Carbon Capture and Storage

Definitions straight from our experts for top carbon capture and storage (CCS) and subsurface geology terms.

Carbon Capture and Storage Terms

Explore commonly used CCS terms below, check out our Carbon Capture and Storage FAQ page for more in-depth info, or visit our Carbon Storage Services page to learn more about working with us. 

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45Q is a tax credit that producers can claim for use of various Carbon Capture, Utilization and Storage (CCUS) technologies. A predetermined amount dependent on the project type can be collected for each sequestered or utilized metric ton of CO2 per year.

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Carbon Capture and Storage (CCS) Risk

Carbon capture and storage risk is the probability of an adverse outcome occurring as a result of a CCS project.

To learn more about CCS risk, read our blog "Understanding and Mitigating Carbon Capture and Storage (CCS) Risk", or download our white paper "Managing Carbon Capture and Storage (CCS) Risk".

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CO2 Resistant Cement

CO2 resistant cement is a cement blend that is specifically designed to resist to corrosive properties of injected CO2.

Class II Injection Well

Class II refers to a type of injection well that is intended to inject Class II fluids (typically brines).

Class VI Permit

The Class VI permit is issued by the U.S. Environmental Protection Agency (EPA) to regulate the injection of carbon dioxide as a part of geological storage.

CO2 Compression Facility

A CO2 compression facility is a building that contains carbon dioxide compression machinery that pressurizes the carbon before being transported via pipeline for geological storage or other utilization.

CO2 Plume

A CO2 plume refers to the physical area that a CO2 stream occupies underground.

CO2 Source

A CO2 source refers to anything that produces carbon emissions. CO2 sources can be naturally occurring (like plant respiration or volcanic eruptions) or human in origin (industrial facilities, car exhaust, etc).


Completion, also known as intelligent completion, is a type of CCS system that can monitor and control carbon storage in real time.

Depleted Oil and Gas Reservoir

A depleted oil and gas reservoir is a reservoir that used to produce oil or gas, and can now be used to trap carbon, natural gas and other buoyant fluids.


The United States Department of Energy (DOE) is a department of the U.S. federal government that manages national energy policies and governs nuclear power throughout the country. The DOE operates a database with information on proposed, currently active, and ended carbon capture and storage projects across the world.

Economic Risk

Economic risk in carbon storage is risk resulting from financial or economic factors of a CO2 injection and storage project.


Enhanced Oil Recovery (EOR) is a process that enables the extraction of crude oil that could not be extracted otherwise.


The United States Environmental Protection Agency (EPA) is an independent agency of the U.S. federal government responsible for protecting the environment. The EPA collects information surrounding CO2 storage with the Greenhouse Gas Reporting Program (GHGRP).

Fracture Pressure

Fracture pressure is the pressure present in the injection zone. The Class VI permit regulated by the EPA restricts fracture pressure to 90% of the formation's fracture gradient.

Geological Storage

Geological storage (also simply referred to as carbon storage or CO2 sequestration) is the practice of storing pressurized carbon dioxide in underground geologic formations to prevent it from escaping into the atmosphere. Common subsurface areas to store carbon include depleted oil and gas reservoirs, saline formations and non-usable coal beds.

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Injection Reservoir

An injection reservoir is an underground formation that is used to inject and store carbon. Examples of injection reservoirs are saline aquifers and depleted oil and gas reservoirs.

Injection Stream

An injection stream refers to a stream of CO2 that is being injected into an underground formation for sequestration.

Injection Zone

An injection zone is a subsurface area that collects fluids from an injection well.


The California Low Carbon Fuel Standard (LCFS) is a program in the state of California that is intended to reduce greenhouse gas emissions from fossil fuel production, industrial process, and various other sources of CO2. The LCFS program awards one credit to producers for each metric ton of CO2 reduced.

Leakage Pathway

A leakage pathway refers to a passage in which sequestered CO2 escapes from a subsurface storage reservoir. Potential leakage pathways are faults, fractures, legacy wellbores and poor well construction practices.

Liquid CO2

Liquid CO2 refers to carbon dioxide that is in a liquid state. To reach a liquid state, CO2 must be pressurized to a certain point.

Monitoring Well

A monitoring well is a well used to observe groundwater and geological information deep underground.


Measurement, Reporting and Verification (MRV) is a process consisting of several steps that allow for the measurement of CO2 emissions reduced by a singular method.

Policy and Stakeholder Risk

Policy and stakeholder risk in carbon capture, utilization and storage is risk created by regulations and regulatory bodies as well as project stakeholders like investment partners and local community members.

Saline Reservoir

A saline reservoir is a subsurface body of rock having sufficient porosity and permeability to store and transmit fluids that is saturated with saline (brine) water.

Stratigraphic Test Well

A stratigraphic test well refers to a hole or well that is drilled to gather information about the subsurface conditions.

