The Study Of Rheological Properties Of Hydrate Slurry Formed From Mudflows In South China Sea

Natural gas hydrate(NGH)is a kind of clean and new energy that was widely distributed in deep-sea water.There are many traditional hydrate exploitation methods.In consideration of the characteristics of gas hydrate deposits in the South China Sea,Zhou proposed the solid fluidization method,the core idea of which was to break up the hydrate reservoir and inject seawater to fluidize it,then transported the slurry through the pipeline to the engineering vessel for deep decomposition.In this process,the hydrate slurry rheological properties are significant for pipeline transport and blockage risk assessment.In this study,the slurries with different mass fractions were prepared from marine sediments in the South China Sea,and the formation of hydrate experiments were carried out in a high-pressure rheometer with the slurries mentioned above.The study focused on the rheological properties of hydrate slurry at different marine sediments mass fractions and different hydrate saturation,and provided the reference data for solid fluidization method.Firstly,the physical properties of marine sediments were analyzed,including particle size distribution,material composition and microstructure.Different mass fractions of marine sediments slurry were prepared,and shear ramp tests and oscillatory scans were carried out to investigate the influence on rheology of marine sediments mass fraction.Secondly,the formation of methane hydrate experiments were carried out in the mud slurry to obtain the slurry viscosity during hydrate formation and to study the influence on the initial pressure and the mass fraction of marine sediments to the viscosity of hydrate slurry and the formation of hydrate slurry.The experimental results showed that when the mass fraction was high and the amount of hydrate formation was large,the increase of hydrate viscosity was large.When the pressure was high and the amount of formation hydrate was large,the increase of viscosity of hydrate formation was large.Finally,heating tests were conducted within the slurry to obtain hydrate slurries with different mass fractions and different saturations,and the effects of hydrate saturation and marine sediment mass fraction on the rheological properties of the slurry were analyzed.Experimental results showed that hydrate slurry was viscoelastic fluid and the existence of hydrate could increase the yield stress of the slurry.The higher the mass fraction of marine sediment and the hydrate saturation,the higher the yield stress of the slurry.At the beginning of the heating experimet,the amount of hydrate decomposition was large and the viscosity of the slurry decreased sharply;at the later stage,the hydrate decomposition was almost complete and the slurry showed a smooth flowing state.At the same time,the hydrate slurry exhibited solid state characteristics in the frequency sweep,and the greater the hydrate saturation,the more solid characteristics showed.