A New Advance in Window Exit Milling Using Aluminum Casing

Abstract Two methods are commonly used to produce window exits in multilateral wells. One implements premilled window technology, while the other involves steel casing milling. Steel casing milling generates steel cuttings that can be challenging to circulate to surface during wellbore cleanout and can hinder equipment in subsequent downhole operations. Premilled windows eliminate steel debris; however, they require that the main bore casing string be oriented. This paper describes an additional approach that does not create steel milling debris nor requires orientation of the casing string, which can result in significant time savings and risk reduction. This approach involves an all-aluminum casing exit joint (hereon referred to as ACE joint) coupled to a lower coupling with a latch profile in which service tools can be landed to perform junction construction. This new technology, including design rationale, development, installation procedures, subsequent testing, and field trial results are discussed within this document. The ACE joint was designed, manufactured, and deployed in a multiwell, TAML 5 multilateral field development containing bilateral and trilateral wells. To create the window exit, the ACE joint and latch coupling are made up to the main bore production casing and cemented in hole. An orientation tool is then run in hole (RIH) and latched into the joint latch coupling, obtaining coupling orientation. The whipstock and mill assembly is then configured at surface to the desired millout orientation, RIH, and latched into the ACE joint for subsequent milling operations. Lab testing has been performed to qualify the ACE joint for suitable milling performance, corrosion resistance, and drilling wear resistance; all with positive results. Field installations have also been successful, with bi and trilateral wells having laterals exceeding 2000 m in length being created without problem. The tests and field installations demonstrate the ACE joint is now a proven technology, confirming the window geometry post millout to be acceptable for lateral drilling and completion operations. This new approach to window millout technology represents an improvement to existing steel casing milling technology, providing a more suitable solution for removal of milling debris and a more simple installation process.