Through the life-time of a production field in the offshore petroleum industry it is normal to drill several new wells for both production and injection purposes. The initial well template, either at the platform or at a subsea installation, has space for a fixed total number of wells. When this limit is reached an old well needs to be plugged and the well slot reused to allow new wells to be drilled.
In order to re-use well slots and benefit from full diameter when constructing the new well, it is required to remove the tubulars in the upper part of the plugged well. The outside of these tubulars are normally in contact with cement or settled particles from shut-in drilling fluids. Removing the tubular through the cement or settled particle is always challenging and there is need for using new techniques.
In order to address the dominating effects in these operations, down-scaled laboratory tests are performed. The experiments reported here are performed by pulling steel pipes out of a cemented annulus. The pipes used in the tests are down-scaled from typical casing sizes. They are either normal pipes, grooved pipes or pipes with and without collars. Two setups with different geometries are used. The first is selected to study the de-bonding effect from the cemented annulus and the mechanical friction that must be overcome to remove the pipe. The other setup is designed to show the effect of collars when pulling out the tubulars. Since most tubulars in wells have collars between each stand with extended diameter, this effect is important to consider when comparing laboratory results to field operations.
Results show that the loosening force (de-bonding) and pulling force can be significantly reduced by manipulating the pipes with grooves prior to pulling them out. Further, the results show that the most significant resistance when pulling the tubulars are caused by the collars outside the pipe. It is also observed that the effect of collar is significantly reduced when the pipe is grooved between the collars. In total these results provide improved understanding on the dominating effects when pulling pipes from packed wellbore annulus.
