Terminology

Generic terms

• Accident: event that affects completely and directly humans and environment in a negative manner.
• Impact: an impacting phenomenon that occurs for sure. An impact, as presented and defined through the GEOENVI project, is an unavoidable consequence of the geothermal project. Disturbance and nuisance are inconveniences caused by geothermal activities. For purpose of classification, we identify disturbance and nuisance as an impact.
• Impacting phenomena (or dangerous phenomena) = event that might possibly have damaging consequences over human or environment, resulting from the emergence and occurrence of a critical event linked to geothermal operations
• Life cycle assessment (LCA): Life-cycle assessment is a method to assess environmental impacts associated with all the stages of a product's life from raw material extraction, through materials processing, manufacture, distribution, use, repair and maintenance, and disposal or recycling. This includes operation of the technology/facility/product as well as all upstream processes (i.e., those occurring prior to when the technology/facility/product commences operation) and downstream processes (i.e., those occurring after the useful lifetime of the technology/facility/product), as in the ‘cradle to grave’ approach. LCA aims to compare the full range of environmental damages of any given product, technology, or service
• Risk:  In a given place and time, combination of the probability of occurrence of an event, the stakes and the vulnerability. A risk, as presented and defined through the GEOENVI project, is characterized by an event, more or less predictable, resulting from geothermal operations and generating potential consequences on human and the environment (ecosystems, atmosphere, and underground water).

