Well decommissioning has been shown to account for 49% of the total cost of decommissioning an offshore asset and, over the next decade, total expenditure is estimated at £7.5 billion (O&GUK Decom Insight 2018). So, what is ’well decommissioning’ or ‘well abandonment’ and why does this piece account for such a significant proportion of the total cost?
To try and answer that question, this presentation will start with an overview of well construction and consider key aspects of the well construction process that impact decommissioning.
The approach to well decommissioning is often described as ‘rocks up’. The engineers planning the abandonment have to understand the rock structures that have been drilled through to design an appropriate abandonment. This includes understanding the pressure and flow potential that may exist within the various rock formations and the strength of sealing formations that may be relied upon to isolate that pressure. With that basis, engineers must then identify what has to be removed from the well to allow suitable barriers to be installed in the wellbore.
The rig package that is required to execute the work can then be considered. On older offshore platforms the rig equipment may not be serviceable, or the rig could have been removed altogether. There may also be a need to upgrade platform facilities and utilities to support the rig operation.
For a subsea well which may have been drilled using a semi-submersible drilling unit, the starting point is to assume a similar rig but there are alternatives.
Looking ahead, there are some interesting new technologies in development that could have a significant impact on the cost of well decommissioning.
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N242, Sir Ian Wood Buildng, Robert Gordon University
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