Bulk petroleum geochemistry of shales from the onshore Rio del Rey Basin, Cameroon

Abstract

Petroleum production in the Rio del Rey Basin, which is an extension of the Niger Delta of Nigeria into Cameroon, has been limited to the Tertiary offshore portion since the late 1970s. Owing to declining reserves in this offshore portion, the onshore Cretaceous portion of the basin attracted significant attention in the last decade. In the present study, shales from outcrops in the onshore portion of the basin were analyzed to evaluate their potential as source rocks, assess hydrocarbon generation, and highlight their significance for exploration. Outcrop observations, total organic carbon (TOC) measurements, and Rock-Eval pyrolysis were used to generate data for these investigations. Rock-eval S2 values (0.42–3 mg HC/g rock) based on measured present-day TOC values (0.58–2.44 wt%) of the shales studied signify poor to fair source rock potentials, whereas calculated S2 values (1.74–8.19 mg HC/g rock) based on estimated original TOC values (0.67–2.87 wt%) produced fair to good source rocks containing Type Ⅱ/III kerogen, which were transformed by maturity to the present-day Type Ⅲ/Ⅳ kerogen. Maturity of the samples based on Tmax values varying between 439 and 471 °C are equivalent to maturity values ranging between 0.74% Rr and 1.32% Rr, and these represent the peak oil to condensate/wet gas zones of hydrocarbon generation. These results demonstrate that mature source rocks are present in the onshore part of the Rio del Rey Basin, and thus, it is suitable for petroleum exploration.

Keywords

• Shale
• Rio del Rey Basin
• Total organic carbon
• Rock-eval
• Petroleum geochemistry
• Cameroon