Potential upgrade strategy of lift boats or crane vessels to P&A jackups

In a low offshore price market environment, the day rate for a standard jackup rig is very low and all units are competing for similar jobs independent on their generation. To guarantee a sufficient utilization rate in the near future against these units it is beneficiary to position with a multipurpose jackup design in the market, which can be utilized in multiple offshore segments.

The prospective challenges in reducing the costs for the decommissioning of production platforms might be a good reason for the demand of such a unit. As shown in the figure below, one main issue is an uneven high decommissioning cost distribution between P&A and structure removal. Further, the involvement of multiple entities for P&A and structure removal leads to the requirement of a big operator’s project management team. This drives the current market leaders for decommissioning of platforms to integrate in their portfolio the P&A working scope horizontally in their business model with a low expenditure allocation towards P&A. 

Based on a strategy with already available assets, it is beneficial having a multipurpose jackup, which is a living quarter or a crane vessel dependent on the market demand. To realize such a business case, major reinforcement of current lift boat designs should be avoided to make these units still cost-effective to be used as living quarters. Dwellop has been realizing such an approach with the GMS Evolution 6104, which has been equipped with a C-shaped P&A cantilever design. The abandonment of the complete interior cantilever equipment brings the weight down below 400mt and offers a horizontal pipe deck capacity of 120mt. Equipped with a transversal skidding system, the unit is capable intervening a 3x3 well slot pattern with a 2,5m well spacing as illustrated in the picture below.

To increase the flexibility of the vessel, the P&A cantilever package has to be a modularized plug & play design. When the P&A package is not required, it is stored in the harbor. This even opens the possibility to upgrade available units in the market and allows an easier entry of decommissioning companies to the P&A market.

 The following design shows a different concept of a rigless P&A package with a fully equipped cantilever, which makes the design less independent from the vessel interior outfitting. The cantilever package requires a very small and effective footprint with reduced bending moments induced in the hull. It avoids additional high costs to reinforce the hull of current lift boats and even keeps the low fuel costs for these self-propelled units. This is mainly accomplished by the hydraulic driven P&A package. It allows minimizing the amount of steel for the mast and distributing the main loads of the cantilever between the two skidding units, which avoids big bending moments inside the cantilever. This fact reduces the forces acting on the beams, which makes an upgrade of potential lift boats feasible. In addition, the hydraulic concept increases the variable deck load (VDL) capacity due to lower centre of gravity compared to conventional hoisting systems.

For the modular design, it is recommendable to locate all necessary equipment for P&A inside the cantilever except the mud pumps and active tanks. The integration of the mud farm and mud pumps inside the lift boat in combination with the living quarter capacity improves further the utilization of such a unit as support for light rigless P&A technology on top of downgraded production platforms, which are not accessible by a cantilever. On the other hand, the cantilever also has to be light enough to make the assembly of the P&A cantilever as less complicated as possible.

The total weight of the P&A cantilever for the assembly is designed not to be heavier than 400mt. In the case of a suitable crane vessel with accessibility to the stern side, the crane is able to equip itself with the P&A cantilever package and even can be used to transport the drill pipe boxes similar to the SWIFT10 design from the P&A cantilever to the supply boats. The horizontal racking boxes for different pipes sizes up to 9 5/8” are modularized and allows tripping times of 450 m/hr for a Super Single, which has already been approved by Shell. It reduces the number of required lifts and does not require a lifting permit. However, the boxes can also be handled without any problem by a small deck crane on a lift boat. As back up for the pipe boxes, a slide and wireline roller system can be used to mechanically transport the pipes single by single to the pipe deck.

 A potential upgrade to a hybrid unit for coiled tubing jobs increases its operational envelope and safety by performing all operations as standard procedures and reducing its assembly time for various different well intervention operations. The versatile design is permanently equipped with an injector head in the mast, but also allows dissembling the coiled tubing drum from the cantilever rear as shown in the drawing below. By integrating a vertical automated racking system for drillpipes on the C-side, the view from the driller’s cabin to the well center is free and allows performing P&A operations with a minimum amount of workers on the rig floor. Additional, the drill pipes do not occupy the pipe deck, which keeps the non-productive time as low as possible. Beyond the P&A scope, the rigless hoisting system is also able to perform life well intervention similar to a snubbing unit, which further increases its operational envelope towards production enhancement.

 The main features of such modularized P&A cantilever designs open the possibility to increase the operational envelope of existing lifting boats or to enhance the lifting boat designs to make the potential upgrade possible. This multi-purpose approach accomplished by Dwellop and Herrenknecht Vertical might be a good starting point to integrate the P&A package in the business structure of decommissioning market leaders such as crane or accommodation contractors. However, such major upgrades to existing vessels lead to an integrity stress check of the potential lift boat by the vessel designers, because it needs to be reverified and certified by DNV/ ABS.