Terms and definitions used in the Geological and Bioregional Assessment Program are available online.

accumulation: in petroleum geosciences, an ‘accumulation’ is referred to as an individual body of moveable petroleum.

activity: for the purposes of geological and bioregional assessments, an activity is a planned event associated with unconventional gas resource development. For example, activities during the exploration life-cycle stage include drilling and coring, ground-based geophysics and surface core testing.

aquifer: rock or sediment in a formation, group of formations, or part of a formation that is saturated and sufficiently permeable to transmit useful quantities of water.

asset: an entity that has value to the community and, for the purposes of geological and bioregional assessments, is associated with a GBA region. An asset is a store of value and may be managed and/or used to maintain and/or produce further value. An asset may have many values associated with it that can be measured from a range of perspectives; for example, the values of a wetland can be measured from ecological, sociocultural and economic perspectives.

avoidance: averting the risk by deciding not to start or continue with the activity that gives rise to the risk. For the purpose of geological and bioregional assessments, the decision not to start an activity is mandated by the locally relevant legislation.

baseflow: the portion of streamflow that comes from shallow and deep subsurface flow, and is an important part of the groundwater system

bed: in geosciences, the term ‘bed’ refers to a layer of sediment or sedimentary rock, or stratum. A bed is the smallest stratigraphic unit, generally a centimetre or more in thickness. To be labelled a bed, the stratum must be distinguishable from adjacent beds.

bore: a narrow, artificially constructed hole or cavity used to intercept, collect or store water from an aquifer, or to passively observe or collect groundwater information. Also known as a borehole or piezometer.

causal network: graphical models that describe the inferred cause-and-effect relationships linking development activities with ecological, economic and/or social values – referred to as endpoints – that are to be protected.

causal pathway: for the purposes of geological and bioregional assessments, the logical chain of events either planned or unplanned that link unconventional gas resource development and potential impacts on water and the environment.

charge: in petroleum geoscience, a ‘charge’ refers to the volume of expelled petroleum available for entrapment.

coal: a rock containing greater than 50 wt.% organic matter.

conceptual model: an abstraction or simplification of reality that describes the most important components and processes of natural and/or anthropogenic systems, and their response to interactions with extrinsic activities or stressors. They provide a transparent and general representation of how complex systems work, and identify gaps or differences in understanding. They are often used as the basis for further modelling, form an important backdrop for assessment and evaluation, and typically have a key role in communication. Conceptual models may take many forms, including descriptive, influence diagrams and pictorial representations.

condensate: condensates are a portion of natural gas of such composition that are in the gaseous phase at temperature and pressure of the reservoirs, but that, when produced, are in the liquid phase at surface pressure and temperature.

confined aquifer: an aquifer saturated with confining layers of low-permeability rock or sediment both above and below it. It is under pressure so that when the aquifer is penetrated by a bore, the water will rise above the top of the aquifer.

consequence: the outcome of an event and has an effect on objectives.

contaminant: a biological or chemical substance or entities that are not normally present in a system or any unusual concentration (high or low) of a naturally occurring substance that has the potential to produce an adverse effect in a biological system.

contamination: an increase in the concentration of a biological, chemical or physical property that has the potential to produce an adverse effect in a biological system.

context: the circumstances that form the setting for an event, statement or idea.

conventional gas: conventional gas is obtained from reservoirs that largely consist of porous sandstone formations capped by impermeable rock, with the gas trapped by buoyancy. The gas can often move to the surface through the gas wells without the need to pump.

cumulative impact: for the purposes of geological and bioregional assessments, total impact on endpoints from multiple stressors, and their interactions, due to multiple developments in multiple industries.

dataset: a collection of data in files and/or databases or delivered by services that comprise a related set of information. Datasets may be spatial (for example, a shape file or geodatabase or a Web Feature Service) or aspatial (for example, an Access database, a list of people or a model configuration file).

depocentre: an area or site of maximum deposition; the thickest part of any specified stratigraphic unit in a depositional basin.

development: a phase in which newly discovered oil or gas fields are put into production by drilling and completing production wells.

dome: a type of anticline where rocks are folded into the shape of an inverted bowl. Strata in a dome dip outward and downward in all directions from a central area.

drawdown: a lowering of the groundwater level caused, for example, by pumping.

driver: the major external driving forces that have large-scale influences on natural systems. Drivers can be natural or anthropogenic forces.

