Geochemical characteristics and genetic origin of crude oil in the Fushan, sag, Beibuwan Basin, South China Sea
Geochemical characteristics and genetic origin of crude oil in the Fushan, sag, Beibuwan Basin, South China Sea
复制标题
南海北部湾盆地福山凹陷原油地球化学特征及成因
DOI：
10.1016/j.marpetgeo.2019.104114
复制
发表时间：
2020-02-01
影响因子：
4.2
通讯作者：
Pan, Zhejun
中科院分区：
文献类型：
--
作者：
Gan, Huajun;Wang, Hua;Pan, Zhejun
福山凹陷是南海北部湾盆地重要的含油气单元。然而，石油与烃源岩之间的成因关系尚不清楚。本文收集了洼陷43份泥岩样品和22份原油样品，进行了分子地球化学和同位素分析，探讨了这一关系。地球化学资料表明，六沙岗组泥岩生油潜力较差，TOC值在0.45 ~ 2.19 wt%之间，干酪根以II型为主。本研究确定了两种类型的原油。第一类A类油包括A(1)亚群和A(2)亚群，具有低成熟度、低饱和烃含量和较轻δ C-13值的特征。A组烃源岩为缺氧-缺氧淡水环境，陆生高等植物较多，被子植物较少。el(1)(1)储层A(1)亚群油与el(1)(2)储层A(2)亚群油的成熟度相对较低。A(1)亚群和A(2)亚群原油分别与el (1) ~ el(1)(2)和el (2)(1) ~ el(2)(1)烃源岩关系密切。第二类油（B组和C组）成熟度较高，饱和烃含量较高，δ C-13值较大。B组烃源岩沉积在盐度较低的淡水环境中，被子植物和陆生高等植物的输入比C组多。B组原油分为两个亚组，其中B-1亚组原油成熟度较高，烃源岩沉积盐度较低，陆源高等植物输入比B-2亚组多。华厂隆起埃尔斯(3)(1)组B1亚群油可能与埃尔斯(3)(1)烃源岩有关，白莲洼陷南部斜坡区埃尔斯(2)(2)(2)储集层B-2亚群油可能与埃尔斯(2)(2)和埃尔斯(3)(1)泥岩混合烃源岩有关。C组原油主要分布在华厂隆起埃尔斯(2)(2)和埃尔斯(3)(1)储层中，其油源为埃尔斯(3)(2)泥岩。根据凹陷的油源对比，el(2)的mfs可能划分为两个油气区。B组和C组油属于下储层，而A组油只出现在上储层。凹陷特殊的两层构造地层格架和断裂带的输运能力是控制不同组油分布和聚集的主要因素。研究明确了油类的类型、油源关系和不同组油类的空间分布。研究结果对凹陷进一步的油气勘探和资源评价具有指导意义。
The Fushan sag is an important petroleum-bearing unit in the Beibuwan Basin, South China Sea. However, genetic relationship between oil and source rocks has not been well understood. In this work, 43 mudstone samples and 22 crude oil samples in the sag were collected for molecular geochemical and isotopic analyses to investigate this relationship. The geochemical data shows that the mudstones in Liushagang formation have poor to good oil generation potential with TOC ranging from 0.45 to 2.19 wt% and the kerogen is mainly type II. Two types of crude oils were identified in this study. The first type of Group A oils including the subgroup A(1) and subgroup A(2) has the characteristics of low maturity with low saturated hydrocarbon content and lighter delta C-13 values in the Huachang uplift. The source rocks for the Group A oils were deposited under suboxic to oxic and freshwater environment containing more terrestrial higher plant and less angiosperm. The subgroup A(1) oils in Els(1)(1) reservoirs are separated from subgroup A(2) in the Els(1)(2) reservoirs by relatively lower maturity. The subgroup A(1) and subgroup A(2) oils are closely related to the Els1 to Els(1)(2) and Els(2)(1) to Els(2)(1) source rocks, respectively. While the second type of oils including Group B and Group C oils has higher level of maturity with higher saturated hydrocarbon content and heavier delta C-13 values. The source rocks of Group B oils were deposited in a freshwater environment with lower salinity, and more angiosperms and terrestrial higher plants input than those of Group C oils. Two subgroups are divided in the Group B oils, of which subgroup B-1 oils have higher maturity and their source rocks were deposited in lower salinity with more terrestrial higher plant input than that of subgroup B-2 oils. The subgroup B1 oils occurring in the Els(3)(1) reservoirs from the Huachang uplift are likely related to Els(3)(1) source rocks, while subgroup B-2 oils in the Els(2)(2) reservoirs from the southern slope area of the Bailian subsag is linked with mixed source of Els(2)(2) and Els(3)(1) mudstones. The Group C oils are distributed in Els(2)(2) and Els(3)(1) reservoirs in the Huachang uplift and their oil source are from Els(3)(2) mudstones. Two petroleum plays are likely divided by the mfs in Els(2) based on the oil-source correlation in the sag. Group B and Group C oils belong to the lower play, and Group A oils only occur in the upper play. The distribution and accumulation of different groups of oils are mainly controlled by the special two-layered tectonostratigraphic framework and the transport ability of fault zone in the sag. This study clarifies the types of oils, as well as the oil-source correlation and the spatial distribution of different groups of oils. The results could benefit the further petroleum exploration and resource evaluation in the sag.