ELECTRICAL RESISTIVITY TOMOGRAPHY CHARACTERIZATION OF THE KARSTIC ENVIRONMENT OF THE FURNA FEIA CAVE (BARAUNA / RN) INTEGRATED WITH LIDAR TECHNOLOGY
Description
Studies related to the genesis and geometric characterization of karst features may contribute to a better understanding of the fluid behavior in these important reservoirs since they can work as flow barriers, ducts or even as reservoirs. Within the context, the Furna Feia caves, located in Baraúnas city/RN in the carbonates of Jandaíra Formation in the Potiguar Basin were selected for a geophysical characterization of karst features. Thereby, the Electrical resistivity method was used as a recognition character, in which the metric resolution allows to identify zones and peaks of different resistivities. The geological characteristics of the investigated area and the target (dimension and depth) are crucial factors for the success of the survey, as well as the choice of the electrode arrangement, the line length, and signal-to-noise ratio. Therefore, the selected cave was imaged and parameterized, comparing the results with the internal imaging obtained with the Terrestrial Laser Scanner (TLS). As a result, for the Furna Feia cave, 4 zones of apparent resistivity were delimited and correlated to the karst hydrological morphogenetic zones. In these zones, it was possible to identify a layer with high permeability that can be an analog, at an outcrop scale, of the Super-K layers found in the Pre-Salt. Was observed in the geoelectric profiles, the anomalies caused by the presence of the Furna Feia cave show divergence in relation to the geometry, position and dimension when compared to the cave geometry acquired with the TLS Because of factors that influence the detection of cavities in a 2D geoelectric profile, such as edge effects, cavity inclination and declination, set of small cavities and fractures near the cave. Based on the information obtained through the geoelectric profiles it is possible to presuppose the evolution of the processes in which the Furna Feia cave was formed. Where the retention of meteoric water at the base of the epikarste may have developed the zone of high permeability (Super-k) with the flow towards the main fractures in the karst.