Source Rock Types and Logging Evaluation in Forced Regressive Systems Tract: Taking the Termit Basin (Niger) as an Example

Key words: 
• forced regressive systems tract /
• source rocks types /
• improve &Delta /
• logR method /
• well logging assessment /
• Termit Basin /
• Niger

Abstract: Nowadays, petroleum geologists have paid more attention to the Forced Regressive Systems Tract (FRST) for the development of effective reservoir rocks therein, however, studies focused on potential source rocks of FRST are rare. In this paper, a combination of lithology, well logging and geochemical analysis data of Termit Basin (Niger) was used to investigate the types, well logging identification and geochemical characteristics of source rocks in FRST. Furthermore, the development of different source rocks have been preliminarily analyzed on the basis of the total organic carbon (TOC) prediction model established by an improved ΔlogR method. Results indicate that 4 types of source rocks occur in FRST:coal/coaly mudstone, shoreface mudstone, deltaic mudstone and offshore mudstone. Offshore source rocks vertically distribute in the bottom sections of FRST, and the shoreface source rocks widely occurred in FRST while the thin coal/coaly mudstone existed associating with coastal marsh and deltaic environment. Shoreface mudstones are classified as good to excellent source rocks with type Ⅱ₂ kerogen and high TOC content; the deltaic mudstones consist of poor to good source rocks with higher heterogeneity than others, while the offshore source rocks are poor due to the dominance of Type Ⅲ kerogen. In this study, a TOC prediction model was established with the value of ΔlogR acquired from a plot of lgR versus Δt. TOC prediction curves from the model of different wells in Termit Basin indicate that most of FRST source rocks in different tectonic blocks have a good to excellent hydrocarbon potential, mainly consist of shoreface source rocks with larger cumulative thickness and higher hydrocarbon potential than others. Based on the evolution progress and the examples of Termit Basin, we can draw the conclusion that excellent source rocks could be occurred in the FRST, and the shoreface mudstones might be their main types of source rocks.