Formation characteristics of waxy oil and gas hydrate and factors affecting viscosity of the hydrate slurry
Waxes,hydrates and their coupled deposition behave as potential risks in the offshore oil and gas multi-phase transport process.Using natural gas,deionized water,3 # industrial white oil and paraffin as the experimental media,and relying on a high-pressure visible reactor,natural gas hydrate formation experiments were conducted in both wax-free and wax-containing systems based on an orthogonal design method,for which the L9(34)and L16(45)orthogonal table was selected.The effects of wax content,stirring rate,fluid equilibrium temperature,water content and initial pressure on equivalent viscosity of hydrate slurry were analyzed via taking fluid equivalent viscosity as the evaluation index.The experimental results show that the constant viscosity value is not sufficient to determine the completion of hydrate formation in the reactor.This is because in the shear stabilization stage,a state of"dynamic equilibrium"is existed between the hydrates leaving stirring central region and the newly generated hydrates in stirring region.Moreover,the higher the wax content,the longer the hydrate growth induction period.In the rapid growth stage of hydrates with wax content of 2%and 3%,the torque and rotational speed underwent two mutations.The first mutation was due to the precipitation of numerous wax crystals,leading to a stronger gel structure of the oil phase in the stirring central region.The second mutation occurred due to the separation of wax-hydrate aggregates from the central stirring central region under centrifugal forceof which the formation is achieved by generating and absorbing a large amount of hydrate onto precipitated wax crystals.The research results hold significant theoretical implications and practical value for the safe operation of deep-water oil and gas pipelines.