Abstract
At some point, an oil or gas well inevitably shifts from asset to liability, whether the result of reaching its economic limit, sustaining irreparable damage or being a disposable exploratory well. At the end of its life cycle, a well must be plugged and abandoned (P&A); while adhering to regulatory and environmental standards, its supporting infrastructure must be carefully dismantled to ensure that it poses no safety or environmental threats and any useable components salvaged to help defray costs. In addition to creating significant safety and environmental hazards, failure to properly abandon a well can lead to a noncompliant status with regulatory agencies and undermine an operator's image. Despite its multiple liabilities, abandonment offers no real return on investment (ROI), underscoring the importance of minimizing cost while still ensuring a safe and regulatory compliant operation. One of the main challenges is to retrieve the wellhead without damage so that it can be used again.
Clearly wells in onshore or shallow water offshore environments present little difficulty in accessing the wellhead and carrying out the required P&A operations. However the most challenging wells to P&A are deepwater wells where the wellhead is located on the ocean floor often at considerable depth so that physical access to it is infinitely more challenging. In this subsea environment there exist two different approaches to the problems associated with well abandoned and wellhead recovery. These involve internal cutting of the surface and conductor casings combined with either internal or external latching of the wellhead.
In this paper the authors will review these two different approaches, comparing their viability and describe in detail the external latching system which offers some distinct advantages in the P&A process. They will go on to provide some detailed case studies which illustrate its’ successful use in various deepwater offshore operations.
