TSB Offshore completes decommissioning studies for gas fields in the Mediterranean Sea. The studies included platforms composed of large modular topsides and fixed jackets, requiring specialized, dynamically-positioned semi-submersible crane vessels (SSCV) to lift.

TSB determined that the sheer size and weight of these platforms would result in increased complexities upon decommissioning, such as requiring a Dive Support Vessel (DSV) to section the jackets using diamond wire cutting system (DWCS) operated by an ROV. In addition, even the most capable of SSCV’s operating in the market today would be required to remove the platforms in multiple lifts.

Evolving Technology for Conventional Methods

The process for removing a platform has largely remained unchanged in the last few decades. However, TSB’s study highlights an ever-present trend in conventional fixed platforms: they are getting bigger and heavier. This is, in part, due to fact that current technology allows fixed platforms to be installed in deeper waters to tap into previously inaccessible oil reservoirs directly or through multiple subsea tiebacks. These larger structures require the heavy-lift vessels (HLV) used to install and decommission them to grow accordingly.

“As operators look to the near-future for removing these platforms, they will have to be conscious of the ever-evolving market of heavy-lift vessels.”

The largest HLV’s today can lift up to 10,000 tons. Even still, this pales in comparison with the largest fixed platforms weighing over 50,000 tons. As operators look to the near-future for removing these platforms, they will have to be conscious of the ever-evolving market of heavy-lift vessels.

Rigs-to-Reef Candidates

TSB also considered the option of a Rigs-to-Reef approach to decommission the platforms. Platform size, complexity, structural integrity and location are key considerations in evaluating its reefing potential. Structures that are more structurally complex provide more surface area for marine habitats. Platforms that are unstable, contaminated may create hazards for marine life and are generally not candidates for reefing.

“TSB has overseen the reefing of a number of structures in the Gulf of Mexico and looks to do the same in other parts of the world.”

TSB noted that, although these Mediterranean platforms would be obvious candidates for Rigs-to-Reef in the Gulf of Mexico, this approach is unprecedented in the Mediterranean. There is a lack of an established regulatory body in the Mediterranean dedicated to decommissioning, an issue that is quite commonplace throughout the world. Today, operators and governments alike are looking to companies like TSB to guide them through a potential Rigs-to-Reef process. TSB has overseen the reefing of a number of structures in the Gulf of Mexico and looks to champion the benefits of reefing in other parts of the world.