A geothermal well is a machine system that reaches into Earth to collect natural heat for electricity, heating, or industrial use. Instead of burning fuel, it uses the temperature increase with depth to access hot rock, hot water, or steam. The well, casing, pumps, and surface equipment work together to move thermal energy from underground to where people can use it.
This makes geothermal energy valuable because it can provide steady power day and night.
Key Facts
- Geothermal gradient is the rate temperature increases with depth, often about 25 to 30 °C per km in many regions.
- Thermal energy transferred to a fluid can be estimated by Q = mcΔT.
- Useful heat transfer rate is P = Q/t, where P is power in watts.
- A production well brings hot fluid to the surface, while an injection well returns cooled fluid underground.
- Well casing and cement protect groundwater and keep the borehole stable under pressure.
- Geothermal electricity often uses steam or a heated secondary fluid to spin a turbine connected to a generator.
Vocabulary
- Geothermal well
- A drilled borehole designed to bring heat from underground rock or fluid to the surface.
- Geothermal gradient
- The increase in Earth temperature with depth below the surface.
- Production well
- A geothermal well that carries hot water or steam upward for energy use.
- Injection well
- A geothermal well that sends cooled water back underground to maintain pressure and recharge the reservoir.
- Heat exchanger
- A device that transfers thermal energy from one fluid to another without mixing them.
Common Mistakes to Avoid
- Assuming geothermal wells create heat, which is wrong because they collect heat already stored in Earth.
- Ignoring the geothermal gradient, which is wrong because depth strongly affects whether the rock is hot enough for useful energy.
- Confusing production wells with injection wells, which is wrong because one brings hot fluid up and the other sends cooled fluid back down.
- Forgetting heat losses in pipes and equipment, which is wrong because not all underground thermal energy reaches the final user.
Practice Questions
- 1 A geothermal region has a temperature gradient of 30 °C per km and a surface temperature of 15 °C. Estimate the rock temperature at a depth of 3.5 km.
- 2 Water flows through a geothermal system at 12 kg/s and cools from 160 °C to 90 °C. Using c = 4180 J/(kg °C), calculate the thermal power transferred.
- 3 Explain why a geothermal power plant may need both a production well and an injection well to operate sustainably.