松辽盆地西斜坡稠油特征及成因

Characteristics and Genesis of the Western Slope Thick Oils in Songliao Basin

松辽盆地西斜坡稠油特征及成因制约着油气的勘探和开发。通过稠油族组成、同位素、色谱、质谱等分析及与斜坡和拗陷内原油、油源岩对比研究,确定西斜坡原油为经长距离运移且遭生物降解、水洗氧化的稠油,以密度相对较低、粘度相对较高为特点,稠变程度为中等—严重级别。油源主要为拗陷内青山口和嫩江组湖相泥岩,烃源岩自成熟排烃以来,向西的运移聚集可明显划分出三期。

The western slope of Songliao Basin spans two oil areas of Daqing and Jilin and its prospecting area is about 4.3×10 4 km 2 . The following oil and gas fields, Fulaerji and Taobao oil field, Pingyang oil and gas field, Tumuji oil sand, Alaxin, Erzhan and Baiyinnuole gas field, have been found early or later since 1960s. Saertu and Gaotaozi oil beds are main target strata and the type of oil and gas fields belongs to lithological and structure lithological character. The western slope oils have the characteristics of relatively low density, middle viscosity, richness in non hydrocarbon and low content of asphalt. The analysis of GC and GC MS shows the biodegradation and the feature of multiple filling of oil. The 25 norhopane series are absent in the biodegraded oils from all oil fields of western slope, including the Tumuji oil sand. The carbonate isotopic values of western slope oils are -29‰～-32‰, that of kerogen are -22‰～-24‰ of Jurassic coal rock and are -27‰～-31‰ of Qingshankou and Nenjiang mudstone. The maturity degree of source rocks of the western slope is very low, the calculated R o value of western slope oils are 0.75‰～0.95% based on the index of methyl phenanthrene and methyl dibenzene thiophene. So, the source rocks of western slope oils are mainly the Qingshankou lacustrine mudstone of central depression. The K Ar chronology data of reservoir bed authigenic illite of four wells, that is well Ta 20, Du 66, Fu 42 and Lai 24, is 56Ma, 45Ma, 35Ma and 35Ma respectively and the above well location is from east to west successively. So, the migrating period of the western slope oil is three stages at least.