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Chapter Two Origin of Crude oil The main origin of crude oil is still unknown, the first theories about the origin of crude oil referred to non-organic origin as raw resources for the formation of oil, but the recent theories assume the organic resources as raw resource of oil. And most scientists agreed on that, but still the processes that are applied on those organic resources a controversial point. Generally, when we study the formation of oil origin, we have to read conditions called geological wall and they are:1- Oil exists in sedimentary rocks that are accumulated in water ocean 2- Oil is a mixture of very complex hydrocarbonic resources because of the variety of resources that form it or the variety of natural conditions that help forming it. 3- Oil is usually existed in rocks that are formed in geological ages between (pecandren – pelsteren) before about (13-600) million years 4-usually, temperature is not more than 100%. 5- Oil is formed in a medium that the proportion of oxygen decreases in. 6- When oil is found its pressure is between (14.7 – 10000 psi). 1 7- The time of oil formation, moving, and accumulation is one million year approximately. The non-organic theories assume that there are chemical reaction among water CO2 and other organic materials like carbides and carbonates in the underground. Although oil can be prepared in laboratory by some non-organic reactions, geological proofs refer to the lack of these materials in nature. Oil is formed in (big oil accumulations) But organic theories refers to that oil may be formed by the decomposition of organic materials that were parts of the composition of animals bodies that lived in geological ages. Classification of Crude Oil There is no inclusive and satisfying classification. Of the most known classification is which depends on molecular weight. 1- Classification depends on one of the physical properties of oil like specific gravity (API) by the standard of the American petroleum institute and weight by the standard of (Bume). This classification clarifies what crude oil contains of light and heavy compounds. Ex:1- Crude oil of 35 oC 2- Crude oil of 30 oC API= sp.Gr=0.85 API= sp.Gr=0.85 Oil unit measurement is API according to American petroleum institute. 2 When Sample 1 is distilled, it gives light distilled like Gasoline by higher proportion than the second type gives. * API value is inversely relative with specific weight. 2- Classification depends on hydro carbonic composition for crude oil Based on this classification, oil crude divided into:A- Paraffin Base B- Asphalt Base C- Mixed Base There is another type of Hybrid Base which contains Naphthenic and quantity of paraffin candles . This classification is made by taking a sample from oil to be classified, and is distilled, then the remain of the distillation is taken and examined if contains less than 20% of paraffins, then it is Asphalt. If 20% -50% then it is mixed base, if more than 50% is considered paraffin base. This classification is considered as useful for oil refineries that it gives real clue about the nature of the oil products and how to refine crude oil and the difficulties the factory faces. 3- The third classification depends on hydro carbonic composition for two of crude oil distilled to be classified. That they both are considered as a guide to the classification like (A) Kerosene: which is the first guide between ( 275-300) Co in normal air pressure (B) Lubricating oil (second guide) between (275 – 300) Co in pressure (40) ML mercury according to the specific weight (API) for these two distilled of oil. See table (1-2) P.38 3