摘要:
本文详细研究了珠江口盆地东部某单井钻遇原油和储层抽提物的地球化学特征结果表明,该圈闭内的原油均为成熟原油,它们富含饱和烃馏分而贫极性组分;位于圈闭上部的原油(埋深2005m及其以上)在地质历史时期曾遭受过轻度的生物绛解作用.但是,由于该圈闭上一条近东西向断层的发育,使得不同深度间隔内的原油正构烷烃分布特征有着较大的差异,且降解程度最重的两个顶部原油具有较高的饱和烃含量和热成熟度。充分显示了其混合特征。
Abstract:
The geochemical characteristics of extracts from the crude oils and reservoir bed taken from a well drilled in Pearl River Mouth Basin(PRMB) were investigated in detail. The trap on which the well was drilled was cut by a sub-EW direction normal fault. And study of the seismic section passed the well revealed that the fault has ever had three main developments. Fractionation results indicated that both the crudes and the extracts were richer in saturates(63.34-73.03%) and poorer in polar fraction(non-hydrocarbon+asphaltene, 11.31-20.43%).And saturate to aromatic ratios being larger than 3(the maximum up to 6.21) suggested their higher rank of maturation level. GC patterns of the saturates showed that there are tow major types of crudes in the trap. One is minor biodegrated, which occurred in the upper section(2005m and its above), and the other was normal, which distributed in the lower section(below 2005m).Furthermore, because of the injection of the oil with much higher maturity and lower molecular weights the top two ranked the highest maturity of the biodegraded oils, thus their n- alkane carbon number distribution appeared saw- toothed shape. Therefore, the biodegraded oil can in turn be divided into two sub-types: mixed vs. non-mixed. GC/MS analyses for the saturates confirmed that the crudes have ever experiienced higher geotemperature due to the discovery of diadrimanes and 8. 14-secohopanes. And the presence of oleanane implied the terrestrial origin of the oils while the dominant C30 4-methyl steranes in the sterane kingdom revealed evriched algal organic input in the source rocks. The fault development survey revealed that the essential cause responsible for the varying geochemical features of the upper biodegraded oils was resulted from the reaccumulation of the oils in the trap. The development of the fault resulted in the escaping of the underlying highly mature crudes from their initial reservirs and immidiately migrating upward along the fault. They favorably entered the shalowest reservoirs owing to differential accumulation, resulting in the ever-biodegraded oils upgrated their maturity and enriched in lihter carbon isotope composition and lower molecular weight n- alkanes because of mixed with the reaccumulated hydrocarbons.
点击查看大图
下载:
