Abstract
Offshore Mahakam is one of the fields developed by Total E&P Indonesie. Some of the areas in this field have challenging drilling conditions consisting of hard and thick carbonates as well as interbedded carbonates, sandstone, and shale, which naturally pose a risk of high-impact damange to cutters, especially PDC cutters. These challenging zones were encountered in 12.25-in or 8.5-in hole sections, where multiple bit runs were normally required to drill to the section total depth (TD) due to a low penetration rate as a result of worn or broken bit cutters. This situation reduced the drilling efficiency in those specific areas.
The conical diamond element (CDE) bit was proposed as a means of more efficient drilling in these challenging carbonates and interbedded formations. The unique 3D geometry of the conical diamond elements, which were placed across the bit blade, provided not only a superior impact and wear resistance, but also a concentrated point load onto the formation, which failed and fractureed the hard-to-drill rock more efficiently. The CDE also featured a diamond layer that is twice as thick as that of a conventional PDC cutter, enhancing impact strength and improving overall bit durability. For the specific high-impact formation in offshore Mahakam field, the presence of the CDE would give an ultimate protection to the conventional PDC cutters and therefore preserve the bit cutter sharpness in order to maintain the performance until end of the run.
CDE bits were utilized in three (3) different areas: M, P, and J in Offshore Mahakam. One well was drilled in M and P area, while five (5) wells were drilled in J area. Most of them were used to penetrate hard and high-impact carbonates in 12.25-in section. The performance was excellent, with an ROP improvement of 101.4% in M, 82% in P, and up to 41.3% in J area (compared with offset wells). Various CDE bit designs were implemented in J area, and each design had a specific benefit which continuously improved the ROP from one well to another. In J area 8.5-in section—which has interbedding carbonates, sandstones, and shales layers—the CDE bit performed very well, drilling the section to TD in one run, eliminating two unnecessary bit trips that the offset well had experienced. Compared with the offset well, there was up to a 60% ROP improvement in the 8.5-in section.
