Oil-based drilling fluid technology in horizontal wells with unconventional oil-gas reservoir

In this paper, the oil-based drilling fluid system is researched by orthogonal experiments, which the formulation is optimized, the asphaltic filtrate reducer, high temperature organic clay, high temperature wetting agent, ultra-fine calcium carbonate (less than 6 μrn of average diameter) and kinsite are applied in this drilling fluid system. The laboratory evaluation results show that this oil-based drilling fluid has good performances of rheology and high temperature stability, the contamination tolerance of cuttings and NaCl are both 20%, and the density difference between top and bottom is less than 0.02 g/cm3 after holding for 120 h at 130°C. The application in well Pul-FPl shows that the borehole diameter enlargement rate is only 8.2%, and the average ROP is 7.05 m/h.