dry gas: natural gas that is dominated by methane (greater than 95% by volume) with little or no condensate or liquid hydrocarbons

ecosystem: a dynamic complex of plant, animal, and micro-organism communities and their non-living environment interacting as a functional unit. Note: ecosystems include those that are human-influenced such as rural and urban ecosystems.

effect: a specific type of an impact (any change resulting from prior events). For the purposes of the impact analysis for the geological and bioregional assessments, an effect is the change in node B due to a change in node A; for example, a change in vegetation removal due to a change in civil construction.

endpoint: for the purposes of geological and bioregional assessments, an endpoint is a value pertaining to water and the environment that may be impacted by development of unconventional gas resources. Endpoints include assessment endpoints – explicit expressions of the ecological, economic and/or social values to be protected and measurement endpoints – measurable characteristics or indicators that may be extrapolated to an assessment endpoint as part of the impact and risk assessment.

erosion: the wearing away of soil and rock by weathering, mass wasting, and the action of streams, glaciers, waves, wind, and underground water.

exploration: the search for new hydrocarbon resources by improving geological and prospectivity understanding of an area and/or play through data acquisition, data analysis and interpretation. Exploration may include desktop studies, field mapping, seismic or other geophysical surveys, and drilling.

extraction: the removal of water for use from waterways or aquifers (including storages) by pumping or gravity channels. In the oil and gas industry, extraction refers to the removal of oil and gas from their reservoir rock.

fault: a fracture or zone of fractures in the Earth’s crust along which rocks on one side were displaced relative to those on the other side

field: in petroleum geoscience, a ‘field’ refers to an accumulation, pool, or group of pools of hydrocarbons or other mineral resources in the subsurface. A hydrocarbon field consists of a reservoir with trapped hydrocarbons covered by an impermeable sealing rock, or trapped by hydrostatic pressure.

floodplain: a flat area of unconsolidated sediment near a stream channel that is submerged during or after high flows

flowback: the process of allowing fluids and entrained solids to flow from a well following a treatment, either in preparation for a subsequent phase of treatment or in preparation for clean up and returning the well to production. The flowback period begins when material introduced into the well during the treatment returns to the surface following hydraulic fracturing or refracturing. The flowback period ends when either the well is shut in and permanently disconnected from the flowback equipment or at the start up of production.

flowback water: the fluids and entrained solids that emerge from a well during flowback.

formation: rock layers that have common physical characteristics (lithology) deposited during a specific period of geological time.

fracture: a crack or surface of breakage within rock not related to foliation or cleavage in metamorphic rock along which there has been no movement. A fracture along which there has been displacement is a fault. When walls of a fracture have moved only normal to each other, the fracture is called a joint. Fractures can enhance permeability of rocks greatly by connecting pores together and for that reason, fractures are induced mechanically in some reservoirs in order to boost hydrocarbon flow. Fractures may also be referred to as natural fractures to distinguish them from fractures induced as part of a reservoir stimulation or drilling operation. In some shale reservoirs, natural fractures improve production by enhancing effective permeability. In other cases, natural fractures can complicate reservoir stimulation.

geological formation: stratigraphic unit with distinct rock types, which is able to mapped at surface or in the subsurface, and which formed at a specific period of geological time

groundwater: water occurring naturally below ground level (whether stored in or flowing through aquifers or within low-permeability aquitards) or water occurring at a place below ground that has been pumped, diverted or released to that place for storage there. This does not include water held in underground tanks, pipes or other works.

groundwater-dependent ecosystem: ecosystems that require access to groundwater on a permanent or intermittent basis to meet all or some of their water requirements.

groundwater discharge: water that moves from a groundwater body to the ground surface or surface water body (e.g. a river or lake).

groundwater recharge: replenishment of groundwater by natural infiltration of surface water (precipitation, runoff), or artificially via infiltration lakes or injection.

groundwater system: see water system.

hazard: an event, or chain of events, that might result in an effect (change in the quality and/or quantity of surface water or groundwater).

hydraulic fracturing: also known as ‘fracking’, ‘fraccing’ or ‘fracture simulation’. This is a process by which geological formations bearing hydrocarbons (oil and gas) are stimulated to increase the flow of hydrocarbons and other fluids towards the well. In most cases, hydraulic fracturing is undertaken where the permeability of the formation is initially insufficient to support sustained flow of gas. The process involves the injection of fluids, proppant and additives under high pressure into a geological formation to create a conductive fracture. The fracture extends from the well into the production interval, creating a pathway through which oil or gas is transported to the well.

