In geothermal drilling application, one of the challenges faced by drilling engineers is the optimization of drilling bit which govern the key success of drilling performance. It should be aligned with recent key performance indicator such as meet the subsurface target comprehensively while optimizing the drilling cost. A typical formation in geothermal wells that consists of various types of volcanic and igneous rock should be identified carefully because the high range of hardness and abrasiveness value will respectively affect the bit. Hence, the improvement of conventional drilling bit should be carried out to enhance the drilling performance.

For so many years, Tungsten Carbide Insert (TCI) bits were implemented in the geothermal drilling application because it is believed to be the most effective bit to drill hard formation. However, the TCI bits are limited by the maximum revolution the bit can achieve before the bearing seal fails. In some application, it needs 3 to 4 TCI runs to finish 9.875-in section. Some of the bits were also pulled out of the hole with undergauged condition due to formation abrasiveness. Implementing a conical diamond element (CDE) on a PDC can increase the bit durability. CDE provides significant improvement of wear and impact resistance to the bit. The point loading of this cutter is more concentrated to the formation, allows the bit to remove the rock in more efficient way. It has been discussed that the CDE bit can improve the ROP and meterage drilled, eliminating the tripping time due to bit changes as it does not have KREV limitation, and has a better trajectory control.

Usually, 3-5 TCI bits were used to drilled 9.875-in section in one of geothermal well located in Hululais Field, Sumatera, with average meterage of 200 – 250 m per bit. Drilling dynamics FEA modeling was performed prior to the run of CDE bit to check the drill string vibration and provide stable drilling parameter roadmap for this bit. A CDE bit was run to drill this section and the result was excellent by drilling 600 m in a single run. The ROP was improved by around 35% compared to the maximum TCI's ROP. The bit generated less reactive torque fluctuation compared to TCI, allowed the bit to have better directional control. The CDE bit was pulled out of the hole with good dull grading (2-1-WT-A-X-I-CT-TD). By improving the ROP and eliminating the tripping time, the drilling cost can be reduced.

With the downturn of oil and gas business, geothermal projects in Indonesia is raising. CDE bit is becoming a breakthrough to optimize the drilling operation in by substituting TCI runs with huge amount of potential cost savings.

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