CARACTERIZAÇÃO DE RESERVATÓRIOS ÍGNEOS NA BACIA DE SANTOS ATRAVÉS DOS MÉTODOS GEOTÉRMICOS, SÍSMICOS E DE PERFILAGEM

Abstract

The Santos Basin is the largest producer of hydrocarbons in Brazil, and throughout its geological history, has undergone four magmatic events of great magnitude, three occurred in the Cretaceous and one in the Eocene, they are: (i) Valanginian-Hauterivian, related to the rift phase (135.5 ± 0.7 Ma); (ii) Aptian, in the post-rift phase (114.3 ± 1.1 Ma); (iii) Santonian-Campanian, related to the drift phase (83.3 ± 0.66 Ma to 72.4 ± 4.9 Ma); (iv) Eocene, also in the drift phase (49.9 ± 0.45 Ma). In this way, igneous bodies can be observed in the pre-, intra- and post-salt. The purpose of this project was to identify and describe potential igneous reservoirs, mainly volcanic, with the capacity to store oil and gas in the Santos Basin. This was accomplished through a multi-geophysics approach that integrated geothermal, seismic and geophysical logging data. With specific objectives of analysing variations in physical properties, both at the surface and in the subsurface, this study investigated how magmatism not only thermally influences the environment - as evidenced by the geothermal method - but also how it affects other physical properties observed both in seismic and in wells. The database consists of wells and seismic lines requested from the National Petroleum, Natural Gas and Biofuels Agency (ANP). Additionally, geothermal data was requested from the Geothermal Laboratory of the National Observatory (LabGeotON) and information on seabed temperature measurements from the Brazilian Navy. Combining interpretations of results from geothermal, seismic, and well logging methods revealed four (4) areas of gradient anomalies and five (5) areas of heat flow anomalies in the Santos Basin. These findings were confirmed in the subsurface layers through calculations of crustal temperatures and were corroborated by seismofacies derived from the seismic sections. The possible origins of these anomalies range from thick layers of evaporites to magmatic deposits. Several igneous bodies, both intrusive and extrusive, were interpreted, along with different seismofacies and geometries of sills, dikes, conduits/pipes, craters, volcanoes, intrusive and extrusive complexes, conduits, chimneys, lava flows, among others. Despite the predominance of basic igneous rocks, occurrences of intermediate and ultrabasic igneous rocks were also observed. This suggests a diversity in the composition of magmas, indicating variable conditions of pressure, temperature and chemical composition throughout the magmatic process. Among the zones of interest delimited in the geophysical profiles, it is observed that potential promising reservoirs can be found in the economic basement of the Camboriú Formation, in fractured intrusive bodies, at the base of volcanic tuffs and at the top of volcanic flows with more vesiculated regions. The zones of interest comprise combined sections of high values in the resistivity profile, high to medium values in the sonic profile, low density and neutrons. On the other hand, sections with vesicles filled with clay minerals and calcites represent an obstacle to the development of a good permo-porous system in these reservoirs. The integration of methods for characterizing igneous rocks and evaluating the potential of oil and gas reservoirs has proven to be very effective in identifying structural elements and physical properties, contributing significantly to the understanding and more accurate exploration of these resources. Overall, these strategies strengthen the project's integrated approach, showing a combination of geophysical techniques for a comprehensive analysis of igneous rocks and their potential impacts on the exploration of natural resources.