Gas Hydrate in Fine-grained Sediments — Laboratory Studies and Coupled Processes Analyses

Abstract

Methane hydrates in marine and permafrost sediments are potential energy resources (Boswell, 2009; Collett, 2002). The total amount of carbon trapped in gas hydrate exceeds the sum of all other forms of conventional fossil fuels (Kvenvolden, 1988). However, the dissociation of methane hydrates can accelerate climate change (Archer, 2007; Ruppel and Pohlman, 2008), cause ground subsidence and trigger seafloor landslides (Grozic, 2010; Hornbach et al., 2007; Kvalstad et al., 2005). Hydrate-bearing sands are considered most favorable for future gas production (Boswell and Collett, 2006; Boswell, 2009; Boswell and Collett, 2011). However, over 90% percent of the global hydrate mass is found in fine-grained sediments (Boswell and Collett, 2008). To date, there has been minimal research in hydrate-bearing fine-grained sediments. The central themes of this research are the fundamental understanding of hydrate formation and dissociation in fine-grained sediments, and the associated physical processes. The discussion ranges from the particle-scale to the macro-scale. This includes the shift in the phase boundary associated to curvature effects, the particle-displacive morphology, diffusion induced Leisegang bands and two hydrate formation patterns in gas-filled openings. We develop laboratory techniques that emulate natural gas hydrate formations. The experimental results illustrate the hydrate formation process via different strategies that aim to accelerate the gas supply to the hydrate formation front. In addition, simulations of physical properties of hydrate-bearing fine-grained sediments address the segregated morphology of hydrates in fine-grained sediments and the change in physical properties induced by cryogenic suction. We explore potential methods to produce gas from hydrate-bearing fine-grained sediments. The analyses on gas production centers on the technical viability of depressurization, thermal stimulation and chemical stimulation.