Abstract: In view of the difficulties during workover treatments in Jidong Oilfield, such as circulation loss, slow water cut recovering, serious formation damage, a novel technique named Fuzzy-Ball was applied based on the temporary blocking mechanism analysis of Fuzzy-Ball workover fluids. The Fuzzy-Ball can self-match leak passages completely during workover, and then flow back automatically from formation. Laboratory evaluation showed that the workover fluids could be stable for more than 15 days, enhance formation pressure bearing capacity, up to 7 MPa, and invade formation less than 8 cm. What is more, the core permeability can recover up to 90%. Well L12-6 and NP23-X24091 are two examples for the application effects. The water cut of well L12-6 recovered only in 3 days, oil productivity increased more than 3 tons per day and water cut reduced by 30% after the pump inspection by Fuzzy-Ball workover fluid. For well NP23-X24091, formation bearing pressure capacity was enhanced up to 6~7.5 MPa after the fuzzy-ball workover fluid blocking formation and squeezing cement, oil productivity increased more than 10 tons per day, and water cut reduced by 5%. The indoor and onsite experiments proved that the Fuzzy-Ball workover fluid had good effect of blocking and less damage to formations.