Microcosmic Characteristics of Hydrate Formation and Decomposition in the Different Particle Size Sediments Captured by Cryo-Sem

In is paper, the hydrate decomposition behaviours in the sediments were captured by the Cryo-SEM method, and the microcosmic characteristics of sand production during the decomposition process were analyzed. (1) The gas hydrate decomposition increases pore space and reduces reservoir strength: The expansion action of decomposition water & gas, softening action of decomposition water and compression action by overlying stress (crustal stress) promoted sand production, deformation and subsidence of NGH reservoirs in the mining process. (2) Decomposition of NGH has a greater impact on sediments with smaller particle size. (3) The particle size of NGH may be larger than the particle size of mud in the reservoirs, and acting as "gravel" plays a certain role in sand control. Therefore, the particle size of NGH cannot be ignored in the design of sand control. (4) It has been revealed and verified that sputtering (splashing) is a unique process for sand production caused by NGH decomposition. In other words, the rapid expansion of the volume by decomposed gas and water from NGH leads to eruption and sputtering of hydrate particles, providing the driving force for sand migration, which is the different way of sand production in conventional oil and gas.