东营凹陷南斜坡特高蜡油的成因

东营凹陷南斜坡王古1、新角1奥陶系古潜山原油具有特高含蜡特征(40%～60%),同区下第三系孔店组原油含蜡量也明显偏高(28.85%～31.7%)。不同层系的原油烃类化学成分分析、油源对比结果表明,研究区高蜡油成因不同于上覆第三系沙河街组,前者为深部油源,第三系孔店组为其重要烃源岩之一;后者主要源自正常油窗内沙河街组四段烃源岩。生物标志物定量分析结果表明,区内烃源岩沥青与原油中的蜡质烃含量随成熟度增加而增加,反映热成熟度是控制该区高蜡油形成的重要因素之一。东营凹陷湖沼相成因的孔店组烃源岩含有相对较高的陆源高等植物,是导致该区高蜡油形成的另一重要因素。综合分析认为,东营凹陷南斜坡高蜡油的形成主要与烃源岩相对较高的热成熟度及烃源岩含有丰富的可提供蜡质烃的成烃母质(主要指孔店组二段)有关,气侵与油气运移分馏效应的影响甚微。

Origin of superhigh wax content oils in southern slope zone of Dongying Depression

Oils produced from Wanggu-1 and Xinjiao-1 wells' Ordovician buried-hill reservoirs in the southern slope zone of Dongying depression are characterized by superhigh wax content(40%-60%),and the wax contents of oils produced from Tertiary Kongdian Fm reservoirs in the same area are also relatively high(28.85%(-31.7%)).Chemical composition analysis and oil-source rock correlation of crude oils from different layers show that the origin of Ordovician high wax content oils in the study area is different from that in the overlying Tertiary Shahejie Fm.The former are derived from the deep source,as represented by the source rocks in Kongdian Fm.The latter are mianly sourced by the 4~(th) member of Shahejie Fm within normal oil window.Absolute quantification of biomarkers shows that the bitumen contents of source rocks and waxy hydrocarbon contents of crude oils in this area increase with increasing maturity,indicating that thermal maturity is one of the major factors controlling the formation of highly waxy oils in this area.The Kongdian Fm source rocks of limnetic facies in Dongying depression contain relatively abundant terrigenous higher plants,which is another major factor causing the high wax content oils in this area.It is believed,based on comprehensive analysis,that the relatively high maturity and abundant parent materials capable of generating waxy hydrocarbons in the source rocks(the 2~(nd) member of Kongdian Fm) are the major causes of the formation of high waxy oils in the southern slope zone of Dongying depression.Contrary to this,the influences of gas invasion and hydrocarbon migration fractionation are insignificant.