Methane Hydrate Formation and Decomposition Characteristics in Different Types and Contents of Marine Clay Minerals

Natural gas hydrates (NGHs) are widely distributed in fine-grained sediments composed of silt and marine clay minerals. Compared with sandy sediments, clay minerals exhibit characteristics of large specific surface area, high hydrophilicity, and low permeability. However, the influences of clay minerals on hydrate formation and decomposition characteristics remain unclear. In this study, experiments were designed to investigate the influence of clay types and contents. The results showed that the characteristics of hydrate formation and decomposition show significant differences among different types of clay mineral sediments. The hydrate formed in pure Illite has the highest saturation (21.8%) and final water conversion ratio (55.54%). Kaolin is more unfavorable for hydrate decomposition; the gas recovery ratio and water yield in pure kaolin are only 16.8% and 21.1 g, respectively. In addition, an increase in clay content can lead to a decrease in hydrate formation rate, cause a reduction in reservoir permeability, and significantly limit hydrate decomposition. Compared with Illite and kaolin, the change in chlorite content has the least influence on methane hydrate formation. These findings can provide deep insights into the resource estimation of silty-clay NGH and help to develop specific exploitation strategies for silty-clay hydrate reservoirs.