Drilling the 12¼-in hole in southern Kuwait usually starts in a shale formation and continues through interbedded sandstone, limestone, and shale. The unconfined compressive strengths throughout the section vary from 6,000 psi to 10,000 psi. The bit types typically used in this section are six-bladed PDC bits with either 16-mm or 19-mm cutters. Because fields in the area are development fields, the main objective for the operator is to achieve the best rate of penetration (ROP) and complete the section as quickly as possible. A common objective was decided on between the operator and bit provider to design a bit to drill the 12¼-in section in one run with ROP above the current benchmark.

Different design configurations with different blade counts, cutter sizes, and cutting structures were analyzed using dynamic simulation based on finite-element analysis (FEA). The simulations were run in a dynamic environment to arrive at a design suitable to drill the application. The cutters were designed to withstand excessive wear, enabling the cutters to stay sharper for a longer interval and drill faster relative to previously used bits until the end of the run. Once the suitable bit was designed, different parameters were run in the simulation to define a set of parameters to be applied while drilling the actual well.

The offset wells had delivered ROP in the range of 83–93 ft/h. The new design drilled the entire section in one run in 8.7 hours, attaining an ROP of 108.6 ft/h. This represents an ROP improvement of 18% over the benchmark ROP, setting a new benchmark ROP for this application.

A combination of changing the bit configuration and cutter type along with the optimized cutting structure enabled the bit to last longer and drill faster than previous bits, saving the operator the cost for the associated drilling hours.

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