Hydrocarbon potential and depositional paleoenvironment of a Middle Jurassic succession in the Falak-21 well, Shushan Basin, Egypt: Integrated palynological, geochemical and organic petrographic approach
Hydrocarbon potential and depositional paleoenvironment of a Middle Jurassic succession in the Falak-21 well, Shushan Basin, Egypt: Integrated palynological, geochemical and organic petrographic approach
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DOI：
10.1016/j.coal.2019.103374
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发表时间：
2020-02
影响因子：
5.6
通讯作者：
A. Mansour;E. Geršlová;I. Sýkorová;Dominik Vöröš
中科院分区：
文献类型：
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作者：
A. Mansour;E. Geršlová;I. Sýkorová;Dominik Vöröš
埃及西北沙漠最顶端的下侏罗统和中侏罗统富含有机碎屑岩和少量碳酸盐沉积被认为是非常重要的生储集层。尽管对它们的源岩特征和含油气潜力进行了一些研究，但对它们的沉积古环境和古氧化还原条件仍然知之甚少。在目前的研究中，对这些沉积物的有机质丰度、生烃潜力和热成熟度、总硫(TS)含量和有机岩石学特征进行了评价。利用甲藻包囊(甲藻包囊)、颗粒有机质组成和有机岩石学特征研究了沉积古环境。根据TS与总有机碳(TOC)的关系和主要来自于孢粉相分析的干酪根类型，对氧化还原条件进行了评估。TOC含量显示出以干酪根III类(倾向于天然气)为主的烃类的中等至良好的生成潜力。基于Tmax和RR的热成熟度指示了石油窗口的成熟阶段。孢粉学分析在Khatatba组上部产生了保存良好、生物地层学上有用的恐囊。共鉴定出81种，隶属于54属，具有中等多样性的胞囊、孢子和花粉粒。淡水藻类、鞭毛虫和微孔虫测试衬里在研究间隔内零星地被记录下来。根据采集到的标志性恐龙的首次井下出现(FDA)资料，将哈塔巴组上部的孢粉测年确定为巴松晚期-卡洛纪，并对其沉积环境进行了解释，推断出3种沉积环境。代表最顶端的Ras Qattara和Yakout红页岩段的下层段沉积于河流-湖泊环境，根据红棕色砂岩和红色页岩的颜色推断，那里的含氧条件占优势。中间层段横跨单元IIB、Kabritt和单元III，在缺氧-亚缺氧环境下沉积于三角洲-浅海环境。上段为亚缺氧条件下古生产力高的河流三角洲-浅海相沉积的单元I和单元IIA。单元IIA上间隔中的一个样本反映了缺氧环境。
The topmost Lower and Middle Jurassic formations of organic-rich clastics with minor carbonate deposits were recognized as very significant source/reservoir rocks in the North Western Desert of Egypt. Although several studies are devoted to their source rock characteristics and petroleum potential, the depositional paleoenvironment and paleoredox conditions are still poorly understood. In the current study, these sediments were assessed in terms of their organic matter richness, hydrocarbon generative potential and thermal maturity, total sulfur (TS) contents and organic petrographic characteristics. Depositional paleoenvironment was investigated using dinoflagellate cysts (dinocysts) and the composition of particulate organic matter along with organic petrographic characteristics. Redox conditions were assessed based on TS- total organic carbon (TOC) relationship and type of kerogen that was derived mainly from palynofacies analysis.TOC contents show fair to excellent generative potential of hydrocarbons mainly of kerogen type III (gas-prone). The thermal maturity, based on Tmaxand Rr, indicates mature stage of oil window.Palynological analysis yielded poor to rich intervals of moderately-preserved, biostratigraphically useful dinocysts in the upper part of the Khatatba Formation. An assemblage of 81 species belonging to 54 genera of moderately diverse dinocysts, spores and pollen grains was identified. Freshwater algae, acritarchs and microforaminiferal test linings are sporadically documented within the studied interval. Based on the first downhole appearance (FDA) of the recovered marker dinocyts, the upper part of the Khatatba Formation was palynologically dated as late Bathonian-Callovian.The depositional environment was interpreted and three environments were deduced. The lower interval representing the topmost Ras Qattara and Yakout Red Shale Member was deposited in a fluvial-lacustrine environment, where oxic conditions prevailed as deduced from the color of reddish-brown sandstone and red shale. The middle interval spans Unit IIB, Kabrit and Unit III, which accumulated in a deltaic to shallow marine environment under dysoxic-suboxic settings. The upper interval covers Unit I and Unit IIA that have been deposited in a fluvio-deltaic to shallow marine with high paleoproductivity under suboxic conditions. One sample in the upper interval in Unit IIA reflected anoxic setting.