The intermediate phase on South Mahakam (SMK) field presented technical and economical challenges due to multiple bit runs, attributable to thick carbonates with Unconfined Compressive Strength (UCS) up to 30K psi. The typical phase is either 12-1/4" or 8-1/2", reaching 1600m long with 90% containing the carbonates. Initially, different configurations of 8-1/2" Polycrystalline Diamond Compact (PDC) bits with durability in mind were selected but failed to deliver performance with more than 1 run required. Poor post-run dull gradings were observed reflecting broken/worn out cutters, and even blades ring out.

A recent campaign on SMK introduced two new 12-1/4" bit designs. First, a Hybrid bit (Roller Cone – Fixed Cutter PDC) was selected following a positive global experience on hard formations. A second trial involved a PDC with a Conical Diamond Element profile in the secondary cutter row – aimed to deliver high loading point to fracture hard formations and ease drill out. Both designs managed to drill the section in 1 run and delivered record speed.

The Hybrid bit managed to deliver at an almost double Penetration Rate (14.9 m/hr) than previous runs. Its durability was however limited by the seal life of the Cone. During run, a real-time monitoring of parameters and Minimum Specific Energy (MSE) was performed to detect for failures. Despite the precautions, a seal was damaged and the bit was undergauged. A control trip was triggered eliminating the cost saved for drilling in 1 run.

Conversely, the PDC with secondary conical elements delivered higher performance (29.6 m/hr) with dull grading allowing for a re-run under the same conditions. The bit became the standard for SMK, continuously delivering the phase in 1 run, a saving of 5 days.

This paper will analyze the cause of the Hybrid bit damage and how parameters monitoring did not pick up failure signals. It will also highlight the success of the bit conical elements in terms of practicality and effectiveness for drilling hard carbonates in SMK.

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