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

摘要： 氦气因长期未被作为一种独立资源类型进行勘探，其成藏机理研究薄弱，至今尚未形成完备的氦气成藏理论体系。前人虽对壳源氦气的成藏条件与富集规律进行了有益探索，但因难以有效预测富氦气藏的有利发育区，其理论指导价值大打折扣。为从理论上阐明大—中型氦气田分布的主控因素及其可预测性，通过对四川盆地典型含氦—富氦气藏的解剖，厘定了气藏中氦气的主要来源，并系统论述了含油气盆地壳源氦气聚集成藏与分布的理论基础及预测指标。取得以下主要认识：①四川盆地不同构造层气田/气藏（上构造层侏罗系金秋气田、中构造层二叠系—三叠系川南地区多目的层气田群、下构造层灯影组大探1井富氦气藏和安岳气田贫氦气藏）中的氦气均主要来源于气藏储层所在层系，这一特征在四川盆地有广泛体现；基于四川盆地、塔里木盆地和鄂尔多斯盆地典型油气田不同层系天然气⁴⁰Ar/³⁶Ar比值的年代积累效应进一步排除了各层系气藏中氦气主要来源于基底岩系的可能性。②“壳源氦气主要源自储层所在层系”的理论基础在于油气的横向运移距离一般远大于垂向运移距离，在此条件下壳源氦气的成藏与分布遵循“源控论”，且储层所在层系通常即为主力氦源岩。而此前简单地将氦气的主要来源归因于基底花岗岩、变质岩体的部分含氦—富氦气田/气藏，可能受限于传统认识，需重新审视其氦气来源。③氦气藏分布受烃源岩和氦源岩“双源”控制；氦气藏规模主要取决于氦源岩的生氦能力，可通过氦气生气强度指标进行预测；氦气含量因受“双源”因素共同制约，预测难度较大，但在地层厚度、储层厚度、地层压力系数和测试产量等参数明确的条件下亦有成功案例（如大探1井灯影组气藏）。

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