Abstract: Well R-504 is the .rst producer in Lumaila Oil.eld deployed by CNPC Iraq Branch, with completion depth of 3436m and the target layer of Zubair. The geological structure of the target formation is complicated with existing drilling .uid loss, so wellbore unstability, bit freezing, and .uid loss are tend to happen. Through a number of lab experiments and .eld tests, the drilling .uid is determined to be salinity resistant polymer system. The application proves that the reology of the .uid is good, and it has strong inhibition and temperature stable ability. According to the characteristics of multi pressure system in Lumaila area and large dif.culty of dealing with complex accidents, the treatments of easily loss plugging and accident handling are programmed, which greatly decreases the drilling lifetime.