苏北盆地溱潼凹陷阜二段泥页岩生烃演化模式

The hydrocarbon generation evolution model of mudstones and shales in the second member of Funing Formation in Qintong Depression, Northern Jiangsu Basin

摘要

苏北盆地溱潼凹陷阜宁组二段(阜二段)发育多种岩性类型的烃源岩,为古近系页岩油层系的主要烃源岩。选取溱潼凹陷阜二段不同亚段、不同岩性的岩心样品,基于岩心观察、薄片鉴定、矿物成分X线衍射分析资料,采用总有机碳测定、岩石热解、生烃动力学和高温高压模拟等实验,分析研究区阜二段不同岩性烃源岩的生烃条件,揭示主要岩性烃源岩的生烃动力学特征,建立主要岩性烃源岩的生烃演化模式。结果表明:溱潼凹陷阜二段不同岩性烃源岩的生烃条件存在比较明显的差异,阜二段中下部页岩(含灰云页岩、灰云质页岩、纹层状泥灰岩)有机质类型相对较好,以Ⅰ和Ⅱ₁型为主,生烃活化能相对较低,最大生烃转化率和累积生烃率较高;中下部泥岩(含灰云泥岩、灰云质泥岩、泥灰岩)有机质类型相对较差,以Ⅱ₂和Ⅱ₁型为主,生烃活化能相对较高,最大生烃转化率和累积生烃率较低;上部泥岩(含灰泥岩)的有机质类型以Ⅱ₁和Ⅰ型为主,生烃活化能整体略高于中下部页岩的,最大生烃转化率和累积生烃率在中下部页岩和泥岩之间。阜二段不同岩性烃源岩的生烃动力学特征和生烃率主要受有机质类型影响,随氢指数升高,不同岩性烃源岩的平均生烃活化能先减小后缓慢增大,累积生烃转化率逐渐增大。阜二段3种主要岩性类型为灰云质泥岩、含灰泥岩和灰云质页岩,生烃模式存在一定的差异,开始大量生油时的R_o分别为0.58%、0.64%、0.74%,对应深度分别约为2105、2450、2805m,达到生油高峰与结束生油时的温度及对应的成熟度大致相当,R_o分别为0.92%~0.95%和1.47%~1.55%,对应深度为3460~3555和4840~4980m。不同岩性烃源岩的生油窗范围存在一定差异,其中灰云质泥岩的生油窗范围较宽,含灰泥岩的次之,灰云质页岩的生油窗范围较窄。该结果为研究区阜二段页岩油富集层段分布及有利区的预测提供依据。

Abstract

There are various hydrocarbon source rocks with different lithologies in the shale-oil layer of the second member of Funing Formation in the Qintong Depression, Northern Jiangsu Basin, which are the main source rocks for the Paleogene shale oil layers in the study area. This study selected core samples of different sub-members and lithologies from the second member of Funing Formation in Qintong Depression. Based on core observations, thin-section analyses, and X-ray diffraction for mineralogical composition, combined with geochemical analyses including total organic carbon determination and rock pyrolysis, the hydrocarbon generation potential of various lithological types of source rocks in the study area was systematically evaluated. Hydrocarbon generation kinetics experiment and high-temperature, high-pressure hydrocarbon generation simulation experiments were conducted to elucidate the kinetic characteristics of hydrocarbon generation for the dominant lithological source rocks. Hydrocarbon generation models were subsequently established for the three primary lithological types of source rocks. The research results show that there are significant differences in the hydrocarbon generation conditions of different lithological types of source rocks in the second member of the Funing Formation within this area. Shales in the middle and lower sections (including carbonate-bearing shale, carbonatic shale and laminated marl) exhibit relatively superior organic matter types, predominantly Type Ⅰ and Type Ⅱ₁. These rocks feature lower activation energy for hydrocarbon generation, higher maximum hydrocarbon conversion rates, and greater cumulative hydrocarbon yields. Mudstones in the middle and lower sections (including carbonate-bearing mudstone, carbonatic mudstone and argillaceous limestone) contain relatively poorer organic matter types, mainly Type Ⅱ₂ and Type Ⅱ₁. They require higher activation energy for hydrocarbon generation while displaying lower maximum hydrocarbon conversion rates and reduced cumulative hydrocarbon yields. Mudstones in the upper section (mainly including calcitic-bearing mudstone) are dominated by Type Ⅱ₁ and Type Ⅰ organic matter. Their activation energy for hydrocarbon generation is moderately higher than that of shales in the middle and lower sections, with maximum hydrocarbon conversion rates and cumulative yields intermediate between those of shales and mudstones in the middle and lower sections. The hydrocarbon generation kinetics characteristics and hydrocarbon generation efficiency of different lithological types of source rocks in the second member of the Funing Formation are primarily controlled by organic matter types. As the hydrogen index (HI) increases, the average activation energy of various lithological source rocks all decreases initially then gradually rises, while cumulative hydrocarbon generation conversion rates progressively increase. The three main lithological types in the second member of Funing Formation are calcareous-dolomitic mudstone, calcareous-bearing mudstone, and calcareous-dolomitic shale. Their hydrocarbon generation patterns exhibit certain differences. The vitrinite reflectance (R_o) values at the onset of significant oil generation are 0.58%, 0.64%, and 0.74%, corresponding to depths of approximately 2105, 2450, and 2805 m, respectively. The temperature and corresponding maturity at which peak oil generation and the end of oil generation occur are roughly similar, with R_o values ranging from 0.92% to 0.95% and 1.47% to 1.55%, corresponding to depth ranges of approximately 3460-3555 and 4840-4980 m, respectively. There are certain differences in the oil generation window ranges: the carbonatic mudstone exhibits the broadest oil window, the calcitic-bearing mudstone has an intermediate range, and the carbonatic shale shows the narrowest window. The research results provide geochemical evidence for the distribution of the rich shale oil layers and the prediction of favorable areas in the second member of Funing Formation in Qintong Depression.

关键词

苏北盆地 / 溱潼凹陷 / 阜二段 / 泥页岩 / 页岩油 / 生烃模拟 / 生烃演化模式

Key words

Subei Basin / Qintong Depression / second member of Funing Formation / mudshale / shale oil / hydrocarbon-generating simulation / hydrocarbon generation evolution model

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基金资助

国家科技重大专项(2024ZD1400100)

中国石化科技部项目(P23190)