Alternative Perforating Method for PWC®

Key facts
• Customer: Undisclosed supermajor
• Location: North Sea, UKCS
• Well type: Old exploration well at HP/HT-field
• Key benefits: Proving that PWC® can be applied in wells where perforating guns are unsuitable

The customer’s challenge
A subsea well which was to be abandoned, had a live annulus which required to be isolated before the full abandonment could be safely completed. Isolation had to be achieved without damaging the external casing, which was not possible with standard TCP perforating guns as the internal 7” casing with flush connections was touching the inside wall of the 9 5/8” outer casing. A standard perforating gun would either shoot through both casings or create insufficient annular access for the standard PWC® solution.

The HydraWell solution
As HydraWell could not use the tubing conveyed perforating guns that are part of its standard PWC® – perforate, wash, cement – solution, the company had to identify an alternative method of creating access to the live annulus, which in turn would enable sufficient washing and cementing to provide the required isolation.

As a result, HydraWell altered the design of its HydraHemera™ jetting system to work in conjunction with a third-party supplier of a hydraulic perforating system. The hydraulic perforating system cuts slots in the internal casing without the use of explosives, but through use of blades and hydraulic pistons.

The challenge with using the hydraulic perforating tool’s casing cuts are that they are made in the opposite direction of normal right-hand rotation and are therefore incompatible with the washing tool of the standard HydraHemera™ system. HydraWell’s Stavanger office therefore had to redesign the jetting angles to optimise the washing tool, then test the solution, including determining the optimal spacing for the cuts downhole.

Once sufficiently tested, HydraWell’s Aberdeen operation conducted the P&A operation offshore, where the hydraulic perforating system cut slots in the internal casing before HydraWell ran its specifically adapted HydraHemera™ jetting tool to clean and cement the annulus.

The benefits
HydraWell proved that operators do not always require traditional perforating guns to conduct a P&A job. The project successfully showed that HydraWell’s PWC® method can be applied in wells where, for technical reasons, perforating guns cannot be used. The newly applied method is also highly relevant for countries where access to explosives are restricted, or where a low spread cost (such as land operations) permits the impact of the additional duration required to be more than offset by the reduced service costs.

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