Rheological investigation of hydrate slurry with marine sediments for hydrate exploitation

Solid fluidization is a novel method for marine hydrate exploitation. The rheological characteristics of hydrate slurry are significant for hydrate fluidization and safe transportation. This work used a high-pressure rheometer to form hydrate slurries with marine sediments in the South China Sea. The results indicated that the higher the sediments concentration, the more significant the viscosity change after hydrate formation. Subsequently, staged heat injection was designed to simulate the dissociation process during hydrate exploitation and obtain the slurry with different hydrate volume fractions. Oscillatory measurements investigated the viscoelastic behavior of each hydrate slurry. The results suggested that both mudflows and hydrate slurries displayed viscoelastic fluid characteristics. The presence of hydrate dramatically increased the storage modulus of the slurry, and the yield stress would increase 2–700 times with hydrate increasing. Furthermore, a critical hydrate volume fraction was proposed at which the yield stress would rise sharply. A simple equation was developed to describe the relationship between this parameter and sediments concentrations. The increasing trend of yield stress changed little with hydrate increasing when the sediments concentration was less than 20 wt%, and a water conversion less than 15% was suggested to get a fluidized slurry with yield stress below 100 Pa.