塔河油田混源油地球化学及多元数理统计学对比研究

混源油的定量判识是当前石油地质地球化学研究的热点与难点。以塔里木盆地塔河油田奥陶系中聚集的混源油为典型研究实例,通过地质地球化学与数理统计学相结合的方法,探索了定量研究混源油的方法,取得良好效果。原油地球化学研究结果表明,塔河油田原油普遍混源,并表现出多期充注特征,早期充注原油遭受了生物降解,因此目前原油中的轻烃、链状烃、规则甾烷等生物标志物主要反映的是后期充注原油的特征,不能很好地指示早期充注原油。据此,选择受生物降解影响相对较小的三环萜烷和藿烷定量数据,采用多元数理统计学交替最小二乘算法进行了原油成因研究,综合分析后认为现今混源油中可划分出4个端元,其中端元1和2可能主要代表了中上奥陶统烃源岩的贡献,而端元3和4则可能主要代表了寒武系烃源岩的贡献。塔河主体区以寒武系原油聚集为主,而外围地区则以中上奥陶统原油聚集为主,并且在整个塔河油田,总体上以寒武系原油的贡献比例相对最高。这一综合对比研究表明,多元数理统计学方法在混源油的比例计算、端元分析等方面具有重要作用,是对传统地球地球化方法研究的有效补充,值得推广应用,此外,研究认识还为区域油气勘探提供了新的参考信息。

Comparative Study of Geochemistry and Multivariate Data Analysis on Mixed Oils Accumulated in Ordovician Reservoir in Tahe Oilfield,Tarim Basin, NW China

Quantificational discrimination of mixed oils is a hot concept and difficult point in petroleum geology and geochemistry research. This article shows a case study on Tahe oilfield, Tarim Basin, NW China. Comparative study of geochemistry and multivariate data analysis indicate that oils accumulated in Ordovician reservoir in Tahe oilfield are characterized by multi-stage hydrocarbon generation and mixed sources. The early-stage generated oils were biodegraded, thus the light hydrocarbons, alkanes, and regular steranes in present oils show features of later-stage generated oils. Quantitative data of tricyclic terpanes and hopanes with little influence of biodegradation were calculated through Alternating Least Squares algorithm. The results show that there were four end-member oils contributed to the mixed oils in this region. The end-members 1 and 2 indicate middle-upper Ordovician source rocks, and the end-members 3 and 4 indicate Cambrian source rocks. In the main area of Tahe oilfield, oilsgenerated from the Cambrian source rocks were more than those from the middle-upper Ordovician source rocks. But in the area around the main area, the middle-upper Ordovician source rocks were the major contributors. For the whole oilfield, the Cambrian source rocks were more important. This comparative research shows that the multivariate data analysis plays significant role in calculating proportions of mixed oils and identifying end-member oils. As an effective complement to traditional geochemistry study, multivariate data analysis is worthy to be popularized