Posted on 13.10.2010 - 12:00 UTC in ROV NEWS by Rons_ROV_Links
SeaBotix Inc. of San Diego, California was contacted by world renowned oil and gas service supply company FMC Technologies in Norway with an urgent requirement. Three subsea manifolds were installed in the North Sea as part of the Statoil Vega oil-gas wells. There were three small caps missing and without the caps installed production from the wells could not begin.
FMC was faced with only two choices. One was to recover each of the 160 tonne modules and install the cap. The other was to send in a small ROV with a torque tool to install the caps. A decision was quickly made that sending in a small ROV was preferred over the multimillion dollar task of lifting the manifolds, not to mention downtime.
The work was to be carried out at 365 meters depth and required carrying, maneuvering, and operating a heavy torque tool. To further complicate things, the operation was to occur in a very confined space. The obvious choice was to turn to SeaBotix whose systems are optimized to be as small as practical, yet still be able to carry and precisely deliver larger sensors and tooling while maintaining their renowned stability. The obvious choice was the SeaBotix LBV600-6, which is capable of diving to depths up to 600 meters while carrying a suitable payload, yet is still small enough to fit into the manifold. Timing was critical and arrangements were quickly made on the required equipment to tackle the job. The elapsed time from receipt of the purchase order to shipment was 5 days.
Working in cooperation with Norwegian company Sperre AS, a team was quickly put together to tackle the challenge. SeaBotix built two LBV600-6 systems and shipped to Sperre AS for modifications to carry the torque tool. David Whillas of SeaBotix Australia flew to Norway to help in the modifications and mission planning. A mockup structure was built at the Sperre AS facility where the solution could be tested and proven.
Only minor modifications were required to make the LBV600-6 ready to complete the job. The torque tool was mounted in front of the camera housing with a right angle drive. Because the caps were in such confined areas the LBV had to approach sideways, making visual confirmation more of a challenge. The lateral thruster was critical to being able to accomplish this as well as to securely mate the tool to the mount, as well as develop enough force to set the threads. It was found that the module was so tight the additional outboard thrusters on the LBV600-6 had to be removed.
With the systems completed, tested, and proven, the next step was the first module offshore. Weather in the North Sea can be poor, but fortunately the first module operation would be from a platform. The team mobilized the equipment out to the platform immediately. In addition to the customized LBV there would be a work class ROV for support as well as an inspection class ROV.
The plan was to send the LBV down in a basket with tether coiled inside. Once at depth the work class ROV would open the basket and free the tether. Conditions were reasonable and a green light was given. David was at the controls of the LBV while experienced work class ROV pilots operated the WROVs. The LBV was deployed and lowered to depth where the WROV easily opened the cage and freed the tether. Once free, David began piloting the LBV into the module for the first cap installation.
David was able to quickly locate the fitting missing the cap when he piloted the LBV into position. The area was extremely confined and David had to use the lateral thrust to push the torque tool with the cap onto the threads. Only a few moments and the torque tool was in place. The torque tool was operated from the LBV operator control unit and managed to easily tighten the cap into place. David then maneuvered the LBV back into the basket and the system was recovered to the surface. The first of three manifold caps were installed and it was noted there were some very relieved people on board.
The next two caps would require more time as a support vessel was needed. An Acergy ROV vessel was sourced and hired for the job. The team once again mobilized for phase two. Conditions were not as favorable with higher sea states and currents. The LBV would be deployed from the moon pool aboard the Acergy vessel. Waves were thrashing around inside the pool and the conditions continued to worsen.
Deployment was altered due to the deteriorating conditions. The LBV was deployed in the basket which reached the sea floor in about an hour. David piloted the LBV into the second module only to discover that a temporary test cap was installed. The LBV had to be recovered to the surface so that the new cap could be removed from the torque tool and the LBV sent back down to remove the test cap. During recovery to the surface the WROV accidentally removed the basket lid from the hinges and the recovery was a bit hair-raising.
With the new cap removed from the torque tool the LBV was sent back down. This time David was able to get into the module and remove the test cap. Now the LBV had to be recovered to the surface for fitment of the replacement cap. Once again, the LBV was sent down. Just as before, David navigated into the module and installed the new cap: Two down, one to go.
The third module was close and plans were quickly made to move on to the final installation. Utilizing the same techniques as the second manifold the LBV was sent down. A small mirror was attached to the torque tool see around the corner to determine if a blind cap was fitted or tube end. It was discovered that a tube end was fitted, which was there to protect the threads. David easily managed to remove the tube end and after recovery to the surface, the LBV was re-deployed to install the third and final cap.
With all modules successfully repaired there were very happy individuals, as literally millions of dollars in recovery and re-installation work was avoided. The production could now begin. Comments were made several times that small ROVs have never been used at such depths for such precise and complicated work. It was a great accomplishment for all involved.