Abstract: In view of the low window-opening rates/failures in window-opening caused by the thick and strong casings used in deep/ultra-deep wells, poor formation drillability, and the tendency of cutters to wear out prematurely, we have innovatively designed a strong double-action lateral-cutting drill bit for forming windows. In this design, we considered the stability of the drill bit during the window-opening drilling and the uniformity of load distribution. The crown of the drill bit was thus designed with a depressed cone-double-arc surface and a columnar surface. The design was based on the concept of having " equal cutting, power and wear" in the cutters, and a layout with cutters arranged in a spiral and vertically staggered pattern; the resulting drill bit is capable of cutting laterally through metals in a highly effective manner and drilling through rock at high speeds. The processing and fabrication of this novel window-opening drill bit were completed via research on proprietary processing techniques, and field tests on this drill bit have also been performed. The results of these tests have shown that the novel drill bit developed in this work has 2.6 times the window-opening efficiency of conventional grinder-type milling cones for window-opening, due to its optimized cutter layout, flat contour profile, shorter cutting surface, lower aspect ratio, stronger lateral cutting forces at the window, and the fact that it produces large sheet-shaped iron shavings when it cuts through the tubular casings of a wellbore. Hence, the use of this novel drill bit reduces the time required to open windows as well as the associated costs, and this drill bit is highly suitable for window-opening and lateral drilling operations in the hard strata of deep/ultra-deep wells.

Key words: deep wells, window-opening drill bit, drill bit design, drill bit processing, strong lateral-cutting, lateral drilling for window-opening