Adaptability evaluation of formate solution to saturated brine sulfonated drilling fluids

Potassium-based solution with high concentrations is brought into saturated brine sulfonated drilling fluid in the complex ultra-deep wells, which can reduce the solid content of high-density drilling fluid, improve the thermal stability of the drilling fluid, temperature resistance of key treatment agents and the drilling speed in the extremely thick ultra-deep salt formation, and slow down the drilling corrosion. At the same time, formate drilling fluids have the advantages of inhibitive ability, good quality of mud cake, low annular pressure lost and friction coefficient. This article discussed the solubility of barite in potassium formate solution and its tolerance to salt and calcium. The experimental results showed that barite was almost insoluble in potassium solution so that the formate solution of 30%~70% was used to improve the density of base fluid and then choosing barite to aggravate it was feasible. In addition, the solubility of sodium chloride and gypsum in formate solution both reduced by different degrees, which could be used to further increase the tolerance to salt and calcium of sulfonated drilling fluid.