Preliminary geochemical investigation of some crude oils from the Niger Delta Basin Nigeria

Geochemical studies on twenty-eight crude-oil samples from nine oilfields, onshore-offshore parts of Niger Delta Basin, were performed to classify the oils into various classes, determine the bulk compositions of oils, organic matter inputs, source depositional environment, thermal maturation, and in-reservoir processes, for petroleum system prediction. The oils were fractionated into individual bulk compositions of saturates, aromatics, resins, and asphaltenes (SARA), using the Iatroscan thin-layer chromatography-flame ionization detector (FID) technique. Column chromatography was utilized to separate the saturates, and were further analyzed with gas chromatography-FID for n-alkane and acyclic isoprenoid distributions. SARA results, classified the oils into: paraffinic (>72%Hc, sat/arom: 2.61-3.68); paraffinic-naphthenic (63-70%Hc, sat/arom:1.77-2.31) and aromatic-naphthenic/aromatic-intermediate (<60%Hc, sat/arom: <1.44) oils, generated from source rocks of terrigenous-deltaic origin. Pristane/phytane and n-alkane/isoprenoid ratios delineated the oils into terrigenous (Type III kerogen) and mixed (terrigenous-marine) Type II/III kerogen organic matter source, deposited in oxidizing to transitional environment conditions. Thermal maturity parameters suggest the oil originated from source rocks of early to peak oil window maturity. Additionally, n-alkane/isoprenoid and saturate/aromatic ratios established evidence of biodegradation in a few samples across the depobelts. However, SARA compositions, n-alkane, and isoprenoid distributions of the oils critically permit preliminary assessment study, consequently allows a first-hand geochemical interpretation of the Niger Delta petroleum systems.

对尼日三角洲盆地陆上-海上部分九个油田的二十八个原油样品进行了地球化学研究，旨在将原油分类，确定原油的总体组成、有机物质输入、源沉积环境、热成熟度和储层内过程，以预测石油系统。采用Iatroscan薄层色谱-火焰电离检测器（FID）技术，将原油分为饱和烃、芳香烃、树脂和沥青质（SARA）的单个总体组成。利用柱色谱分离饱和烃，并进一步用气相色谱-FID分析正构烷烃和非环异戊二烯分布。SARA结果将原油分为：石蜡烃（碳氢化合物含量>72%，饱和烃/芳香烃：2.61-3.68）、石蜡烃-环烷烃（碳氢化合物含量63-70%，饱和烃/芳香烃：1.77-2.31）以及芳香烃-环烷烃/芳香烃-中间型（碳氢化合物含量<60%，饱和烃/芳香烃：<1.44）原油，这些原油源自陆源-三角洲源岩。植烷/菲烷和正构烷烃/异戊二烯比值将原油划分为陆源（III型干酪根）和混合型（陆源-海洋）II/III型干酪根有机物质来源，沉积在氧化至过渡性环境条件下。热成熟度参数表明，原油源自早期至峰期成熟窗口的源岩。此外，正构烷烃/异戊二烯和饱和烃/芳香烃比值在沉积带内的一些样品中建立了生物降解的证据。然而，SARA组成、正构烷烃和异戊二烯分布的原油对初步评估研究至关重要，从而允许对尼日三角洲石油系统进行直接的地球化学解释。