hydraulic fracturing fluid: the fluid injected into a well for hydraulic fracturing. Consists of a primary carrier fluid (usually water or a gel), a proppant such as sand and chemicals to modify the fluid properties.

hydrocarbons: various organic compounds composed of hydrogen and carbon atoms that can exist as solids, liquids or gases. Sometimes this term is used loosely to refer to petroleum.

hydrogeology: the study of groundwater, including flow in aquifers, groundwater resource evaluation and the chemistry of interactions between water and rock.

impact: the difference between what could happen due to changes associated with development of extractive industries, such as shale gas development, and what would happen without development. For the purposes of the geological and bioregional assessments, impacts are adverse changes to endpoints that represent the ecological, economic and/or social values to be protected. Impacts can be a direct or indirect consequence of single or multiple developments. For example, an impact of unconventional gas resource development could be a decrease in the persistence of the grey grasswren.

invasive: for the purposes of the geological and bioregional assessments, refers to a species that (i) has successfully established outside its natural range as a result of human actions, deliberate or inadvertent, that have enabled it to overcome biogeographical barriers; (ii) gone on to has spread rapidly over substantial distances from sites of introduction; and (iii) has the potential to have harmful effects on components of the natural environment.

landscape class: for the purposes of geological and bioregional assessments (GBA), a collection of ecosystems with characteristics that are expected to respond similarly to changes in groundwater and/or surface water due to unconventional gas resource development. Note that there is expected to be less heterogeneity in the response within a landscape class than between landscape classes. They are present on the landscape across the entire GBA region and their spatial coverage is exhaustive and non-overlapping. Conceptually, landscape classes can be considered as types of ecosystem assets.

level of concern: rating that describes assessment of potential impacts on an endpoint in the causal network. This rating is based on evaluation of likelihood and consequence and takes into account compliance with existing regulatory controls and operational practice.

likelihood: the chance that something might happen.

management: for the purposes of geological and bioregional assessments, a coordinated set of activities and methods used to minimise and control risks.

marl: a sedimentary rock containing calcareous clay

material change: for the purposes of the geological and bioregional assessments, an expression of the severity or consequence of a change. A change that exceeds defined thresholds in terms of magnitude, extent, duration, timing or frequency that is likely to require local-scale assessment, mitigation and monitoring.

mitigation: minimising the risk by removing the risk source, or changing the likelihood or consequences of the activity that gives rise to the risk.

mudstone: a general term for sedimentary rock made up of clay-sized particles, typically massive and not fissile

oil: a mixture of liquid hydrocarbons and other compounds of different molecular weights. Gas is often found in association with oil. Also see petroleum.

operator: the company or individual responsible for managing an exploration, development or production operation

petroleum: a naturally occurring mixture consisting predominantly of hydrocarbons in the gaseous, liquid or solid phase.

play: a conceptual model for a style of hydrocarbon accumulation used during exploration to develop prospects in a basin, region or trend and used by development personnel to continue exploiting a given trend. A play (or group of interrelated plays) generally occurs in a single petroleum system.

precautionary principle: a mandate to address uncertainty and to ensure that potential impacts, though not well-defined or understood, are considered in decision making.

process: for the purposes of geological and bioregional assessments, a naturally occurring mechanism (for example, groundwater drawdown) that could change a characteristic of an endpoint.

production: in petroleum resource assessments, ‘production’ refers to the cumulative quantity of oil and natural gas that has been recovered already (by a specified date). This is primarily output from operations that has already been produced.

recharge: see groundwater recharge.

reserves: quantities of petroleum anticipated to be commercially recoverable in known accumulations from a given date forward under defined conditions. Reserves must further satisfy four criteria: they must be discovered, recoverable, commercial and remaining (as of the evaluation date) based on the development project(s) applied.

reservoir: a subsurface body of rock having sufficient porosity and permeability to store and transmit fluids and gases. Sedimentary rocks are the most common reservoir rocks because they have more porosity than most igneous and metamorphic rocks and form under temperature conditions at which hydrocarbons can be preserved. A reservoir is a critical component of a complete petroleum system.