Supercritical CO2

Supercritical CO2 is carbon dioxide that has reached or exceeded critical temperature and pressure.

Technical Risk

Technical risk in carbon capture and storage is risk arising from the technical aspects of executing a CCS project.


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Subsurface Geology Terms

Explore commonly used subsurface geology terms below.

2D, 3D, 4D Seismic

Seismic surveying can take the form of 3 different variants: 2D, 3D and 4D. 2D seismic creates a map of subsurface structures using linear survey lines, 3D seismic utilizes a grid of sensors to map a volume of subsurface, and 4D seismic demonstrates the 3D data across different time periods.


An anticline is a fold in rock (typically arch-shaped) in which rock layers are upwardly convex.


An aquifer is an underground layer of water-bearing rock that can transmit groundwater into wells and springs.


A basin refers to a depression in the crust of the Earth in which sediments accumulate. Basins usually are created by plate tectonic activity and subsidence.


Bioturbation is the disturbance of sedimentary deposits via the burrowing, ingestion, and defecation of sedimentary grains by living organisms.


Caprock is a layer of mostly impermeable rock such as shale and limestone that is typically found above reservoir rock.

Carbonate Rock

Carbonate rock is a class of sedimentary rock that consists mostly of dolomite, calcite and aragonite. Limestone and chalk are examples of carbonate rocks.


Casing refers to a pipe that is inserted into a borehole to stabilize the well, keep the oil stream pure and avoid leaching of the oil into groundwater.

Clastic Rock

Clastic rock is a type of rock formed from broken sediment fragments that came from other rocks. Sandstone, siltstone and shale are all typical kinds of clastic rocks.


CMG is used by geologists to refer to Computer Modeling Group's GEM reservoir modeling simulation software.


Completion, also known as intelligent completion, is a type of CCS system that can monitor and control carbon storage in real time.

Contour Map

A contour map is a map with multiple lines displaying areas of equal elevation. Contour maps are also known as topographic maps.

Core Analysis

Core analysis is the practice of measuring and analyzing underground formations through collecting samples using conventional (plug) analysis, whole core analysis or sidewall core analysis.


A craton is a section of continental crust that has remained free of tectonic or orogenic movement for a significant amount of time.

Depositional Environment

The depositional environment refers to an area that consists of deposited sediments. Factors such as location, climate, and precipitation can create depositional environments


Diagenesis is the change of sedimentary materials into rock, due to low-level changes in pressure and temperature.


Dolomite is a type of rock (also called Dolostone) composed chiefly (> 90%) of dolomite.

Dynamic Reservoir Model

A dynamic reservoir model is a computer run of a reservoir model over time to examine the flow of fluid within and from the reservoir. Dynamic models include the petrophysical characteristics required to understand the behavior of the fluids over time.

Effective Porosity

Effective porosity is the amount of a rock's total void space that is able to contribute to fluid flow.


Facies refers to the attributes of rock that show the origin and demonstrate that it is not the same as surrounding formations.


A fault refers to a discontinuity, fracture, or zone of fractures between two blocks of rock. Faults make it possible for these blocks to move, which can be rapid or slow.


Fibers, also known as natural fibers, are fibers that originate from geological processes.

Gamma Ray Log

A gamma ray log is a commonly used method to measure the amount of gamma rays that a formation emits.


Heterogenous refers to rock located in a reservoir or subsurface formation that has variation in the makeup.

Induced Seismicity

Induced seismicity is seismic activity caused by human actions, typically associated with saltwater injection wells. Most induced seismicity is of a low magnitude.


In-situ refers to "in the original place".


Intercrystalline refers to the area that occurs or exists between the crystals or crystallites that make up a rock.


Intergranular refers to the area that occurs or exists between the grains or granules that make up a rock.


Karst topography is a geological formation that arises from the dissolution of widespread carbonate rocks, resulting in characteristic features such as sinkholes, caves, and pockmarked surfaces.


Limestone is a type of sedimentary rock consisting mostly of calcite that forms from organic, chemical, or detrital sources.


Lithology refers to the visible characteristics of rocks such as their mineral composition, grain size, texture, and color.

Magnetometer Survey

A magnetometer survey is a research tool that uses variations in the earth's magnetic field to help geologists map underground formations.


Permeability refers to the capacity of a rock to allow the passage of fluids and is commonly quantified using units such as darcies or millidarcies.


Petrel is a software platform used for exploration and production in the petroleum industry. Petrel can help experts:


Petrophysics refers to the study of rock properties and how they interact with fluids. Petrophysics is often used to examine underground reservoirs.

Phreatic Zone

A phreatic zone is a subsurface zone of soil or rock in which all pores and interstices are filled with fluid.


A plateau is a flat, elevated landform that rises sharply above the surrounding area on at least one side.


Porosity denotes the proportion of pore volume or void space within a rock, which can potentially hold fluids.

