Oil families, oil–source rock correlation, basin modeling, and implication for petroleum systems, Termit Basin, Niger

Abstract

In the first comprehensive study of the Termit Basin petroleum system, an integrated organic geochemistry and basin modeling study of potential source rocks and related oils was conducted to evaluate source rock potential, classify oil families, establish oil–source correlation, and explain the distribution of petroleum systems. Six hundred forty-three cutting samples from the Paleogene Sokor1 Formation, Upper Cretaceous Yogou and Donga Formations, and Lower Cretaceous K1 Formation were analyzed using total organic carbon, Rock-Eval pyrolysis, vitrinite reflectance, and kerogen element analysis. The results suggest that the Sokor1, Yogou, and Donga Formations are poor to excellent source rocks with type I, II, II-III, and III kerogen, and most of the samples are thermally mature and within the oil window. Samples from the K1 Formation have poor organic richness and are thermally mature to postmature. In vertical, samples from the upper member of the Yogou Formation have greater organic matter richness and contain more oil-prone type I and oil-prone type II organic matter than those from the lower member. In horizontal, samples from the Donga Formation on the east side of the basin are dominated by very oil-prone type I and oil-prone type II organic matter and have higher hydrocarbon generation potential than those on the west side, which mainly contain oil- and gas-prone type II-III and gas-prone type III organic matter. One-dimensional basin modeling results demonstrate that the Sokor1 source rocks are mature in the northwestern part of the basin, are immature on the eastern side at present-day, and oil generation began in the early Oligocene. The Yogou source rocks are in the early oil to wet gas stage at present-day, and oil generation began at the end of the Late Cretaceous. The Donga source rocks are in the late oil to dry gas stage at present-day, and oil generation commenced in the middle Late Cretaceous. The maturation of these source rocks increased rapidly during the Oligocene due to active rifting. Three families (I, II, and III) were identified by hierarchical cluster analysis, principal component analysis, and stable carbon isotope compositions for 97 oil samples and eight rock extracts. Most of the oils (family I) were derived from Yogou source rocks, and their extensive distribution and wide range of thermal maturities are closely related to the large area of mature Yogou source rocks in the basin. Family II oils occur in the northwestern part of the basin and are genetically related to Sokor1 source rocks. The family III oil occurs on the east side of the basin and originated from the Donga Formation. This study confirms the existence of three petroleum systems between the Paleogene and Upper Cretaceous and helps to identify exploration prospects and guide petroleum resource assessment in the Termit Basin.