德国奥尔登堡大学Amoako Kojo课题组近日取得一项新成果。他们探究了加纳Saltpond盆地原油的有机地球化学——有机源输入、沉积环境和热成熟度。该研究于2024年4月17日发表于国际一流学术期刊《地球化学学报》杂志上。

据介绍，位于加纳南大西洋边缘的Saltpond盆地是一个重要的石油勘探地区，但其得到的研究关注相对有限。先前的研究已经检测了它的源岩成分，但缺乏原油有机化学的数据，阻碍了对盆地石油系统和演化的理解。为了解决这一问题，研究人员利用气相色谱—质谱和气相色谱—同位素比质谱分析了Saltpond盆地原油中的生物标志物和稳定碳同位素比值，以阐明有机质的来源、沉积环境和热成熟度。

研究人员将结果与南大西洋边缘西非部分(即Tano盆地和Niger三角洲盆地)的石油进行了比较，以确定潜在的相关性，并深入了解区域差异。分子和同位素结果揭示了来自较低等海洋生物的有机物的显著普遍性。Saltpond石油样品的有机质沉积和保存模式表明了一种缺氧的海洋过渡环境，这与传统的陆地主导环境的认识相矛盾。此外，降解过程有可能模糊陆地和海洋有机质来源之间的区别，这突出了过渡海洋环境中有机质动态的复杂性。分子热成熟度指标分析表明，Saltpond油主要从早期成熟阶段显示热成熟的烃源岩中排出。相关性分析揭示了产自Saltpond盆地与产自Tano盆地和Niger三角洲盆地原油的成因差异，主要是由于有机源输入和沉积环境条件的差异。

Saltpond原油的陆相有机质输入量低于Tano盆地原油，而Tano盆地原油陆相有机质输入量也低于Niger三角洲盆地原油。此外，其古沉积环境与Tano盆地(缺氧过渡性海相—湖泊环境)、Niger三角洲盆地(缺氧—低氧陆源三角洲或海相或湖泊环境)有明显差异。Saltpond油的热成熟度范围与Tano盆地相当，但低于Niger三角洲盆地。这些发现为Saltpond盆地的油气生成历史和独特的有机地球化学特征，提供了有价值的见解，对该地区的勘探、生产和环境管理工作至关重要。此外，对比研究表明，南大西洋边缘西非段不同的生物、地质和古环境条件形成了不同的石油类型。

附：英文原文

Title: The organic geochemistry of crude oil in the Saltpond Basin (Ghana): Organic source input, depositional environment, and thermal maturity

Author: Amoako, Kojo, Zhong, Ningning, Osei-Boakye, Nancy Pearl, Apesegah, Ebenezer

Issue&Volume: 2024-04-17

Abstract: The Saltpond Basin, situated within the South Atlantic margin of Ghana, is a significant area for petroleum exploration but has received relatively limited research attention. Previous studies have examined source rock composition, but data on crude oil organic chemistry are lacking, hindering understanding of the basin’s petroleum system and evolution. To address this gap, we analyzed biomarkers and stable carbon-isotope ratios in Saltpond Basin crude oil using gas chromatography–mass spectrometry and gas chromatography–isotope ratio mass spectrometry to elucidate organic matter source, depositional environment, and thermal maturity. Findings were compared with oils from the West African segment of the South Atlantic margin, namely the Tano Basin and the Niger Delta Basin, to identify potential correlations and gain insights into regional variations. Molecular and isotopic results unveiled a significant prevalence of organic matter derived from lower marine organisms. Patterns of organic matter deposition and preservation in Saltpond oil samples suggested a suboxic marine transitional environment, contradicting conventional understanding of terrestrial dominance in such settings. Moreover, the potential for degradation processes to obscure differentiation between terrestrial and marine organic matter origins underscores the complex nature of organic matter dynamics in transitional marine environments. Analysis of molecular thermal maturity indices suggested Saltpond oils were expelled from source rocks exhibiting thermal maturity at the early maturity stage. Correlation analysis unveiled genetic disparities among crude oils sourced from the Saltpond Basin and those from the Tano and Niger Delta Basin, primarily due to variations in source input and depositional environment conditions. Saltpond oil exhibits lower terrestrial organic input than Tano Basin’s crude oils, which also have less terrestrial input than Niger Delta Basin crude oils. Additionally, its paleodepositional environment notably differs from oils in the Tano Basin (anoxic transitional marine-lacustrine settings) and the Niger Delta Basin (suboxic–oxic terrigenous deltaic or marine or lacustrine environments). Thermal maturity range of Saltpond oil is comparable to oils in the Tano Basin but lower than oils in the Niger Delta Basin. These findings provide valuable insights into petroleum generation history and unique organic geochemical characteristics within the Saltpond Basin, essential for exploration, production, and environmental management efforts in the region. Furthermore, correlation studies provide evidence that distinct biological, geological, and paleoenvironmental conditions shaped various oil types in the West African segment of the South Atlantic margin.

DOI: 10.1007/s11631-024-00692-4

Source: https://link.springer.com/article/10.1007/s11631-024-00692-4