1. Definition
Primary cementing may lead to mud losses due to excessive injection pressure of the cement slurry, fracturing of the formation, and the top of cement not reaching the desired height. In such cases, special tools are required for two-stage or multi-stage cementing operations.
2. Cementing Procedures
1. After completing the first stage cementing operation, immediately drop the opening plug according to the floating equipment and record the opening time.
2. Open the two/multi-stage cementing collar. Follow the manufacturer’s procedure to determine the opening pressure of the stage tool and the exact time for the opening plug to land.
3. With the stage collar opened, start circulation with a low pump rate, keeping the mud level under control. Increase the pump rate only when it is certain that no cuttings or cement contamination will cause bridges and compromise circulation due to fracturing below the stage collar.
4. During circulation and after bottom’s up, record the pressures at each different flow rate.
5. Prepare for the second stage cement job as per the Cementing Programme.
6. Perform the second stage operation as soon as the cement setting time of the first stage is complete.
7. Arrange the by-pass manifold at the rig floor with double lines (pumping and reversing out).
8. Keep the casing in tension with the slip elevator as required by casing hanging calculations.
9. Prepare the wellhead (with partially made up bolts) and Blowout Preventer lifting system to quickly hang the casing string after the second stage cement job.
10. With the mud well balanced, insert the closing plug into the cementing head. Check the stop pin, indicating flag, and the circulation manifold.
11. Pump the first cushion and pump the cement slurry.
12. Launch the closing plug and verify its release.
13. Displace the slurry.
14. Configure the surface mud system to recover the excess cement slurry, spacer, and contaminated mud.
15. Use the pressure recommended by the manufacturer to close the stage collar. After pressure testing, gradually bleed off pressure.
16. Wash through all the inlets in the wellhead and BOP stack with water.