The International Association of Drilling Contractors published new well control guidelines for geothermal wells in May, giving operators a geothermal-specific framework for drilling, completion, intervention and permanent abandonment. The IADC Geothermal Well Control Guidelines mark a new chapter in the group's broader Geothermal Well Construction Guideline, which is still being written chapter by chapter.
"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 its Well Control workgroup. Deer said the goal was not to rewrite oil and gas well control rules but to build "a geothermal-specific knowledge base that people could draw from."
The guidelines build on the committee's first chapter, a geothermal well classification system published in early 2025. Douglas Gourlay, Senior Drilling Engineering Advisor at H&P and chair of the IADC Geothermal Committee, said the classification chapter set common definitions and temperature and pressure characteristics for each well class, and that well control "was one of the first groups to build off of this classification."
Temperature pushes past standard equipment ratings
Geothermal wells can exceed 300°C (572°F), while oil and gas wells are already classed as high-temperature above 150°C (300°F). Standard oil and gas downhole electronics, measurement-while-drilling tools and rubber elastomers are typically rated to only 175-180°C. That gap, plus the thermal cycling geothermal wells undergo, can fatigue materials and cause equipment failure or a loss of well integrity. Deer said the industry sees "a lot of wells that exceed the temperature ratings of our industry's standard equipment," adding that the temperature ranges remove the predictability drillers rely on in conventional operations.
Aquathermal events drive the pressure risk
The guidelines tie temperature management directly to pressure management. In geothermal wells, fluid behavior follows a thermodynamic balance rather than simple fluid weight, and even a small drop in hydrostatic pressure can flash superheated water into steam, a rapid volume expansion the guidelines call an aquathermal event. Where oil and gas well control focuses on containing high formation pressure, geothermal wells are typically underpressured, so the danger is a sudden pressure drop rather than a kick. Deer said an aquathermal event "can happen so violently and so quickly" that it can tear equipment apart with "no real controllability to it." He said a well cannot be killed with mud weight the way an oil and gas well can; cooling it too fast can collapse the steam column and create a vacuum that collapses the casing or the open hole.
For sub-hydrostatic formations, the guidelines recommend underbalanced operations to control fluid influx at the surface. For overpressured formations, they recommend managed pressure drilling to control the annular pressure profile without triggering lost circulation. Operators must also maintain two independently validated barrier envelopes: a primary hydrostatic fluid column, and a secondary set of mechanical barriers such as the BOP stack, casing strings, wellhead and cemented sections. The guidelines call for pressure-testing the mechanical barriers before operations start and real-time monitoring of annulus pressure during them.
Training requirement adds a geothermal-specific layer
The guidelines also mandate geothermal-specific well control training for Class 3 wells and above, on top of accredited oil and gas well control training, with ongoing testing, drills and on-the-job evaluation of personnel. Deer said only a few instructors worldwide currently have geothermal well control experience, and said the fundamentals carry over from oil and gas but the cause and effect differs: oil and gas wells run on hydraulics, he said, geothermal wells on temperature.
Three more chapters, covering drilling rigs and equipment, drilling technology, and well design, are still being written. Gourlay said the full Geothermal Well Construction Guideline is expected by the end of 2026 or early 2027, though he called the delivery timeline "somewhat fluid." Chapters will be released separately as they are completed.
