Module handling system widens scope for subsea interventions from Helix vessel

March 10, 2016
Helix Well Ops (UK) Ltd. has expanded the subsea intervention capability of the monohull MSV Seawell, the oldest vessel in the company's fleet.

Jeremy Beckman

Editor, Europe

Helix Well Ops (UK) Ltd. has expanded the subsea intervention capability of the monohullMSV Seawell, the oldest vessel in the company’s fleet. Since 1987, Seawell has performed riserless light well intervention (RLWI) in the North Sea and elsewhere for programs ranging from logging, light perforation and zonal isolation to decommissioning of live and suspended subsea wells.

The vessel deploys the company’s subsea intervention lubricator (SIL), a single-trip, riserless system that can access large bore subsea wells. The SIL’s hydraulic control system is connected to the topsides’ hydraulic generation and distribution equipment and also interfaces with the client’s subsea systems and subsea trees.

Recently, Helix commissioned a new module handling system (MHS) from Royal IHC to enable deployment fromSeawell of the company’s larger, third-generation 73⁄8-in. SIL, in addition to the more established 51⁄8-in. SIL. Unlike the vessel’s previous derrick system, which could only handle the smaller SIL in several separate pieces, the MHS can stack up the complete 73⁄8-in. SIL and deploy it to the seafloor in a single lift.

IHC’s solution is a taller, integrated steel tower construction supporting the various systems for handling subsea equipment, with twice the payload capacity of the old derrick. The main hoist’s 150-metric ton [165-ton] capacity also facilitates handling of christmas trees (XTs).

MSV Seawell prior to refit. (All images courtesy Royal IHC)">MSV Seawell prior to refit. (All images courtesy Royal IHC)

The MHS accommodates storage of the SIL, fully assembled and tested, on a pallet on the parking position, saving rig-up time offshore. A support structure with access platforms on the pallet enables lateral support of the assembly. The pallet transfers the SIL to a position above the moonpool where the assembly is lifted and lowered through the splash zone by two cursors, with four guide wires preventing unintended movement of the SIL. Two pod-line systems then guide the SIL control umbilical and kill line to the seabed. Active heave compensation allows the pod- and guide-line winches to effect a swift and secure landing, and disconnection.

Following award of the contract in February 2014, IHC designed, constructed, assembled, tested, and commissioned the structure entirely in-house, with installation completed in June 2015. “It was a tight fit to get the new [larger] tower fitted on theSeawell,” said lead engineer Jurgen Zijlmans, “but that turned out well due to our engineering efforts and QA/QC checks prior to the installation.

“At that time the vessel was undergoing a comprehensive refit at the Damen Vlissingen yard in the Netherlands which included installation of new engines and work on the diving spread. After removal of the old derrick structure, the area around the moonpool was also modified to accommodate the new tower structure. Installation of the tower, skidding system and main winch on deck, and of the HPU and PVU below the deck, proved to be relatively straightforward due to the collaboration between IHC, Damen and the client, with interfaces agreed early on during the project.”

Simplified maneuvers

According to Zijlmans, the MHS allows Helix to optimize the operational steps for RLWI in numerous ways. “Key to a swift and efficient deployment is the assembly and testing of the SIL kit in the harbor. The stack is then stored on the parking position and can be deployed from the vessel in a single lift offshore due to the large hook height.

“Another benefit is easier maneuvering of XTs. There are a total of nine winches in the MHS: the main hoist handles the payload, which allows for active heave compensation with an in-line heave compensator. At the same time, four guide-lines and a pod-line are kept taut to the subsea tree with tensioners. These systems are all moving simultaneously, and it is of great assistance to the operator that the control system is monitoring the equipment. The operator can thereby focus on critical elements of the operation while the system keeps an eye on system limits/boundaries.”

The controls on the new handling tower are fully redundant, Zijlmans added, with a hot standby feature to guarantee availability and reliability. “The new control cabin has two Cyberchairs for the two operators, space for the SIL operator, and a central position for communication and CCTV equipment. This way the entire operation can be monitored easily.

“In operation, six tensioners, an in-line main hoist heave compensator and several winches can be moving at the same time, all managed from an integral control system. All systems are interconnected and can be controlled from the Cyberchairs, preventing damage to the system, or accidents. In addition, the SCADA system assists the operators with pre-set alarms and provides a clear overview of the fully interlocked systems. Furthermore, the cursor system allows the SIL to be guided through the moonpool in a controlled and safe manner, even in high sea states. The system should be able to handle both sizes of SIL up to a significant wave height of 5 m [16.4 ft].

Seawell with IHC Module Handling System (main tower, SIL support structure). (All images courtesy Royal IHC)">Seawell with IHC Module Handling System main tower, SIL support structure. 

“Finally, the MHS includes a skidding system that can skid the SIL to a parking position for storage during vessel transits. When the vessel arrives at the offshore well location, the SIL can be skidded to the moonpool for deployment relatively quickly.

“Compared with handling equipment on other light well intervention vessels or rigs, ours is a truly integrated design that takes into account the constraints of an existing vessel - theSeawell - and the client’s needs: the system is optimized with regard to Helix’s equipment and the operations Helix performs. Eventually this should reduce the time taken offshore to complete intervention campaigns.”

IHC and Helix jointly developed the specifications for the MHS. “Helix’s starting point was to obtain a DNV WELL-1 and WIU-1 class notation for vessel-mounted systems associated with well intervention,” Zijlmans explained. “Basically, the MHS became a “non-drilling” drilling rig, designed according to DNV OS-E101. IHC teamed up with DNV at an early stage prior to award of the contract in order to secure these notations.” All the safety-critical passive heave compensation systems are ATEX hazardous zone rated to ensure the vessel motions can continue to accommodate well intervention operations. All the MHS’ drives are shut down should a potentially dangerous emergency shutdown situation arise.

Last month,Seawell was undergoing final preparations in port at Avonmouth, western England, before sailing to the North Sea to resume RLWI operations using the new equipment. “As far as we know, the other Helix assets are fit for work and do not need any refits,” Zijlmans said. “However, the major operational benefits that the MHS provides should also gain interest among other players in the RLWI field.”