Experimental Study On Inhibition Mechanism Of PVCap On Methane Hydrate Formation

Natural gas hydrate was one of the new energy sources with broad development prospect because of its advantages of cleanliness,abundant reserves and high energy density.However,hydrate formation during deepwater drilling and oil and gas gathering and transportation will blocke pipelines,affected operation safety and caused economic losses.Adding low dose hydrate inhibitors to delay hydrate formation was the most widely used and effective method at present.Kinetic inhibitors had the advantages of low cost,small dosage and good effect.However,the mechanism of action was still unclear and the cognition was still lacking,which seriously limited the research and development and field application of such inhibitors.By means of laboratory experiments,this paper revealed the action mechanism of the dynamic inhibitor PVCap and the key influencing factors that controled the effect of PVCap,which provided theoretical basis and technical support for the research and development,optimization of the dynamic inhibitor and hydrate prevention and development in oil and gas field.In this paper,PVCap series polymers with different molecular weights and different hydrophilic/hydrophobic properties were designed,synthesized and characterized.The effects of PVCap concentration（0.5-2.0 wt%）,molecular weight(24500-325200 g·mol^-1),and hydrophilic/hydrophobic properties（D1 and D2）on the inhibition performance of methane hydrate were investigated,and revealed the mechanism of action of PVCap,PVCap may be by slowing down to suppress the dissolution of methane hydrate nucleation.In the hydrate induced nucleation stage,the higher the concentration,the higher the molecular weight and the stronger the hydrophilicity of PVCap,the stronger the inhibition ability of methane dissolution and the longer the hydrate induced nucleation time.In the hydrate growth stage,the higher the concentration of PVCap,the stronger the hydrophilicity,the smaller the hydrate production,the lower the hydrate generation rate;With the increase of molecular weight,the inhibition ability of PVCap on methane hydrate growth increased continuously.Methane hydrate formation experiment and multi-component gas phase equilibrium experiment were designed to compare the hydrate inhibition performance of PVCap,PVP-K90 and ethylene glycol respectively.At the same concentration,the inhibition ability of PVCap on methane hydrate nucleation was slightly worse than that of PVP-K90.But the inhibition of hydrate growth was stronger.The inhibition effect of 2.0 wt%PVCap solution and 20 vol.%ethylene glycol solution on hydrate formation was studied with multi-component gas in an oilfield in South China Sea as simulation medium.The results showed that both of them have certain inhibitory effect on hydrate formation from multi-component gas.