CARRYING OUT NEAR-BALANCED DRILLING BY ISOLATING BOREWALL USING CEMENT SLURRY

Near-balanced drilling technology is carried out to ensure the downhole safety during drilling, and intermediate casing is used for isolating the sand-drifting zone, caving shale formation, water layer and multiple pressure intervals.However, there are limitations and disadvantages, e.g., the complicated intervals drilled before setting the intermediate casing are difficult to deal with;high cost of setting the intermediate casing;inefficient isolating of some intervals due to the limitations of the casing programs and the unknown factors when drilling the exploration wells, which in turn affects drilling operation.In Jiangsu Oilfield, a method is found in practice of isolating the complicated intervals using cement slurry, thus carrying out safe drilling.This method is described in the paper, i.e., after penetrating the complicated interval, a certain volume of cement slurry is pumped down and then raise the pressure by closing the well, causing the cement slurry entering into the bore wall, consolidating the drifting sand and gravel and plugging the water layer.The method can increase the well stability extremely.In wells Min20-13 and Dun1-3, by using this method of cement squeezing, the upper sand-drifting layer and gravel layer, as well as the lower sloughing layer were effectively isolated, and the densities of drilling-in fluid were reduced from 1.15-1.16g/cm3 to 1.05-1.08g/cm3, and the production rate was also effectively increased.In addition, the borehole stability in upper section is very important for realizing the near-balanced drilling using the emulsified diesel oil.