Newly launched IADC document guides best practices, training for geothermal well control

By Stephen Whitfield, Senior Editor

Geothermal wells face well control challenges different from those seen in oil and gas operations, primarily due to extreme temperatures, highly fractured abrasive rock formations and the rapid flashing of superheated water into expanding steam if hydrostatic pressure drops. This rapid flashing of steam, also known as an aquathermal event, can compromise normal well control or circulation operations.

In May, the IADC Geothermal Committee released the IADC Geothermal Well Control Guidelines, outlining well control best practices for drilling, workover and well service operations.

It establishes a comprehensive framework for managing well control risks across the entire lifecycle of geothermal wells, from drilling and completion to intervention and permanent abandonment.

“We had to set some kind of baseline with all of this,” said Toney Deer, Vice Chair of the IADC Geothermal Committee and head of the Well Control workgroup. “We weren’t trying to rewrite the rules for well control in oil and gas by any means, but we needed to have a geothermal-specific knowledge base that people could draw from.”

The well control guideline document is another chapter of the committee’s broader Geothermal Well Construction Guideline, still under development; the first chapter, covering geothermal well classification, was published in early 2025.

“Everything we’re doing with these chapters is building off of that initial classification we did last year,” said Douglas Gourlay, Senior Drilling Engineering Advisor at H&P and Chair of the IADC Geothermal Committee. “We had to ensure everyone was speaking the same language as there were various definitions being used in the geothermal space. Therefore, we had to define the classes of wells first, how to characterize them, the different temperature and pressure characteristics in each well. Well control was one of the first groups to build off of this classification. It shows what you should do with different classes of geothermal wells.”

Addressing unique geothermal challenges

The well control guideline document notes that geothermal well control practices are adapted from conventional oil and gas well control but modified to address the unique challenges of geothermal environments. In particular, pressure and temperature are critical differentiators between the two environments; understanding those differentiators is important for a company to shape an effective well control strategy.

The temperatures seen in geothermal environments can degrade downhole equipment and trigger severe thermal stress on well casings. A geothermal well can see temperatures exceeding 300°C (572°F), while oil and gas wells that exceed 150°C (300°F) are already considered high-temperature. In standard oil and gas drilling, downhole electronics, measurement while drilling tools and rubber elastomers are typically rated to 175-180°C. Additionally, geothermal wells experience substantial temperature fluctuations – also known as thermal cycling – causing materials to repeatedly expand and contract. This thermal cycling can induce material fatigue and lead to equipment failure or loss of well integrity.

“There are a lot of wells that exceed the temperature ratings of our industry’s standard equipment,” said Mr Deer, who also serves as Director of Training and Chair of Geothermal Development at the Well Control School. “Those temperature ranges take the predicted nature out of drilling. You’ve got to be prepared for that.”

Managing geothermal systems also requires specialized strategies distinct from standard oil and gas operations. The document addresses the thermal impacts on downhole tools, soft seals and the use of managed temperature or continuous circulation systems to mitigate heat.

The document emphasizes that temperature management cannot be isolated from pressure management, addressing how elevated temperatures interact with hydrostatic pressure.

In geothermal environments, fluid dynamics are dictated by a delicate thermodynamic balance rather than simple fluid weights. The document cautions that even a minor drop in hydrostatic pressure can cause superheated water to flash into explosive steam, leading to rapid volume expansion and blowout risks.

Pressure management helps prevent this from happening. While oil and gas drilling focuses heavily on containing high formation pressures, geothermal operations typically deal with underpressured formations where the primary danger is a sudden drop in hydrostatic pressure. Unlike conventional oil and gas wells, geothermal operators must manage the pressure spikes caused by aquathermal events. Maximum pressure definitions for equipment are strictly based on the highest anticipated surface pressure to maintain a reliable safety margin.

“Aquathermal events can happen so violently and so quickly. If they start tearing the equipment apart, there’s no real controllability to it,” Mr Deer said. “If you close in the well, you can’t kill it with mud weight like you can with an oil and gas well. You would have to kill the well by cooling it off. But if you cool it off too fast, it will collapse the steam column, which would create a relative vacuum. That could collapse your casing, your open hole or both. Any of those scenarios means you’ve just lost the whole asset.”

The IADC document outlines risk-tailored control methods based on a specific pressure regime, advising against relying solely on traditional heavy overbalanced mud systems. For sub-hydrostatic environments, where the fluid pore pressure is lower than the normal hydrostatic pressure, the document recommends underbalanced operations to safely control the handling of fluid influx at the surface. This helps prevent formation damage. For overpressured environments, the document recommends managed pressure drilling to allow for precise control of the annular pressure profile to prevent formation fluid influx while avoiding lost circulation.

The document also mandates a two-barrier philosophy, ensuring that at least two independently validated barrier envelopes (primary and secondary) prevent unintended fluid flow to the surface during all phases of well operations. The primary barrier is typically the hydrostatic column of drilling fluid. Its role is to exert enough pressure to control formation pressures and prevent fluid influx. It requires a documented plan to monitor for mechanical and corrosive degradation.

The secondary barrier is comprised of mechanical components and engineered structures, such as the BOP stack, casing strings, wellhead and cemented sections. These secondary barriers are only activated if the primary barrier fails.

It recommends explicitly verifying the barriers before operations start — the document suggests pressure-testing mechanical barriers and monitoring fluid levels and densities. It also recommends real-time tracking of barrier integrity, including monitoring annulus pressures for aquathermal expansion to prevent casing collapse or burst.

Human factors — in particular, the potential human errors that could lead to aquathermal events and/or well control incidents — are also recognized as a significant operational hazard.

The guideline mandates comprehensive occupational-level training programs, including geothermal-specific well control training for the appropriate well classification for Class 3 wells and above. The geothermal-specific training, which is done in addition to an accredited oil and gas well control training, needs to be individually completed and assessed. Companies are also mandated to maintain ongoing assessment and verification of personnel competency through testing, drills and on-the-job evaluations to ensure sustained proficiency.

“There are only a few instructors in the world right now that have any geothermal experience at all, and there’s a huge misconception of what it actually entails,” Mr Deer said. “People think it’s all the same as oil and gas, and that’s not correct. The fundamentals are the same, but the cause and effect of various things and how you handle the well, that’s completely different. Oil and gas wells are a function of hydraulics, and geothermal wells are a function of temperature. That’s a huge distinction.”

Three other chapters of the IADC Geothermal Well Construction Guideline, covering drilling rigs and equipment, drilling technology and well design, are still under development. That comprehensive guideline is expected to be completed by the end of 2026 or early 2027, though Mr Gourlay said the timeline for delivery is somewhat fluid. Separate chapters will become available as they are finished. DC

Click here to access the IADC Geothermal Well Classification document.

Click here to access the IADC Geothermal Well Control Guidelines.