Geothermal Energy

Geothermal Energy

A form of renrewable enerigy derived from heat source below the surface of the Earth, coming from heated groundwaters or heated rocks.

Elements of a Geothermal System

1. Heat source

2. Reservoir rock

3. Cap rock

4. Hydrothermal convection

Classification of Geothermal Systems according to Heat Transfer

1. Convective Geothermal Systems

2. Conductive Geothermal Systems

Classification of Geothermal Systems according to Temperature Range

1. High Enthalpy

2. Moderate Enthalpy

3. Low Enthalpy

Convective Hydrothermal Resources

1. Hot-water-dominated

2. Vapor-dominated

Hot Rock Resources

1. Solified (Hot dry rock)

2. Part still molten (magma)

Other Hydrothermal Resources

1. Sedimentary Basin

2. Geopressured

3. Radiogenic

Convective Geothermal System

Geothermal systems associated with regions of young volcanism characterized by the presence of a porous and pervious reservoir rock at shallow to moderate depths (100m to 4.5 km), with most of the heat being transferred by convection. It uses turbines & generators.

Water-dominated

A form of convective geothermal system produced by large volumes of groundwater circulating from the greater depths to shallow depths within a permeable reservoir at constant temperature.

Vapor-dominated

A form of convective geothermal system that produces steam from the boiling saline waters within the deep, low permeability rocks, which can generate a high energy output.

Dry or Superheated fields

Other name for Vapor-dominated convective geothermal system

Conductive Geothermal System

Geothermal systems characterized by high prosity systems at hydrostatic pressure, commonly associated with sedimentary basins, with geopressured and hot-dry rock systems. It utilizes heat transfer thru rocks and sediments.

Basin

A conductive geothermal system that is high porosity under hydrostatic pressure.

Oil fields

A conductive geothermal system that is high porosity with pressures exceeding hydrostatic pressure and comes from ancient marine organisms.

Hot-dry-rock system

A conductive geothermal system that is low porosity conductive environment. It is where water that is injected into deep hot dry rocks is heated and then pumped to the surface.

Enthalpy

A measurement of energy in a thermodynamic system. It is the heat change @ constant P. It is the total heat content of a system.

Geothermometers

Mineralization that can be used as indiicators for geothermal exploration due to their P/T condition formation.

Equilibrium Geothermometer

Geothermometer that assumes that geothermal fluids & reservoir rocks maintain a balanced state.

Non-equilibrium Geothermometer

Geothermometer that operates without considering whether the geothermal fluid is in equilibrium with the rocks.

Types of Geothermometers

1. Alteration Geothermometer

2. Mineral Geothermometer

Alteration Geothermometers

1. Silicification

2. Silica sinter

Mineral Geothermometers

1. Epidote

2. Smectite

3. Illite

4. Calcite

5. Silica

6. Kaolinite

7. Halloysite/Pyrophyllite

Silicification

Silica replaccement that forms from high to low temperature.

Silica sinter

Direct deposition of amorphous, hydrated silica, or Opal, at high temperature.

Epidote

Mineral geothermometer that appears at conditions with temperatures around 250–340°C.

Smectite

Mineral geothermometer that appears at conditions with temperatures at about ~100 °C.

Illite

Mineral geothermometer that appears at conditions with temperatures around 230–320°C.

Calcite

Mineral geothermometer that appears at low temperatures and alkaline environments.

Silica

Mineral geothermometer that appears at high temperatures and acidic environments.

Kaolinite

Mineral geothermometer that appears at low temperatures and acidic environment, and forms when steam mixes with meteoric waters due to throttling.

Halloysite / Pyrophyllite

Mineral geothermometer that appears at high temperatures and acidic environment, and originates from magmatic fluids.

Flash Steam geothermal plant

A geothermal plant that generates electricity by extracting high-pressure hot water from deep underground. As the water rises to the surface, the pressure drops, causing it to rapidly "flash" into steam. This steam then drives a turbine connected to a generator, producing electricity.

• It is less efficient when operating with lower-temperature resources.

Binary cycle geothermal plant

A geothermal plant that transfers heat from moderate-temperature geothermal water to a secondary fluid with a lower boiling point, typically a hydrocarbon like isobutane. This secondary fluid vaporizes and drives a turbine to generate electricity, while the geothermal water is reinjected into the ground. This process allows electricity generation from lower-temperature geothermal resources.

• It is more efficient and able to utilize lower-temperature geothermal resources.

Dry steam geothermal plant

A geothermal plant that uses hydrothermal fluids that are already mostly steam, which is a relatively rare natural occurrence. It uses steam directly from geothermal reservoirs to drive a turbine connected to a generator, producing electricity.

• This method is one of the simplest geothermal power technologies, requiring high-temperature steam from the ground without additional processing.