深部热流体活动背景下氦气的成因来源与运聚机制——以莺歌海盆地乐东底辟区为例  

Genetic source,migration and accumulation of helium under deep hydrothermal fluid activities:A case study of Ledong diapir area in Yinggehai Basin,South China Sea

作　　者：冯子齐 郝芳[1,2] 胡林 胡高伟 张亚震 黎阳明 王维[1,2] 李昊 肖俊杰[1,2] 田金强 FENG Ziqi;HAO Fang;HU Lin;HU Gaowei;ZHANG Yazhen;LI Yangming;WANG Wei;LI Hao;XIAO Junjie;TIAN Jinqiang(State Key Laboratory of Deep Oil and Gas,China University of Petroleum(East China),Qingdao 266580,China;School of Geosciences,China University of Petroleum(East China),Qingdao 266580,China;Laboratory for Marine Mineral Resources,Qingdao Marine Science and Technology Center,Qingdao 266237,China;Hainan Branch of CNOOC(China)Co.,Ltd.,Haikou 570312,China)

机构地区：[1]深层油气全国重点实验室(中国石油大学(华东)),山东青岛266580 [2]中国石油大学(华东)地球科学与技术学院,山东青岛266580 [3]青岛海洋科技中心海洋矿产资源评价与探测技术功能实验室,山东青岛266237 [4]中海石油(中国)有限公司海南分公司,海口570312

出　　处：《石油勘探与开发》2024年第3期655-666,共12页Petroleum Exploration and Development

基　　金：国家自然科学基金(41821002,42272163,42072167);崂山实验室科技创新项目(LSKJ202203403);中海石油(中国)有限公司海南分公司“南海大中型天然气田形成条件、勘探潜力与突破方向”项目(KJZH-2021-0003-00)。

摘　　要：基于地球化学参数及分析数据,应用热守恒方程、质量平衡定律及瑞利分馏模型等方法,通过对莺歌海盆地乐东底辟区的壳源氦气原位产率和外部通量、幔源初始氦浓度及热驱动机制等定量分析,探讨深部热流体活动背景下氦气的成因来源及运聚机制。研究结果表明:(1)乐东底辟区氦气的来源以壳源氦为主,幔源为辅。其中,研究区幔源^(3)He/^(4)He值为(0.002~2.190)×10^(-6),R/R_(a)值为0.01~1.52,测算幔源He贡献占比为0.09%~19.84%,占比较小;而壳源贡献占比则高达80%以上。(2)壳源氦的原位^(4)He产量仅为(4.10~4.25)×10^(-4)cm^(3)/g,外部^(4)He通量则显著高值,为(5.84~9.06)×10^(-2)cm^(3)/g,表明壳源氦气以外部输入为主,推测与地层流体受大气补给以及深部岩石-水相互作用有关。(3)底辟区深部热流体活动显著影响地温场,^(3)He初始质量体积与对应焓的比值(W)为(0.004~0.018)×10^(-11) cm^(3)/J,来自深部地幔的热贡献(XM)为7.63%~36.18%,揭示底辟热流体对幔源^(3)He迁移具有一定的热驱动作用。(4)研究区氦气的初次运移方式以平流为主,二次运移受控于水热脱气和气液分离过程;氦气从深部至浅部的运移过程中,CO_(2)/^(3)He值由1.34×10^(9)升至486×10^(9),指示受到壳幔混合和脱气效应影响,存在CO_(2)规模性析出和^(3)He的明显逸散。在深部热流体影响下,氦气运移聚集机制包括:深部热驱动扩散、平流释放、垂向水热脱气,浅部横向迁移、远离断裂的圈闭聚集,分压平衡、完整密闭的盖层封存等方面。Based on the geochemical parameters and analytical data,the heat conservation equation,mass balance law,Rayleigh fractionation model and other methods were used to quantify the in-situ yield and external flux of crust-derived helium,and the initial He concentration and thermal driving mechanism of mantle-derived helium,in the Ledong Diapir area,the Yinggehai Basin,in order to understand the genetic source and migration&accumulation mechanisms of helium under deep hydrothermal fluid activities.The helium in the Ledong diapir area is primarily derived from the crust and a small amount from the mantle.For mantle-derived helium,the ^(3)He/^(4)He values are(0.002–2.190)×10^(-6),the R/R_(a) values are 0.01–1.52,and the contribution is estimated to be 0.09%–19.84%,suggesting a relatively small percentage.In contrast,the contribution of crust-derived helium is more than 80%.For crust-sourced helium,the in-situ ^(4)He yield is only(4.10–4.25)×10^(-4) cm^(3)/g,while the external ^(4)He flux is significantly high,being(5.84–9.06)×10^(-2) cm^(3)/g,indicating that crust-sourced helium is dominated by external input,which is speculated to be related to atmospheric recharge of formation fluids and deep rock-water interaction.Deep hydrothermal fluid in the diapir area significantly affects the geothermal field.The ratio of the initial mass volume of ^(3)He to the corresponding enthalpy(W)is(0.006–0.018)×10^(-11) cm^(3)/J,and the thermal contribution from the deep mantle(XM)is between 7.63%and 36.18%,suggesting that the diapir thermal fluid plays a certain role in driving the migration of mantle-sourced ^(3)He.The primary migration of helium in the study area is dominated by advection,and the secondary migration is controlled by hydrothermal degassing and gas-liquid separation.During the migration of helium from deep to shallow,the CO_(2)/^(3)He value increases from 1.34×10^(9) to 486×10^(9),indicating the large-scale precipitation of CO_(2) and apparent escape of ^(3)He due to the effect of crust-mantle mixing

关 键 词：深部热流体 氦气 成因来源 运移聚集机制 乐东底辟区 莺歌海盆地 

分 类 号：TE122[石油与天然气工程—油气勘探]