Abstract: During drilling in the SACHA Block of Ecuador, downhole troubles often occurred at φ215.9 mm hole section, such as bit balling, hole collapse, tight points met in tripping, logging and liner running. In order to solve these problems, a strong-inhibition plugging microemulsion drilling fluid was developed by using environmentally friendly organic inhibitor SUPHIB, semi-permeable diaphragm MS and isolating membrane agent EX, its performance was evaluated by means of laboratory experiments. The research results showed that this system had good performance after being boiled at 100 ℃ for 16 h, with good inhibition and plugging effect, the recovery rate of TENA cutting reached over 90%, expansion ratio and plugging rate were 1.32% and 99% respectively for high-porosity high-permeability reservoir cores. It has been successfully applied to 8 wells in SACHA Block, no bit balling, tripping sticking ro drag in logging and liner running occurred, and average hole enlargement rate at φ215.9 mm hole section dropped to less than 10%. It is shown that the problems that occurred at φ215.9 mm hole section in the SACHA Block of Ecuador can be solved effectively by using strong-inhibition plugging microemulsion drilling fluids.