OIL FAMILIES AND GEOCHEMICAL COMPOSITION OF DEVONIAN OILS AT THE RECHITSA FIELD, PRIPYAT BASIN, BELARUS

IF 1.8 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
Evgenia Leushina, Timur Bulatov, Yauheni Kaleichyk, Arina Goncharova, Elena Kozlova, Lyudmila Torshina, Alina Bazhanova, Anna Eroshenko, Andrei Khaletski, Mikhail Spasennykh
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引用次数: 0

Abstract

The sedimentary column at the Rechitsa oilfield in the Pripyat rift basin, Belarus, is dominated by an Upper Devonian synrift succession. The succession includes uppermost Frasnian and mid-Famennian salt units which are about 1000 m and 2000 m thick respectively. Reservoir rocks consist of sandstones and carbonates in the intra-, inter- and sub-salt successions. In this paper, the geochemical analysis of 15 oil samples from different stratigraphic intervals at the Rechitsa field is used as a basis for reservoir characterisation. Geochemical studies included biomarker and stable C, N and S isotope analyses.

Four genetic oil groups were identified and are referred to as Groups A to D. Oils in Group A came from upper intra- and inter-salt reservoir rocks; the oils are early mature, enriched in heavy (C36+) hydrocarbons, heteroatoms, aryl-isoprenoids and gammacerane, with low Pr/Ph = 0.6 and a sulphur isotope composition averaging 22.7‰ CDT. Oils in Group B were from sub-salt reservoirs and are at peak maturity with Pr/Ph = 1, an increased proportion of C27 regular steranes, and a sulphur isotope composition of 8.1‰ CDT. The single oil sample in Group C was from a Proterozoic reservoir. The oil was overmature with a low content of heavy fractions, heteroatoms and steranes; its hopanes composition indicated that it was generated by the same source rock as the oils in Group B. Oils in Group D came from inter-salt reservoir rocks and were composed of a mixture of Groups A and B oils in roughly equal proportions, as indicated by their average isotope, molecular and biomarker compositions.

Observed differences in oil composition were explained in terms of contributions from at least two different source rocks together with variations in source rock maturity. Group A oils were interpreted to have been generated by Famennian carbonate-rich source rocks containing dominantly marine and bacterial organic matter deposited in an anoxic evaporitic setting. Source rocks for Groups B and C oils were suggested to be composed of OM-rich marine shales of Frasnian age or older.

The geochemical characteristics of the Devonian oils from Rechitsa field, and the oil-oil and oil- source rock correlations reported, will contribute to a better understanding of the petroleum system in the Pripyat Basin although direct oil- source rock correlations are not yet available. The presence of at least two source rocks for the Rechitsa oils has been suggested, respectively comprising carbonates in the inter-salt succession and marine shales and/or carbonates in the sub-salt succession. The main controls on oil composition in the Devonian reservoir units were the varying contributions from the different source rocks and differences in source rock thermal maturity associated with variations in burial depth and tectonics, together with the stratigraphic distribution of reservoir units which was in turn controlled by the presence of the thick Frasnian and Famennian salt units.

白俄罗斯普里皮亚季盆地雷奇察油田的石油家族和德文系石油的地球化学组成
位于白俄罗斯普里皮亚季断裂盆地的雷奇察油田的沉积柱以上泥盆统同向断裂演替为主。该演替包括最上层的弗拉斯年和中期的法门年盐单元,厚度分别约为 1000 米和 2000 米。储层岩石包括盐内、盐间和盐下演替中的砂岩和碳酸盐岩。本文以雷奇察油田不同地层区间的 15 个石油样本的地球化学分析为基础,对储层特征进行了分析。A 组的石油来自盐内和盐间储层的上部岩石;这些石油属于早熟石油,富含重烃(C36+)、杂原子、芳基异戊烷和伽马塞烷,Pr/Ph = 0.6 较低,硫同位素组成平均为 22.7‰CDT。B 组石油来自盐下储层,处于成熟高峰期,Pr/Ph = 1,C27 正甾烷的比例增加,硫同位素组成为 CDT 的 8.1‰。C 组的单一油样来自一个新生代储油层。D 组油类来自盐间储油层岩石,由 A 组和 B 组油类的混合物组成,比例大致相同,其平均同位素、分子和生物标志物组成也表明了这一点。据解释,A 组石油是由富含碳酸盐的法门纪源岩生成的,其中主要含有在缺氧蒸发环境中沉积的海洋和细菌有机物。雷奇察油田泥盆纪石油的地球化学特征以及所报告的石油-石油和石油-源岩相关性,将有助于更好地了解普里皮亚季盆地的石油系统,尽管目前还没有石油-源岩的直接相关性。有人认为,雷奇察石油至少有两种源岩,分别是盐间演替中的碳酸盐岩和盐下演替中的海相页岩和/或碳酸盐岩。泥盆纪储油层单元中石油成分的主要控制因素是不同源岩的不同贡献、与埋藏深度和构造变化相关的源岩热成熟度差异,以及储油层单元的地层分布,而储油层单元的地层分布又受到厚的弗拉斯年和法门年盐层单元的控制。
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来源期刊
Journal of Petroleum Geology
Journal of Petroleum Geology 地学-地球科学综合
CiteScore
3.40
自引率
11.10%
发文量
22
审稿时长
6 months
期刊介绍: Journal of Petroleum Geology is a quarterly journal devoted to the geology of oil and natural gas. Editorial preference is given to original papers on oilfield regions of the world outside North America and on topics of general application in petroleum exploration and development operations, including geochemical and geophysical studies, basin modelling and reservoir evaluation.
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