巴西桑托斯盆地盐下拗陷期湖相烃源岩发育条件及其地质意义  

Potential of lacustrine source rock in the pre-salt depression stage and its geological significance in Santos Basin,Brazil

作　　者：李丹 程涛 尹川 贾怀存 李明刚 刘正 LI Dan;CHENG Tao;YIN Chuan;JIA Huaicun;LI Minggang;LIU Zheng(CNOOC International Ltd.,Beijing 100028,China)

机构地区：[1]中国海洋石油国际有限公司,北京100028

出　　处：《海洋地质与第四纪地质》2024年第4期145-154,共10页Marine Geology & Quaternary Geology

基　　金：中海油“十四五”重大科技项目“两岸一带重点区油气勘探评价关键技术”(KJGG2022-0902)。

摘　　要：目前勘探成果已证实桑托斯盆地盐下断陷期Picarras组(PIC组)-Itapema组(ITP组)泥岩为一套优质的深水湖相烃源岩,但对于拗陷期Barra Velha组(BV组)浅水湖相烃源岩的发育条件与沉积模式一直尚未开展系统研究。为厘清该盆地盐下拗陷期烃源岩发育特征,本文通过古生物学、地球化学等资料对拗陷期BV组沉积时期古地理-古气候背景、古水环境进行恢复,认为拗陷期BV组沉积时期为宽浅咸水湖泊,干旱的气候背景下较易形成盐度分层,从而在湖泊底部形成缺氧环境,利于有机质的保存。在拗陷期BV组沉积时期盆地及周缘火山活动频繁,同时发育了多期海侵,为湖泊水体带来丰富的营养物质,利于藻类勃发。充足的物质基础以及有利的有机质保存条件使其具备优质烃源岩发育条件。通过古生物、古地理与地震相综合分析,建立了桑托斯盆地盐下拗陷期湖相烃源岩发育模式,为巴西桑托斯盆地的油气勘探部署,以及拗陷期浅水盐湖烃源岩发育条件分析提供了新的方向和思路。About the lacustrine source rocks in the pre-salt of Santos Basin,the present exploration confirms that the lacustrine source rocks of Picarras(PIC)Formation-Itapema(ITP)Formation in the pre-salt rift period are high-quality source rocks.Due to the lack of drilling data,it is difficult to confirm whether the high-quality of lacustrine source rocks are developed in Barra Velha(BV)Formation.To clarify the development characteristics of the source rocks in the pre-salt depression stage(BV Formation development period),the paleogeography,paleoclimate,and paleo-water environment of BV Formation in the depression period of the basin were restored using paleobiology and geochemistry data.It is considered that the BV Formation in the depression period was a wide shallow saline lake.Under the arid climate background,it was easy to form salinity stratification;and an anoxic environment was formed at the bottom of the lake,which was beneficial to the preservation of organic matters.Geochemical analysis showed that during the deposition of BV Formation,volcanic activities around the basin were frequent,and multiple transgression occurred,which brought rich nutrients to the lake water and was conducive to the growth of algae.Sufficient material and favorable preservation conditions for organic matters benefited to high-quality source rocks development.At last,the development model of lacustrine source rocks in the pre-salt depression was established,which provided new direction to the exploration to the source rocks in the depression stage of Santos Basin.

关 键 词：湖相烃源岩 发育条件 盐下拗陷期 桑托斯盆地 

分 类 号：P736[天文地球—海洋地质]