Sarulla eyes full geothermal output recovery with mitigation technologies

A well drilled in 2023 added 20 MW, and a second one is planned for 2026.

Sarulla Operations Ltd., which operates Indonesia’s biggest geothermal plant, plans to drill more wells to bring its 330-megawatt capacity back to full strength after output dropped to 240 MW six years ago due to problems with acidic wells in North Sumatra.

The company is deploying another production well next year, apart from using acid-resistant alloy casings—specifically CR2507 Super Duplex liners—to address wells that had turned highly acidic to pH < 3.2, along with an advanced scaling clean-out method that since 2024 uses bullhead acidizing, and soon, artificial intelligence (AI)-based predictive maintenance to boost generation.

The company’s shift to digital operations involves using real-time monitoring and predictive analytics. “I can check turbine temperature and well pressure directly from my laptop or phone,” Chief Operating Officer Riza Pasiki said in an interview with Asian Power. “The next step is AI integration—using data to tell us when to replace oil, tune turbines, or optimise performance automatically.”

“Geothermal is a complex, living system,” he said. “The potential beneath the surface is vast, but our current production remains below what the reservoir can actually deliver.”

“Our main focus now is to maximise what’s already available in our concession area so that both our stakeholders and the country benefit from it,” he added.

The company did not provide a target for achieving full capacity but a well drilled in 2023 has produced 20 MW more, and the second one is planned for 2026. It is “proceeding very cautiously due to the significant costs involved,” it said in a separate statement.

At full capacity, Sarulla’s three power units produce 330 MW across four reservoirs, including Namora-I-Langit field (NIL) and Silangkitang (SIL). Whilst SIL continues to generate 110 MW reliably, NIL’s wells have been plagued by acidic fluids that corroded steel casings and cut flow rates starting in 2019.

Rather than abandoning the site, SOL used smaller acid-resistant alloy casings to keep the wells running.

“We could have abandoned the project when the fluid turned acidic, but we didn’t,” Riza said. “We installed alloy-lined pipes, and while output dropped due to smaller diameters, the wells survived—and we kept the lights on.”

The company has since applied corrosion inhibitors across surface pipelines and replaced key materials with high-grade alloys, making Sarulla the only geothermal project in Indonesia operating acidic wells economically at scale.

It also developed an in-house chemical clean-out solution—now implemented through bullhead acidizing—which removes scaling without drilling rigs or coil tubing. “We created our own formula—just pour it down the well, and it cleans itself. It has worked 100% in six wells so far,” Riza said.

The innovation has drawn interest from both local and foreign geothermal operators, including a technical delegation from Kenya that visited in late 2024.

Sarulla’s tariff with state utility Perusahaan Listrik Negara remains below benchmark levels, constraining margins as recovery costs rise. It is pushing tariff reforms and fiscal incentives through the Indonesian Geothermal Association.

“If waste-to-energy plants can get attractive tariffs, why can’t geothermal—an even cleaner and baseload renewable source—receive the same treatment?” Riza asked.

Sarulla supplies about 12% of North Sumatra’s power and 14% of Indonesia’s 2,744-MW geothermal capacity. The company is preparing to expand into the Sibual-buali field, which could add 50 MW under the 2029 national power plan.

“With better tariffs and continued innovation, we can accelerate the recovery of NIL and move forward to develop Sibual-buali,” he said. “Sarulla’s experience shows that resilience, technology, and collaboration are key to sustaining Indonesia’s geothermal future.”