Circulation repair cementation is used when cement behind casing has a poor CBL and zonal isolation is required.

The casing is perforated in two places, a retrievable packer is set between the perforations and a circulation test is carried out.

If circulation is possible at a sufficient rate, a cement retainer is set in a position between the perforations and cement circulated behind the casing.

The cement retainer is drilled out later, together with the cement inside the casing.

If no adequate circulation can be established, even after spotting acid, the casing may be re-perforated in an attempt to establish circulation over a shorter interval. If this fails, a block squeeze will be carried out.

Procedure

The following procedure should be adhered to when carrying out circulation/squeeze cementation repair.

1. Use the cement bond evaluation log to determine the interval to be repaired.
2. Run bit and scraper.
3. If there are any perforations to be protected below the repair zone, set a drillable bridge plug approximately10 ft below the planned depth of the bottom repair‑perforations.
4. Perforate the casing at the top and bottom of the repair interval if required.
5. Set a retrievable packer between the perforations.

6. Establish circulation carefully, preferably using a solids-free fluid. Circulate at increasing rates until the pressure at the perforations equals the fracture closure gradient, unless specified differently in the programme. If problems occur use the following guidelines to decide the next course of action.

• If it is possible to circulate at a rate greater than 1 bbl/min. continue with item 7.

• If it is possible to circulate at a rate less than 1 bbl/min, attempt to circulate 15 % HCl around (Confirm acid volume and concentration with Cementing Contractor). If it is possible to circulate at a rate greater than 1 bbl/min. continue with item 7.

• If it is not possible to circulate, spot 10 bbls of 15 % HCl and soak for ten minutes. (Confirm acid volume and concentration with the Cementing Contractor). If it is possible to circulate at a rate greater than 1 bbl/min. continue with item 7.

• Re-perforate at some point between current perforations. If it is possible to circulate at a rate greater than 1 bbl/min. continue with item 7.

• Pooh with retrievable packer and CARRY OUT block squeeze.

9. Pooh with the retrievable packer.
10. Set the cement retainer 5 ft above top of bottom perforations on electric wireline (better depth accuracy).
11. Rih with the cement retainer stinger on drainpipe to 30 ft above cement retainer. Circulate at least 120 % of the drillpipe contents and STAB stinger into the cement retainer.
12. Re-establish circulation rates versus pressures.
13. Pull out of cement retainer approx. 5 ft.
14. Pump 10 bbls of flush followed by the cement slurry to a level 1 000 ft above the cement retainer. Apply back pressure on the annulus to balance the cement column.
15. Stab back into the cement retainer immediately and displace cement until balance point. The cement slurry volume should be enough to give a theoretical TOC inside the casing of 250 ft above the top perforations.
16. Pull back immediately but carefully to approximately 60 ft above theoretical TOC and Circulate clean.
17. Pull back one more single, close Hydril and apply maximum allowable surface pressure. The hardening time will be advised by the Mud and Cement Laboratory. Ensure a minimum of 50 ft of cement is left above the top perforations.
18. POOH.
19. RIH and drill out the cement and cement retainer/bridge plug.
20. Run cement bond log to evaluate repair.