Mid Nam Phong Formation in Thailand’s Sinphuhorm Field consists of hard and abrasive sandstone with unconfined compressive strengths (UCS) of 12,000–24,000 psi. Polycrystalline diamond compact (PDC) drill bits used for the 8.5-in. section through this formation were providing low rates of penetration (ROPs) and showing heavy wear, with just 50–180 meterage drilled per run. Multiple bit runs were raising drilling costs. A new drill-bit design to address these challenges is presented.

Rolling cutter (RC) 616—an 8.5-in. drill bit with 16 mm cutters that rotate 360°—is holding the ROP record in offset wells, delivering 3.1 m/h compared with the average 2.15 m/h, a 44% improvement. Rolling elements use the entire circumference of the cutting edge to cut the formation, enabling them to stay sharper and longer. Conical diamond elements (CDE), which provide improved impact strength and greater resistance to abrasive wear, replaced some of the conventional cutters. Based on this result and lessons learned, a new and more robust bit design was proposed featuring 19 mm rolling cutters and conical diamond elements. To combat the damaging vibration observed in offset wells, which could further reduce ROP and increase the likelihood of premature drill-bit and downhole tool failure, a special bottom hole assembly that combined a rotary steerable system and a downhole motor was deployed to reduce stick/slip. Comprehensive simulations provided a detailed road map of drilling parameters that were used to minimize shock and vibration.

The new 8.5in. drill bit and BHA drilled the entire section through the Mid Nam Phong Formation in one run and at a record ROP of 4.9 m/h—58% higher than the maximum rate achieved by the RC616 bit—saving 57.8 hours. The assembly also drilled an additional 179 meterage into the Lower Nam Phong Formation, eliminating the separate bit run that had been required in offset wells. The customer saved 2.9 days or USD 130,000 in total and a new standard of drilling performance was established.

The new concept of PDC bit combining 19 mm rolling cutters and conical diamond elements expands the limit of PDC bit durability drilling hard and abrasive sandstone formation. This new type of bit can efficiently drill in those challenging geological condition reducing the drilling time and cost.

This paper will discuss the application and evolution of rolling cutter bits, along with the results achieved by this bit.

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