Precambrian Basement

Precambrian basement refers to rock of Precambrian age composed of igneous or metamorphic rocks. Basement rocks typically have different densities, acoustic velocities, and magnetic properties from overlying rocks.

Pressure Gradient

A pressure gradient can be determined by calculating the variation in pressure over a specific distance, typically expressed in units of psi/ft or kPa/m. In regions with normal pressure, there is a predictable increase in pressure as depth increases. For freshwater, the standard hydrostatic pressure gradient is 0.433 psi/ft or 9.792 kPa/m, while for water containing 100,000 ppm total dissolved solids (a common type of water found in the Gulf Coast), it is 0.465 psi/ft or 10.516 kPa/m. When the pressure deviates from this norm, it is classified as either high or low pressure.

RCAL (routine core analysis)

Routine core analysis (RCAL) is a periodic set of measurements executed on both whole cores and core plugs. Doing RCAL helps experts predict reservoir behavior and performance, and inform procedure selection.

Relative Permeability

Relative permeability refers to the ratio of the material permeability to the free space permeability (also known as vacuum permeability). Geologists can use relative permeability to find out the ability of varying fluids to flow when combined.

Reservoir Rock

A rock formation that can hold and transport fluids underground is called a reservoir rock, which is characterized by its ability to maintain enough porosity and permeability.

Resistivity Log

A resistivity log denotes the ohm-m expressed resistivity of the formation, documented as a record.

Rock Core

A rock core is a sample of a rock formation collected from the subsurface via a specialized drill bit.

Rock Matrix

The rock matrix in sedimentary rocks (such as sandstones and conglomerates) refers to the smaller interstitial particles situated between larger particles or encompassing them.


Sandstone is a type of clastic sedimentary rock characterized by predominantly sand-sized grains.

SCAL (Special Core Analysis)

Special core analysis (SCAL) is a procedure used to perform flow experiments on core plugs. SCAL allows for realistic simulation of rock properties and expansion of routine analysis measurements.

Sedimentary Rock

Sedimentary rock is created on the Earth's surface when sediments sourced from weathered rocks, biogenic processes, or solution precipitation accumulate and undergo deposition.


Seismicity is the occurrence or frequency of earthquakes in a region.


Shale is a sedimentary rock with a fine-grained texture, produced by the compaction of clay- and silt-sized particles into slim, relatively impenetrable strata.

Sidewall Core

Sidewall core analysis typically consists of measurements usually taken from the side of the borehole. Sidewall coring gives the operator flexibility when it comes to the sample location.

Static Earth Model

A static earth model is a model of a specific volume of the subsurface that incorporates all the geologic characteristics of a reservoir. Such models are used to quantify characteristics within the subsurface volume that are relatively stable over long periods of time and can, therefore, be considered static.

Structural Map

A subsurface map known as a structural map portrays the height of a specific formation, reservoir or geologic marker in space via contours, revealing folds, faults, and other geological structures in a clear manner.

Subaerial Exposure

Subaerial exposure is geological regions where the upper boundaries of rock or sediment are visible at the Earth's surface.


The subsurface refers to the stratum or strata below the earth's surface.

Sucrosic Porosity

Sucrosic porosity refers to vuggy porosity within rocks (typically dolomite) made up of sugar-like (sucrosic) granular crystals.

Tonne vs Ton

Although the words "tonne" and "ton" sound similar, there is a difference between these two terms. A tonne refers to an imperial unit of mass equal to 2,240 lbs (1,016.047 kg), whereas a ton refers to a metric unit of mass equivalent to 2,204.6 (1,000 kg) lbs.

Total Porosity

Total porosity is an equation used to determine the ratio of a rock's complete pore space compared to the bulk volume.

True Vertical Depth

True vertical depth refers to the vertical distance, measured from the drill floor or Kelly Bushing, to a single point in depth or in a well.

True Vertical Depth Subsea

True vertical depth subsea is the absolute vertical distance between mean sea level and a point in depth or in the wellbore.


An unconformity refers to a geological boundary that divides older and younger rocks, indicating a discontinuity in the geological history.

Vadose Zone

A vadose zone refers to a subsurface zone of soil or rock containing fluid under pressure that is less than that of the atmosphere. Pore spaces in the vadose zone are partly filled with water and partly filled with air.


A variogram is a statistical function that involves two points and depicts the correlation, continuity, or disparity between the sample values as the distance between them increases.

Vuggy Porosity

Vuggy porosity consists of gas- or fluid-filled openings typically found in a carbonate rock matrix that are large enough to be seen with the unaided eye. Well-connected vuggy porosity can form high permeability zones in the subsurface.

Well Log

A well log is a recording that documents one or more physical parameters within and/or around a well, in terms of either depth or time, or both.

Whole Core

Whole core analysis refers to the practice of examining the total length of a core.

Wireline Logging

Wireline logging refers to the constant measurement of geological formations to inform subsurface operation decisions.

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