Abstract: In order to resolve the problems of hole shrinkage,bit balling and borehole instability in mudstone section of the Xinjiang Tahe Oilfield,a new polyamine drilling fluid was applied in section 2 and section 3 of Well DuH 4.Laboratory test shows that the new polyamine drilling fluid system has strong inhibition and good lubrication property.Its application in section 2 of Well DuH 4 effectively solved sticking and bit balling problems in the mudstone section,preventing any complications,resulting in the reduction of 15 days in drilling cycle than offset Well DuH 1.In section 3 of the Well DuH 4,it has solved the problems of borehole instability and tight holes caused by complex hydration swelling of gypsum mudstone and shale,the drilling cycle time was 50 d shorter than Well DuH 1,and average hole enlargement rate was only 4.37%.The successful application of novel polyamine drilling fluid in Well DuH 4 shows that the drilling fluid can effectively solve tight hole and bit balling in mudstone rocks,ensure the safe drilling,reduce drilling cycle time,and improve drilling efficiency.