acid gas

A gas that can form acidic solutions when mixed with water. The most common acid gases are hydrogen sulfide [H₂S] and carbon dioxide [CO₂].

annulus return

The space between the inlet and outlet piping in an oil and gas well that allows for fluid and other drilling substances to exit.

api gravity

A measure of the relative density (weight per volume) of a petroleum liquid compared to the density of water. Oils are categorized by their API gravity as follows: extra-heavy (<15 API), heavy (15–22 API), medium (22–32 API), light (32–42 API), ultra-light (42–52 API), and condensate (>52 API).

asphalt

A petroleum product output in PRELIM that is a cement-like material obtained by petroleum processing and contains bituminous material as the predominant component. It is used primarily for road construction.

asset

An oil and/or gas field or sub-basin currently producing hydrocarbons.

associated gas

Methane or other gaseous hydrocarbons that occur in crude oil reservoirs either as free gas (associated) or as gas in solution with crude oil (dissolved gas). “Natural gas” can refer either to the methane alone or to the mixture of methane and other hydrocarbons.

bitumen

A naturally occurring viscous (thickened) mixture, such as oil sands and tar sands. These extra- heavy oils are comprised mainly of hydrocarbons heavier than pentane and may contain sulfur compounds. In its natural viscous state, bitumen is not recoverable at a commercial rate through a conventional well.

boe

Barrel of oil equivalent (BOE) is a unit of volume that equates to the amount of energy released by burning one barrel of crude oil. Typically, 5,800 SCF of natural gas is equivalent to one BOE.

bunker fuel production

Heavy fuel supplied to ships and aircraft, consisting primarily of residual and distillate fuel oil for ships and kerosene-based jet fuel for aircraft.

ch₄

The chemical formula for methane, a potent greenhouse gas.

classification bounds

The collection of characteristics used for sorting oils and gases, including API gravity, sulfur content, production volume, depth, flaring-to-oil ratio, water-to-oil ratio, and gas-to-oil ratio. The quantification of these limits is specified on the OCI⁺ Methodology page.

co₂

The chemical formula for carbon dioxide.

combustion

Part of the downstream portion of the oil and gas supply chain that entails burning petroleum products (through chemical oxidation) to generate light, power, or heat.

condensates

A light liquid hydrocarbon mixture that occurs when associated gas is present in an oil field. Lease condensates are recovered from field facilities. Plant condensates are recovered at the inlet of natural gas processing plants.

consumers responsibility

GHG emissions resulting from the end uses of oil and gas.

deep conversion refinery

Part of the midstream portion of the oil supply chain, this is a complex refinery configuration used to turn the heaviest oils into petroleum products. Techniques can involve using high temperatures and catalysts to separate (or crack) hydrocarbons and then reject the excess carbon (a process called coking) and/or add hydrogen (hydrotreating) in order to increase production of the highest-value petroleum products.

decommissioning

The process of ending oil and gas operations, which includes plugging and abandoning old wells as well as closing other aging assets.

depleted reservoir (oil and gas)

A depleted reservoir can be defined as a reservoir in sub-surface sand or rock formation that has previously produced oil or gas and its production volume is in significant decline.

diesel production

A petroleum product output in PRELIM that is composed of a blend of distillates obtained from refining. Diesel is primarily used as transportation fuel for freight trucks and heavy-duty vehicles. The boiling point and specific gravity are higher for diesel fuels than for gasoline.

dilbit

Bitumen diluted with one or more lighter petroleum products, typically natural gas condensates such as naphtha, to make it easier to transport in a pipeline.

distillates

A general classification for one of the petroleum fractions produced in a refinery’s distillation operations. Distillates include diesel fuels and fuel oils.

downstream

The end of the oil and gas supply chain that involves transporting petroleum products to markets and putting them into end use, including, but not limited to, combustion.

dry gas

Gas from a well that produces little or no condensate or natural gas liquids but rather is mostly pure methane. Also known as lean gas.

emissions drivers

The particular characteristics that are most likely responsible for increasing the GHG emissions from the production of an oil or gas compared to other factors. These categories are flaring, land use, production steam, venting, fugitive methane emissions, pumping, upgrading, petcoke combustion, refinery heat, refinery hydrogen, liquefaction, natural gas power, and other end use.

end use

A general term for the part of the downstream portion of the oil and gas supply chain that involves the consumption of all petroleum products, whether they are combusted, used as feedstock for consumer products, or otherwise marketed.

enhanced oil recovery (eor)

A general term for chemical, thermal, and other practices and techniques required to extract oil and gas from fields as they deplete, using pressure, injection, heat, and steam.

extraction

Part of the upstream portion of the oil and gas supply chain that entails drilling, fracturing, mining, or otherwise accessing oil and gas resources.

