油藏储层中不同赋存状态烃类地球化学特征:Ⅰ链烷烃——以鄂尔多斯盆地三叠系延长组为例

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

通过对鄂尔多斯盆地西峰油田三叠系延长组六个油砂样品中游离烃、封闭烃、碳酸盐胶结物烃、束缚烃和石英颗粒包裹体烃的分步分离和抽提,并对每类烃的不同馏分进行GC-MS分析。根据所分析样品的成岩作用序列,结合样品的结构特征,表明这一方法是可行的。通过对不同赋存状态链烷烃的研究表明,研究区正构烷烃峰型为单峰型,碳数分布广,具较弱的奇碳优势。烃类的母质类型显示为Ⅰ—Ⅱ型干酪根,形成于开阔水体条件下还原的淡水湖相环境。Pr/Ph比值、CPI值,在不同赋存状态烃中差异比较明显,大体上从游离烃、封闭烃、胶结物烃、束缚烃到包裹体烃有减小的趋势。结合其族组分特征,反映了油气演化的阶段性及其成藏期次和油藏微观的不均一性。

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.