Research On Protection Workover Fluid For Low-pressure And High-permeability Reservoirs In Dagang Oilfield

Dagang Oilfield has entered the middle and late development stage, as the continuous decline in the formation energy, about more than 70% of the oil wells in the process of repairing wells appeared different degree of workover fluid leakage phenomenon. In the 20%-30% of the wells leakage is more serious (leakage is greater than 20m3), due to the large number of leakage of the working fluid, a lot of wells can not establish a normal working cycle. The result is that:the time of repairing well is prolonged, the cost of repairing well is improved, and the time of oil well operation is short, the waste water in the well is long and the recovery rate is low.In this paper, the main reasons for the damage are obtained by analyzing the damage factors of the oil field in the south of the oil field. First, the formation of low energy leakage caused serious pollution, the two is the high pressure and low permeability water sensitive phenomenon seriously cause pollution, three is the poor oil, four is the poor compatibility of the fluid with the formation fluid. At the same time for low pressure and high permeability reservoir the good foaming technology and stable foam technology were developed through synergies, hydration effect, mobility control technology,and innovative formed a set of low cost filling nitrogen preparation technology,which developed a new low density nitrogen microbubbles workover fluid system. The system can not only reduce the pressure of the liquid column, reduce the pressure difference, but also has a certain strength and toughness, which can be deformed and can be compressed, which can be used for various types of leakage channels, and can be used to open up a new path for the low pressure wells.Through comprehensive performance evaluation, the foaming capacity reached 760mL, half life reached 501 seconds, the foaming capacity in salt water reached 495mL, half life was 436 seconds and the oil/water interfacial tension reached 10-1mN/m. The time of stable foaming agent is more than 2 days, and endurance is strong, low density nitrogen micro foam repair fluid system do not need foaming equipments compared wtih similar technology.