Abstract: In order to solve the problems such as formation hydration,erosion,borehole collapse,loss of circulation,which are likely to occur during drilling fluid conversion after gas drilling,the gas-drilling fluid alteration process after gas drilling was studied.Three kinds of risks associated with conventional gas-drilling fluid conversion were analyzed.According to wettability reversal theory,spraying wet reversal agent to borehole to make it oil-wet for keeping borehole stability.The procedure includes pulling the bit back up to the last casing,then rotating bit,spraying wet reversal agent to change the borehole wettability.Finally,the drilling bit can be run to the bottom,and pumping drilling fluids at low flow rate while tripping out at slow speed.The application of the procedure in Well Yuanye HF-1 in Yuanba Block showed,the operation time was only 47% that of conversional method,and the consumption of wet reversal agent was only 13% of that in conversional ways,was no trouble occurred.It indicated that new alteration process for gas-drilling fluid was safe,simple,economic,and effective,could provide technical support for drilling fluid alteration after gas drilling in the future.