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Atlas Copco considers the importance of pressure in geothermal drilling

Demand for faster and more efficient geothermal drilling could be met by using higher pressure compressors, according to Atlas Copco Portable Energy product marketing manager Dmitry Karablinov.

“Two very different forms of pressure are shifting the landscape of geothermal drilling,” he said. “While commercial pressure requires faster drilling, engineers are re-examining the operating pressures they require from their compressors in order to meet these rising demands.

“Until recently, the accepted norm for operating pressure had settled at 25bar, which was perfectly acceptable for water well drilling where average wells are between 100m and 150m in depth and most jobs could be completed in a single day.

“However, conventional geothermal drilling applications require companies to make two holes in one location. Unlike water well applications, geothermal drilling is happening far below the water table, where back pressure slows down the drilling process.

“In a competitive market with rising labour costs, companies are therefore seeking faster drilling techniques.”

Karablinov believes that the answer lies in the use of 35bar compressors but cautions that the drive for productivity has to be balanced against the need to reduce fuel consumption.

Atlas Copco recently carried out field trials in Sweden which confirmed that drilling at a higher speed from the beginning reduces fuel consumption compared with starting at a lower pressure.

“The aim was to drill two geothermal wells, each 200m in depth,” said Karablinov. “The first hole followed the conventional approach of drilling at 25bar for the first 50m, 30bar up to 100m and 35bar for the final 100m. The second was drilled at 35bar throughout.

“From the start, drilling at 35bar achieved a greater depth more quickly than the conventional approach. By the time the conventional approach reached 50m, the higher pressure drilling had reached 72m and went on to complete the 200m hole in three hours and 55 minutes, a task which took five hours and 35 minutes using the conventional approach.

“Although the higher pressure drilling used more fuel while working, it finished the job at 321litres, whereas the conventional drilling continued for a further one hour and 40 minutes and eventually finished at the point where 357litres of fuel had been consumed.”

Atlas Copco believes that the test showed that speed of drilling and fuel efficiency no longer need to be mutually exclusive.

“In the real world, the result is that operators can complete a job in one day that would have previously taken more time,” said Karablinov. “This operational efficiency enables them to move to another location the following day.

“The additional 10bar of pressure allows users to drill deeper below the water table. This is important for geothermal, coal bed methane and exploration drilling, where you need to drill faster and operational efficiency has utmost importance. These are major considerations when the drilling depth exceeds 150m, and when drilling is occurring against a high water table.

“Overall, we expect higher pressures can give more benefits for deep geothermal drilling, but that is yet to be established. Greater potential lies not in increasing pressure, but in optimisation. In other words, the goal is to set optimal pressure and flow for specific well design and soil conditions. In this way it is possible to address the major drilling objectives, which could be minimisation of costs, higher speed and different manageable trade-offs.”

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