Burial and thermal history modeling and petroleum potential evaluation of the northwestern Niger Delta, Nigeria [Modelação da evolução térmica e do soterramento e avaliação do potencial petrolífero do noroeste do Delta do Níger, Nigéria]
Department of Geology and Mineral Sciences, University of Ilorin, Nigeria; Department of Physics, University of Uyo, Nigeria; Shell Petroleum Development Company, PortHarcourt, Nigeria
One of the major hydrocarbon exploration risks or constraints in the Niger Delta is the complex nature of the petroleum systems, as there is lack of geochemical data from deeper and older potential strata. In this study, 1D models of burial and thermal histories were constructed from stratigraphic and well-log data in order to assess the petroleum potential of part of the northwestern Niger Delta basin using Cauldron and PetroMod software. The thermal maturation of the source rock intervals was reconstructed based on crustal thinning during rift, break up, and drift during the Lower and Upper Cretaceous. Bottom-hole temperature data were used to estimate present-day subsurface temperature. Results show that the Eocene and Paleocene source rocks attained sufficient thermal maturities to contribute oil and gas into the Oligocene and Miocene clastic reservoirs. In Operation Mining License (OML) 1 and 40, the Paleocene, which is overmature (modeled Ro% ranges from 0.9 to 3 Ro %) at present, entered the oil window and expelled most of its oil during late Eocene. In the present day, it could be expelling minor volumes of dry gas. The Eocene source rock intervals appear to be the most active at present, having entered the oil window during Oligocene and attained present-day maturities in the range of 0.62 to 0.90 Ro% in most of the wells. However, in OML 38, with relatively higher sedimentation rates, the Paleocene source rocks are presently at the peak of hydrocarbon generation and expulsion whereas the Eocene source rocks in most of the wells are barely mature. The Oligocene intervals in the wells studied are not mature according to modeled vitrinite reflectance ranging from 0.4 to 0.52R% at present day. At present time, average cumulative oil generated and expelled from Paleocene source rocks in OML 1 and 40 are 98,000 kg/m2 and 77,500 kg/m2, respectively. The Eocene source rocks stand at 73,000 kg/m2 and 35,000 kg/m2, respectively. In OML 38, average cumulative oil generated from Paleocene and Eocene source rocks are 95,000 and 51,000 kg/m2, respectively. Only 76% and 1.9% of the generated hydrocarbon have been expelled, respectively. It is only from the Paleocene interval of Abiala 1 (OML 40) that a substantial amount of gas (65,000 kg/m2) has been generated. © 2012 LNEG - Laboratório Nacional de Geologia e Energia IP.
burial (geology); computer simulation; crustal thinning; gas field; heat flow; hydrocarbon exploration; hydrocarbon reservoir; Paleocene-Eocene boundary; potential flow; sedimentation rate; software; source rock; thermal maturity; Niger Delta; Nigeria