Determinação Da Resistividade Elétrica De Águas Interticiais Usando Perfilagem De Potencial Espontâneo.

The self-potential (SP) log is a useful tool for estimating groundwater resistivities. Since it is dominantly of electrochemical origin, a simple equation, SP = -Klog (Rmf=Rw), relates the SP deflection opposite a permeable bed to the resistivity contrast between its formation water (Rw) and that of the invasive mud filtrate (Rmf). K is a parameter strongly dependent on the temperature. This equation works successfully for concentrated solutions rich in sodium chloride. For dilluted multi-salt solutions very poor results are normally obtained. Based on the formulation proposed by Gondouin et al. (1957) and using chemical analysis of groundwaters a modified SP equation was developed which provides excelent results for the São Sebastião aquifer system in the Recôncavo Basin, Brazil. The procedure may be easily adapted to other groundwater reservoirs.