Abstract
Multilateral wells offer many benefits over conventional wells, including reduced overall drilling costs, lower environmental effect, increased total recovery, greater access to production intervals, and subsequently improved well production rates. However, it can be difficult to achieve a good quality casing window through which an additional lateral branch can be successfully drilled and completed. As bottomhole assemblies (BHAs) become more advanced, involving longer and stiffer strings of tools, and as completion design becomes more intricate, more attention must be given to the way the casing window is created because this is the foundation of multilateral well design. Track-guided milling systems have emerged as effective and accurate methods by which to control casing window geometry, and this paper will focus on recent advances in track-guided, precision window milling technology and its effect on multilateral well design.
To avoid potential problems in running drilling assemblies or liner/completion strings, advanced milling technology should be used to create the casing window. During conventional milling, it is commonly difficult to control the action of the mill as it cuts through the casing; poor control creates a casing window that could, as a result of right hand rotation during milling, rolling-off to one side, leading to a skewed or shortened aperture. Uncontrolled and undefined window geometry introduces additional risks when re-entering a lateral wellbore, such as nonproductive time (NPT) and equipment damage. A good quality casing window, with precisely controlled length and width, helps ensure that drilling and completion equipment can exit the aperture without problems and facilitates repeatable re-entry access to both the mainbore and the laterals in future interventions. The quality of the casing window is just as critical in multilateral wells as in conventional sidetracking or whipstock operations.
Advances in modern casing milling technology are pioneering improved multilateral well designs. Multilateral wellbore junctions can now be placed in deep, high-angle wells without compromising drilling or completion operations by using a track-guided milling system to create improved casing windows.
