Evolução termal de potenciais reservatórios na porção leste da bacia do Parnaíba

Abstract

In the last few decades, the Parnaíba Basin is being subject of study since it was discovered its high potential on natural gas exploration. In this scope, the study area is located on the eastern part of the basin, northern region of Brazil, in which outcrop sandstones and siltstones of the Cabeças (Devonian) and Poti (Carboniferous) Formation, reservoir rocks of Parnaíba Basin. Subordinately, magmatic rocks are present corresponding to two intrusive events of Mesozoic ages attributed to the Mosquito and Sardinha formations. The first event is related to the breakup between the North America and South America, and the second, between South America and Africa, whose processes of magmatic intrusion in the Paleozoic rocks changed not only the petrographic characteristics of these rocks, but also modified the properties of the reservoir rocks in the basin, being these alterations identified during exploration stages. It was collected samples of sedimentary rocks in drilled core and outcrops, in which were applied method of Thermochronology by Fission-tracks in apatite and zircon, and petrography, with the objective to integrate data of thermal history and physical properties of the rocks, relating to petroleum systems in the region. The results of Fission-tracks in apatite and zircon indicated that the magmatic event of the Sardinha Formation (Cretaceous) was the major influence in the portion of the basin. In near portion of the magmatic rocks, the paleotemperatures have overcome 300 °C, condition that altered the reservoirs. The high temperatures mobilized hydrothermal fluids which altered the rocks by dissolving minerals and precipitation of carbonate cement in the pore space. In portions where the thermal influence is attenuated, in terms of maximum paleotemperature, the conditions become favorable for the non-thermal alteration of reservoirs.