riparian: within or along the banks of a stream or adjacent to a watercourse or wetland; relating to a riverbank and its environment, particularly to the vegetation.

risk: the effect of uncertainty on objectives (AS/NZS ISO 31000:2009). This involves assessing the potential consequences and likelihood of impacts to environmental and human values that may stem from an action, under the uncertainty caused by variability and incomplete knowledge of the system of interest.

sandstone: a sedimentary rock composed of sand-sized particles (measuring 0.05–2.0 mm in diameter), typically quartz.

sediment: various materials deposited by water, wind or glacial ice, or by precipitation from water by chemical or biological action (for example, clay, sand and carbonate).

sedimentary rock: a rock formed by lithification of sediment transported or precipitated at the Earth’s surface and accumulated in layers. These rocks can contain fragments of older rock transported and deposited by water, air or ice, chemical rocks formed by precipitation from solution, and remains of plants and animals.

sedimentation: the process of deposition and accumulation of sediment (unconsolidated materials) in layers.

seismic survey: a method for imaging the subsurface using controlled seismic energy sources and receivers at the surface. Measures the reflection and refraction of seismic energy as it travels through rock.

shale: a fine-grained sedimentary rock formed by lithification of mud that is fissile or fractures easily along bedding planes and is dominated by clay-sized particles.

shale gas: generally extracted from a clay-rich sedimentary rock, which has naturally low permeability. The gas it contains is either adsorbed or in a free state in the pores of the rock.

spring: a naturally occurring discharge of groundwater flowing out of the ground, often forming a small stream or pool of water. Typically, it represents the point at which the watertable intersects ground level.

stress: the force applied to a body that can result in deformation or strain, usually described in terms of magnitude per unit of area, or intensity.

stressor: for the purposes of geological and bioregional assessments, a stressor is a physical, chemical or biological agent, environmental condition or external stimulus that might contribute to an impact.

structure: a geological feature produced by deformation of the Earth’s crust, such as a fold or a fault; a feature within a rock, such as a fracture or bedding surface; or, more generally, the spatial arrangement of rocks.

surface water: surface-expressed waters that are either permanent or ephemeral.

tight gas: tight gas is trapped in reservoirs characterised by very low porosity and permeability. The rock pores that contain the gas are minuscule and the interconnections between them are so limited that the gas can only migrate through it with great difficulty.

toxicity: inherent property of an agent to cause an adverse biological effect.

trap: a geologic feature that permits an accumulation of liquid or gas (e.g. natural gas, water, oil, injected CO2) and prevents its escape. Traps may be structural (e.g. domes, anticlines), stratigraphic (pinchouts, permeability changes) or combinations of both.

unconfined aquifer: an aquifer whose upper water surface (watertable) is at atmospheric pressure and does not have a confining layer of low-permeability rock or sediment above it.

unconventional gas: unconventional gas is generally produced from complex geological systems that prevent or significantly limit the migration of gas and require innovative technological solutions for extraction. There are numerous types of unconventional gas such as coal seam gas, deep coal gas, shale gas and tight gas.

water allocation: the specific volume of water allocated to water access entitlements in a given season, defined according to rules established in the relevant water plan.

water system: a system that is hydrologically connected and described at the level desired for management purposes (e.g. subcatchment, catchment, basin or drainage division, or groundwater management unit, subaquifer, aquifer, groundwater basin)

water use : the volume of water diverted from a stream, extracted from groundwater, or transferred to another area for use. It is not representative of ‘on-farm’ or ‘town’ use; rather it represents the volume taken from the environment.

well: typically a narrow diameter hole drilled into the earth for the purposes of exploring, evaluating, injecting or recovering various natural resources, such as hydrocarbons (oil and gas), water or carbon dioxide. A well is sometimes known as a ‘wellbore’.

well barrier: envelope of one or several dependent barrier elements (including casing, cement, and any other downhole or surface sealing components) that prevent fluids from flowing unintentionally between a bore or a well and geological formations, between geological formations or to the surface.

well integrity: maintaining full control of fluids (or gases) within a well at all times by employing and maintaining one or more well barriers to prevent unintended fluid (gas or liquid) movement between formations with different pressure regimes, or loss of containment to the environment

well pad: the area of land on which the surface infrastructure for drilling and hydraulic fracturing operations are placed. The size of a well pad depends on the type of operation (for example, well pads are larger during the initial drilling and hydraulic fracturing than at production).

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