Optimization design of drilling fluid and completion fluid for reservoir protection in Nanbu 35-2 Oilfield

The conventional drilling fluid and completion fluid is not suitable for the development of viscous oil reservoir in Nanbu 35-2 oilfield, due to high porosity and permeability in this area, and the high viscosity and density of the crude oil, as well as the high content of gel and asphalt materials that cause the poor flowability. Combined with the use of activating agent HXJ, the polymer micro cation drilling fluid, PEM polyol drilling fluid, synthetic based drilling fluid and active completion fluids are optimized. By laboratory tests on drilling fluid performances, the compatibility of drilling fluid and completion fluid with formation fluid, and the influencing tendency of HXJ on the core permeability recovery show that all the three drill ing fluid systems are suitable for field drilling, and as compared with other systems, the filtrate of synthetic drilling fluid has the most remarkable effect on dropping crude oil viscosity, and then follows PEM polyol drilling fluid with HXJ and polymer micro cation drilling fluid. Adding of HXJ in drilling fluid and completion fluid can reduce the oil water interface tension, drop the viscosity of crude oil, and is beneficial for viscous oil production. The synthetic based drilling fluid obtained the highest core permeability recovery, which is over 85% , and the drilling fluids with HXJ was over 83%, which is 13% higher than the completion fluid without HXJ. The optimized drilling fluid and completion fluid all obtained good formation protection results.