A strategic well was drilled in 2001 (highly productive well with low CO2 content despite its age). A cellar cleaning campaign was performed on 03/2016, while the well was in production (450,000 sm3/day of gas). The 20" casing was found parted below the Starting Head at the cellar level, with evidence of corrosion. The cut had been buried in sediment for an unknown period and prolonged exposure to water and sediment accumulated in cellar was suspected.

Wellhead movement due to thermal expansion (axial and lateral) was reported during monitoring. Additionally, annulus B, formed by the 13-3/8" casing × 9-5/8" casing annulus was pressured with 16 bars.

The wellhead was found not directly supported by the landing base and axial/torsional force cycles during production/shutdown periods generated fatigue on the 20" casing. This load combination, added to lack of inspections and cleaning on cellar resulted in the failure of 20" casing at surface.

Heavy workover remedial options were studied with prospective high costs and long delays. At the same time a Call for Tenders was launched to find solutions to safely put back well in production at the shortest possible delay. Boots & Coots/Halliburton proposal was selected for engineering and execution. The operation was treated as a Workover (well secured and capped with BOP). Main stages involved:

  • Installation of Downhole plugs, monitor of annular pressures and bleed off operations.

  • Surface installations removal. Cellar Floor and one wall removal (trench excavation).

  • 50 cm below cellar excavation to find 20" casing in good conditions. Cut corroded section of 20" casing.

  • Build foundations and rig up Strand-Jack Crane. Cap well with BOP, install tensioning spool system and Tension the inner csg & tbg to 465 kips to get 34 mm displacement and compensate the thermal retraction (Engineering calculations using WellCat™ Software).

  • Replace the 20" corroded section with 2 new half-moon 20" casing sections (welded).

  • Finally release tension on an engineered landing base specially built for purpose.

The objectives were fully achieved through this innovative and multidisciplinary engineering and operational approach. Three months of preparation and engineering were required. The operations were carried out safely (0 incidents) and cost effectively (heavy workover to change wellhead avoided). The well was re-connected and put back in production in April 2017. Production is currently at former levels (430,000 sm3/day peaks-choke not fully open).

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