济阳坳陷下第三系湖相生油岩的微观特征

利用背散射电子成像技术、扫描电镜和能谱分析对山东济阳坳陷下第三系主要湖相生油岩的微观组构、成分特征进行了高分辨率的观察和分析,同时对其中藻类化石丰度进行了定量统计。结果显示,这些生油岩既有共性又有显著的差异。共性表现在它们都具有纹层状构造,而且有机质都特别丰富,呈纹层分布。差异性表现在纹层单元的成分明显不同:富有机质纹层页岩由有机质纹层和粘土矿物纹层组成;钙质纹层页岩则有两种情况:一类由有机质纹层和钙质超微化石纹层组成,另一类由有机质纹层和粗粒方解石纹层组成,粗粒方解石中含有钙质超微化石;钙质纹层泥岩由细粒方解石纹层和含有机质的粘土矿物纹层组成。生油岩中有机质的分布也有两种形式:一类是有机质纹层,另一类则是藻类化石层,如沟鞭藻化石层和钙质超微化石 (颗石藻 )层.

Micro-characteristics of Paleogene Lacustrine Petroleum Source Rocks in Jiyang Depressio

The Jiyang depression is one of the subbasins of the Bohai Gulf Rift Basin in th e eastern China. About 65 oil fields have been discovered in this depression ove r the past 30 years and the oil mainly derived from three types of finely lamina ted lacustrine rocks of Shahejie Formation( Eocene-Oligocene).These source roc ks are organic-rich laminated shale, calcareous laminated shale and calcareous laminated mudstone.High resolution studies have been carried out on these petro leum source rocks by scanning electron microscope(SEM), backscattered electron i magery(BSEI) and energy dispersive spectrometry(EDS). The results show that thes e source rocks are all laminated sedimentary rocks, and organic matters are very abundant in it, but they have the different sediment composition. 　　Organic-rich laminated shale is composed of organic matter lamination and c lay mineral lamination; The clay-rich laminae range in thickness from 15 to 100 μm and are predominantly composed of illite(80%). In addition, they have subsid iary components which comprise ankerite(5～10%), pyrite(1～3%),quartz(1～2%) and feldspar(1％～2%) along with trace amounts of apatite(0.03%). In contrast， the organic-rich laminae are thinner than the clay-rich laminae, ranging from 6～ 50 μm and are predominantly composed of amorphous organic matter(20％～70%)，as well as organic matter, these laminae also contain detrital clay (predominantly illite), silt-sized quartz, feldspar(1%～2%),and pyrite(1%～3%). Displacive ca lcite layers were also present. The calcite in these layers consits of low-Mg, non-ferroan calcite.In addition to the characteristic "beef" texture of this ca lcite, these layers also contain pyrite framboids,detrital quartz and ankerite. Calcareous laminated shale is composed of organic matter lamination and coccoli th or coarse calcite lamination; The coccolith laminae laminae is composed almos t wholly of one species, Reticulofenestra bohaiensis and the coarse grained calc ite lamine are composed of coarse calcite(10～20 μm) and also contain coccolths .Within the coccolith laminae, the size of coccolith ranges from 2 to 5 μm , an d it has a good preservation. Within the coarse calcite laminae, the coarse cal cite are sparry calcite characteristically by its overgrowth, and the coccolths have a poor preservation characteristics such as dissolution.This indicated that the coccolith-bearing coarse calcite laminae may be rystallized from the disso lution of coccolth laminae. Organic matter laminae is mainly composed of the lat h of amorphous organic matter and contain trace amounts of detrital clay. The th ickness of organic-rich laminae range from 15 to 50 μm and the thickness of th e calcite laminae range from 40 to 130 μm. Another important phenomenon is that there are dinoflagellates laminae in the organic-rich laminae. These dinoflage llates laminae are also composed of one species, Feramo(Fig.3). 　　Calcareous laminated mudstone is composed of finely grain calcite laminatio n and organic-rich clay mineral lamination. The clay-rich laminae range in thi ckness from 50～250 μm and are predominantly composed of illite(70%) and organi c matter ( organic matter may be formed by sublaminae in clay-rich laminae). Th ey also contain fine grained calcite(5%) and silt-sized detrital quartz(3%). In contrast, the carbonate-rich laminae are predominantly composed of micrrn size d and fine grained calcite which form layers 30～100 μm in thickness. The dinof lagellates laminae is also discovered in the organic-bearing clay-rich laminae (Fig.6).