Evaluating the impact of hydrodynamic flow on the hydrocarbon potentials of the Cretaceous Anambra basin, Southeastern Nigeria

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.