Study of Decomposition and Evolution of Impurity-Containing System Hydrate Sediments in Pipe Walls

Natural gas hydrates have vast reserves in marine sediments and high-latitude permafrost regions, making the study of their decomposition characteristics highly significant. This study uses high-pressure reactor experiments to investigate the decomposition characteristics of pipeline hydrate deposits containing sand and oil under thermodynamic inhibitor conditions. The experiments found that the decomposition of hydrates is influenced by sand particle size, sand content, and oil content. Fine sand (<48 μm) promotes hydrate decomposition, while decomposition is inhibited when the sand content exceeds 6%. A small amount of coarse sand (106-120 μm and 120-180 μm) initially promotes decomposition, but as the sand content increases, it transitions to inhibiting decomposition. The presence of white oil reduces the permeability of the ethylene glycol solution, inhibiting hydrate decomposition, and as the white oil content increases, the decomposition rate significantly decreases. In addition to affecting the decomposition rate, impurities also affect the decomposition pattern. Furthermore, the decomposition mechanisms and models for hydrate deposits containing sand and oil under different conditions are proposed. This study provides theoretical support for deepwater-oil and gas pipeline flow assurance and hydrate resource development.