Abstract: The formations penetrated during drilling in the Block D in Myanmar are characteristic of high dipping, multiple fault zones, high formation pressures, water sensitive shales and developed fractures. Borehole wall collapse, hole washout (100%) and pipe sticking caused by borehole wall collapse (32 times in a single well) have been the problems frequently encountered during drilling and unlikely to be solved by conventional KCl polymer drilling fluid and protecting the borehole wall by multiple casing strings. The conventional KCl drilling fluid has thus been modified through laboratory experiment. In the new drilling fluid, an optimized emulsified asphaltene with particle sizes in micrometers is used as an additive for borehole wall collapse controller, KCl and poly glycol as main shale inhibitors, PAC as filter loss reducer, and sulfonated polymer as high temperature stabilizer. Compared with the previously used KCl polymer drilling fluid, the rate of swelling of shale cutting sample tested with the new mud has been reduced by 15%, and the recovery of shale cuttings on hot rolling test increased by 50%. Good performance of the new mud in controlling borehole wall collapse has been obtained, together with other measures such as increasing mud weight, optimizing the properties of drilling fluid, and reducing API filter loss. With the new mud, the rate of bore hole washout has been reduced from 100% to 20%, the drilling time saved by 20%, the time efficiency of well drilling increased by 35%. This new drilling fluid technology has effectively solved the borehole wall collapse frequently encountered in wells drilled in Block D, where high dipping and high pressure were of great concern.