Abstract: Influenced by fault-nose structure,Oilfield S in western Bohai Sea area has 52 faults in 4 categories. During the drilling,the fault type fracture zone is encountered,and the formation pressure bearing capacity is low,resulting in loss of return leakage. By analyzing the leakage mechanism of the oilfield,the leakage prevention technical scheme is formulated from the aspects of leakage risk assessment,drilling fluid performance control scheme and ECD accurate prediction and control. For the malignant lost circulation wells in the oilfield,the high pressure-bearing plugging technology is used to solve the problem of low plugging success rate of the fault lost circulation wells,which is of great guiding significance to the development of fault leakage prevention and plugging technology in Bohai Oilfield.

Key words: western Bohai Sea area, fault, characteristics of mud loss, mechanism of mud loss, high pressure-bearing plugging technology