An original experimental set-up was developed and used for studying crystallization and rheology of methane hydrate/water/dodecane system under laminar flowing. Dynamic viscosity and conversion of water and gas into gas hydrate crystals were measured during the process for various water contents. Experimental results were explained by means of a model including nucleation, growth and agglomeration. Due to the high value of crystal and drop concentrations, agglomeration takes place through three-bodies collisions between one water drop and two already formed agglomerates. Resulting agglomerates were considered as fractal-like ones. During crystallization and agglomeration, the effective volume fraction of drops and porous agglomerates is increased, then suspension viscosity increases. When all water drops are crystallized, agglomeration stops and viscosity do not change.