苏北盆地溱潼凹陷阜二段不同岩性烃源岩的地球化学特征及生烃潜力对比

Geochemical Characteristics and Hydrocarbon Generation Potential of Different Lithologic Source Rocks in the Second Member of Funing Formation in Qintong Sag,Subei Basin

古近系阜宁组二段是溱潼凹陷页岩油勘探的主要目标层系,具有良好的油气勘探前景。前人已经对研究区阜二段烃源岩生烃潜力及地球化学特征开展了比较系统的研究,但对阜二段不同亚段、不同岩性烃源岩地球化学特征及形成环境的差异性研究还相对薄弱,给研究区阜二段页岩油甜点预测、资源潜力评价以及油气源分析带来困难。本文选取阜二段具代表性的泥页岩样品,利用地球化学分析手段,对不同亚段、不同岩性烃源岩的地球化学特征、生烃潜力和形成环境进行对比研究。结果表明,研究区阜二段E_(1)f_(2)^(4)、E_(1)f_(2)^(5)烃源岩有机质丰度最高,以Ⅱ_(1)型有机质为主;E_(1)f_(2)^(2)、E_(1)f_(2)^(3)烃源岩有机质丰度较高,以Ⅱ_(1)型和Ⅱ_(2)型有机质为主;E_(1)f_(2)^(1)烃源岩有机质丰度相对较低,有机质类型主要为Ⅱ_(2)型。研究区阜二段烃源岩岩性比较复杂,主要包括泥岩、钙质泥岩和钙质页岩等。泥岩主要分布于E_(1)f_(2)^(4)、E_(1)f_(2)^(5),有机质丰度最高,以Ⅱ_(1)型与Ⅰ型有机质为主,沉积于弱氧化-弱还原的淡水环境,主要为低等水生生物为主的混源型有机质。钙质页岩与钙质泥岩主要分布于E_(1)f_(2)^(1)、E_(1)f_(2)^(2)以及E_(1)f_(2)^(3),其中钙质页岩有机质丰度较高,有机质类型主要为Ⅱ_(1)型,部分为Ⅱ_(2)型,沉积于强还原的咸水环境,混源型有机质来源;钙质泥岩有机质丰度为低-中等,有机质类型以Ⅱ_(2)型为主,含少量Ⅱ_(1)型与Ⅲ型,沉积于半咸水的还原环境,为混源型有机质来源。阜二段烃源岩处于低成熟-成熟阶段。可以根据Pr/Ph、Ga/C_(30)H、C_(24)TeT/C_(26)TT以及ααα20RC_(27)甾烷/ααα20RC_(29)甾烷等参数的分布特征把阜二段三类不同岩性的烃源岩区分开。这些认识可为研究区阜二段不同层段和不同岩性烃源岩的油气资源潜力评价、油源对比和页岩油勘探提供地球化学依据。

The second member of Paleogene Funing Formation(E_(1)f^(2))is the main target interval of shale oil exploration and has good prospects of oil and gas exploration in Qintong Sag.Predecessors have studied the hydrocarbon generation potential and geochemical characteristics of source rocks in the E_(1)f^(2) in the study area systematically,but the study on the geochemical characteristics and forming environment of source rocks in different sub-members and lithology of the E_(1)f^(2) is still relatively weak,which brings difficulties to the prediction of shale oil sweet spots and resource potential evaluation,as well as the correlation of oil-sources in the E_(1)f^(2) in the study area.In this paper,some representative shale samples of the E_(1)f^(2) in typical wells are selected,and the geochemical characteristics,hydrocarbon generation potential and formation environment of different sub-sections and lithologic source rocks of E_(1)f^(2) in the study area are compared by using geochemical experimental techniques.The results show that the source rocks of E_(1)f_(2)^(4) and E_(1)f_(2)^(5) in the study area have the highest abundance of organic matter,mainly typeⅡ_(1) organic matter.The abundance of organic matter in E_(1)f_(2)^(2) and E_(1)f_(2)^(3) source rocks is high,mainly typeⅡ_(1) andⅡ_(2) organic matter.The abundance of organic matter in E_(1)f_(2)^(1) is relatively low,and the type of organic matter isⅡ_(2).The lithology of source rocks in the E_(1)f^(2) in the study area is relatively complex,mainly including mudstone,calcareous mudstone and calcareous shale.Mudstone is mainly distributed in E_(1)f_(2)^(4) and E_(1)f_(2)^(5),with the highest abundance of organic matter,mainly typeⅡ_(1) and typeⅠorganic matter,deposited in weak oxidation-weak reduction freshwater environment,mixed source organic matter dominated by lower aquatic organisms.The calcareous shale and calcareous mudstone are mainly distributed in E_(1)f_(2)^(1),E_(1)f_(2)^(2) and E_(1)f_(2)^(3).The organic matter abundance of calcareous shale is higher,and the organic matter type is mainly typeⅡ_(1),a fewⅡ_(2),which is deposited in a strongly reducing saline water environment and mixed source organic matter source.The organic matter abundance of the calcareous mudstone is low-medium,and the type of organic matter type is mainlyⅡ_(2),with a small amount ofⅡ_(1) andⅢ,which is deposited in the reducing environment of brackish water and is the source of mixed source organic matter.The source rocks of E_(1)f^(2) are in low mature-mature stage.According to the distribution characteristics of Pr/Ph,Ga/C_(30)H,C_(24)TeT/C26TT andααα20RC_(27) sterane/ααα20RC_(29) sterane,the source rocks of three different lithologies in the E_(1)f^(2) can be distinguished.These understandings can provide geochemical basis for the evaluation of oil and gas resource potential,oil-source correlation and shale oil exploration in different intervals and lithologic source rocks of the E_(1)f^(2) in the study area.