The Bongor Basin is a typical lacustrine passive-rifted basin situated in the West and Central African Rift System (WCARS). It has experienced two phases of tectonic inversion and features a complex process of petroleum generation and accumulation. A total of 41 crude oil samples from the basin were geochemically analyzed to investigate their compositions of molecular markers. The results show that the oils have similar origins and are likely to belong to the same oil population. However, there are significant differences in geochemical characteristics and physical properties, caused by the secondary alteration. The relative contents and distribution patterns of normal alkanes and acyclic isoprenoids indicate that some of the oils have suffered biodegradation to varying degrees. The samples can be divided into three categories according to their relative degrees of degradation: normal oil, slightly biodegraded oil (PM 1–3), and severely biodegraded oil (PM 5–7). The burial depth of oil reservoirs in this area is the predominant factor impacting on the level of biodegradation. Crude oils in reservoirs with burial depths of less than 800 m are all severely biodegraded, while oils in reservoirs with burial depths greater than 1300 m have experienced no evident biodegradation. In reservoirs with burial depths between 800 m and 1300 m, the biodegradation degrees vary from normal to severely biodegraded. Oil reservoirs with burial depths less than 1300 m and adjacent to major faults are readily subject to biodegradation, while reservoirs with similar burial depths, but a certain distance away from major faults, have suffered no evident biodegradation. Moreover, if primary reservoirs have been modified by tectonic activity after accumulation, the crude oils are more likely to be biodegraded. Faulted anticline traps may create more favorable geological conditions for preservation of crude oil than reverse extrusion anticline reservoirs. This study may provide practical guidance for the assessment and prediction of oil quality in future oil exploration.

邦戈尔盆地是一个典型的湖相被动裂谷盆地，位于西非和中非裂谷系统（WCARS）。经历了两个构造反转阶段，具有复杂的油气生成和聚集过程。对来自该盆地的 41 个原油样品进行了地球化学分析，以研究它们的分子标记组成。结果表明，这些油类具有相似的来源，很可能属于同一个油类群体。但由于次生蚀变，地球化学特征和物理性质存在显着差异。正构烷烃和无环类异戊二烯的相对含量和分布规律表明，部分油品发生了不同程度的生物降解。样品根据其相对降解程度可分为三类：普通油、轻度生物降解油（PM 1-3）和重度生物降解油（PM 5-7）。该区油藏埋藏深度是影响生物降解程度的主要因素。埋深小于 800 m 的油藏原油均发生严重的生物降解，而埋深大于 1300 m 的油藏则未发生明显的生物降解。埋深800～1300m的油藏，生物降解程度从正常到严重不等。埋深小于 1 300 m 且靠近主断层的油藏容易发生生物降解，而埋深相近但距主断层有一定距离的油藏，没有遭受明显的生物降解。此外，如果原生储层在成藏后受到构造活动的改造，原油更有可能被生物降解。断层背斜圈闭可能比逆挤压背斜油藏为原油保存创造更有利的地质条件。该研究可为未来石油勘探中的油品质量评价和预测提供实践指导。