白云凹陷第三系储层中铁白云石的成因机理及与CO_2活动的关系  

Forming mechanism of ankerite in Tertiary reservoir of the Baiyun sag,Pearl River Mouth basin,and its relationship to CO_2-bearing fluid activity

作　　者：庞江 罗静兰[1] 马永坤 蔡国富 雷川[1] 李弛[1] 李晓艳 张月霞 PANG Jiang;LUO Jinglan;MA Yongkun;CAI Guofu;LEI Chuan;LI Chi;LI Xiaoyan;ZHANG Yuexia(State Key Laboratory of Continental Dynamics , Northwest University ,Xi'an, 710069;Research Institute , Shenzhen Branch of China National Offshore Oil Corporation Limited , Shenzhen, Guangdong, 518067;Sichuan Key Laboratory of Shale Gas Evaluation and Ejcploitation Chengdu ,610091)

机构地区：[1]西北大学大陆动力学国家重点实验室,西安710069 [2]页岩气评价与开采四川省重点实验室,成都610091 [3]中海石油(中国)有限公司深圳分公司研究院,广东深圳518067

出　　处：《地质学报》2019年第3期724-737,共14页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号41572128);国家科技重大专项(编号2016ZX05026-003-005;2016ZX05026-003-003)资助成果

摘　　要：白云凹陷第三系储层中发育大量的铁白云石,受研究区热流背景的影响,铁白云石主要见于高地温梯度地区埋深1000～3000m、地层温度60～130℃的浅—中部地层中及CO_2热流体活动区域。铁白云石的δ^(13)C值(-2.83‰～-1.83‰)具有无机成因的特征,与研究区气藏中幔源岩浆成因CO_2的δ^(13)C值较为一致,铁白云石的δ^(18)O值(-9.45‰～-5.37‰)和^(87)Sr/^(86)Sr值(0.7101～0.7161)也反映了其沉淀受到深部热流体活动的影响。以两口典型CO_2气井为例,储层中流体包裹体均一温度及蒙脱石向伊利石的演化特征证明储层经历了热流体侵入;CO_2热流体活动区域不仅是铁白云石集中分布地带,并出现片钠铝石+铁白云石+菱铁矿等示踪CO_2运移、聚集的自生矿物组合。地层中铁白云石、高岭石含量与气藏中CO_2的含量呈正相关关系,绿泥石含量与CO_2、铁白云石含量呈反消长关系。高地温梯度地区丰富的CO_2热流体活动是该地区储层中铁白云石沉淀与含量高的重要原因,无机岩浆成因CO_2是铁白云石沉淀的主要碳源,CO_2热流体充注造成绿泥石等黏土矿物异常转化,为铁白云石沉淀提供了所需的Fe^(2+)、Mg^(2+)离子。Abundant ankerite occurs in the Tertiary reservoir of Baiyun Sag, Pearl River Mouth Basin. Influenced by heat flow background in the study area, ankerite is mainly distributed in the high geothermal gradient area with shallow-medium burial depths from 1000 to 3000 m and temperature between 60~130℃. The δ13C value(-2.83‰^-1.83‰) of the ankerite, which is consistent with that of magmatic origin CO2 in the gas pool, indicates its inorganic origin. The values(-9.45‰^-5.37‰) of δ18O and 87Sr/86Sr(0.7101~0.7161)also show that precipitation of the ankerite was affected by the deep hydrothermal fluid activity. Case study of two typical CO2 gas wells shows that the homogenization temperature of fluid inclusions and evolution of montmorillonite to illite prove that the reservoir underwent thermal fluid invasion. CO2 thermal fluid activity regions are not only the concentrated distribution area of ankerite but also the places hosting typical authigenic mineral assemblage of dawsonite+ankerite+siderite, which can trace CO2 migration and accumulation. The contents of ankerite and kaolinite in the formation are positively correlated with that of CO2 in the gas pool, and the content of chlorite is negatively correlated with that of CO2 and ankerite. Aabundant CO2 hydrothermal activity was the main reason for the precipitation of developed ankerite in the high geothermal gradient area. CO2 of inorganic magmatic origin was the main carbon source for precipitation of the ankerite. The abnormal transformation of clay minerals(such as chlorite) caused by CO2 thermal fluid charging provided the necessary Fe^2+, Mg^2+ ions for precipitation of the ankerite.

关 键 词：铁白云石 CO2 热流体 成因模式 第三系储层 白云凹陷 

分 类 号：P618.13[天文地球—矿床学]