RIASSUNTO
Abstract
Historically, the applications of window milling tools and methods were limited to remedial operations. The main bore would be sidetracked only in the event of irretrievable fish, collapsed casing, depleted reservoir, etc. In recent years however, the re-entry drilling has become an increasingly popular option for production optimization as a result of advanced developments in the milling, drilling and measurement tools and technology.
One of the important aspects of re-entry drilling is to mill a window in the existing casing and sidetrack the well bore. Past experience shows that inadequate planning for a window milling project has resulted in either an aborted attempt or premature failure in the hole.
In order to achieve a successful window milling operation, the following ten (10) points must be addressed and situations resolved prior to commencing with the casing exit operation; (1) Selection of best place to set and to orient the whip-stock, (2) Hole angle, (3) Radius of curvature (build, drop, left or right tum) in the vicinity of casing exit, (4) Whip face orientation methods (MWD, gyros), (5) Flexure characteristics of the bottom hole assembly and resulting dogleg severity, (6) Length of sidetracking assembly, (7) Depth of rat hole to facilitate drilling objective (short, medium or long radius) after milling window, (8) Casing conditions, (9) Formation types, and (10) Retrievability of whip-stock assembly.
This paper will discuss the above points in detail using data from actual field runs. The field runs will be selected from a large database of window milling jobs maintained over the last 10 years. Additionally, the paper will present recommendations and guidelines for planning a successful window-milling project.
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