(659d) Simulations of CO2+N2 Exchange in CH4 Hydrate Reservoirs

In 2013, The International Energy Outlook (EIA, 2013) projected that global energy demand will grow by 56% between 2010 and 2040. Despite strong growth in renewable energy supplies, much of this growth is expected to be met by fossil fuels. Concerns ranging from greenhouse gas emissions to energy security are spawning new interests for other sources of energy including renewable and unconventional fossil fuels such as shale gas and oil as well as gas hydrates. Development of new and alternative resources like natural gas from gas hydrates can play a major role in ensuring adequate future energy supplies in the United States and the world. According to recent estimates, natural gas hydrate reservoirs are likely to contain more carbon than in all other fossil fuels combined. Field-scale experiments and the equipment required for the production are very expensive. Reservoir simulators can be used to predict the production potentials of hydrate wells and to determine which technique best suits for hydrate reservoir.  Different techniques currently being proposed for production of CH₄ from hydrate deposits include depressurization, thermal stimulation and chemical inhibitor injection method. These processes involve dissociation of hydrates and release of large amounts of water, which may cause geomechanical stress on the reservoir leading to subsidence. A series of experimental studies over the last decade have reviewed the feasibility of using CO₂ or CO₂+N₂ gas mixtures to recover CH₄ gas from hydrate deposits, which would serve the dual purpose of CO₂ sequestration and production of CH₄ while maintaining the geo-mechanical stability of the reservoir. In order to analyze CH₄ production process by injection of CO₂ or CO₂+N₂ gas mixtures in gas hydrate reservoirs, a new simulation tool was developed to account for the complex thermodynamics of multi-component hydrates – including the potential for multiple hydrate phases comprised of varying hydrate solid crystal structures - called Mix3HydrateResSim (Mix3HRS). In this work, Mix3HRS is used to simulate the behavior of CH₄-CO₂-N₂-hydrate systems under non-isothermal conditions by considering various scenarios of CO₂ or CO₂+N₂ gas mixture injection into CH₄ hydrate-bearing sediment and production of the gas products from the subsequent gas exchange. A set of different numerical simulations were performed to predict the production of methane from geologic formations via CO₂ injection using two different conditions: equilibrium and kinetic conditions. In these numerical simulations, a five-spot well pattern with an injection well in the center and production wells in the corners of the five-spot pattern was be considered. The objective of these different numerical investigations was to demonstrate the ability of Mix3HydrateResSim in examining the feasibility of injecting CO₂ into natural gas hydrate bearing reservoirs to produce CH₄ while simultaneously sequestering CO₂.