Asset Retirement Obligation Series
Conductor Removal: What does it really take?
The next step in the decommissioning process is pulling the conductors and removing the topside facilities, also called the deck. While this can be done in various sequences, in this email we will address the most common process we see, and the associated costs.
Evaluating Costs Before Removing the Deck!
If you have continued your focus on planning, the deck removal process should be relatively smooth. The largest factor driving cost at this step is the derrick barge. TSB has maintained documentation on the cost data affecting the various steps in the decommissioning process for 30 years. Derrick barge costs are no exception. Below is a chart illustrating 20 years of price data for 6 commonly used barge sizes. It’s easy to see why controlling this cost is essential.
More Than One Way to Remove a Deck
Conductor Removal Using Jacks
The use of jacks will lift the full conductor length, heavier strings and following with the platform crane once the string gets within its lifting capacity. The strings are then cut into manageable sections as they are lifted and handled by the platform crane and loaded onto boats or barges for transport to shore. The spread used with this method has an obvious lower unit rate but takes more time.
Conductor Removal Using a Derrick Barge
Lifting the conductors/drive pipes utilizing the derrick barge, pulling much longer and heavier sections at a time and loading them on a material barge for transport to shore. This method saves valuable time but the asset rate is substantially higher.
Three Ways of Cutting
The above standard methods of conductor removal are possible to do in most cases while the platform is still in place. The conductors are required by regulation to be severed 15 feet below the mud line and removed. One of three ways of cutting the conductors below the mudline is normally used:
- Abrasive – Very efficient, clean, and environmentally friendly
- Mechanical – light weight and tools can be custom designed for the job
- Explosive – Fastest most efficient method of severing but can create environmental challenges due to presence of marine mammals. This method also bells (splits and expands) the cut zone. This makes it impossible to get the conductors through the conductor bell guides in the jacket. This must be considered when planning the DB capacity and time factor.
How Long Will It Take?
Once the deck has been prepped with the proper lifting attachments and the deck legs have been cut from the jacket piling, the lifting of the deck is a fairly fast process. See chart below: