The objective of the operation was to permanently abandon the well by retrieving sections of casing and placing full-bore cement plugs across sealing formations in the subsurface. BAS-3O is a challenging well with large diameter casings and an S-shape trajectory with a sharp kick-off and a long 65-degree inclination section. Next to that, the well was originally drilled with a deviated wellhead to help with the sharp kick-off, which adds additional challenges during rig-up and when running tools.
For the operations, a large drilling rig (T-46) was selected to tackle the well challenges. The retrieval of large sections of casing required high pulling capabilities. Next to that, the placement of remedial cement plugs required high torque capabilities of the top drive.
During the first phase of the project, a Perforate-Wash-Cement (PWC) system was deployed in which the 11 ¾” was perforated and the poorly cemented annulus washed free of cement. Within the same run, a mechanical cement base and a full-bore cement plug was placed within the 65-degree deviated Zurich section, saving rig time and resources for the client.
Following the plug placement, 2800m of 11 ¾” casing was retrieved from the well. The retrieval of the 11 ¾” casing paved the way for setting the second cement plug in the Vlieland Claystone formation within the 13 3/8” casing, also at 65-degree deviation.
The subsequent retrieval of 1900m of 13 3/8” casing faced several challenges. The casing was stuck within barite solids of the original drilling Oil Based Mud (OBM). Even the large pulling capabilities of the T-46 were unable to retrieve the casing in one section. A strategy was set up to cut & retrieve the casing in several sections, for which a combined pulling & mud motor cutting BHA was used. Although the top section was quite easily retrieved, the problems persisted even with small sections of casing deeper in the well. Similar issues were faced when retrieving the 16” casing from the well. With careful planning of cutting depths and analysis of the downhole situation, the required casing sections could be removed. The well was abandoned by placing the third and fourth cement plugs within Ieper and the Rupel Clay formations.
In January 2022 the surface plug was placed and the challenging BAS-3O well had been successfully abandoned.