Classification of liquid hydrocarbons

This article treats classification of liquid hydrocarbons .

By source

To measure and compare the production of Oil various countries, it are necessary to know exactly of what one speaks. The term “oil” is actually rather vague. The total production of liquid hydrocarbons can break up as follows:

1. “ Oil brut ” (or “ brut ”, crude in English) indicates the oil which is in the liquid state in the layer and runs freely, under pressure at the beginning of the exploitation of a well and by pumping when this well becomes exhausted after one long period of working

See also: Oil

One speaks about “ Gross conventionnel ” to be more restrictive, while insisting on the exclusion of the categories which follow. ASPO defined a category even more exclusive, oil known as “ régulier ”, which adds a classification by source, excluding the deep Offshore (more than 500 meters of water) and the areas located beyond the polar circles, but which includes the condensates.

2. “ condensats ”, known as also “ pentane plus ” or “ C5+ ”, or “ liquids of gas naturel well; ”: this name indicates the light fraction energy of the Pentane (C₅H₁₂) until the Heptane (C₇H₁₆) or the Octane (C₈H₁₈). With the difference of the crude, the condensates are not liquid in the layers, but gas (because of temperature), and condenses when they are cooled by the relaxation on the outlet side of the well. They are in general associated with the Natural gas, but also with gas associated with the oil fields.

It is an important contribution to the world provisioning, about 6 Mbep/j, and they are of more than liquids of very high-quality (light and containing few Soufre).

It is rather rare that the quantities concerning the condensates are given explicitly, they are almost always included in crude oil, except for the countries of OPEC, because they are excluded from the quotas. It also happens that the condensates produced by the deposits worked for crude oil are taken into account this one, but that those produced by the gas layers are counted separately (it is the case in the United States for example).

3. “ gas naturel liquids; ” (ethane, propane, butane - C2 with C4) remain gases with room temperature, but are liquefied in the factories which treat gas, by Cryogénie. One speaks about “ liquid of factory of naturel ”. Butane and propane are often called Petroleum gas liquefied (LPG), but, in this name, one does not distinguish those which come from the natural gas factories and those which come from the refining of the oil (which contains also butane and propane in solution).

4. extra-heavy oils, too viscous to be sold directly (nontransportable by pipeline), can be put on the market by two methods:

* One produces Syncrude of it. One finds this type of production to the Canada (Athabasca: 600 kb/j approximately) and with the Venezuela (valley of the Orénoque: more 550 kb/j). It is produced via expensive operations, in particular the addition of Hydrogène and the vapor injection and/or solvents.

* the extra-heavy oil (of these two same areas) sold not transformed into syncrude (thus of low value). It either is mixed with light hydrocarbons (condensates, gross light, syncrude or Naphta) to give a sufficiently fluid mixture for transport out of pipeline, or in the form of emulsion in water (Orimulsion ® vénézuélienne).

*Actuellement, only Athabasca and the valley of the Orénoque produce extra-heavy oils, but there are reserves (much smaller) at other places: Madagascar, Russia, Alaska, India…

5. liquids of synthesis produced starting from coal and of natural gas. The South Africa is by far the first producer (165 kb/j) and uses especially coal as raw material. Many projects are being studied in various countries (Qatar, China, etc)

6. the “ profit of raffinage ”: the Refinery S, grace in particular to the Hydrocraquage (hydrogen addition) produce liquids overall a little less dense than the crude than they buy, there is thus a profit in volume which it is necessary to take into account as a category of production if it is wanted that the figures of production and consumption coincide. It is somewhat misleading, since the profit of refining is obviously not an energy source. It is an effect of the practice to measure oil in volume, whereas it would have been more rigorous to measure it in mass, or better still in Calorific value (what is not practiced, seems it, that in New Zealand).

Comments

These multiple categories make difficult the evaluation of the production and the reserves, because much of sources quantities without indicating give clearly which categories are taken into account or not. It is often difficult to compare two countries while being certain to have figures including the same thing exactly. Moreover, the limits between categories are sometimes fuzzy: thus, it is considered in general that the limit between bitumens and gross conventional is with 15°API (see low), but this value is arbitrary. For Venezuela, it is located at 10°API. Part of the quantities which it advertisement must thus be transferred in the category of nonconventional oils.

One often speaks about oil “ conventionnel ” against “ not conventionnel ”, but there too this distinction is prone to interpretation. Often, oil “ conventionnel ” indicates categories 1,2 and 6, sometimes only category 1. Some classify even like “ non-conventionnels ” certain crude oils with high production costs, coming from layers in Offshore oil rig very deep (and here still the limit is variable: 300,500 or 1 000 meters of water), polar regions (Sea of Barents and Alaska, inter alia) or of mature layers in tertiary phase of recovery (for example by injection of CO₂).

By quality

Oils (which it is of the conventional crudes, condensates, or syncrude) are not all of the same quality. Various scales make it possible to compare oils between them. Most important are the density and the content of Soufre.

the “ API degree ” (conceived by the American Petroleum Institute) is used in the Anglo-Saxon system to measure the density of a liquid, in particular of oil. For example, if a liquid has an API degree of 10°API at a temperature of 15 °C, this liquid has a density of 1,00 (either that of water, 1 kg/liter) at the same temperature. Thus 22°API with 15 °C = 0,9218 of density to 15 °C and 35°API with 15 °C = 0,8498 of density to 15 °C. The lower limit of conventional oil is generally placed at 15°API.
On generally speaks about heavy crude for less 20°API, means in 20 with 30°API and light beyond, but these terminals vary according to the countries. The lightest oils are coveted by the refiners, because they directly give many light cuts of great value (diesel, gasoline, Naphta). Contrary, heavy oils give more products, such as Bitume S and residual Fioul, that should either be sold such as they are at low prices, or to convert into lighter cuts, in particular by Hydrocraquage (hydrogen addition).

the sulfur content varies considerably one layer with the other and thus from one commercial mixture to another, of 0,03 % with some 5 %. Sulfur is polluting that the refiners must withdraw (at least in the countries having laws against the acid rains), it thus decreases the value of the crude. One places in general at 1.5 % of sulfur limit between oil “ doux ” ( sweet ) and “ aigre ” ( sour ).

In addition to these two principal scales, there are many other quality standards, among which one can quote the Viscosité, the Acidité, ratios between types of hydrocarbons (Cyclique S or not, saturated or not), and contents of Azote, metals heavy S, salt S, etc

Comments

The price of a given oil is given compared to the crudes which are used as reference (Brent in Europe, West Texas Intermediate in the United States, Minas in Southeast Asia, etc). An oil given, according to its quality and its distance from the market (to reflect the price of transport, which reaches 4 sometimes Euro S by barrel), sees itself allotting a differential of price compared to the crude of reference. This differential is generally negative, since the crudes which are used as reference are oils of very good quality and available close to the centers of consumption. It also varies according to the market.

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