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KEROGEN: COMPOSITION AND CLASSIFICATION

BY

OLATINPO, OLUSEGUN AYOBAMIMATRIC NO: 14/68ET003

APRIL 29, 2015

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OUTLINE

• What Kerogen is• Composition of Kerogen• Classification of Kerogen• Summary and Conclusion

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WHAT KEROGEN IS Defined by solubility:

Organic Matter insoluble in organic solvents because of the large molecular weight up to several thousand Daltons

Defined by petroleum: • Organic Matter capable of producing petroleum• End result of diagenesis stage during the process of

petroleum formation is conversion of organic matter to kerogen

Extraction method alters kerogen properties: physical, compositional, and structural!

• Can be mixed with other insoluble OM: tar, asphaltene, bitumen!

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Ingredient for generating kerogen • For kerogen to be generated, organic matter must be present in

abundance • Organic matter is accumulated mostly in a dispersed state in

predominantly clay-sized marine deposits • It comprises mainly algae and plants, and some animal matter • However, the type and amount of kerogen generation from organic

matter in a basin depends on: nature of the organic matter in the sediments abundance of the organic matter thermal maturity (degree of cooking by heating) of the

organic matter during burial nature and type of environment in which the organic matter

accumulated

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NOTE!!!

* The amount of Organic Matter in source rocks is critical because < 75% of the Organic Matter is converted to petroleum.

* Ideally the Organic Matter content of the source rock should not < 0.5%. If it is > 50%, however, the rock is termed an oil shale.

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“The decomposed components of bacteria, zooplankton (esp. foraminifers &

crustaceans), macro benthos, etc along with that from primary producers (i.e. molecules derived from proteins, carbohydrates, lipids, lignin) form the organic matter that is found

in sediment” (Armstrong, 2010)

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COMPOSITION OF KEROGEN• Organic matter is divided into:

1. Humic OM: results in the formation of coal & gas.

2.Sapropelic OM: gives rise to liquid & gaseous HCs.

• On average, the composition of organic matter in sediment is as follows: 40% Proteins 40% Carbohydrates 10% Lipids 10% Lignin

• These materials are supplied by: Trees, Herbaceous plants, Fungi, Algae, Protozoa, Bacteria, and Faeces

• All of these + Time + Temperature + Pressure = KEROGEN

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Composition (in wt %) of Living Matter

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CLASSIFICATION OF KEROGEN

• The extreme types of disseminated organic matter correspond to the class of Kerogen formed.

• According to the van Krevelen diagram, kerogens can be classified based on the ratios of H/C and O/C.

• The different classifications include:Type I kerogenType II kerogenType III kerogenType IV kerogen

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Type I kerogen or Liptinite

• Rich in lipids particularly aliphatic chains with derivates of oils, fats, & waxes

• Derived from algae present in fresh water lakes & lagoons.

• Abundant in lacustrine source rocks.

• High proportion of H:C ratio (1.6- 1.8) and low O:C ratio (0.06)

• Usually with the exception of a few algae (e.g. Botryococcus sp.) most of the organic matter is unrecognizable. The prolific oil shales of Colorado, Utah, Wyoming (Green River shales) seem to result from a combination of both algae and mirobial lipids.

• Oil prone; yields high (up to 80%).

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Lacustrine Oil Shale From Queensferry (Q0309). Botryococcus Sp. Arrowed (Redfern, 2010)

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Type II kerogen or Exinite

• Most prolific global source rocks • Rich in lipid • It is an admixture of

i. Marine material - phytoplanktons , zooplanktons, algae

ii. Terrestrial (plant) material- spores, pollen, and cuticle

• Its assemblages dominate in the marine source rocks e.g. Kimmeridge Clay Fm (NS), Akata Fm (ND)

• Intermediate H:C (about 1.3) & intermediate O:C (0.1) • Oil & gas prone; yields 40—60% • Sulphur, where present, influences the timing and rate of

maturation of Type II kerogen.

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A Photomicrograph Showing Type II Kerogen Assemblage (Redfern, 2010)

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Type III kerogen (or Vitrinite)

• Rich in lignin derived from woody land plant debris

• The debris occurs abundantly in coals

• Low H:C ratio (< 1.0) & high O:C ratio (0.15)

• Low yield for oil but gas prone

• Low in aliphatic compounds but rich in aromatic compounds

• Example of vitrinite-dominated source rocks include the Carboniferous Coal Measures of the southern North Sea basin

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Type IV kerogen (or Inertinite)

• High in carbon and very low in hydrogen

• Often termed “dead-carbon”

• No effective potential to generate petroleum

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SUMMARY AND CONCLUSION

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I APPRECIATE YOUR ATTENTION