Natural gas hydrates exist in large quantities in nature and represent a potential source of energy, mostly in the form of methane gas. Knowledge about hydrate formation in clayey sand is of importance for understanding the production of methane gas from hydrate reservoirs, as well as for understanding the impact of global warming on the stability of subsurface gas hydrates. In this paper, we explore the effect of clay content on methane gas hydrate phase transitions in unconsolidated sand at realistic reservoir conditions (P = 83 bar and T = 5–8 °C) both experimentally and numerically. Kaolin clay was mixed in pure quartz sand in a series of experiments where the clay content ranged from 0 wt % to approximately 12 wt %. Simulations of these experiments were set up in TOUGH+HYDRATE. In the kinetic reaction model, particle size was used as a proxy for kaolin content. The growth of methane hydrates from water (0.1 wt % NaCl) and methane were visualized and quantified by magnetic resonance imaging with millimeter resolution. Dynamic imaging of the sand revealed faster hydrate growth in regions with increased clay content. NMR T 2 mapping was used to infer the hydrate phase transition characteristics at the pore scale. Numerical simulations showed also faster growth in materials with a smaller mean particle size. The simulation results showed a significant deviation throughout the hydrate growth period. The constraints of both the experimental and modeling setups are discussed to address the challenges of comparing them.

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This study explores the relationships that sedimentation rate and transport properties have with the formation and evolution of hydrates in fine-grained marine sediments and their corresponding bottom simulating reflector (BSR) responses. Using a series of one-dimensional simulations of multiphase, multicomponent flow and transport of mass and heat through porous media, a slab of sediments through sedimentation is modeled. The boundary conditions are set to emulate the pressure and geothermal gradients and its resulting gas hydrate stability zone (GHSZ). Hydrates are formed by injecting methane gas through the bottom of the grid and letting it migrate and reach the boundary of stability. The resulting hydrate accumulation is subjected to different sedimentation rates and replicated with different intrinsic permeability. With sedimentation, the geothermal gradient is displaced upward and the boundary of stability shoals. Through methane recycling, the distribution of phases changes through cycles of slow melting and rapid reformation. This results in a dynamic flow barrier that relocates the base of the GHSZ over geological time, in response to the variations of both pressure and salinity. The characteristics of a BSR response will be tied to the stage of the melting cycle.