Caracterização de uma unidade potencial produtora de gás natural não convencional em folhelho (Shale gas): Formação Pimenteiras, leste da Bacia do Parnaíba

Abstract

Shale gas has emerged as an alternative energy source to conventional hydrocarbons in the last years. Despite the potential that Brazilian basins have to exploit this resource, few studies have been made to verify that potential. In this aspect, the Pimenteiras Formation (Parnaiba Basin) arises as one of the promising units for this type of potential. Based on this, this study aimed to characterize black shales of Pimenteiras Formation in the east of Piaui as a potential producer of unconventional natural gas. For this purpose were performed facies analyses and 17 samples collected in the best outcrops and, finally, a laboratory phase resulting in chemical and mineralogical analyzes (X-ray Diffraction, X-ray Fluorescence, SEMEDS, Chromatography and Gamma ray spectrometry) on the samples. The facies analysis shows the great extent of the epicontinental Paleozoic ancient sea in the Parnaiba Basin, where the shales are shown predominantly aluminous, however ferruginous, due to the laterization effect (post-depositional alteration). The samples show evidence in presence of organic matter (C221-I14 - picene; C1oH8 - naphthalene; C13H10 o fluorene) as well as anornalous detection of CO2. Despite the very low methane production, these shales show cumulative production, which is a promising factor in a possible biogenic methane production (action of bacteria). The high ratio Th/U suggests deposition in intermediate conditions of oxygenation, but in good condition for preservation of organic matter. Such evidence, as well as significant, are very promising and justify the need for new exploration efforts to obtain more information of the Pimenteiras Formation potential as unconventional reserves of natural gas.