Successful Dual Casing Exits are becoming more commonplace in today's oil field. However, there are still many challenges involved with this type of work. This paper will outline the successful completion of a two well campaign carried out in the Arabian Gulf along with the problems encountered, lessons learned, the post job conclusions and the recommended way forward for future jobs.

The task for this campaign was to design, build and supply a system that would be able to set inside 4 ½" casing and successfully mill a window out of this smaller pipe into the surrounding cement then mill out through the larger 9 5/8" casing. Having milled the window through both sizes of casing, a rat hole would have to be drilled deep enough to suit the subsequent drill ahead BHA. Although these window milling BHA's were to be conveyed using pipe, like traditional TTRD exits, this campaign would utilize PDM motors to provide the rotation for sidetracking the wells.

On both occasions, the sidetracks were completed and the customer was able to continue the drill ahead operations as planned. There were many lessons learned throughout the campaign. From the initial design stages, through the manufacturing phase and finally onto the operational issues, the lessons learned were significant and will be used in the future advancement for this type of work.

This technical paper will show the importance of this campaign which, with the lessons learned, will lead to many more successful dual casing exits being carried out.


The primary objective for this campaign was to sidetrack out of the existing 4 ½" and 9 5/8" casing which would provide the customer with a long, full gauge window in each of his two wells.

The system used for both sidetracks would utilize a specially design whipstock with a multi-angled ramped surface to accommodate the window milling BHA. This ramped surface would have to be designed with the dual exit in mind as standard equipment was deemed unsuitable for this application.

The whipstock would be set in place using a hydraulically actuated expandable anchor which utilizes two sets of slip segments, set at 90 degrees apart. This configuration enables the system to center itself in the well bore during the setting sequence, ensuring a secure anchoring during the sidetracking operations.

Both dual casing exits would be carried out utilizing a snubbing unit on a floating barge in the Arabian Gulf. Drill pipe would be used to convey both the whipstock and the window milling assemblies in and out of the well bore. An MWD system would be used to ensure that the whipstock was set at the required orientation and a PDM motor would be utilized in the window milling BHA to provide the rotation for the sidetracks.

Pre-Job Planning

The pre-job planning stage is vitally important to any job and this campaign was no different. Several discussions were held between our operational staff and the customer to determine the best plans for both wells.

The original plan was to run and set the whipstocks on the drill pipe, detach the running assembly from the whipstock once set, and pull out of the well. The second BHA would contain the window mill, PDM motor, MWD and associated equipment. On both wells, the BHA's would be conveyed into the hole using a snubbing unit.

However, it was decided to run and set the whipstock and mill the first 4 feet of the sidetrack on the drill pipe. This would then be pulled from the well and the PDM would be added with the MWD to complete the window and drill the required rat hole.

The final technical proposal was presented to the customer and the plan for both sidetracks was agreed upon.

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