THE USE OF RESISTIVITY METHOD IN FRACTURED SANDSTONES CHARACTERIZATION OF ITARARÉ GROUP– PARANÁ BASIN

Abstract

Geoeletric surveys were carried out on sandstones of Itararé Group, Paraná Basin, as a contribution to a comprehensive research project on fractured reservoirs (Modres Project). The main objective of this study to determine the resistivity of fractured rocks from Itararé Group Paraná Basin. Particularly fractures acting as barriers or conduits influencing resistivity by diferential water percolation. The study area involves the Rivadávia Farm, located close to the Vila Velha Park, formed by rocks of Campo Mourão Formation, represented by a thick portion of psamitics rocks informally called Arenitos Lapa-Vila Velha. The field survey was carried out on a regular mesh with fifteen parallel lines, with 10 meters spacing. Several dipole-dipole electrode spacing were used, including 5, 10, 20, 30 and 40 meters. Data processing started with the apparent resistivity pseudosections plot, followed by of 2D inversion models. Inversion results allow to correlate the resistivity values with diverse geologic features, particularly with the layers geometry and the contact between different lithologies. It was observed that the structural conditioning, represented by fractures and faults, influences the resistivity values. Resistivity highs had been correlated with mapped faults, possibly indicating closed type of faults, while lows can indicate open ones, with higher porosity which propitiate water percolation. The results show high values (thousand of Ohm.m), somehow uniformly distributed, even in the most sandy levels, indicating very low permeability for the Itararé sandstones.