field depth

The depth of an oil or gas field, measured in feet to the well bore. For vertical wells, this is equal to the depth below the surface. Offshore wells are measured from the ocean floor. For inclined or horizontal wells, this depth can exceed the vertical depth below the surface.

flaring

The process of combusting and disposing of associated gas that is produced with oil, which occurs for different reasons, including emergency relief, because equipment does not exist to gather and sell the gas on the market, or the associated gas is uneconomical for sale. Flaring also occurs intermittently at gas fields under emergency conditions.

flaring efficiency

The share of gas that is completely combusted to carbon dioxide.

flaring intensity

The magnitude of flaring relative to the actual conditions modeled by OPGEE.

flare rate (or flare volume)

The amount of gas flared, measured in standard cubic feet of gas per day.

flaring-to-gas ratio

A metric comparing the volume of gas released into the atmosphere to the volume of gas produced for human use. This useful measure of upstream efficiency is reported in terms of SCF of gas flared per SCF of gas produced.

flaring-to-oil ratio

An upstream operating decision regarding the amount of gas flared for every barrel of oil produced, measured in standard cubic feet of gas per barrel.

fuel oil

One of the petroleum product outputs in PRELIM that is less refined than gasoline so it can be burned in a furnace or boiler. Fuel oil includes distillate fuels (Nos. 1, 2, and 4) and residual fuels (Nos. 5 and 6).

fugitive emissions

Unintended equipment leaks of a gas (including the potent greenhouse gas methane) into the atmosphere from the processing, transmission, and/or transportation of oil and gas.

gas-to-oil ratio

The estimated total amount of gas production associated with the production of one barrel of oil, measured in standard cubic feet of gas per barrel.

gasoline production

A petroleum product output in PRELIM that is a complex mixture of relatively volatile hydrocarbons used primarily in motor vehicles with spark-ignition engines that is produced in different amounts depending on an oil’s characteristics, the refinery configuration, and global demand.

global warming potential (gwp)

An index used to compare the relative radiative forcing of different greenhouse gases without directly calculating the changes in atmospheric concentrations. GWPs are calculated as the ratio of the radiative forcing that would result from the emission of one kilogram of a greenhouse gas to that which would result from the emission of one kilogram of carbon dioxide over a fixed period of time, such as one hundred years or shorter timeframes.

greenhouse gases (ghgs)

Those gases, such as carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), that are transparent to solar (short-wave) radiation but opaque to infrared (long-wave) radiation, thus preventing long-wave radiant energy from leaving Earth’s atmosphere. The net effect is a trapping of absorbed radiation and a tendency to warm the planet’s surface.

greenhouse gas emissions (ghg emissions)

Emissions of long-lived climate-impacting gases, measured in CO₂ equivalent (eq.) units using the global warming potential of each gas.

hydraulic fracturing

Fracturing a rock by pumping fluid into a well at high pressure. This technique can be used to extract oil or gas from rock formations, including shale.

hydroskimming refinery

Part of the midstream portion of the oil and gas supply chain, this is one of the simplest refinery configurations that separates lighter oils into its hydrocarbon components using heat (distillation) and employs other basic treating processes to remove hydrogen gas in order to make high-octane gasoline.

industry responsibility

GHG emission resulting from the oil and gas industry, including producers, refiners, processors, and shippers.

jet fuel

One of the petroleum product outputs in PRELIM that is used in jet aircraft engines. It includes kerosene-type jet fuel and naphtha-type jet fuel.

kerosene

A light petroleum distillate that is used in jet fuel and other aircraft, space heaters, cook stoves, and water heaters and is suitable for use as a light source when burned in wick-fed lamps.

land use

A variable that represents the impacts generated upstream when oil and gas production releases carbon stored in the soil and requires the removal of biomass, the latter of which engenders both foregone carbon sequestration and emissions from the decomposition of the biomass. This is one of the emissions drivers identified in the OCI⁺.

lca

Lifecycle Assessment (LCA) is the systematic set of procedures for compiling and examining the inputs and outputs of materials and energy and the associated environmental impacts directly attributable to the functioning of a product like oil and gas throughout the entire petroleum life-cycle.

lean gas

See dry gas.

liquefied petroleum gas

A petroleum product output in PRELIM that is also referred to as LPG or liquid petroleum gas and made up of a group of lighter hydrocarbon gases, primarily propane and butanes. These gases may be marketed individually or mixed. LPG excludes ethane.

liquefied natural gas

Natural gas (primarily methane) that has been liquefied by reducing its temperature to -260 degrees Fahrenheit at atmospheric pressure.

medium conversion refinery

Part of the midstream portion of the oil and gas supply chain, this is an extension of a hydroskimming refinery that separates medium-gravity oils into their hydrocarbon components using heat and pressure (vacuum distillation) as well as a process called catalytic cracking that breaks heavier hydrocarbons into gasoline, diesel, and other distillate feedstocks.

