An operator is drilling exploration wells near Xanab field in Mexico's Southwest Marine region. The 8 1/2-in. hole section is difficult to drill, with damaging shocks and vibrations occurring in the hard/ interbedded Cretaceous carbonates. These formations, with relatively high unconfined compressive strength (UCS) of 15,000 to 28,000 psi combined with alternating lithologies with chert nodules, have been drilled mostly with roller cone IADC-527X bits. Although the roller cone produced vibration-free operations, suboptimal rates of penetration (ROP) and short run lengths resulted in multiple trips to total depth (TD) of the section. Attempts were made to design polycrystalline diamond compact bits (PDCs) that could endure the difficult downhole environment by increasing diamond volume per blade. However, when encountering the hard formations, high vibration levels were still causing broken cutters in the nose/shoulder areas. In a new exploration well, a new fixed cutter bit was used. The bit is equipped with stinger conical diamond elements (CDE) with an ultrathick diamond layer that improves impact resistance, along with PDC cutters. A modeling system based on finite-element analysis (FEA) was used to design a new-type eight-bladed hybrid bit by positioning CDEs and PDCs from bit center to gauge on all eight blades. The unique cutter pattern would fail the rock with a combination of plowing and shearing action. To ensure all CDEs engage the formation at the beginning of the run, the elements were positioned at a height equal to the top edge of the conventional PDC cutters. This strengthens the bit by leveraging the superior impact strength of the CDEs. To deliver sufficient torque and to keep a vertical trajectory, a rotary steerable system (RSS) was selected, with an integrated positive displacement motor (PDM) to supply additional power.
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