How are wells drilled?

Answer 1

Geothermal production wells are drilled by large drilling rigs. A large bit is used, with water circulated into and out of the hole to remove the stuff drilled out. Long sections of pipe are screwed together to form the shaft. Eventually, the well must be drilled sideways, instead of straight down, to actually get steam from the reservoir (which is usually not a very thick area). To do this, a slight ramp would be placed at the bottom of the well, to start angling the bit in the desired direction. Typically, at this point another company would attach a sensor to the shaft right after the drilling bit, so that the location of the bit can be determined underground. With a series of these ramps, the bit can slowly be redirected to whatever direction is wanted.

Once the well is drilled, a liner is hung. A solid liner is usually used to several thousand feet, after which a slotted liner is used, to allow steam into the well.

Although depths will vary, these wells are typically drilled 5000 - 12000 feet or more. Running a drilling rig will typically cost over $100,000 a day, with a month or two necessary to drill a well.

Note that these wells are not needed for residential geothermal installations. A well such as what is described above is likely to provide 40,000 pounds of steam an hour at a pressure of several atmospheres, and would likely contain harmful gases that would need to be treated. One or two of these wells could provide enough power to power a small town.