Abstract: The Anjihaihe Formation formation in the third spud-section of Well H101 in the Southern Margin of Junggar Basin is dominated by mudstone.During drilling, shale hydration expansion and the dispersal mud may sometimes make it difficult to maintain desirable performances with high specific-gravity oil-based drilling fluid.At the same time, borehole wall collapse, sticking and other downhole problems may be encountered.To eliminate these problems, high specific-gravity oil-based drilling fluids have been designed and deployed.With consideration to specific characteristics of the Anjihaihe Formation, the performance of the oil-based drilling fluid and the requirements of drilling operations, a formula for high specific-gravity oil-based drilling fluid has been determined.In addition, its rheology, stability and pollution resistance performances were assessed.Relevant results showed that, the rheology, stability and pollution resistance capacities of the drilling fluid can meet the design requirement.The density of the high specific-gravity oil-based fluid is up to 2.46kg/L during drilling of the in the Anjihaihe Formation in the third section interval of the Well H101.No downhole problems have been encountered except a few sticking situations.Average ROP in the third section is 6 times higher than those of adjacent wells in the area, whereas the drilling cycle shortened more than 100 d.Relevant results showed that the high density oil-based drilling fluid system could effectively remove stuck drilling pipe, avoid lost circulation downhole fault in Anjihaihe Formation drilling process.In addition, the system could improve the rate of penetration and reduce drilling costs.