In the last two years, an operator has been performing drilling and completion from an existing well's slot to access geological targets means a sidetrack operation is conducted in a cased hole. This initiative needs to be efficient in budget-wise and regulation as well.
Cased hole sidetrack operation can be challenging, particularly when the milling assembly has to cut dual-casing due to the existing well condition and the geological target requirement. The centralizer and casing collar position inside the wellbore is considerably to select the kick-off point and optimize the well's trajectory. Besides, the work sequence and the Bottom Hole Assembly (BHA) selection are significant to avoid costly multiple trips. Moreover, a unique challenge to ensure the window is in good condition when the wireline logging job needs to conduct in an open hole.
This paper provides a case study of performance improvement of dual-casing sidetrack in 9.625 in and 13.375 in within the last 2 years. The study was started by modeling the BHA which generates the least amount of vibrations to pass through the window. Further, a comparison between a bi-mill and a tri-mill BHA includes the position of each mill and the milling parameters to achieve the most efficient result. Doglegs severity within the interval depth of setting the whipstock is also taken into account since the dogleg through the window can create additional issues. There was no casing collar locator logging job run as the tool will not able to identify the collar position in the 13.375 in the casing string. Therefore, historical data on the casing tally and the well's information has become essential for determining the whipstock setting depth.
This integrated and collaborative planning has resulted in a successful dual-casing exit operation during the last two years in Mahakam offshore. Improvements made in the engineering and operations have successfully overcome the challenge identified in the initial period of the campaign.