白音查干凹陷达尔其油田原油的分类与生物降解作用

Oil classification and biodegradation in Daerqi oilfield, Baiyinchagan depression

根据原油的物性、族组成、生物标志化合物参数及生物降解特征,将达尔其油田原油分为5种类型。(1)第一类为稀油。原油粘度和密度低,族组成以饱和烃组分为主,非烃和沥青组分含量低,甾烷异构化指标高,未遭受生物降解,成熟度较高。(2)第二类为原生未熟特稠油。原油粘度特大,密度相对较高,族组成以非烃和沥青质组分为主,饱和烃含量低。甾烷异构化指标低,未遭受生物降解。(3)第三类为第一类与第二类原油的混合产物,且以第一类为主。(4)第四类属普通稠油,原油密度、粘度相对较高,为第一类原油生物降解而形成的。(5)第五类原油是第三类原油生物降解的产物,原油密度和粘度与第四类原油相近,但甾烷异构化指标相对较低。除了第二类原油(未熟特稠油)来源于浅部都红木组一段未熟烃源岩外,其他四类原油都来源于(或主要来源于)深部腾格尔组和阿尔善组二段成熟度较高的烃源岩。

Based on oil physical features, group compositions, biomarker compounds and biodegradation, the crude oil in the Daerqi oilfield is classified into five types.Type I oil is a low viscosity and density, light oil. Its group composition is predominately the saturated hydrocarbon, with a low contents of nonhydrocarbon and asphaltic components. This type of oil is unbiodegraded, with a high sterane isomerization index and maturity. Type Ⅱ oil is immature and extremely viscous, with a relatively high density. Its group composition is dominated by nonhydrocarbon and asphaltic components, with a low content of saturated hydrocarbon. This type of oil is unbiodegraded, with a low sterane isomerization index. Type Ⅲ oil is a mixed product of type I oil and type Ⅱ oil. Type Ⅳ oil is a common viscous oil, with a relatively high viscosity and density, which is formed by biodegradation of type I oil. Type V oil could be caused by biodegradation of type Ⅲ oil. Its density and viscosity are similar to that of type Ⅳ oil, but sterane isomerization index is relatively low. Excluding the type Ⅱ oil (immature and extremely viscous oil) from the shallow immature source rock of the Duhongmu Formation, all the oil of other four types are mainly derived from the higher mature, deep-seated source rocks of the Tenggeer Formation and/or A' ershan Formation.