Geophysical and Sedimentological Characterization of a Tar Sand Rich Area in South-western Nigeria.

Abstract

Although huge deposits of tar sands have been discovered in parts of south-western Nigeria, detailed geological studies of many locations are yet to be executed. Such studies would not only help in quantitative evaluation but also help in generating baseline data that would help in evolving exploitation technique that will be environmentally friendly. Vertical electrical Soundings of southwest Okitipupa were extensively carried out while core samples were studied in order to generate subsurface model of the study area. Detailed sedimentological studies of core samples were also executed. Correlations of geoelectric sections with borehole litho-logs revealed three layers from top to bottom of lateritic soil/clay, shale and sand/bituminous sand. The depth to tar sand horizon ranged from 0.5 to 50.0 m. Groundwater level of about 13 to 15m measured in dug wells occur above tar sand horizon. The most abundant mineral in the tar sand is quartz with subordinate amounts of microcline, muscovite and biotite. The medium grained and moderately sorted nature of the tar sands coupled with low amount of fine particles, indicate that the oil sand reservoir is of good quality. Open cast mining can be employed but precaution must be taken to prevent blowout that may be induced by the overlying water bearing horizon. The fairly thick impervious clayey overburden will prevent pollution of groundwater by waste likely to be associated with tar sand exploitation.

Key words: Tar sand, electrical sounding, correlation, horizon, particles, groundwater.