Geothermal

A form of renewable energy derived from heat sources below the surface of the Earth, coming from heated groundwater or heated rocks.

Geothermal Energy

An area where there is manifestation of geothermal activity on the Earth’s surface, or where there is a known geothermal reservoir.

Geothermal Field

Classification of Geothermal Fields:

1. Semithermal 2. Hyperthermal wet 3. Hyperthermal dry

It produces hot water to 100C

Semithermal Fields

Produces hot water and steam.

Hyperthermal wet fields

Produces dry saturated or superheated steam.

Hyperthermal dry fields

The hot, permeable part of a geothermal system where hot water or steam is extracted from.

Geothermal reservoir

The system encompassing from the hydrological input (recharge) from a reservoir to the output through manifestation, or directly to a plant.

Geothermal system

Elements of a geothermal system:

1. Heat source

2. Reservoir rock

4. Cap rock

4. Hydrothermal convection

The source of heat within a geothermal that occurs either as magma intrusions or rocks within remnant heat.

Heat source

Permeable and porous rock containing heated fluids.

Reservoir rock

Impermeable rock preventing heated fluids from escaping.

Cap rock

Movement of fluids due to heat.

Hydrothermal convection

What are the classification of Geothermal Systems according to MODE OF HEAT TRANSFER?

1. Convective Geothermal System

2. Conductive Geothermal System

What are the classification of Geothermal Systems according to TEMPERATURE RANGE?

1. High Enthalpy

2. Moderate Enthalpy

3. Low Enthalpy

Geothermal systems associated with regions of young volcanism characterized by the presence of a porous and previous reservoir rock at shallow to moderate depths with most of the heat being transferred by convection.

Convective Geothermal System (100 m to 4.5 km)

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.

Water dominated

Types of Water dominated Geothermal Systems

1. Hot water fields

2. Wet stream fields

Dry or superheated fields is a from of convective system that produces steam from the boiling saline waters within the deep, low permeability rock, which can generate a higher energy output.

Vapor dominated (Dry saturated steam fields)

Geothermal systems characterized by high porosity systems at hydrostatic pressure, commonly associated with sedimentary basins, with geopressured and hot dry rock systems.

Conductive Geothermal System

Types of Conductive Geothermal Systems

1. Basin

2. Oil Fields

3. Hot dry rock system

High porosity under hydrostatic pressure.

Basin

High porosity with pressured exceeding hydrostatic pressure.

Oil Fields

Low porosity conductive environment.

Hot dry rock system

A mixture of water, non condensable gases (NCGs), and a number of chemical constituents.

Geothermal Fluids

Types of Geothermal Fluids

1. Chloride waters

2. Acid sulfate waters

3. Bicarbonate waters

4. Mixed waters

Surface features which are products of geothermal processes from beneath the surface.

Geothermal manifestations

Springs heated by an underground thermal source, making the water’s temperatures higher than the air temperature.

Hot Spring

Eruptive hot springs that periodically eject fountains of heated water and steam.

Geyser

Thermal manifestations that emit mixtures of steam and other gases.

Fumaroles

A form of fumarole that emits sulfurous steams.

Solfatara

A pool of bubbling, acidic mud that can emit steams and decompose surrounding rocks into mud.

Mud pool

A nonthermal manifestation of hydrothermal or geothermal systems.

Kaipohan or Cold springs

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

Geothermometers

Types of Geothermometers

1. Alterations

2. Minerals

Silica replacement that forms from high to low temperature

Silicifiation

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

Silica sinter

Appears at conditions with temperatures greater than 200C.

Epidote

Appears at conditions with temperatures at about ~100C.

Smectite

Appears at conditions with temperatures greater than 200C.

Illite

Appears at low temperatures and alkaline environments.

Calcite

Appears at high temperatures and acidic environments.

Silica

Appears at low temperatures and acidic environment and forms when steam mixes with meteoric waters due to throttling.

Kaolinite

Appears at high temperatures and acidic environments and originates from magmatic fluids.

Halloysite/Pyrophyllite