What are hydrocarbons and how are they formed?

IEA Energy Training Week

Paris, April 4, 2013

Master of Advanced Studies in International Oil and Gas Leadership

Giacomo Luciani

Oil and Gas are Hydrocarbons

Molecules take different shapes

Defining “Oil”

• Oil is a mixture of hydrocarbon molecules of different complexity and arrangements.

• At atmospheric conditions, the smaller molecules are gases, the larger are liquids; but if many very large molecules prevail, then the mix may no longer flow.

• We call “oil” a mix of hydrocarbons which is liquid and flows at atmospheric conditions.

The source of oil

• Kerogen is a mixture of organic chemical compounds that make up a portion of the organic matter in sedimentary rocks.[1] It is insoluble in normal organic solvents because of the huge molecular weight (upwards of 1,000 daltons) of its component compounds. The soluble portion is known as bitumen.

• When heated to the right temperatures in the Earth's crust, (oil window ca. 60–160 °C, gas window ca. 150–200 °C, both depending on how quickly the source rock is heated) some types of kerogen release crude oil or natural gas, collectively known as hydrocarbons (fossil fuels).

• When such kerogens are present in high concentration in rocks such as shale they form possible source rocks.

• Shales rich in kerogens that have not been heated to warm temperature to release their hydrocarbons may form oil shale deposits.

Alternative histories

• Oil shale ≠ shale oil • Shale oil is oil (not kerogen) which remains

trapped in a non permeable rock (AKA “tight oil”) • If oil is not trapped, it will migrate from the

source rock • If it meets a layer of non-permeable rock (a cap)

an oil accumulation is formed • If it is not trapped by a cap, it will migrate to the

surface. Here the lighter molecules evaporate, and the heavier molecules remain in place: bitumen, tar sands…

14 Source: IFP School

Source Rock

Tight Oil: light oil in

very low quality

reservoir

Heavy & Extra Heavy Oil

Oil or Tar Sands or Bitumen

Oil Shale: immature source rock

Kerogen Oil Shale Oil: Oil in Shale

Typology of oil resources

Light

Medium

Heavy Reservoir

© OECD/IEA 2011

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Box 3.2 Definitions of different types of liquid fuels

For the purposes of this chapter, the following definitions are used (Figure 3.13):

Oil comprises crude, natural gas liquids, condensates and unconventional oil, butdoes not include biofuels (for the sake of completeness and to facilitate comparisons,relevant biofuel quantities are separately mentioned in some sections and tables).

Crude oil makes up the bulk of the oil produced today; it is amixture of hydrocarbonsthat exist in liquid phase under normal surface conditions. It includes light tight oil. Italso includes condensates that aremixed-in with commercial crude oil streams.

Natural gas liquids (NGLs) are light hydrocarbons that are contained in associated ornon-associated natural gas in a hydrocarbon reservoir and are produced within a gasstream. They comprise ethane, propane, butanes, pentanes-plus and condensates.

Condensates are light liquidhydrocarbons recovered fromassociatedor non-associatedgas reservoirs. They are composed mainly of pentanes and higher carbon numberhydrocarbons. They normally have an American Petroleum Institute (API) gravity ofbetween 50° and 85°.

Conventional oil includes crude oil and NGLs.

Unconventional oil includes extra-heavy oil, natural bitumen (oil sands), kerogen oil,gas-to-liquids (GTL), coal-to-liquids (CTL) and additives.

Biofuels are liquid fuels derived from biomass, including ethanol and biodiesel.

Figure 3.13 Liquid fuel schematic

Conventionaloil

Unconventionaloil

Oilsupply

Biofuelssupply

Ethanol

Otherbiofuels

Biodiesel

Oilproduction

Refineryprocessing

gains

Crude oil

Natural gasliquids

Extraheavy oil

Gas toliquids

Oil sands

Coal toliquids

Kerogenoil

Additives

Other crude

Lighttight oil

Condensate

Ethane,propane,

butanes andpentane

Liquidssupply

Upward revisions to reserves in fields already discovered, by both field extensions andenhanced oil recovery techniques, amounted to some 13 billion barrels in 2010. Thus, total

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