Beneath the volcanic highlands of West Java, drill bits don’t last long. The geothermal formations there — dense, abrasive, punishing — have a way of grinding conventional equipment into retirement long before a section is complete. For drillers, that means costly trips to surface, replacement hardware, and lost time in rock that won’t wait.
So when a new kind of bit — built around conical diamond elements rather than the roller cones that dominate geothermal drilling — was sent down into that same rock, no one was predicting records. What came back up told a different story.
Why geothermal drilling is so brutally hard on equipment
Geothermal reservoirs aren’t just hot — they’re hostile. The formations that host them are typically volcanic and pyroclastic rock, materials that rank among the hardest and most abrasive that drillers encounter anywhere in the industry. Every rotation of a bit in that environment is a small act of attrition.
The pressure to drill fast isn’t purely about efficiency. Reservoir sections in geothermal wells are prone to formation breakouts and swelling clays — conditions that worsen the longer a hole sits open. Operators want to drill each section in a single continuous run, without pulling the string to swap hardware.
Traditional roller cone tungsten carbide insert (TCI) bits are the industry standard for volcanic rock, and for good reason. Their design, though, includes bearing seals with a finite lifespan measured in revolutions. Push a TCI bit far enough and the bearing fails — at which point the entire drill string must be tripped to surface, the worn bit replaced, and the assembly run back down. In deep geothermal wells, that sequence can consume days and significant cost.
A diamond geometry designed for the toughest rock
The conical diamond element bit takes a fundamentally different approach. Built on a polycrystalline diamond compact (PDC) platform, it replaces flat cutters with a three-dimensional conical geometry on each cutting element — a design change that alters how force is applied to the rock.
Rather than scraping across a broad surface, each conical element concentrates force onto a single small contact point. This technique, known as point-loading, fractures high-compressive-strength rock far more efficiently than conventional flat PDC cutters. Because the CDE bit is a PDC-based design, it carries no moving or rotating parts — no bearing seal to fail. The reliability constraint that limits TCI bits in long sections simply doesn’t apply.
The design also addresses a persistent trade-off in hard-rock cutting: impact resistance and wear resistance are typically difficult to achieve together. CDE geometry is engineered to provide both, which matters in abrasive volcanic formations where bits face multiple failure modes simultaneously.
Field results: two sections, two single runs, one surprising outcome
The test case was a well in the West Java geothermal field, where CDE bits drilled two separate sections. The first, a 12.25-inch section, covered 660 meters. The second, a 9.875-inch section, reached 799 meters. Both were completed to total depth in a single run.
During drilling, both bits demonstrated the capability to exceed 50 meters per hour in rate of penetration. Drillers deliberately throttled back to 20–30 m/h to manage hole cleaning — a practical constraint, not a limitation of the bit itself. Even at that controlled pace, the CDE bits achieved a 20% higher rate of penetration compared to offset wells drilled with conventional TCI bits.
The most notable detail came when the bits were pulled from the hole. Both were assessed at dull grades of 0-0 and 1-1 — effectively near-pristine condition. Retrieving a bit in re-runnable shape from hard volcanic rock is an unusual result, with direct implications for future well costs.
What faster drilling actually means in dollars
Speed and reliability translate directly into cost. On this single well, the combination of faster penetration rates and eliminated bit-trip time produced approximately $398,000 in drilling cost savings.
Bit trips rank among the most expensive non-productive time events in any drilling operation. Pulling and rerunning a drill string in a deep geothermal well can stretch well beyond hours, and rig time is never cheap. The reusable condition of the retrieved bits adds further forward-looking savings — fewer replacement bits need to be purchased for subsequent wells, reducing procurement costs on top of operational gains already realized.
For geothermal energy — a source whose development economics are heavily front-loaded — shaving nearly $400,000 from a single well’s drilling budget represents a meaningful shift in project feasibility.
A small bit with larger implications for geothermal energy
Geothermal energy is increasingly recognized as a stable, baseload renewable source capable of generating power around the clock regardless of weather. High upfront drilling costs have consistently slowed its expansion, making it harder to compete with other renewables on a development-cost basis.
The West Java results suggest CDE technology may be applicable well beyond a single field. Many volcanic geothermal reservoirs around the world share similar hard-rock geology, and the conditions that made this trial successful aren’t unique to Indonesia. The technology isn’t yet proven across the full range of geothermal environments, and a single field trial is a starting point rather than a conclusion. But if subsequent wells in other volcanic fields produce comparable results, the case for rethinking the industry standard will be difficult to ignore.
Carlos is an engineer with strong expertise in technical and industrial topics. He previously worked at international companies such as Siemens and speaks Spanish, German, English, and Italian.
