Historically, in CT/TT application, sidetracking through the casing requires multiple trips to effectively produce a useable window for the next directional drilling assembly. The number of trips needed depends upon the performance of the window milling system and the comfort level of the system operator.

This paper presents an innovative one trip casing exit system especially tailored for the CT/TT operation. The system includes a hydraulically set anchor which can pass through a restriction and expands to a larger diameter, a whipstock, that incorporates a hydraulically activated hinge mechanism, which provides the optimum trajectory for the mill with multiple ramps for strategically guiding the milling tool, a lead mill with tightly spiraled blades dressed with cylindrical inserts for aggressive milling action and a retrieval tool in case the system is to be recovered.

The paper will also present a detail description of validation surface test equipment for a 4 1/2" × 7" TT system, test procedure and test results. The test set up included a 90 ft. long ‘I’ beam test bed, triplex pumping unit, data acquisition system and video camera for recording the milled window profile and rat hole conditions.

The initial test objectives were

  1. to functionally test the anchor and hinge mechanism;

  2. test the TT Whipstock system inside a test fixture and successfully mill a window;

  3. evaluate various mill configurations utilizing the TT Whipstock system.

The second test objectives were

  1. to mill window in the 7"–26#, P-110 casing buried in a 3' × 3' × 40' concrete block;

  2. drift directional drilling assembly through the window consisting of 31/8" O.D. mud motor with a 3.2 degree bent housing and 33/4" × 41/8" Bi-Center bit below the motor;

  3. Retrieve the system with a hook. All of the objectives were successfully achieved.

Additionally, the paper will detail field runs of above described system along with lesson learned, conclusions and way forward.


The new TT Whipstock system offers operators a cost effective alternative to pulling production tubing from existing wells prior to performing re-entry operations. The TT Whipstock system is specifically designed to pass through the tubing ID, and once below the tubing string can be hydraulically anchored inside the casing to enable sidetracking operations. The system may be deployed on coiled tubing or jointed pipe. The TT whipstock incorporates proven system design principles of matching ramp to lead mill profile angles with multi-angle ramp configuration, (1).

Existing TT Sidetracking Systems involve multiple trips in hole to deploy the system, and then mill the window. Typically this may involve setting an anchor, surveying the orientation of the anchor, running the whipstock assembly, and finally milling the window.

The initial design criteria was for a single trip Thru Tubing whipstock system, with which the system could be conveyed in hole, orient and set the system, and mill the window in the same trip. Utilizing the principles of the mono bore single trip whipstock system a solution was formulated, (2), (3).

System Configuration

This TT Whipstock system is designed to be a true single trip system whereby the following tasks are performed during a single trip in hole.

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