Abstract: With the deepening of exploration and development of Bohai Oilfield,extended reach wells have become the focus of current development. But the oilfield has complex stratigraphic conditions,and many challenges are faced in the development of extended reach wells,such as frequent drilling accidents,difficulty in improving efficiency and reservoir leakage. In order to solve this problem,the synthetic-based drilling fluid BIODRILL S system is introduced,which has low viscosity and high cutting,high demulsification voltage,low filter loss,stable rheology,good coating inhibition and plugging ability,and strong resistance to rock cuttings and seawater pollution ability. In the field application,the performance of this system remains relatively stable during the drilling of extended reach well section,and the returned cuttings are complete,showing good inhibition and rock carrying capacity. Meanwhile,the friction coefficients in the casing and in the open hole are only 0.15 and 0.20,respectively,which have good lubricity and can effectively solve the problems of difficult sand carrying,high friction resistance and low drilling time in extended reach well.

Key words: synthetic-based drilling fluid, gas to oil, rheological characteristic, Bohai Oilfield, extended reach well