Casing cementing – is a way of fixing wells by cementing the hole annulus.
The casing is the stanchion of casing pipes, which is intended for fastening boreholes, as well as for isolation of productive horizons during operation. It consists of a casing sequentially attached with the help of bolts or welding. Cementing of wells is carried out for:
• Isolation of permeable horizons from each other and prevention of reservoir fluids flows in casing space;
• Keeping casing in suspense state;
• Protection casing from the influence of aggressive corrosive formation fluids;
• Elimination of defects in the well casing bracing;
• Creation of dividing screens that prevent well from watering;
• Building bridges in the well;
• Reinforcing the borehole walls;
• Sealing the outfallin the case of well abandonment.
CEMENT BRIDGE INSTALLATION
During the installation of cement bridges in disposal wells they are primarily washed within 1.5 – 2 cycles for equalization of densities of the washing liquid in the well tubing and hole annulus. The prepared volume of cement slurry is pumped into the well tubing and forced by wash solution to balance the fluid pillars in well tubing and the hole annulus.The volume of displacement liquid is determined in this way: first the height of the pillar, which takes the cement slurry in column, is determined by dividing the volume of the cement slurry injected into well tubing (in liters) per volume of one meter of production string (in liters). Then this value is subtracted from the total length of the well tubing dropped in the well.The resulting value is multiplied on the volume of 1 m of well tubing and in that way the amount of displacement fluid is determined. Well tubing shoe is raised to the upper limit of the set by the bridge and the cement slurry excess is washed.
Then the well tubing is raised to 20 – 30 m, the well is filled and it’s needed to wait for cement hardening. After finishing the WOC period the depth of the bridge disposition and its hardness is checked by well tubing fit, and tightness of the bridge is checked by crimping.
Clay solution, water cement slurry and water clay slurry are used as the liquid carriers. Injection of sealing materials is continueduntil full circulation is restored. After that, a cement bridge is installed straight away.