Modelagem da resposta de depósitos de hidratos de metano no leque deposicional do Amazonas, Brasil, submetidos a aumentos de pressão e temperatura

Abstract

Gas hydrates are solid crystalline compounds, in which gas molecules are trapped within polyhedral cavities formed by water molecules. In nature, they occur in permafrosts and within oceanic sediments, where the conditions of high pressures and low temperatures keep them stable. In the Brazilian continental margin, gas hydrates (predominantly methane) have been recovered on the Amazon Deep-sea Fan (in the Amazon River Delta region). Several studies have been developed recently, in order to investigate the methane hydrate stability zone (MHSZ) behavior of oceanic hydrates and potential methane releases into the ocean. However, the effect of simultaneous pressure and temperature variations on methane hydrate deposits, in millennia time scales, is still a field to be explored. This work aimed to investigate, through mathematical modelling and numerical simulation with the TOUGH+HYDRATE code, the response of methane hydrates within the feather edge of the MHSZ on the Amazon Deep-sea Fan, to simultaneous pressure and bottom water temperature increases, since the Last Glacial Maximum up to present days. The results indicated that, for 600 meters water depth (mwd), the thickness of the MHSZ decreased, the MHSZ disappeared in the model and then a new MHSZ developed close to the top of the model. For 650 mwd and 700 mwd, the MHSZ thickness decreased, but the MHSZ did not disappear in the models. Gaseous methane was released into the ocean only in the model for 600 mwd (approximately 66 kg, from 14.000 to 6.000 years before present).