Abstract: In order to solve the problems of poor stability,weak compressive strength,poor cuttings carrying capacity and defoaming when drilling in oil reservoirs when using conventional foam drilling fluids under high temperature in deep zones,research was conducted on high temperature resistant foam drilling fluid for deep wells.Six groups of preliminary formulas of high temperature resistant foam drilling fluids for deep well were formulated through the research and development of key treatment agents,including FPTO-1(foaming agent),WPTO-1(foam stabilizer)and YZTO-1(shale inhibitor),as well as the optimization of their dosages.After evaluating laboratory performance,the drilling fluid formula was optimized by comprehensive evaluation of its temperature resistance,oil resistance,inhibition and compression resistance.In these cases,they had a the temperature resistance of 150℃,oil resistance 30% and compression resistance 28 MPa.The drilling fluid was tested in the depth from 3 837.00 m to 5 173.50 m of Well Hashen 2, and the test showed that high temperature resistant foam drilling fluid could maintain stable performance and good cuttings carrying capacity at temperature of 137℃.The research results indicated that this high temperature resistant foam drilling fluid broke through the depth limit restricting conventional foam drilling fluids,with excellent comprehensive performance and application prospects.