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Glossary
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Aquifer: permeable body of rock containing water. The most superficial aquifers contain fresh water used for human consumption. The ones at greater depth are filled with salty water that is unsuitable for any human needs. These are called saline aquifers.
Brine: very salty water, i.e. containing high concentration of dissolved salts.
Caprock: impermeable layer of rocks that acts as a barrier to the movement of liquids and gases and which forms a trap when overlying a reservoir.
CCS: CO2 Capture and Storage.
CO2 plume: spatial distribution of the supercritical CO2 within the rock units.
CSLF: Carbon Sequestration Leadership Forum. An international climate change initiative that is focused on the development of improved, cost-effective technologies for the separation and capture of carbon dioxide and its transport and long-term safe storage.
Enhanced Oil Recovery (EOR): a technique that improves oil production by injecting fluids (like steam or CO2) that help mobilize the oil in the reservoir.
EU Geocapacity: a completed European research project that assessed the total geological storage capacity that exists in Europe for anthropic CO2 emissions.
GESTCO: a completed European research project that assessed the geological storage possibilities of CO2 in 8 countries (Norway, Denmark, UK, Belgium, Netherlands, Germany, France and Greece).
IEA-GHG: International Energy Agency – Greenhouse Gas R&D programme. An international collaboration which aims to: evaluate technologies for reducing emissions of greenhouse gases, disseminate the results of these studies, and identify targets for research, development and demonstration and promote the appropriate work.
Injectivity: characterizes the ease with which a fluid (like CO2) can be injected into a geological formation. It is defined as the injection rate divided by the pressure difference between the injection point inside at the well base and the formation.
IPCC: Intergovernmental Panel on Climate Change. This organization was established in 1988 by WMO (World Meteorological Organization) and UNEP (United Nations Environment Programme) to assess the scientific, technical and socio-economic information relevant for the understanding of climate change, its potential impacts and options for adaptation and mitigation. IPCC and Al Gore were awarded the Nobel Peace Prize for 2007.
Lithostatic pressure: the force exerted on a rock below ground surface by the overlying rocks. Lithostatic pressure increases with depth.
Microseismicity: slight tremor or vibration in the earth's crust, unrelated to earthquakes, which can be caused by a variety of natural and artificial agents.
Natural analogue: naturally occurring CO2 reservoir. Both leaking and non-leaking sites exist, and their study can improve our understanding of the long-term fate of CO2 in deep geological systems.
Overburden: the geological strata lying between the reservoir cap rock and the land surface (or seabed).
Permeability: property or capacity of a porous rock to transmit a fluid; it is a measure of the relative ease of fluid flow under a pressure gradient.
pH: measure of the acidity of a solution, where pH 7 corresponds to neutral.
Porosity: percentage of the bulk volume of a rock that is not occupied by minerals. These gaps are called pores and they can be filled by various fluids; typically in deep rocks this fluid is salty water but it can also be oil or gas like methane or also naturally formed CO2.
Reservoir: body of rock or sediment that is sufficiently porous and permeable to host and store CO2. Sandstone and limestone are the most common reservoir rocks.
Supercritical: the state of a fluid at pressures and temperatures above critical values (31.03 oC and 7.38 MPa for CO2). Properties of such fluids are continuously variable, from more gas-like at low pressure to more liquid-like at high pressure.
Well (or borehole): a circular hole made by drilling, especially a deep hole of small diameter, such as an oil well.
Going further:
Source: The European Network of Excellence on the Geological Storage of CO2
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