs were simply attributed to basement granite and metamorphic rock masses might be limited by traditional understanding and should be re-examined. (3) The distribution of helium reservoirs is controlled by a “dual-source” system comprising both hydrocarbon source rocks and helium source rocks. The helium reservoir scale is mainly determined by the helium-generating capacity of helium source rocks, which can be predicted using the helium gas generation intensity. Helium content is difficult to predict due to the joint constraints of “dual-source” system. However, there are successful cases under the condition that parameters such as formation thickness, reservoir thickness, formation pressure coefficient, and test production rate are well constrained, as demonstrated by the Dengying Formation gas reservoir in Well Datan1.

Key words: helium, Source Control Theory, helium source rock, helium gas generation intensity, Jinqiu gas field, Well Datan1, Anyue gas field, Sichuan Basin