多元统计分析在油源对比中的应用——以渤海湾盆地歧口凹陷滨海地区中浅层系混源油为例

Application of multivariate statistical analysis in oil and source correlation: a case study of mixed-source oils from middle and shallow strata in coastal area of Qikou Sag, Bohai Bay Basin

  • 摘要: 渤海湾盆地歧口凹陷滨海地区是近年来大港油田增储上产的重要目标,该地区中—浅层系原油来源复杂,混合严重,次生变化明显。多元统计分析方法是一种高效率、便捷且具有高精度的数据处理手段。近年来,许多学者在不同地区的油气源对比中运用该方法取得了较为丰富的研究成果,但针对多元统计分析在混源油油源对比中的应用研究仍有待进一步加强。为此,以油气地质地球化学理论为指导,在揭示研究区中—浅层系原油(沙一段、东营组、馆陶组、明化镇组)和主力烃源岩(沙三段、沙一段、东三段)地球化学特征的基础上,应用聚类、主成分和判别分析方法,开展油源对比。结果表明,歧口凹陷滨海地区各层系烃源岩成熟度差异较小,沙一中、沙一下烃源岩品质更好;烃源岩生烃母质以混合来源为主,其中沙一中、沙一上和东三段形成于弱还原、淡水条件,沙三段、沙一下烃源岩形成于还原、淡水—微咸水条件。研究区的次生变化以生物降解作用为主,不同层系原油可分为两类:其中Ⅰ类原油分布在沙一段,具有低Pr/Ph值、高三环萜烷的特点,主要以沙三段、沙一下和沙一中烃源岩混合供烃;Ⅱ类原油分布在东营组、馆陶组和明化镇组,具有较高Pr/Ph值、低三环萜烷的特点,主要以沙一上和东三段烃源岩混合供烃。应用判别分析验证这两类油—源,获得初始验证率100%,交叉验证正确率90.0%,表明油源对比结果可靠。研究成果揭示了多元统计分析方法在混源油油源对比中的良好应用前景。

     

    Abstract: The coastal area of the Qikou Sag of Bohai Bay Basin has become an important target for increasing reserves and production in the Dagang Oilfield in recent years. In this area, crude oil from the middle and shallow strata of the region exhibited complex origins, severe mixing, and significant secondary alterations. Multivariate statistical analysis is an efficient, convenient, and accurate data processing method. In recent years, many researchers have applied this method to hydrocarbon source correlation in various regions, yielding fruitful research results. However, its application in source correlation of mixed-source oils requires further development. Guided by petroleum geology and geochemistry theory, this study characterized the geochemical characteristics of crude oils from the middle and shallow strata (the first member of the Shahejie Formation, Dongying Formation, Guantao Formation, and Minghuazhen Formation) and main source rocks (the third member of the Shahejie Formation, the first member of the Shahejie Formation, and the third member of the Dongying Formation). Then, cluster analysis, principal component analysis, and discriminant analysis were applied for oil and source correlation. The results demonstrated that the maturity of source rocks in different strata of the coastal area of the Qikou Sag was relatively similar, and the middle and lower units of the first member of the Shahejie Formation had better hydrocarbon quality. The precursor for hydrocarbon generation of these source rocks was mainly of mixed origin. The middle and upper units of the first member of the Shahejie Formation and the third member of the Dongying Formation source rocks were deposited under weakly reducing, freshwater conditions, while the third member of the Shahejie Formation and the lower unit of the first member of the Shahejie Formation source rocks were formed under reducing, fresh to brackish water conditions. The main secondary alteration in the study area was biodegradation. The crude oils from different strata could be classified into two types: Type Ⅰ crude oil, distributed in the first member of the Shahejie Formation, was characterized by low Pr/Ph values and high tricyclic terpane content. It mainly originated from a mixture of source rocks in the third member of the Shahejie Formation and the middle and lower units of the first member of the Shahejie Formation. Type Ⅱ crude oil was distributed in the Dongying Formation, Guantao Formation, and Minghuazhen Formation. It featured high Pr/Ph values and low tricyclic terpane content, and was mainly originated from mixed source rocks in the upper unit of the first member of the Shahejie Formation and the third member of the Dongying Formation. Discriminant analysis was applied to validate the oil and source correlation results, resulting in an initial classification accuracy of 100% and a cross-validation accuracy of 90.0%. These results indicated that the oil and source correlation results were reliable. The study reveals the promising application potential of multivariate statistical analysis method in source correlation for mixed-source oils.

     

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