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Geothermal well introduction

What is a geothermal production well? 

A geothermal production well produces fluid heated by the natural heat of the earth. Geothermal fluids may be steam or hot water and in California have total dissolved solid concentrations of up to 250,000 parts per million (about seven times above sea water). Very hot geothermal fluids may be used for electrical power generation. Cooler (but still quite hot) geothermal fluids are used for projects such as space heating, aquaculture, snow melting, food processing, dehydration, and hot tubs and spas.

How is a geothermal well drilled?

High-temperature, Water-dominated ReservoirsThe methods and equipment used to drill geothermal wells in high-temperature, water-dominated reservoirs are very similar to those used to drill oil and gas wells. Conventional rotary drilling rigs and drilling equipment are used and drilling fluid—also called drilling mud—is circulated through the well to bring the cuttings back to the surface and to cool the well.

Steam-dominated Reservoirs 
Because conditions in steam-dominated reservoirs differ significantly from those in water-dominated reservoirs, drilling procedures do as well. In a steam-dominated reservoir, a typical well is drilled with drilling mud to a point above the first anticipated steam entry. Then high-pressure air is used. Mud would plug the fractures and pore spaces in the formation and much less steam would be produced.

Low-temperature Water-dominated Reservoirs
As conditions in low-temperature, water-dominated reservoirs usually are similar to those found when drilling water wells, the same equipment can be used and water can be substituted for drilling mud as the circulating fluid.