The effect of different sediment conditions on CO2-CH4replacement in natural gas hydrates

Abstract

Natural gas hydrates are the largest reservoir of natural gas on earth and represent an important solution for the transition from the actual energy scenario to a renewable one. Methane, contained in hydrate reservoirs, can be replaced with carbon dioxide, so that the obtained fuel is neutral in terms of climate-changing emissions and therefore equivalent to renewable energy sources. The experimental tests presented in this paper are devoted to study the CO2-CH4 replacement process in natural gas hydrates in presence of water salt. Test are carried out in a lab scale reactor of 1 l volume. The investigation aims at obtaining data on methane recovery rate, CO2 sequestration, composition of the obtained outlet CO2/CH4 mixture, as well as spatial distribution of hydrates thanks to the analysis of temperature profiles. Temperature analysis is used to determine hydrates' spatial distribution within the sediment. The number of methane hydrate moles formed with salt water is lower than that with pure water. During CO2 injection, not only CH4-CO2 replacement took place, but also new CO2 hydrate formation. The exchange factor, in fact, ranges from 0.11 to 0.4 for tests with salt.