No abstract

Through tubing operations currently provide oilfield operators with an attractive method for significantly enhancing production at a relatively low cost. ?This paper will present a newly developed and innovative system for initiating a production casing sidetrack below the production tubing. The system uses coiled tubing technology and blends the special techniques of both drilling and window milling operations using coiled tubing. Development details emphasized will be the overall system design, performance criteria and equipment evaluation. Introduction Sidetracking through tubing represents a special technical challenge. The casing exit equipment must first pass through the relative small confines of production tubing and then provide a platform within the larger production casing belowfor casing exit operations. This transition from a small to large tubular represents a significant obstacle to the functionality of the system. To function properly, the platform must support the loads imposed during the casing exit activity (milling) as well as provide guidance to subsequent reentry operations. Of course, as always, the technique and associated equipment must be as cost effective as possible in order to fully benefit from the through tubing aspects of this type of well intervention. Various types of through tubing sidetrack methods have been developed for meeting this challenge. To date, the largest number of exits performed utilize a cement plug. Bent downhole motor housings and bent subs are conveyed with coiled tubing and drive a mill to create a casing exit using the cement for support. 1A variation of that method consists of a cement plug with a pilot hole in which a conventional whipstock is placed. Figures 1 and 2 illustrate these methods. Both of these techniques require cement to be placed and therefore are not optimal solutions. True optimization and benefit of through tubing techniques lie in the ability to achieve an exitquickly,with a minimum number of trips in the hole,with minimal risk to the formation,that provides for repeated reentryand a quick return to production. Clearly, a system that does not require cement and does not completely block access to the casing below the platform would be an optimal situation. The only practical manner of providing such a system is to utilize robust component hardware that expands to bridge the distance across the casing bore. Through tubing whipstock systems provide the best method to date to achieve this bridging This technology is in its early stages and only a few whipstock systems are available to the industry. The following text serves to both describe a new system that has been recently developed and to document what has been determined to be the critical design issues relating to this type of casing exit technology.