Modelagem e caracterização de um reservatório granular pela aplicação de métodos geofísicos elétricos e eletromagnéticos.

Abstract

In this dissertation, a three-dimensional model of a section of the granular aquifer of the Sucuru river was built from the application of geophysical electric resistivity method. Additionally it was tested the efficiency of the GPR method for the same purpose. From the 3D model were identified the static level of underground water, the depth of the top of the crystalline basement and the occurrence of a buried paleochannel. Although the method of electric resistivity has provided a more reliable and detailed model, the main features of this model are correlated with those identified by the GPR 2D lines acquired in the area of study. The electrical properties of the sediments were related to their petrophysical properties, in order to support the interpretation of the geophysical model. In the shallower part of the sediments the minerals are denser than the quartz, which in turn predominates in most of the sediments of the area. At the top of the holes there is a predominance of fine sediments, while in the lower part predominates the sediments of larger grain size. The fine sediments tend to have low values of electrical resistivity, except in the unsaturated region, whereas the intervals with lithotypes of greater granulometry tend to present higher values of resistivity, except in regions of high porosity and high water saturation. Regions with smaller total density lithotypes are associated with those with higher porosity, therefore with lower electrical resistivity. The water flow simulations performed in the digital model of the studied aquifer showed that the flow restrictions imposed by the resistive and low porosity and permeability regions generate pressure concentration and high flow velocity places. On the other hand, the paleochannel region identified by the Geophysical study presents low fluid flow velocities and lowest pressures, both caused by the high permeability of the medium in this region.