Evaluating the impact of hydrodynamic flow on the hydrocarbon potentials of the Cretaceous Anambra basin, Southeastern N
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ORIGINAL PAPER
Evaluating the impact of hydrodynamic flow on the hydrocarbon potentials of the Cretaceous Anambra basin, Southeastern Nigeria Godwin Ezekwesili Ene 1 & Celestine Obialo Okogbue 1 & Kalu Mosto Onuoha 1 Received: 5 October 2018 / Accepted: 5 September 2019 # Saudi Society for Geosciences 2019
Abstract Fluid pressure data from wells drilled in the Anambra basin were analysed in order to characterize the regional groundwater dynamics in the Cretaceous formations and to evaluate the possible impact of the hydrodynamic flow of groundwater on the hydrocarbon prospectivity of the basin. The results demonstrate a general northeast to southwest flow, with regions of relatively high topographic expression in the eastern part, where the Cretaceous formations outcrop. These areas correspond to regions characterized by hydrostatic pressure condition, high hydraulic head and high flow strength. Conversely, areas of comparatively lower ground surface elevation, located in the western part of the basin, are associated with regions of overpressure, low hydraulic head and low flux. Two hydrostratigraphic systems, an upper one comprising the Ajali and Nsukka Formations and a lower one comprising the Nkporo Group and Mamu Formation are present. The upper hydrostratigraphic system is prone to downward invasion of the formations by meteoric groundwater, a process that has probably resulted in the devaluation of trapped hydrocarbons into heavy oil and bitumen that occur in the basin. The lower hydrostratigraphic system whose aquifers exist as isolated hydraulic units is considered to be in good hydrodynamic framework conducive for the preservation of hydrocarbons trapped in place. Keywords Hydrodynamics . Hydrocarbon . Groundwater . Hydraulic head . Hydrostratigraphy
Introduction The Anambra basin is one of the component sub-basins of the southern part of the Benue trough, which belongs to the Cretaceous-Tertiary West African Rift Systems (WARS) (Fig. 1). The rift system is traceable from the Niger Delta on the Nigerian Atlantic coastal margin through the Benue Trough to Chad, Niger and Sudan rifts. Hitherto, only the Tertiary Niger Delta is known to contain prolific hydrocarbons; other basins, especially the Cretaceous rifts, have
Responsible Editor: Santanu Banerjee * Godwin Ezekwesili Ene [email protected] Celestine Obialo Okogbue [email protected] Kalu Mosto Onuoha [email protected] 1
Department of Geology, University of Nigeria, Nsukka, Nigeria
remained as frontier areas and are highly under-explored. The discovery of commercial hydrocarbon accumulations in the Termit (Niger), Doba (Chad), and Maglad and Melut (Sudan) rift basins (Schull 1988; Zanguma et al. 1998), which are all Cretaceous systems, has spurred renewed interest in the Nigeria Cretaceous rifts. The Anambra basin has been tested with twenty-seven exploratory (wildcat) and two appraisal wells leading to three oil and eight gas discoveries and an estimated reserve of about one billion barrels of oil and thirty trillion standard cubic fee
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