| dc.description.abstract | Today there are 6944 wells drilled on the Norwegian Continental Shelf (NCS) [3]. All of these wells have to be permanently plugged and abandoned in the future. This will come at an estimated cost of £35- £104 billion (410-1200 billion NOK) [2]. Plug and abandonment (P&A) is therefore a costly liability for oil companies on the NCS, and a focus has been on reducing cost of permanent plug and abandonment (PP&A). The standard NORSOK D-010 is used for the requirements of well integrity in drilling and well operations, which also include PP&A. The length requirements in the standard are based on historic practices. This causes a discussion on these requirements. Creeping shale is a material that is relatively new to be used as a well barrier element (WBE). The material properties of shale, shale being a term for argillaceous rocks, are favorable for use as a barrier. It is also a material that comes with no material cost. In contrast with cement, creeping shale is ductile and will have self-healing behavior. In addition, the permeability of shale can be extremely low, in the nanodarcy scale, 1000 times less than a perfect cement job. This gives ground to allow for a shorter barrier length of creeping shale than the traditional cement.
The debate about continuous versus cumulative verified bond quality is also a hot topic in the industry today. The concept of stacking external barriers is done over an interval where the cumulative length of acceptable bond quality reaches the NORSOK D-010 length requirement. Allowing stacking of barriers over an interval, will reduce risk, cost and time. it will give an even more robust solution. | |
