Geothermal handbook: PlanninG and Financing power Generation t e c h n I c a L r e p o r t 2 / 2

temperature Gradient holes 
are shallow and slim boreholes, usually less than 500 meters
deep and less than 6 inches in diameter, drilled to measure the increase in temperature
with depth. The standard temperature gradient worldwide is around 30°C for each additional
kilometer in depth, resulting in an average temperature of 90°C at a depth of 3 kilometers.
If, in a certain area, the temperature gradient were to increase to 90°C/km, this would result
in a temperature of 270°C at a depth of 3 kilometers and would be very promising for
geothermal power generation, as long as enough steam could be extracted from
the reservoir. Gradient holes also allow the collection of additional samples of fluids for
chemical analysis. It is common to drill three to five gradient holes as part of the exploration
plan for a geothermal greenfield, especially in areas with no signs of recent volcanism. 
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