Effects of Salty Additives in Drilling Fluids on Hydrate Formation Dynamics and Phase Equilibrium

In the drilling process for deepwater and hydrate formations,addingsalty components to drilling fluids is an important way to avoid secondarygeneration of hydrates in the annulus, and the effect of salt solutionson the hydrate generation lays a basis for drilling fluid design.In this study, an evaluation device for the effect of drilling fluidadditives on hydrate formation and phase equilibrium is designed basedon their interaction characteristics. In addition, hydrate generationexperiments were carried out for pure water and three commonly usedsalty additives for drilling fluids. As such, the hydrate phase equilibriumequations under different conditions are established, and the hydratephase change latent heat is further calculated. The results show thathydrate formation can be divided into four stages, i.e., gas dissolution,hydrate crystal nucleation, hydrate particle mass aggregation, andstabilization. Compared with pure water, sodium chloride and potassiumformate solutions can effectively inhibit hydrate formation. At lowerambient temperature, the higher the concentration of potassium formate,the lower the phase equilibrium pressure. On the contrary, at higherambient temperature, the higher the concentration of potassium formate,the higher the phase equilibrium pressure. The incomplete presenceof sodium silicate in water in the form of ions is found to promotemethane hydrate formation. Based on the experimental results of methanehydrate generation in potassium formate and sodium silicate solutionswith different mass concentrations, the phase equilibrium calculationmodels for methane hydrate in both salt solutions were finally established.The latent heat of the phase change distribution of hydrate underdifferent conditions was further calculated. The results of this papercan provide a theoretical basis for the study of deepwater drillingfluid systems and multicomponent annular flow.