Novel insights about petroleum systems from source and reservoir rock characterization, Cretaceous Deposits, Babouri-Figuil Basin, Northern Cameroon

IF 5.6 2区 工程技术 Q2 ENERGY & FUELS International Journal of Coal Geology Pub Date : 2024-03-17 DOI:10.1016/j.coal.2024.104491
W. Gaspard Owona Manga , Javin J. Hatcherian , Paul C. Hackley , Moise Bessong , Carole L. Bapowa , Henri E. Pougue , Arsène Meying
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Abstract

The Babouri-Figuil Basin (BFB) is a frontier basin for petroleum in Cameroon. It belongs to the series of Cretaceous rift basins of the West and Central Rift System (WCARS), the origin of which is related to the opening of the South Atlantic. Within the same rift system, commercial hydrocarbon accumulations have been discovered in Chad, Sudan, Niger and, more recently, in Nigeria (Gongola Basin). The study of the geology of the BFB just recently received considerable attention, mainly because of its presumed hydrocarbon potential. In the pursuit of researching possible petroleum systems in the BFB, the current study provides a first look into the characterization of source and reservoir rock and its integration into a 2D lithostratigraphic model. The study was solely based on outcrop samples. Black shale and massive claystone are good to excellent hydrocarbon source rocks [e.g., up to 38 wt% total organic carbon (TOC), up to 943 mg/g hydrogen index, up to 85 m thickness, up to 20–30 km lateral extension], with moderate to high values of extractable organic matter (e.g., >10,000 ppm). Calcareous claystone, on the other hand, are poor source rocks [e.g., <0.20 wt% TOC]. The samples are thermally immature, except for those located close to volcanic intrusion at Golombe that have reached the threshold for oil generation (Tmax >435 °C, production index >0.1). The petrographic analysis of sandstone revealed that they are fine-grained to coarse-grained, poorly to moderately sorted, texturally and compositionally immature to submature, subarkosic to arkosic arenites. The main diagenetic processes that affected sandstones are as follows: moderate to intense compaction characterized by the development of long, concavo-convex, and sutured contacts between grains; cementation through calcite, iron oxide, and quartz cements; alteration of mica and feldspar grains; partial to complete dissolution of feldspar, mica, amphibole grains, and calcite cement; and the replacement of feldspar and mica grains by clay minerals. Alteration and dissolution increase the porosity of sandstone through the creation of secondary pores. However, mechanical compaction through the development of a pseudomatrix and cementation as pore-filling materials have significantly reduced the quality of sandstone beds as conventional petroleum reservoirs. Hence, the best reservoir-quality sandstones in the basin are generally located in the upper portion of the basin in terms of its lithostratigraphic model. They are the cleanest sandstones with the smallest amount of cement and the lowest ductile grain content (pseudomatrix), with a thickness that varies from 3 m to 120 m and a lateral extension of 20 km. The lithostratigraphic model of the basin is characterized by an extensive lacustrine environment that provided a thick sequence of organic-rich formations; sand deposited as extensive reservoirs sandwiched between shale/claystone beds; the development of stratigraphic traps through lateral facies change; and the widespread deposition of lacustrine and floodplain claystone that provide regional seals. The similarities between the Babouri-Figuil Basin and proven petroleum systems in other WCARS rift basins suggest that the basin may host at least one petroleum system where actively generating source rocks are present.

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喀麦隆北部巴布里-菲吉尔盆地白垩纪矿床,从源岩和储层岩石特征中获得有关石油系统的新见解
巴布里-菲吉尔盆地(BFB)是喀麦隆的一个石油前沿盆地。它属于中西部裂谷系统(WCARS)的白垩纪裂谷盆地系列,其起源与南大西洋的开辟有关。在同一裂谷系统中,乍得和苏丹以及最近在尼日利亚(Gongola 盆地)发现了商业油气储藏。对 BFB 地质的研究最近刚刚受到相当大的关注,这主要是因为它被认为具有油气潜力。为了研究 BFB 可能的石油系统,本研究首次对源岩和储层岩的特征进行了分析,并将其纳入二维岩石地层模型。这项研究完全基于露头样本。黑页岩和块状粘土岩是良好至极佳的碳氢化合物源岩[例如,总有机碳(TOC)高达 38 wt%,氢指数高达 943 mg/g,厚度达 85 米,横向延伸达 20-30 千米],可提取有机物的数值为中等至高等(例如,>10,000 ppm)。另一方面,钙质粘土岩属于贫源岩[例如,435 °C,生产指数大于 0.1]。砂岩的岩相分析表明,它们属于细粒至粗粒、分选差至中等、质地和成分不成熟至亚稳态、亚赤铁矿至赤铁矿。影响砂岩的主要成岩过程如下:中等到强烈的压实,特点是岩粒之间形成长而凹凸的缝合接触;方解石、氧化铁和石英胶结物的胶结;云母和长石岩粒的蚀变;长石、云母、闪石岩粒和方解石胶结物的部分到完全溶解;以及粘土矿物对长石和云母岩粒的取代。蚀变和溶解会产生次生孔隙,从而增加砂岩的孔隙率。然而,通过形成假基质和胶结物作为孔隙填充材料进行机械压实,大大降低了砂岩床作为常规石油储层的质量。因此,从岩石地层模型来看,盆地中储层质量最好的砂岩一般位于盆地上部。它们是最洁净的砂岩,胶结物含量最少,韧性颗粒含量(假矩阵)最低,厚度从 3 米到 120 米不等,横向延伸 20 千米。该盆地岩石地层模型的特点是:广泛的湖沼环境提供了厚厚的富含有机质的地层序列;砂沉积为广泛的储层,夹在页岩/粘土岩床之间;通过横向面层变化形成地层陷阱;湖沼和洪积平原粘土岩广泛沉积,提供了区域封印。巴布里-菲吉尔盆地与其他世界卡斯特罗裂谷盆地已探明的石油系统之间的相似性表明,该盆地可能存在至少一个石油系统,其中有活跃的生成源岩。
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来源期刊
International Journal of Coal Geology
International Journal of Coal Geology 工程技术-地球科学综合
CiteScore
11.00
自引率
14.30%
发文量
145
审稿时长
38 days
期刊介绍: The International Journal of Coal Geology deals with fundamental and applied aspects of the geology and petrology of coal, oil/gas source rocks and shale gas resources. The journal aims to advance the exploration, exploitation and utilization of these resources, and to stimulate environmental awareness as well as advancement of engineering for effective resource management.
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