摘要
Knowledge of the structure and geometry of aquifers is an important prerequisite when one wishes to sit a borehole.Such knowledge is currently obtained by VES(Vertical Electrical Soundings)whose interpretation is not always unequivocal in the sense that several resistivity models derived from VES can explain the same data set.The present study conducted in Obuasi region in Ghana aims at demonstrating the robustness of“cumulative resistivity”method in the characterization of the geometry of aquifers.The methodology developed consisted firstly in carrying out VES.These measurements were then interpreted using“cumulative resistivity method”.Secondly,drillings are conducted at the VES sites and lithologs established from cuttings were compared to the results from VES interpretation.The study reveals that the investigated aquifer consists of a resistant layer consisting of phyllite over 30-40 m topped by a conductive layer of reddish clay 20-30 m thick.These two layers rest on a lower electrical conductivity formation downward.This description can be considered as a typical alteration profile in a volcano sedimentary context.The results also show that the method is quite precise in half of the cases studied but sometimes it is impossible to get rid of the phenomenon of suppression since several layers are merged into a single layer.
