A new type of whole oil-based drilling fluid

To meet the demand of ultra-deep well drilling and shale gas well drilling, organic clay and a oil-based filtrate reducer were developed and a whole oil-based drilling fluid formula was optimized. The performance of organic clay, oil-based filtrate reducer and the whole oil-based drilling fluid were evaluated in laboratory, and the whole oil-based drilling fluid was applied in drilling process for further test of its performance. Long carbon chain quaternary ammonium salt was used as modifying agents when synthesizing organobentonites. Oil-based filtrate reducer was synthesized with monomers of lignite and amine class. The laboratory tests show that the organic clay can effectively increase the viscosity of oil-based drilling fluid and the oil-based filtrate reducer can reduce the fluid loss. Their performances were better than additives of the same kind at home and abroad. The organic clay and oil-based filtrate reducer had great compatibility with the other additives in oil-based drilling fluid. Based on the optimal additives addition amount tests, the whole oil-based drilling fluid formula was determined and the test results show that the performances of the whole oil-based drilling fluids with various densities were great. The laboratory tests show that the oil-based drilling fluid developed was high temperature resistant, even at 200 °C, as density varies from 0.90 to 2.0 g/cm3, it still held good performance with only a little fluid loss, good inhibition, great anti-pollution, and good reservoir protection performance. Field application result shows that the performance of the oil-based drilling fluid is stable with great ability to maintain wellbore stability and lower density than the water-based drilling fluid; drilling bits can be used much longer and the average penetration rate is increased; the oil-based drilling fluid can satisfy the drilling requirements.