Fluid inclusion characteristics and hydrocarbon accumulation stages in lower Cretaceous reservoirs of the central low-uplift zone, central African Doseo basin

Abstract

Research on hydrocarbon accumulation stages in the central low-uplift zone of the Doseo Basin remains scarce, limiting effective exploration efforts in this region. This study investigates fluid inclusions in Lower Cretaceous sandstone reservoir samples using petrographic analysis, microthermometry, and Raman spectroscopy. The results reveal two distinct types of hydrocarbon inclusions. Type I inclusions, primarily distributed along quartz grain fractures and secondary growth margins, formed during the early to middle stages of diagenesis and exhibit yellow-green fluorescence, indicating low-maturity oil filling. Type II inclusions, associated with high-maturity oil filling, developed post-secondary growth along quartz micro-fissures and dissolved feldspar particles, with fluorescence varying from yellow-green to blue-white. The Kedeni reservoirs underwent two hydrocarbon charging phases: an early phase (∼105–85 Ma) characterized by crude oil filling (homogenization temperatures: 90–110 °C) and a later phase (∼50–43 Ma) dominated by natural gas and condensate accumulation (homogenization temperatures: 120–140 °C). These results provide valuable insights into the hydrocarbon generation mechanisms and reservoir evolution in the Doseo Basin.