Experimental study on the formation and storage characteristics of CO2 hydrate under condition of grain gradating: Influence of different particle sizes and ratios

Abstract

CO₂ sequestration in seabed sediments is considered to be a promising way to reduce CO₂ emissions in atmosphere. The formation characteristics and gas storage capacity of hydrate are the critical indicators for measuring the effectiveness of geological sequestration of CO₂ by hydrate method. In this work, the formation processes and storage characteristics of CO₂ hydrate were studied in porous media composed of two single grain sizes (10 and 63 μm), porous media with grain gradatings (10–90 μm and 63–90 μm) of different mass ratios (30%, 50% and 70%) were further investigated. The influence of different gradation ratios on gas consumption rate and gas storage capacities of hydrate was discussed. The results showed that whether the difference in grain gradating between two mixtures was large or small, the larger the ratios of large grains in porous was, the more favorable for the formation of hydrate. The gas storage capacity is far from the gas storage theoretical upper limit of hydrate in the experiment. And geological transformation is necessary in order to increase the gas storage capacity. The gas storage capacity of hydrate decreased in porous media with grain gradating of 63–90 μm as the ratios of large grains increased. The variation of gas storage capacity was non-linear in porous media with grain gradating of 10–90 μm to a certain degree. Compared to the porous media composed of a single grain size (10 μm and 63 μm), the porous media system with 63–90 μm has an inhibitory effect on hydrate formation. However, the porous media system with 10–90 μm can promote the formation process of hydrate. The relevant results will provide essential theoretical support and guidance for CO₂ geological storage in seabed sediments by hydrate method.