Geochemical Characteristics of Oil Sand Extracts in Different State from Sandstone Reservoir: Ⅰ linear hydrocarbon——A case study from Triassic Yanchang Formation in Ordos basin
SHI Ji-an 1 ZHAO Xin 1,2 WANG Jin-peng 1, 2 WANG Qi 1, 2 LU Long-fei 1, 2 WANG Lei 1, 2 WANG You-xiao 1 1 (Key Laboratory of Geochemistry, Lanzhou Institute of Geology, Chinese Academy of Sciences, Lanzhou 730000) 2( Graduate school of Chinese Academy of Sciences, Beijing 100039)
Through the stepwise separation and extract on free hydrocarbon, sealed hydrocarbon, hydrocarbon in carbonate cement, bounded hydrocarbon and inclusion hydrocarbon within quartz grain on six oil sand samples from Yanchang Fm. (Triassic), Xifeng oilfield, Ordos basin, all these hydrocarbons have been analyzed by GC-MS. On the basis of diagenetic sequence, in combination with the feature of the analyzed samples, the results show that this method is practicable. And the study on linear alkane with different existence states shows the n-alkanes with single peak are dominant in the study area with wide range of carbon number and weaker odd-carbon preference. The parent material types of these hydrocarbons are typeⅠ-Ⅱkerogen deposited in the reducing fresh water lacustrine environment. Obvious differences occur in Pr/Ph ratio and CPI value in these hydrocarbons with different existence state. Generally, it has a decreasing tendency from free hydrocarbon, sealed hydrocarbon, cement hydrocarbon to inclusion hydrocarbon, together with their group composition features, this phenomena can reflect the oil generation steps and filling periods of oil pool and microscale heterogeneity within oil pools.