Water-Based Drilling Fluids Technology for High Temperature and High Pressure Wells in Yingqiong Basin

Yingqiong Basin in the South China Sea is characterized by high temperature gradient, high formation pressure, narrow safe density window, so such problems often occur in the condition of high temperature and high pressure as difficulty in control of drilling fluid rheology, lost circulation, electric logging blocked and reservoir pollution. Based on the characteristics of the formations of this Block and through large amount of indoor research, the potassium formate as inhibitor was introduced based on polysulfide system, and the sulfonated material and temperature resistant polymer were selected, which, while improving inhibition, effectively reduced the activity of the system and, through the optimization of weighting materials, improves the rheology of drilling fluid. At the same time, the drilling fluid has low HTHP water loss. A system with density of 2.4 g/cm3 can resist a temperature of up to 200 ℃.Field application results show that the drilling fluid system has good temperature resistance and rheological property, low HTHP water loss and good quality of mud cake. Electric log results show that this drilling fluid system has good reservoir protection effect.