Re-Abandonment - Balance Point Control

Background

The well was drilled in 2012 to a depth of 2635m AH and was found dry. The 13-3/8” and 9-5/8” casing-shoes were set at 564m and 1295m respectively. The well was permanently abandoned by means of 5 cement plugs. The 9-5/8” production casing was cut and retrieved from 600m creating a uncased hole section of 40m between the top of the 9-5/8” and the shoe of the 13-3/8”. Cement plug #4 was set in this open hole section. After removal of the wellhead and demobilization of the rig gas bubbles were detected. As a result an emergency slip-lock head MX2 wellhead and a 4-1/16” X-mass tree were installed.

Objective

The objective was to re-enter the well, find the leak and re-abandon the well.

Execution

Drill a pilot hole through plug #5 and bleed-off any trapped pressure and set and test new cement plugs in order to remove X-mass tree.
Rig down BOP’s and remove 4-1/16” X-mass tree in order to accommodate a 13-5/8” BOP stack.
Re-enter the well by milling trough top cement plugs and plug #4. Try to re-enter the 9-5/8” csg, run a tie-back liner, perform a leak search and re-abandon the well.
Pressure below the shallow plugs could cause pipe-light scenarios. For that reason the HWT600 HWO/snubbing unit was used for milling through top plugs.

Results

Milling through the top plugs was done without problems. Pressure was contained. New plugs were set and tested. The 4-1/16” X-mass tree was removed and a 13-5/8” Snubbing BOP stack was rigged up.
Finding back the original 9-5/8” hole at 600m proofed to be difficult because of the uncased hole section between 560 and 600m. Further attempts to access the original hole were cancelled.
New cement plugs were successfully set and tested and the leakage stopped.