| dc.description.abstract | Developments in drilling have opened for the construction of extended reach wells. They can have large intermediate and reservoir sections, which may need zonal isolation. To isolate the different zones, Welltec has developed an expandable metal packer, called the Welltec Annular Barrier (WAB).
The WAB can be placed inside either a preceding casing or against an open-hole formation. As the WAB is expanded into the formation, a shrink pressure will arise between the wellbore and the WAB. This will lead to a volumetric expansion of the borehole, and eventually fracture of the formation, if the pressure is large enough.
In this thesis, a comparison of the expansion of the WAB is made to a process known as autofrettage. In this process, two cylinders of different sizes are fitted together to create a stronger composite cylinder, which is caused by a shrink pressure between them and residual stresses. An equation for the shrink pressure is developed through the use of well-known equations and relations from mechanics of materials.
A model is developed where the sum of the radial deformations is used as input. It will return the resulting shrink pressure, and WAB and wellbore deformations. The maximum allowable shrink pressure and deformation sum is also presented, if formation properties are defined. The results can be used to determine if any damage will occur to the wellbore
The further the WAB expands into the formation, a higher setting pressure is created, as well as increased sealing potential. Modelling showed it has good potential to create high contact stresses. Design changes are proposed to optimize the functionality of the tool.
Qualifying placement of the WAB in an open-hole to NORSOK D-010 barrier requirement standards could help operators mitigate difficult challenges during drilling and completion, as well as reduce both capital expenditure and operational expense. | nb_NO |
