Geoelectrical resistivity mapping and characterization of bituminous sands at some parts of Eastern Dahomey Basin, SW Nigeria

Abstract

Predicting the variability and subsurface distribution of bituminous sand deposits rely significantly on integrating geophysical techniques such as electrical resistivity mapping with borehole information. While several studies have been conducted to characterize the bitumen-rich sequence of the sedimentary terrain of the study area, there are no or few studies documenting the subsurface architecture of bituminous sands in the transition zones in the study area. This study utilized the integration of 2D electrical resistivity mapping and borehole lithology logs to delineate and characterize bituminous sands in the study area to provide insights into the electrical resistivity signature of bituminous sand deposits within the transition zone in Ondo state, SW Nigeria. Two boreholes (BHI and BH2) and 2D electrical resistivity mapping using dipole–dipole array along five traverses were used for the investigation. A systematic and data-based approach was employed for the mapping of the deposits. The 2D electrical resistivity survey acquisition was carried out on traverses oriented north–south in the direction perpendicular to the sedimentary strike to effectively map the bituminous deposits. The results obtained from the approach employed indicated a maximum of three to four geoelectric layers delineated within the study area. This includes the topsoil, the upper X-horizon, mudstone, and lower Y-horizon. The upper/shallow bituminous sands in the X-horizon, as well as the deeper bituminous sands in the Y-horizon sands, are characterized by a very high resistivity range of about 1000 to about 100,000 Ωm. Findings from this study reveal that the resistivity of bituminous sands in the area is generally high in contrast to the low resistivity signature observed in the sedimentary parts of the area. The results obtained from this study would serve as a means to guide future exploration studies within transition zones in Eastern Dahomey Basin, SW Nigeria.