This scope of work related to a field dating back to the 1960s. Subsequently, the appraisal wells were left in a suspended state with wellheads capped.
Prior to the removal of the caps, the completion of the abandonment and integrity of the plugging needed to be verified. This would enable the monitoring and sampling of any product that may be under the cap, without removing it from the wellhead.
Land-based hot tapping operations are commonplace, with a number of vendors able to supply equipment supported by extensive track records. However, this is not the case for subsea applications as hot tapping equipment is typically much larger and used on subsea pipelines. This led to Proserv developing a bespoke solution.
• Drill a small hole (1/2”) through the wall of a well cap and contain pressure with a double block and bleed valve arrangement
• Have the ability to increase the diameter of the hole to 2” and drill a second hole at 180 degrees in the event the well needs to be killed
• Provide a system whereby a sampling skid could be connected to take samples and monitor the well
• All equipment to be installed, operated and monitored by an ROV
Proserv was approached by the client to devise a method to deploy and install the required hot tap equipment onto two of the well caps, and convert an existing top-side hot tap machine into one suitable for subsea deployment and operation via ROV.
The final system, which took eight months to design and deliver for the client, included:
• A tool that enveloped the large pressure-retaining clamp, provided the ability to open/close the clamp and pressure test the seal against the cap once installed. It also provided exacting alignment and guidance of the clamp over the cap whilst ensuring that the sealing faces were not damaged.
• The deployment frame interfaced with the original 50-year-old guide posts that provided a risk-free coarse alignment of the clamp assembly. Further features meant it provided fine alignment when the assembly was lowered over the cap.
• High-torque hydraulic wrench assemblies that were used to sequentially tighten the clamp around the well cap.
• A neutrally buoyant structure that encases the hot tap machine and allowed it to be delivered by the ROV.
• Control panels and various monitoring features that permitted the equipment to be operated by the ROV, whilst maintaining all the functionality and control of a top-side operation.
• All equipment was transported and deployed in bespoke skids that doubled as service centres for the equipment, allowing major components to be removed and replaced easily.
Proserv’s solution is believed to be the first fully remote, small bore, high pressure hot tap to penetrate through a subsea well cap.
“With this project, Proserv’s Perth team, once again, demonstrated their ability to provide successful solutions for a technology new to our office; all the time supporting the client from problem identification through to design and completion offshore.
“The project provided many challenges, including understanding the hot tapping technology, integrating equipment from multiple vendors and designing various new tools, alongside the usual design challenges of a subsea environment and ROV operations.”
Jakub Kawka, Principal Engineer, Proserv Perth