Abstract
Geological investigation have led to discovery of huge tar sand deposits within Afowo Formation of the Turonian–Maastrichtianage (95.9–66.0 Ma) in the Nigerian sector of the Eastern Dahomey Basin. This study aims at determining the feasibility of exploiting the major hydrocarbon resource steam assisted gravity drainage enhanced recovery technique. Samples from three core holes were dry sievied to determine the particle size distribution and their sections studied using a petrographic microscope. Clay mineral content was determined using X-ray diffraction scanning electron microscopy. The granulometric analysis shows the bituminous sediments to be generally fine grained and moderate to well sorted, and the grains are angular to subangular. Porosity ranges from 15.5 to 33.6 ɸ with average value of 26.4 ɸ, while permeability ranges from 270 to 4800 mD, with an average value of 4800 mD (very high) recorded for the sandstones. Petrographic study, scanning electron microscopy and X-ray diffractometry showed quartz as the dominant mineral component, with subordinate feldspar and other accessory minerals. The predominance of quartz is probably due to its mechanical stability. The low frequency of feldspar is attributable to its susceptibility to chemical breakdown and alteration, respectively, during transport and after deposition, with latter accounting for the observed secondary porosity. Kaolinite is the common clay mineral present in the oil sands and may not have sufficiently reduced the reservoir quality to negatively impacting enhanced recovery operation by steam assisted gravity drainage.
Highlights
The eastern Dahomey basin of the Nigeria sector contains extensive wedge of Cretaceous to recent sediments that thickens towards the offshore up to 3000 m
Exploration for hydrocarbon commenced in this basin in 1908, near Okitipupa, east of Lagos, where bituminous sands outcrop
Representative samples were collected from each lithofacies for laboratory analyses which included: grain size analysis, thin section petrography, X-ray diffractometry (XRD), and scanning electron microscopy (SEM)
Summary
The eastern Dahomey basin of the Nigeria sector contains extensive wedge of Cretaceous to recent sediments that thickens towards the offshore up to 3000 m. Bitumen-impregnated sandstones (tar sand) outcrop in a 120 km by 6 km belt in Southwestern Nigeria from the Okitipupa ridge/ western feather edge of the Tertiary Niger Delta to as far west as Ijebu-Ode in Ogun State, Fig. 1. The geology of these deposits, oil saturation and reserve estimates as well as textural characteristics of the associated sands have been described (Adegoke et al 1980, 1981; Enu 1987). Other relevant studies on the deposit and geology of the basin include works done by (Ako et al 1983; Ekweozor 1986, 1990; Nwachukwu and Ekweozor 1989; Enu 1987, 1990; Enu and Adegoke 1984; Elueze and Nton 2004; Akinmosin et al 2005, 2013; Akinmosin and Osinowo 2008)
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