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What are Geothermal Wells?

What are Geothermal Wells?

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Geothermal drilling

Geothermal wells are wells which tap into the natural geothermal energy found beneath the Earth’s crust. Geothermal energy is thermal energy generated and stored in the Earth. Thermal energy is the energy that determines the temperature of matter. Earth’s geothermal energy originates from the original formation of the planet, from the radioactive decay of minerals, from volcanic activity, and from solar energy absorbed at the surface. Geothermal wells have been used for several decades as an adjunct to existing heating and cooling systems. The systems are designed to use the Earth’ s relatively constant subsurface temperature along with a heat exchanger to either add to or remove heat from a dwelling.

 

What is Geothermal Electricity?

Even though the surface of Earth can get quite cold at times, the area beneath the Earth’s crust has a relatively stable temperature and it is usually very hot. Geothermal energy utilizes this heat to generate electricity called the ‘Geothermal electricity’ and to provide heating to various structures. The energy can either be used directly, in the form of geothermal wells which connect to sources of water and steam heated by the earth, or indirectly, in the case of systems which pump water through hot regions under the Earth’s crust.

 

What are the different types of geothermal wells?

Geothermal wells also known as geo exchange systems have 2 basic designs. They are:

  • Open looped system: in an open looped system, ground water is pumped from water well into a heat exchanger located in a surface dwelling. The water drawn from the earth is then pumped back into the aquifer through a different well, or in some cases the same well. Alternatively, the ground water could be discharged to a surface of water body. In the heating mode, cooler water is returned to the earth, while in the cooling mode, warmer water is returned.
  • Closed loop system: In a closed loop system, an opening (either borehole or trench) is made in the earth. A series of pipes are installed into the opening and connected to a heat exchange system in the dwelling. The pipes form a “closed loop”, and are filled with a heat transfer fluid. The fluid is circulated through the piping from the opening into the heat exchanger and back. The system functions in the same manner as the open looped system, except there is no pumping of ground water. 

 

How is geothermal well constructed?

The methods and equipment used to drill geothermal wells are similar to those used to drill oil and gas wells.

  • High-temperature and Steam-dominated Reservoirs: The drilling fluid-also called drilling mud-is circulated through the well to bring the cuttings back to the surface and to cool the well.  After a well is drilled, often beyond 5,000 feet, steel pipe, called casing, is cemented in place by pumping cement into the annulus (space between the casing and the rock formation). The casing and cement prevent fluids in different zones from mixing with each other or with the produced fluids. It is essential to cement all of the annular space behind the casting. Cement prevents the casing from expanding when heated and helps prevent corrosion.
  • Low-temperature, Water-dominated Reservoirs: Wells in low-temperature, water dominated reservoirs are usually less than 1,000 feet deep. Typically, the well is cased and cemented to appoint above the production zone to prevent polluted surface waters coming from contaminating shallows, water-bearing zones. The standard for this type of well resemble those for other water wells. 

 

How many geothermal wells are there and how much water is produced?

There are about 470 steam wells and 230 high-temperature, hot wells in 10 high-temperature geothermal fields in California. In 2005, over 324 billion kilograms of water was produced from these wells. In addition, there are several hundred low-temperature geothermal wells in the state for which the Division has no records.

Who regulates the wells in US?

The Division regulates all high-temperature geothermal wells on private and state lands. The U.S. Bureau of Land management regulates all high-temperature geothermal wells on federal lands, except for wells on U.S. Navy and Marine bases, which are regulated by the Department of the Navy.

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