鄂尔多斯盆地大牛地气田氦气成藏特征及其贫化主控因素

Helium accumulation characteristics and main controlling factors of helium depletion in Daniudi Gas Field, Ordos Basin

王杰 安川 马亮帮 姜海健 张威 陶成 王付斌 董勍伟

WANG Jie AN Chuan MA Liangbang JIANG Haijian ZHANG Wei TAO Cheng WANG Fubin DONG Qingwei

中国石化 油气成藏重点实验室, 江苏 无锡 214126 中国石化 石油勘探开发研究院 无锡石油地质研究所, 江苏 无锡 214126 中国石化 华北油气分公司, 郑州 450006

SINOPEC Key Laboratory of Petroleum Accumulation Mechanisms, Wuxi, Jiangsu 214126, China Wuxi Research Institute of Petroleum Geology, Wuxi, Jiangsu 214126, China SINOPEC North China Company, Zhengzhou, Henan 450006, China

鄂尔多斯盆地杭锦旗东胜气田和大牛地气田的天然气中发现一定含量的氦气，但大牛地气田氦气平均含量仅为东胜气田的1/4左右，那么在盆地基底和构造背景相似的情况下，究竟是何因素造成二者氦气含量差异如此之大。为此，基于天然气伴生氦气地球化学特征与氦气成藏关键要素的系统分析，发现大牛地古生界天然气中氦气含量介于0.000 1%~0.15%，为低氦—中氦气田；上古生界氦气含量相对较高，纵向上从下往上氦气含量逐渐增加，显示出浅部相对富集的特征。大牛地古生界氦气为典型壳源氦，主要来源于盆地基底的太古宇—中元古界变质岩—花岗岩系，上古生界潜在氦源岩所生成的氦气成藏贡献很小。对比大牛地气田上古生界与东胜气田上古生界氦气的发育地质条件与成藏特征，发现两者基底氦源岩的岩石类型、矿物组成、厚度及U、Th含量均相近，推测基底氦源岩不是造成氦气含量差异如此之大的原因。大牛地仅发育一条二级基底深大断裂，且在燕山—喜马拉雅期活动较弱，造成次一级断裂活动也较弱，氦气由基底氦源岩向上运移以及纵向输导和横向调整都缺乏有效通道；氦气与常规气成藏关键要素组合的时空配置不匹配，氦气仅靠扩散进入大牛地古生界气藏中，造成大牛地气田氦气含量偏低。大牛地气田氦气贫化的主要因素为基底深大断裂及次一级断裂不发育且活动强度弱、氦气与常规气成藏要素组合不匹配、缺乏有效输导体系、氦气运移仅靠浓度扩散。

A certain amount of helium is found in the natural gas of both the Dongsheng and Daniudi gas fields in the Hangjinqi area of the Ordos Basin. However, the average helium content in the Daniudi Gas Field is only about one-fourth of that in the Dongsheng Gas Field. Given the similar basement geology and tectonic background of the basin, it is necessary to investigate the factors leading to this significant difference. A systematic analysis of the geochemical characteristics of associated helium in natural gas and the key factors controlling helium accumulation was conducted. The results revealed that the helium content in the Paleozoic natural gas of the Daniudi Gas Field ranged from 0.000 1% to 0.15%, classifying it as a low- to medium-helium gas field. Helium content in the Upper Paleozoic was relatively higher, and vertically, it gradually increased from the lower to the upper layers, showing relative enrichment in shallower layers. The helium in the Paleozoic source rocks of the Daniudi Gas Field was typical crust-source helium, mainly derived from the Archean-middle Paleoproterozoic metamorphic rock-granite series in the basin basement. The contribution of helium generated by potential helium source rocks in the Upper Paleozoic was minimal. By comparing the geological conditions and accumulation characteristics of the Upper Paleozoic between the Daniudi and Dongsheng gas fields, it was found that the basement helium source rocks in both gas fields were similar in rock type, mineral composition, thickness, and uranium (U) and thorium (Th) contents, suggesting that the differences in source rock were not responsible for the significant difference in helium content. In the Daniudi area, only one second-level deep fault was developed in the basement of the Daniudi area, and its activity during the Yanshanian-Himalayan period was relatively weak, resulting in limited activity of secondary faults. This led to a lack of effective channels for helium to migrate upward from the basement helium source rocks, as well as vertical transport and lateral adjustment. Due to the mismatch in spatiotemporal configuration of key accumulation factors for helium and conventional gas, helium entered the Paleozoic gas reservoirs in Daniudi only by diffusion, resulting in low helium content. Therefore, the main factors contributing to helium depletion in the Daniudi Gas Field are the underdevelopment and weak activity of deep faults and secondary faults in the basement, the mismatch between helium and conventional gas accumulation conditions, the lack of an effective transport system, and the reliance on concentration-driven diffusion for helium migration.

中国石油化工股份有限公司科技部重大项目 P23230;中国石油化工股份有限公司科技部重大项目 P23244

https://doi.org/10.11781/sysydz2025040781