Cementing technology in the environment of oil based drilling fluid with high-pressure narrow-density window

The cementing operation in offshore oil fields is faced with many challenges. For example, circulation loss and gas channeling tend to happen at high-pressure narrow-density windows. When oil based drilling fluid is used, the filter cakes on the cementing wall can’t be removed easily. And the cementing displacement efficiency of highly-deviated directional wells is low. There are some technical measures to solve these problems. First, high-density flushing fluid was adopted to improve the cleaning quality of filter cakes on casing walls and borehole walls in the environment of oil based drilling fluid, after the technical difficulties related with well cementation were analyzed. Second, the polymer reinforced slurry system was adopted and bi-setting slurry column design was optimized based on the dynamic cementing pressure loss calculation and the pressure stability calculation, so that the circulation loss was prevented and the pressure stability of reservoir was realized. And third, the rotating liner cementing technology was adopted to rotate the liner in the process of well cementation so as to improve the cleanout quality of flushing fluid and the displacement efficiency of cement slurry. These technical measures were successfully applied in Weizhou Oil Field for the cementing operation of oil based drilling fluid with high pressure coefficient (1.61 g/cm3), high gas/oil ratio (358 m3/m3) and narrow density window (0.12 g/cm3). And the cementing quality was evaluated as good level.