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Oilonline: EV Offshore inspects five wells for Shell on Corrib Gas Field

By: OilOnline
Friday, September 01, 2006

EV Offshore has successfully completed a series of downhole inspections for Shell E & P Ireland Ltd on the Corrib Gas Field offshore Ireland.

Located approximately 72 kilometres west of the County Mayo coastline in water depths of 350 metres (1,150 feet), the 237 million year-old reservoir lies 3,300 metres under the seabed. When developed, the Corrib Gas Field – which is currently Shell’s second largest UK project – will be produced over a period of between 15 and 20 years. Shell anticipates that the Corrib gas field will eventually supply upwards of 35% of Ireland’s natural gas through 2020.

Although previous owners Enterprise Oil drilled five wells on the Corrib Gas Field between 1997 and 2001, these wells were suspended awaiting completion and subsea tie-back by Shell. Prior to proceeding with their 2006 offshore campaign, Shell elected to inspect and clean the offshore wells. Shell retained EV Offshore to inspect the five wells both before and after wellhead and casing hanger clean-up operations were carried out by clean-up specialists SPS International (SPS).

Faced with the challenge of inspecting and cleaning wells featuring wellheads supplied by three separate manufacturers, various alternatives were considered by EV Offshore, SPS and Shell. Among the options discussed were either a) carrying out the clean-up operations quite separate from the inspection runs, or b) carrying out the clean-up and inspection operations simultaneously. Following much discussion and analysis, all parties agreed that in view of the varying well configurations and time constraints associated with a new design, the best option would be to carry out each inspection run independent of each clean-up operation. In this way, each process would be completely customised to the individual wellhead and its unique characteristics.

The Shell Corrib operation had the potential to become a demanding and lengthy campaign for EV Offshore. To ensure that the wells had been cleaned properly and that no damage had occurred during running, inspections would be run before and after clean-up operations were carried out. The fact that all five wells were situated in a remote field with extremely limited oilfield infrastructure further compounded the situation. The remote location at Corrib meant that back-up equipment was vital, as it would have been very difficult to transport required equipment to the vessel.

EV Offshore carried out the inspections from the MV Bucentaur drilling vessel. Although EV Offshore’s standard CamScan EVO2 inspection camera system remained the pivotal piece of inspection equipment, given the scale of the operation EV Offshore employed a much larger spread of equipment. The Shell Corrib custom spread also featured a back-up CamScan EVO2 with additional umbilicals, two running and flushing tools pre-torqued onto pup joints for ease of deployment, and centralising tools. The CamScan EVO2 offers full, continuous hemispherical viewing – in colour or monochrome – while running downhole. It is also capable of flushing turbid water and dislodging obstructions at target depth to offer a clear view.

The entire spread was mobilised to the MV Bucentaur in an enclosed container that doubled as an onboard workshop throughout the entire operation.

With an inspection team consisting of two technicians and engineers, EV Offshore ran the first two inspection runs on drill-pipe. Each inspection required between eight to 10 hours to run in and out of hole. Following these first two runs, EV Offshore consulted with the Shell representatives, the vessel operators and the EV Offshore support team onshore. It was suggested that in order to save time, the camera and running tools should be run on a motion-compensated winch wire for the remaining inspection runs. By doing so, EV Offshore reduced the running time to just two hours per run, which subsequently reduced Shell’s vessel time and associated costs .

Over the course of 27 days, each of the five wells was fully inspected by EV Offshore in 12 runs, both before and after clean-up operations. Using the CamScan EVO2, EV Offshore provided Shell with high quality images of the conditions within each wellhead. The images were delivered instantaneously via email from the MV Bucentaur to Shell engineers working onshore in Aberdeen. Shell engineers analysed the visual data to assess the internal environment and condition of each individual well. Armed with accurate and timely visual information, Shell engineers used the information to plan each forthcoming clean-up operation. Following each clean-up operation, they were able to assess the footage to decide whether the clean-up process met with their standards.

“We were very impressed with the quality of the images that EV Offshore supplied to us. The clarity was extremely impressive and allowed us to move ahead with confidence to the next phase of development,” said Fraser Stewart, Corrib Subsea Well Engineer for Shell.

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