济阳坳陷古近系沙三下—沙四上亚段咸化湖盆证据及页岩油气地质意义OA北大核心CSTPCD
Evidence of paleogene saline lake basin in the 3rd and 4th members of Shahejie Formation in Jiyang Depression and geological significance of shale oil and gas
济阳坳陷是渤海湾盆地常规油气最为富集的坳陷之一,也是页岩油获得全面战略性勘探突破的坳陷,古近系沙河街组发育沙三下亚段、沙四上亚段2 套主力烃源岩,其沉积环境颇受争议.利用页岩系统取芯井岩石学、元素地球化学、同位素和包裹体等资料对页岩沉积环境进行系统研究.结果表明:古近系沙三下—沙四上亚段页岩为气候控制下的咸化湖盆的产物,主要发育富碳酸盐纹层状岩相,碳酸盐矿物质量分数高,多呈纹层状、透镜状产出,平均质量分数为 43%,背散射扫描电镜下部分页岩样品发现NaCl、BaSO4和SrSO4 典型的咸化湖盆标志性矿物,页岩沉积期水体盐度相对较高;水体环境的w(Sr)/w(Ba)大于 1,Sr元素质量分数大于 500 μg/g,B元素质量分数大于 75×10-6,相当硼质量分数主要分布在 300×10-6～700×10-6,均显示为咸化环境;页岩 w(87 Sr)/w(86 Sr)为 0.710 7～0.712 4,明显高于同期海水的w(87 Sr)/w(86 Sr),结合对应稀土元素Ce正异常特征,认为沉积期水体条件受控于盆地自身环境,与海侵没有必然联系;碳酸盐矿物δ18O主要分布在-11‰～-3‰,δ13 C主要分布在 0～6‰,δ18 O、δ13 C均偏大,与沉积期湖盆气候相对干旱、湖水蒸发作用增强有关;页岩中检测到气液两相原生盐水包裹体均一化温度范围在 32.5～45.3℃,对应盐度范围为 19.21%～27.78%,成岩早期地层流体盐度较高;气候控制下的咸水环境为富碳酸盐页岩形成提供条件,奠定济阳坳陷古近系沙三下—沙四上亚段页岩油富集高产的基础.
Jiyang Depression is one of the most prolific conventional oil and gas depressions in the Bohai Bay Basin,having also withnessed a significant breakthrough in the comprehensive strategic exploration of shale oil.Within the Paleogene Sha-hejie Formation,two primary sets of source rocks,namely the Upper Submember of the Fourth Member(ESS4)and Lower Submember of the third Member(ESX3),are prevalent,with their sedimentary environment being controversial.Evidence from core well petrology,element geochemistry,isotopes and inclusion data suggests that the shale systems in ESS4 and ESX3 originated in a salinized lake basin under climate influences.The main evidence are as follows:ESS4 and ESX3 are predomi-nantly characterized by carbonate-rich laminar shale,with an average carbonate mineral mass fraction of 43%,primarily oc-curring in laminar and lenticular forms.NaCl,BaSO4 and SrSO4 which are typical salty lake basin minerals have been identi-fied in shale samples using back-scattered scanning electron microscope,indicating relatively high water salinity during the shale deposition period.The trace element composition of the shale reflects a salty environment,with the w(Sr)/w(Ba)ex-ceeding 1 and Sr mass fraction surpassing 500 μg/g,while B element mass fraction exceeds 75×10-6,with equivalent B mass fraction ranging mainly from 300×10-6 to 700×10-6.The w(87 Sr)/w(86 Sr)of shale falls between 0.710 7 and 0.712 4,significantly higher than that of contemporaneous seawater.Positive anomaly characteristics of corresponding rare earth ele-ments,such as Ce,suggest that the water conditions during the sedimentary period were influenced by the basin environment rather than transgression events.Carbonate minerals δ18 O range from-11‰ to-3‰,while δ13 C values range from 0 to 6‰.Large δ18 O and δ13 are related to a relatively dry climate in the lake basin and enhanced evaporation of lake water during dep-osition periods.The homogenization temperature of gas-liquid two-phase primary brine inclusions in shale ranges from 32.5℃to 45.3℃,corresponding to salinity ranges of 19.21%～27.78%.This suggests high formation fluid salinity during the early diagenetic stage.The saline water environment under climatic influence played a pivotal role in the formation of carbonate-rich shale,laying the groundword for the enrichment and high yield of shale oil in ESS4 and ESX3 of the Paleogene in Jiyang Depression.
王勇
中国石化胜利油田公司勘探开发研究院,山东东营 257015||页岩油气富集机理与高效开发全国重点实验室,山东东营 257015
地质学
济阳坳陷常规油气页岩油咸化湖盆富碳酸盐纹层状岩相
Jiyang Depressionconventional oil and gasshale oilsalty lake basincarbonate rich laminar lithofacies
《中国石油大学学报（自然科学版）》 2024 (003)
27-36 / 10
国家科技重大专项(2017ZX05049);中石化科技攻关项目(P23084)
评论