Abstract: To reduce the application of oil based drilling fluids in extended reach wells,water based drilling fluids was developed for Liuhua Oilfield.The formulation and properties of the drilling fluids used in different intervals of extended reach wells located at the Liuhua Oilfield,South China Sea, are affirmed by large numbers of tests.Several key characteristics,such as lubrication,inhibitive character and rheology,are analysed by the numbers.It is shown from the results of experiments and field tests that the specially designed KCl/polymer drilling fluids not only possess excellent inhibitive character,but also have proper rheological parameters,good lubricate property and strong ability of anti-contamination for calcium ions.Hence,it can meet the requirements for extended reach drilling in this area.Take the horizontal well Liuhua 111-B3 ERW4 as an example,the performance of the trial test is analyzed and some suggestions for the future work of drilling fluids are provided.