Publication - Independent report

Potential for deep geothermal energy in Scotland: study volume 2

Published: 13 Nov 2013

This independent study investigates the potential for deep geothermal energy in Scotland and the steps necessary for commercialisation.

Potential for deep geothermal energy in Scotland: study volume 2
Glossary

Glossary

Andesite A type of volcanic igneous rock that has small crystals and moderate silica content, and typically forms sheet-like intrusions (dykes and sills) or lava flows.
Archaean A span of geological time between 4,000 and 2,500 million years ago, representing a large part of Earth's early history.
Basalt A type of volcanic igneous rock that has small crystals and low silica content, and typically forms sheet-like intrusions (dykes and sills) or lava flows.
Basaltic-rock A general term referring to basalt and similar rocks.
Batholith A group of more-or-less contiguous intrusions that collectively form a continuous or near-continuous mass that is significantly larger than a typical individual pluton.
Buried hot granite A geological setting relevant to deep geothermal energy assessments, in which an intrusion of granite, ideally with High Heat Production ( HHP) character, occurs beneath a moderately thick (ideally 2-5 km) cover of low thermal conductivity rocks ( e.g. sedimentary rocks or low-silica igneous rocks).
Caledonian Orogeny Collective term for the structural and thermal geological events arising from closure of the Iapetus Ocean and associated collision of continents between approximately 500 and 400 million years ago.
Carboniferous Period A span of geological time between 359 and 299 million years ago.
Crust Earth's outermost layer, comprising a thin 'skin' of relatively cool and brittle rocks sitting directly on the mantle.
Devonian Period A span of geological time between 416 and 359 million years ago.
Diorite A type of igneous rock that has relatively large crystals and moderate silica content, and typically forms intrusions.
Fault A type of fracture formed when a rock mass breaks under strain and the opposing sides of the break move relative to each other and parallel to the fracture. Earthquakes occur when faults form or move.
Fracture A physical break in a rock mass.
Geothermal gradient The rate at which temperature increases with depth in the crust.
Gabbro A type of igneous rock that has relatively large crystals and low silica content, and typically forms intrusions.
Granite A type of igneous rock that has relatively large crystals and high silica content, and typically forms intrusions.
Granitic-rock A general term referring to granite and similar rocks (mainly granodiorite and tonalite).
Granodiorite A type of igneous rock that has relatively large crystals and high silica content, and typically forms intrusions. Granodiorite is usually less chemically evolved than granite.
Heat flow The movement (or transfer) of heat through the Earth. Also the standard measure of the amount of heat travelling through Earth's crust (heat flow = thermal conductivity x geothermal gradient).
Heat production ( HP) capacity The quantity of heat that can be produced by a rock through in situ decay of radioactive elements.
High heat production ( HHP) granite Granite that has an unusually high heat production ( HP) capacity. Also, the intrusion (or pluton) formed of such rock.
Joint A type of fracture formed by simple opening in a rock mass ( i.e. a crack).
Mantle The zone of the Earth immediately beneath the crust and overlying the core.
>Neoproterozoic A span of geological time between 1,000 and 542 million years ago.
Ordovician Period A span of geological time between 488 and 443 million years ago.
Pluton An intrusion of granite larger than approximately one kilometre in diameter at outcrop.
Palaeozoic A span of geological time between 542 and 251 million years ago.
Peridotite A type of igneous rock that has relatively large crystals and very low silica content, and typically forms intrusions.
Permian A span of geological time between 299 and 251 million years ago.
Permo-Triassic A span of geological time encompassing both the Permian and Triassic periods, between 299 and 199 million years ago.
Proterozoic A span of geological time between 2,500 and 542 million years ago.
Pyroclastic rock A type of igneous rock formed by explosive eruption and consisting of an accumulation of rock fragments.
Radiogenic Produced by a process of radioactive decay.
Shale A type of sedimentary rock formed of very fine-grained particles, which can be easily split along closely spaced planes.
Silurian A span of geological time between 443 and 416 million years ago.
Syenite A type of igneous rock that has relatively large crystals and moderate silica content, and typically forms intrusions.
Tectonic plate A rigid, thin segment of Earth's crust and upper mantle which moves horizontally and adjoins other plates along zones of seismic (earthquake) activity.
Tertiary A span of geological time between 65 and 2.5 million years ago. Also known as the Cenozoic Era.
Thermal conductivity A measure of the ability of a material to conduct heat.
Tonalite A type of igneous rock that has relatively large crystals and high silica content, and typically forms intrusions. Tonalite is usually less chemically evolved than granite.
Triassic A span of geological time between 251 and 199 million years ago.
Volcaniclastic rock A type of igneous or sedimentary rock formed of fragments of igneous rock.
Wacke A type of sandstone in which the detrital grains are poorly sorted ( i.e. there is a wide range of grain-sizes). Wackes typically have low proportions of pore space and low permeability compared to well-sorted sandstones.

Abbreviations

μW m -3 = microwatts per cubic metre

g cm -3 = grams per cubic centimetre

mg kg -1 = milligrams per kilogram (equivalent to ppm)

ppm = parts per million

kg m -3 = kilograms per cubic metre

HP = heat production

HHP = high heat production

mW m -2 = milliwatts per metre square

ºC/km = degrees Celsius per kilometre

W m -1 K -1 = watts per metre per degree Kelvin (one degree Kelvin = one degree Celsius)

EGS = Enhanced (or Engineered) Geothermal System

μW = microwatt


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