Well abandonment is a major challenge in the industry from different perspectives, including costs, the amount of effort and technical difficulties involved with permanent wellbore isolation. In recent years there has been an increased focus on plug and abandonment (P&A) operations. Oil and gas producing companies have an enormous asset of wells to be decommissioned due to mature fields all over the world. The North Sea region is not an exception, as it is the mature play experiencing the wave of well decommissioning activity for the last 15 years.
In the North Sea area, nearly two thousand wells are intended to be plugged and abandoned in the upcoming 5-10 years. P&A of wells of North Sea assets is estimated to reach 50 % of decommissioning costs, including platform removals, which compromise 20 % (Vrålstad, et al. 2018). Operators are searching for new technologies that could minimize expenditures on P&A operations as there are no financial benefits from them.
Well abandonment must fulfil local government regulations, which require long-term well integrity and isolating formations between each other and from the surface. A conventional well decommissioning process might be time-consuming due to remedial cementing, casing milling and casing pulling operations with the rig installation.
The main objective of the master thesis is to investigate the ´shale-as-a-barrier´ (SAAB) technique as the alternative solution to conventional well barriers. Naturally occurring barriers may extend over hundreds of meters along the well and eliminate the need for additional sealing of the annulus. Such a technique could simplify the plugging operations and imply significant cost reductions during P&A operations.