ANÁLISE PETROGRÁFICA E PETROFÍSICA DE RESERVATÓRIOS ARENOSOS PERFURADOS PELO POÇO C-IG-98, MUNICÍPIO DE CAPIVARI - SP

Abstract

This paper deals with the analysis of heterogeneous ground water reservoirs based on the study of cores from a well drilled near Capivari, Sao Paulo, by the Instituto Geologico of the Secretaria de Meio Ambiente of the state of Sao Paulo, Brazil. Well C-IG-98 is entirely cored and traverses 300 m of sediments of the Late Paleozoic Itarare Group, mainly very fine to fine sandstones. Four hundred and thirty analyses of porosity and permeability together with conventional petrographic, SEM, and x-ray diffraction studies produced the following observations: a) High water porosity (21%) and permeability (300 mD); b) The two main controls on flow properties are grain size and sorting; c) Diagenetic processes have been important in reservoir zonation, allowing distinction of an upper zone (from 0 to 100 m depth) with better flow conditions than the zone below 100 m. The upper zone is undersaturated with respect to carbonate and exhibits a predominance of kaolinite and illite among the clay minerals. The lower zone is in equilibrium with the carbonate phase and contains calcite concretions; chlorite is always present among the clay minerals.