Abstract: A deflecting tool or whipstock is oriented and anchored in a well casing during a single trip of a running string so that a window can be formed in the wall of the casing at a selected azimuth. The angular orientation of the deflecting tool is measured, and signals representative thereof are transmitted to the surface. When the desired orientation is obtained, the anchor is actuated to prevent movement of the deflecting tool, and the orientation adjusting and measurement and transmission tools are released from the whipstock and removed from the casing by withdrawing the running string which preferably is coiled tubing. Then a downhole motor and milling bit are run into the casing on coiled tubing and operated to form a window through the wall thereof opposite the deflection surface of the whipstock so that a new borehole can be drilled outside the casing.

Abstract: Methods and systems for forming a window through the wall of a well casing to enable a new borehole to be drilled outside the casing include forming a cement plug in the casing, drilling a laterally offset hole in the cement plug, orienting and setting a whipstock in the offset hole, and using the whipstock to drill an elongated window through the casing wall opposite its deflector surface. The drilling steps employ a mud motor having a bent housing that establishes a toolface for the bit, and proper orientation is obtained by downhole measurement and transmission to the surface of orientation signals and downhole adjustment of orientation to a selected toolface value. The whipstock is oriented in the same manner. All drilling and orientation procedures are carried out on coiled tubing to reduce costs.