东海南部中生界烃源岩地球化学特征与分布预测

为探讨东海陆架盆地南部中生界烃源岩的分布特征,充分利用海域钻井、地震资料和烃源岩地球化学数据,在综合分析中生界烃源岩发育条件和地化特征基础上,采用Trinity盆模软件,以区域沉积相研究成果、烃源岩地化指标和暗色泥岩百分含量统计数据为约束条件,预测了中生界有效烃源岩厚度和成熟度的平面分布特征。结果表明:东海南部中生界中下侏罗统福州组和下白垩统受海(或湖)侵影响的深湖.半深湖相烃源岩分布广,厚度大,生油气条件良好。其中,福州组烃源岩为钻井所证实,是海域中生界的主要烃源岩,发育有暗色泥岩和煤两类烃源岩,有机质丰度高,母质类型以Ⅲ型为主,少量为Ⅱ₂型,现今已进入成熟高成熟阶段,整体评价为较好的烃源岩;集中分布在闽江凹陷和基隆凹陷的南部,暗色泥岩厚度介于200~760 m之间,南厚北薄;成熟度R₀介于0.5%~3.5%之间,由西北向东南方向逐渐增熟。下白垩统暗色泥页岩类烃源岩是海域中生界的次要烃源岩,这一认识拓展了东海南部中生界油气勘探的新领域;有机质丰度较低,母质类型为Ⅲ型,已成熟,整体评价为中等~差烃源岩;在闽江凹陷和基隆凹陷广泛分布,暗色泥岩厚度介于50~450 m之间,东厚西薄;成熟度R₀由西向东逐渐增熟。

Geochemical Characteristics and Distribution of Mesozoic Hydrocarbon Source Rocks in the Southern Part of East China Sea

In order to study the distribution characteristics of Mesozoic source rocks in the Southern part of East China Sea,the drilling data,seismic data and geochemical data of hydrocarbon source rocks have been used fully.Based on comprehensive analysis of the depositional conditions and geochemical characteristics of Mesozoic hydrocarbon source rock,the effective thickness of Mesozoic source rock and planar distribution characteristics of maturity have been forecasted by using Trinity basin simulation software and constrained by the study results of regional sedimentary facies,geochemical index of source rock and statistical data of dark mudstone percentage content.The results show that influenced by marine (or lake) transgression,the middle-lower Jurassic Fuzhou Formation and the Lower Cretaceous semi-deep to deep lake facies source rock are distributed widely,with large thickness and good hydrocarbon generation conditions,of which Fuzhou Fm.source rocks have been confirmed by drilling,being the main source rocks in the study area.The Fuzhou Fm.source rocks consist of dark mudstones and coal,with high organic matter abundance,and the organic matter is dominated by type Ⅲ,with minor type Ⅱ₂,being mature to highly mature,evaluated as good quality hydrocarbon source rock,distribute mainly in south of Minjiang depression and Jilong depression.The dark mudstones range from 200 to 760 m in thickness,thicker in south and thin in north.The maturity increases from northwest to southeast direction gradually,with vitrinite reflectance values (R₀) ranging from 0.5% to 3.5%.The Lower Cretaceous dark argillaceous source rocks are the secondary Mesozoic source rocks in the study area.This understanding expands a new field for oil and gas exploration in Mesozoic in southern part of East China Sea.The Lower Cretaceous dark argillaceous source rocks are mature,being moderate to bad quality,with low organic matter abundance,and the organic matter is type III.The Lower Cretaceous source rocks distribute widely in Minjiang Depression and Jilong Depression.The dark mudstones range from 50 to 450 m in thickness,thicker in east and thin in west.The maturity increases gradually from west to east direction.