Environmental issues terminology

• Abandonment (of a well): well abandonment is the last step of a well lifecycle including: well plugging, monitoring of the cement plug and testing of efficiency and well head removal. It shall isolate all permeable and prevent contamination of  freshwater  aquifers and leakage  of  any  wellbore  fluids  to  the  surface.
• Aggression or Extreme natural event: extreme flooding, storm or landslide and so on that were not anticipated in the building parameters of the geothermal operation. It also includes vandalism.
• Alteration of living conditions: long-term modification of lifestyle with no life-threatening consequences.
• Aquifer alteration (including drinking water aquifer): modification of aquifer (chemical, thermal or other). The aquifer can be used for drinking water or for agriculture or for nothing.
• Aquifer depletion (including drinking water aquifer): decrease of fluid reserve that jeopardize resource durability. The aquifer can be used for drinking water or for agriculture or for nothing.
• Binary plant: a geothermal electricity generating plant employing a closed-loop heat exchange system in which the heat of the geothermal fluid (the "primary fluid") is transferred to a lower boiling point fluid (the "secondary" or "working" fluid). The heat causes the second liquid to turn to steam, which is used to drive a generator turbine. 
• Biodiversity alteration: fauna and flora loss or deterioration.
• Blowout: sudden and uncontrolled eruption of gas or fluid at the surface
• BOP: Blow out Preventer, device used to seal well to prevent blowout. Device used in geothermal or oil&gas wells.
• Buildings & infrastructures (consequence on): damage to buildings along public and private buildings including the geothermal power plant.
• Climate change (consequence on): emissions during geothermal operation that contribute to global climate changes.
• Construction work (punctual work): work related to the construction of the surface structure of the geothermal operation (well platforms, geothermal plant and other surface planning and layout).
• Corrosion: deterioration and damaging of tubing, cements and other impermeable barriers between the well and the surrounding rocks and aquifers or of the surface tubing due to a reaction between the material and the geothermal fluid.
• Cultural and natural reservation: surface implantation that de facto, in some context, use land in protected area and can also cause modification of surface water (geothermal or not) organization.
• Decommitment: cover the work carried out during site decommitment (decommitment of surface installation, plugging of well, monitoring of the cement plug and testing of efficiency, removal of well head, security of well and safety facilities installed)
• Degassing: emission of geothermal gas such as H2S or hydrocarbon gases (CO2, N2, etc.) in the atmosphere deliberately or by accident.
• Dry steam plant: take high-pressure hot water from deep inside the earth and convert it to steam to drive generator turbines. When the steam cools, it condenses to water and is injected back into the ground to be used again. Most geothermal power plants are flash steam plants. 
• Effect of operations: the category gathers risks and impacts caused by geothermal operations that concerns mainly surface operations but not only. It includes many impacts related to traffic caused by operations, to the effect of power plants at the surface or to general disturbance.
• Flash steam plant: use steam directly from a geothermal reservoir to turn generator turbines. The first geothermal power plant was built in 1904 in Tuscany, Italy, where natural steam erupted from the earth.  
• Geomechanical disturbance: phenomena that modify the physical properties and characteristics of the rock.
• Geothermal loop (primary loop/ secondary loop): the circuit made by fluid circulation. The primary loop contain geothermal fluid. In binary system, a secondary loop contain a second fluid that has a lower boiling point and is used to generate heat or electricity. In flash system, only one loop exist. 
• Geothermal plant: plant that use underground hydrothermal resources at various temperature and depth to produce electricity and/or heat.
• Global warming potential (GPW): GWP is an index, based upon radiative properties of well-mixed greenhouse gases, measuring the radiative forcing of a unit mass of a given well-mixed greenhouse gas in today’s atmosphere integrated over a chosen time horizon, relative to that of CO2. The GWP represents the combined effect of the differing lengths of time that these gases remain in the atmosphere and their relative effectiveness in absorbing outgoing infrared radiation. The Kyoto Protocol ranks greenhouse gases on the basis of GWPs from single pulse emissions over subsequent 100-year time frames.
• Ground elevation: subsidence or uplift of the ground caused by geothermal operations.
• Induced seismicity: earthquake caused by anthropic activities such as geothermal activities.
• Interconnection of aquifers and disturbance of non-targeted aquifer: connection between two or more aquifers, that may result in aquifer pollution and disturbance by intrusion of mud, inhibitors, fine particles and hot geothermal fluids into non-targeted aquifers.
• Lack of knowledge on geological properties (rock and fluid): lack of preliminary investigations or wrong interpretations that lead to bad estimation of properties of formation and fluid from the geothermal reservoir. The geological and geothermal hazards (hydrodynamic, geochemical and geo-mechanical) also play an important role in miss-interpretation of data and “surprises” during operations over a geothermal site and exploitation.
• Land use: surface implantation of the geothermal plant, including well and transport pipes, that de facto use land (agriculture and farming, tertiary, natural habitat, etc.)
• Leak due to surface installations/operations, explosion: leaks on the surface circuit or surface water reservoir and retention site that can rarely generate explosion.
• Liquid / solid effusion and wastes: effusion of wastes from well drilling and well operations includes cuttings, mud, underground water, geothermal fluids or other liquid and gases (HC, CH4, etc).
• Marine and freshwater pollution: all kind of pollution (chemical, thermal…) of shallow to surface water plans (rivers, lake, wetland, etc.), oceans and their related ecosystems (corals and all flora and fauna present over the ocean floor)
• Non-condensable gases (NGC): The gases that do not condense at the same pressure and temperature conditions as water vapour but remain in the gas phase
• Particulate matter: diesel fuel, dust etc.
• Planned operations: causes mostly related to impacts. These causes are inherent to geothermal project. Some of these causes can be considered as either an operation or a phase of a project (e.g. exploration) during which an impact or risk can occur.
• Pressure/flow changes in reservoir: It concerns the changes in pressure and flow of the targeted aquifer (i.e. hydro-mechanical modifications). This is the case with simple well operation (no reinjection) or partial reinjection of geothermal fluid or low permeability reservoirs.
• Psychological impact: long and short term. May be caused by explosions, induced seismicity, visual and noise disturbances etc;
• Radioactivity: spontaneous transformation of unstable atoms, called radionuclides that release particles and energy in the form of radiation. In geothermal water, some natural radioactivity is sometimes present.
• Reinjection: Underground injection of geothermal fluids, cooled after heat extraction, typically close by the extraction area
• Resource consumption:  Energy, water, material used during the life cycle project.
• Scaling: accumulation of deposit in the surfaces that are exposed to the geothermal fluid.
• Stimulation: a treatment performed to restore or enhance the productivity of a well. This treatment can be done by injecting water at a certain pressure (hydraulic stimulation), by thermal shock injecting cold water in hot rocks (thermal stimulation), or by dissolving some deposited minerals (chemical stimulation).
• Surface disturbances (noise, vibration, dust, smell, land use and visual, etc.): eneric term that include all type of disturbance of neighbours. Vibration can be caused when drilling or because of acting pumps, noise is important during the drilling phase, the operation and work-overs, smell can be caused by motor oil, engine or plant operation. The visual impact concerns mostly the drilling bit installed and dust material can be caused by traffic or during ground operations.
• Surface emission from underground: concern all risks and impacts related to underground operations that have effects at surface. While the source of the phenomena is located underground, the resulting impacts are on surface.
• Surface and underground equipment default: covers tubing, cement and all instruments and well equipment as well as surface tubing, pipes, pumps etc.
• Surface wastes production: this impact only concerns wastes produced by surface operations (e.g. motor oil, construction material waste, broken and used materials etc.)
• Tank: a metal or plastic vessel used to store or measure a liquid.
• Thermal and chemical underground disturbance: this concerns temperature and chemical modifications of the aquifers and reservoirs. It include the targeted aquifer as well as non-targeted aquifers.
• Uncertain context: causes related mostly to risks. It concerns causes that are due to knowledge gap, poor engineering choices or unforeseen natural event
• Underground fluid disturbance: concern all phenomena that can affect the underground fluids. The fluid can be either the geothermal fluid or other untargeted aquifers that were crossed by the wells.
• Underground water:
• Vibroseismic method (or vibrator): an adjustable mechanical source that delivers vibratory seismic energy to the Earth for acquisition of seismic data. Mounted on large trucks, vibrators use a large oscillating mass in direct contact with the ground to put a range of frequencies into the earth. 
• Well design & engineering choices: choices of well design (completion, material, diameter, deviation, etc.) during drilling planned operations according to different parameters such as geology, target reservoir, depth, presence of a shallow aquifer…
• Well testing: covers all work of well testing providing reservoir information (from short and long injection or production well testing to tracer test, interferences tests, fluid and gas sampling)