Abstract:
The difficulty of milling dual casing window with ?139.7 mm is great. The key techniques are analyzed and studied, including the choice of window depth and window azimuth, the calculation of the length of the different gap as well as important nodes, the improvement of milling cones and oblique, the BHA selection, the determination of main widowing parameters, and the approach of walking along the technical casing after windowing. Some conclusions are obtained as following. The window length should be calculated or estimated before windowing. The window azimuth should be at the smaller gap between the double casings. The whipstock with large bevel angle and high beveled hardness should be taken to ensure the oblique angle. The bottom hole assembly with appropriate stiffness should chosen for windowing or test drilling, to avoid too long window because of too much BHA stiffness, which will reduce too much the devel angle of the whipstock and make the whipstock loss angle buildup capacity, and to ensure the angle holding capacity. The parameters should be timely adjusted when widowing, according to the iron, cement blocks and debris situation carried out with the drilling fluid, as well as the footage, which is the key of efficient, fast and safe windowing for dual casing.