1. 云南大学国际河流与生态安全研究院,云南昆明,650500;2. 中国地质调查局南京地质调查中心,江苏南京,210016;3. 安徽省地质调查院,安徽合肥,230001
方朝刚,男,1987年生。高级工程师,博士研究生,主要从事沉积学和非常规油气研究。E-mail:fangchaogang206@163.com。
1. Institute of International Rivers and Eco-security, Yunnan University, Kunming, Yunnan 650500, China;2. Nanjing Center, China Geological Survey, Nanjing, Jiangsu 210016, China;3. Geological Survey of Anhui Province, Hefei, Anhui 230001, China
在无为盆地WWY1井三叠系周冲村组首次发现了异常高压富氦天然气显示,对其中2个气样的气体组分分析发现,He的体积分数分别为4.51%和4.56%,远高于0.1%的氦气工业利用标准；3He/4He值分别为5.50×10-8和6.40×10-8,幔源氦占比仅仅为0.32%和0.40%,应属典型的壳源氦。同时依据δ13CCH4、δ13CCO2、CO2含量及N2含量综合分析认为该天然气为有机成因,其烃源岩类型与研究区广泛发育的二叠系烃源岩相吻合。通过区域地质资料和深部地球物理资料分析认为其氦源极可能来源于古—中元古代基底花岗岩。长江深断裂带可作为联通深部地壳与浅部地层的重要通道,对于氦气扩散外移起到了关键作用。当富氦流体运移至浅部遇到天然气等载体气气藏时,流体的氦浓度迅速降低,氦气大量脱溶进入载体气气藏形成富氦天然气藏,活动的断裂系统和裂缝为其提供了运移和疏导通道。盆地内三叠系周冲村组多套膏岩盖层在一定的埋深条件下形成了超高压封闭条件,有可能是阻止富氦天然气向上扩散的重要原因,膏岩层下白云岩裂缝性储层为其提供了储存空间,具有良好的储盖时空配置关系。下扬子沿江地区具有多个与无为盆地地质条件相类似的同级盆地(如:望江盆地),预示着沿江地区具备十分有利的氦气勘探潜力,此外本次研究提出的氦气成藏模式也可为区域上氦气勘探提供重要的指导意义。
Abnormal high pressure helium-rich natural gas was first discovered in the Triassic Zhouchongcun Formation in Well WWY1 of the Wuwei basin. Gas composition analysis of two gas samples showed that the volume proportions of He were 4.51% and 4.56%, respectively, which were much higher than the industrial utilization standard (0.1%). The two values of 3He/4He are 5.50×10-8 and 6.40×10-8 respectively, and the proportion of mantle-derived helium is only 0.32% and 0.40%, which typically suggests crust-derived helium. The integrated analysis of δ13CCH4, δ13CCO2, CO2 content and N2 content indicates the gas has an organic origin, which is associated with the widespread development of Permian hydrocarbon rock in the study area. Analysis of regional geological and deep geophysical data suggests that the helium source rocks are most likely derived from Paleo- and Meso-Proterozoic basement granites. As an important channel connecting deep crust and shallow strata, the Yangtze River deep fault zone plays a key role in helium migration. When the helium-rich fluid migrates to the shallows and meets the carrier gas reservoir of natural gas, the helium concentration of the fluid decreases rapidly and a large amount of helium diffuses into the carrier gas reservoir to form the helium-rich gas reservoir. During this process, active fault systems and fractures served as effective migration channels. The Triassic Zhouchongcun Formation in the sag has formed an ultra-high pressure confining condition under certain burial depth conditions, which has prevented the upward diffusion of helium-rich natural gas. The fractured dolomite reservoir under the gypsum rock layer provides a storage space, and has a good spatial and temporal configuration of the storage cap. There are several similar basins along the Yangtze River (e.g.Wangjiang basin), indicating that there is a very favorable potential for helium exploration along the Yangtze River Area. In addition, the helium accumulation model proposed in this study can also provide important guidance for regional helium exploration.
方朝刚,章诚诚,滕龙,徐锦龙,李建青,周道容,吴通,邵威.2023.下扬子无为盆地异常高压富氦天然气的发现及其成藏地质条件[J].地质学报,97(5):1641-1654.
FANG Chaogang, ZHANG Chengcheng, TENG Long, XU Jinlong, LI Jianqing, ZHOU Daorong, WU Tong, SHAO Wei.2023. The discovery and formation conditions of helium-rich gas in the Wuwei basin of Lower Yangtze region[J]. Acta Geologica Sinica,97(5):1641-1654.
