Study on the dissociation characteristics of methane hydrate in clayey silts. (28th April 2022) - Yu, Changhong
Highlights: Methane hydrate dissociation characteristics in clayey silts were investigated. Methane hydrate in the small pores dissociates first, then large pores and bulk. Hydrate barrier could form in the surface or internal pores to hinder its growth. Hydrate redistribution could occur due to multi-stage dissociation and reformation. Abstract: Most natural gas hydrate (NGH) resources worldwide are in clayey silt sediments. For the efficient production of NGH, a thorough understanding of the dissociation characteristics of NGH in clayey silt is essential. In this work, an experimental method for clayey silt NGH sample preparation and determination of the dissociation conditions has been established. The dissociation conditions of methane hydrate in clayey silt formed at different initial pressures and water contents have been measured, and the dissociation characteristics have been discussed. Methane hydrate is found to form in pores of different sizes in clayey silts. The filling status of the methane hydrate in the clayey silt pores might affect its dissociation characteristics. As the temperature increases, the hydrate in the smaller pores dissociates first, the hydrate in the larger pores dissociates later, and the final equilibrium conditions are consistent with the dissociation conditions of bulk hydrate. As the initial pressure increases or the water content decreases, the proportion of hydrate in the pores increases. When the clayey silt is saturated (water content 37%), hydrate rapidly forms on the surface, forming a mass transfer barrier and preventing further hydrate formation. The hydrate reforms when the hydrate in the small pores of surface sediments dissociates as the temperature increases. The methane hydrate in clayey silt exhibits multistage dissociation and complex reformation characteristics.