megajoule

A measure of energy that is equal to 1 million joules.

midstream

The middle portion of the oil and gas supply chain that entails refining crude oil or otherwise transforming hydrocarbons into petroleum products.

naphtha

A generic term applied to a refined or partially refined petroleum fraction with an approximate boiling range between 122 degrees and 400 degrees Fahrenheit. Naphtha can be used for petrochemical feedstock, jet fuel, gasoline, solvents, and solvents, depending on its individual characteristics.

n₂o

The chemical formula for nitrous oxide, a potent greenhouse gas.

natural gas liquids (or ngl)

A group of hydrocarbons including ethane, propane, normal butane, isobutane, and pentanes plus hexanes (also known as natural gasoline). They are components of natural gas that are liquid at surface pressure.

off-site emissions

Activities that generate GHG emissions that cross an upstream (or midstream) boundary. In terms of emissions accounting, off-site emissions are considered Scope 2 Emissions. Activities that enter the site count as additional emissions (for example, natural gas purchases) and those that are sent off-site are credited and counted as negative emissions (for example, natural gas sales).

oil assay

A chemical analysis of a crude oil that provides data for refiners to process a crude oil. The OCI⁺ requires that assays are reported in a consistent, standardized format so that they can be input into the OCI⁺ midstream model (PRELIM).

opem

The Oil Products Emissions Module (OPEM) is an engineering-based tool in the original OCI that uses emission factors and operating assumptions for calculating the GHG emissions from the transport and combustion of oil and gas products.

opec

The Organization of Petroleum Exporting Countries, which is an intergovernmental organization whose stated objective is to "coordinate and unify the petroleum policies of member countries." OPEC was created at the Baghdad Conference on September 10-14,1960. Current members (with years of membership) include: Algeria (1969-preset); Angola (2007-present); Ecuador (1973-1992 and 2007-2019); Equatorial Guinea (2017-present); Gabon (1975-1994 and 2016-present); Iran (1960-present); Indonesia (1962-2008 and 2016); Iraq (1960-present); Kuwait (1960-present); Libya (1962-present); Nigeria (1971-present); Qatar (1961-2018); Republic of Congo (June 2018-present); Saudi Arabia (1960-present); United Arab Emirates (1967-present); and Venezuela (1960-present).

opgee

The Oil Production Greenhouse Gas Emissions Estimator (OPGEE) is an engineering-based life-cycle assessment (LCA) tool for the measurement of GHG emissions from the production, processing, and transport of crude oil and gas. The system boundary of OPGEE extends from initial exploration to the refinery entrance gate (oil) or LNG terminal (gas).

petrochemical feedstock

One of the petroleum product outputs in PRELIM that is principally used in the manufacturing of chemicals, rubber, and plastics.

petroleum coke (or petcoke)

One of the petroleum product outputs in OPGEE and PRELIM that is a residue high in carbon content and low in hydrogen. Also termed “petcoke”, this coal-like substance is the final product of thermal decomposition in the condensation process in cracking.

petcoke combustion

Petcoke is produced in large amounts both upstream, when extra-heavy oils are upgraded, and downstream, when heavy and extra-heavy oils are refined. It is produced in smaller amounts when any oil is processed in a deep conversion coking refinery. Burning petcoke for heat or power generation results in higher GHG emissions than other petroleum products.

prelim

The Petroleum Refinery Life-Cycle Inventory Model, a mass and energy-based process unit-level tool for the estimation of energy use and GHG emissions associated with processing a variety of crude oils within a range of configurations in a refinery.

pumping

A variable comprising emissions from the pressure-forcing operation of various secondary-recovery techniques.

refinery configuration

A midstream decision regarding the types of processing units assembled to transform crude oil into petroleum products, including hydroskimming used exclusively for light, sweet oils; medium conversion configurations for medium, sweet and sour oils; and deep conversion configurations for heavy, sweet and sour oils.

refinery heat

Heat generated for use in refining using either refinery fuel gas or natural gas.

refinery hydrogen

Hydrogen produced for use in refining, generally for adding to low-API-gravity, carbon-heavy oils.

refining

Part of the midstream portion of the oil and gas supply chain that entails processing a crude oil and gas mixture to manufacture finished petroleum products, unfinished oils, natural gas liquids, other hydrocarbons, and oxygenates.

residual fuels

One of the petroleum product outputs in PRELIM that is a general classification for heavier bottom-of-the barrel oil residues, known as No. 5 and No. 6 fuel oils, that remain after the distillate fuel oils and lighter hydrocarbons are distilled away in refinery operations. No. 6 fuel oil includes bunker C fuel oil. Residual fuels are used for the production of electric power, space heating, vessel bunkering, and various industrial processes.

