Experimental Study On Inhibition Of Hydrate Particle Aggregation By Deepwater Water-Based Drilling Fluid

During natural gas hydrate drilling in deep water of South China Sea,hydrate formation,aggregation and deposition are easy to occur in water-based drilling fluid,which will block the wellbore.The aggregation of hydrate particles is one of the important reasons for the blockage.Therefore,based on the new idea of not completely inhibiting the formation of hydrate,but focusing on preventing hydrate particle aggregation,thus avoiding wellbore plugging,this paper carries out the analysis of hydrate particle aggregation characteristics in water-based system and the optimization experiment of anti-agglomerants,and constructs the water-based drilling fluid system formula suitable for marine natural gas hydrate drilling.A torque sensor was installed on the high-pressure visible simulation experimental device for the formation and decomposition of natural gas hydrate.the aggregation and adhesion characteristics of hydrate particles in pure water methane system were analyzed by torque test method.Seven kinds of chemical reagents with potential inhibition of hydrate aggregation were selected,and the experimental evaluation of hydrate aggregation prevention was carried out.The results show that in pure water,the torque first increases steadily with the increase of hydrate conversion,and then fluctuates violently.When the hydrate conversion reaches about27%,it is easy to cause flow blockage;among them,the amide amphiphilic reagents CA has the best inhibition effect on hydrate aggregation,and CA with 1 wt% dosage can control the torque value within 9.1 N/cm,which can effectively inhibit the aggregation of hydrate particles,keep hydrate particles dispersed,and reduce the risk of hydrate blockage.An apparatus for measuring the interaction force of hydrate particles was developed.The adhesion force between hydrate particles in gas and liquid cyclopentane phase was analyzed under different concentrations of CA.The results show that CA can significantly reduce the adhesion of cyclopentane hydrate particles in gas,water and liquid cyclopentane systems.Combined with the surface morphology observation and wettability analysis of hydrate particles,the main reason is that CA can change the surface morphology of cyclopentane hydrate particles,form burr like protrusions,increase the surface roughness,reduce the surface hydrophilicity of hydrate particles,and effectively inhibit the aggregation and adhesion between hydrate particles.Through the compatibility experiment of CA and hydrate thermodynamic inhibitor with water-based drilling fluid,it is found that 1 wt% CA and 10 wt% Na Cl can effectively prevent hydrate blockage,and a set of water-based drilling fluid formula suitable for hydrate formation in sea area is further optimized.Comprehensive performance evaluation experiments show that the drilling fluid can inhibit the formation of hydrate and particle aggregation,and has good low-temperature rheology and fluid loss reduction performance,which can satisfy the basic requirements of drilling engineering in hydrate formation.