resource type

An OCI⁺ classification scheme that designates oils and gases into the following categories: extra-heavy oil, heavy oil, medium oil, light oil, ultra-light oil, condensate, wet gas, dry gas, and coal-bed gas.

rich gas

See wet gas.

scf

A standard cubic foot (SCF) is the amount of gas contained in a cube whose edges are one foot long at a temperature of 60 degrees Fahrenheit and a pressure of 101.560 kPa.

scope 1 emissions

Direct operational GHG emissions from sources owned or controlled by an organization, such as on-site electricity generation, steam, heating, cooling, pumping, shipping, and fugitive emissions.

scope 2 emissions

Indirect GHG emissions from the generation of purchased energy and materials consumed by an organization, such as imported electricity or natural gas.

scope 3 emissions

All other indirect emissions that occur across an organization’s value chain, including the end use combustion of various petroleum products.

shale gas

Natural gas produced from wells in shale formations. Shale is a fine-grained, sedimentary rock composed of mud from flakes of clay minerals and tiny fragments of other materials.

sour oil/gas

Oil and gas containing sulfur compounds such as hydrogen sulfide and mercaptans, which are deadly. A sweetening process is used to remove hydrogen sulfide and carbon dioxide from oil and gas streams. Sour gas can also contain high levels of carbon dioxide (acid gas).

sulfur content

The weight percent of sulfur in oils and gases, defined as: sweet (<0.5 percent sulfur) and sour (>0.5 percent sulfur).

sweet oil/gas

See “sulfur content.”

steam

An input needed for thermal recovery (an enhanced oil recovery technique), steam can be generated and used to heat depleted or extra-heavy resources that do not easily flow. Fossil fuels are often used to power steam generation, though solar and other renewable energy sources can be used to lower the emissions impact of steam generation.

steam-to-oil ratio (sor)

An upstream operating decision affecting the amount of steam input for thermal-oil-recovery projects. This ratio measures the rate of steam injection per barrel of oil produced in barrels of water equivalent per barrel of oil.

sulfur content

Oils in PRELIM are categorized according to the amount of sulfur they contain as follows: sweet (<0.5 percent sulfur) and sour (>0.5 percent sulfur). In the case of synthetic crude oils derived from oil sands, the sulfur content is reported after the bitumen is upgraded into synthetic crude oil. The same sulfur content can be used to describe sweet and sour gas.

synthetic crude oil (sco)

An extra-heavy oil, bitumen, or oil sand that, prior to midstream refining, has undergone extensive upstream processing and upgrading to remove a portion of its carbon (in the form of petcoke) and convert it into a synthetic hydrocarbon that simulates conventional oil.

tcm

An abbreviation for “trillion cubic meters” of gas, a volumetric measurement that is equal to approximately 35,300 billion SCF. 1 TCM = 1000 billion cubic meters (BCM).

temperature cut

The range of temperatures that corresponds to the separation of various hydrocarbons in crude oil based on their boiling points.

transportation

The movement of oil and gas between points in the supply chain, including after extraction, when crude oil is moved to a refinery, and after refining, when petroleum products are sold. Transportation GHG emissions vary with the distance traveled, modes of transport, and transport fuels used.

ultra-deep oil/gas

Oil and gas buried in depths exceeding approximately 6,000 feet, which implies that it may be necessary to consider design and/or technology alternatives.

unconventional resource

The definition of what constitutes an unconventional fuel resource changes over time with changes in technology, geology, and the market. Broadly, the term refers to oil and gas types that are not easily accessible.

upgrading

An upstream process in OPGEE that converts extra-heavy oil, bitumen, and oil sands into synthetic crude oils of varying qualities by primarily removing excess carbon and converting it into petcoke.

upstream

The beginning of the oil and gas supply chain that includes resource extraction, production, surface processing and upgrading, waste disposal, and other miscellaneous operations, as well as transporting oil and gas to the refinery or processing plant.

venting

The release of unburned natural gas into the atmosphere caused by operators circumventing closed systems and normal operating practices.

water injection ratio

The amount of water injected into a well to stimulate oil and gas production, measured in barrels of water injected per barrel of crude oil produced.

water-to-gas ratio

A metric that compares the total volume of water produced to the total volume of gas produced. This measured in barrels of water produced per SCF of gas produced.

water-to-oil ratio

The total amount of water generated when producing oil, measured in barrels of water produced per barrel of crude oil produced.

water intensity

An upstream operating decision regarding the amount of liquid water throughput required to produce oil and gas, including both water injected and wastewater generated.

wet gas

Gas that has a relatively high concentration of heavy liquid hydrocarbons such as propane and butane. Correspondingly, wet gas is usually less than 85% methane. Also known as rich gas.

years in production

The time that an oil or gas field has been in active service. Over long periods, this can impact GHG emissions as a field depletes, changing its characteristics and the techniques required both upstream and midstream.