Organic Geochemistry Questions and Answers

Q: Petroleum is formed from oceanic organisms that have large component of.................and therefore less oxygen per carbon than the C6H10O5 of carbohydrates found as three major component of land plants :

The missing component is lipid.Marine plankton and algae are rich in lipids (fats, oils and waxes), which are long hydrocarbon chains with very little oxygen. That hydrogen-rich, oxygen-poor organic matter is what generates oil, whereas land plants are dominated by carbohydrates such as cellulose, built of C6H10O5 units with one oxygen for every carbon or so, which tend to form coal and gas.Fulvic acids are soil humic substances and amino acids are the building blocks of proteins; neither explains the low oxygen content of petroleum. 'Pepofine' is not a recognised constituent.

Q: The correct order of the three stages of transformation of organic matter into hydrocarbons.

The correct order is diagenesis - catagenesis - metagenesis.In diagenesis, at shallow depth and low temperature, organic matter is altered by bacteria and chemical reactions into kerogen, with some biogenic methane. In catagenesis, at greater depth and about 50-150°C, kerogen is thermally cracked to oil and then wet gas: this is the oil window. In metagenesis, at still higher temperature, the remaining material yields only dry gas (methane) and residual carbon.The other orders put catagenesis or metagenesis first, which is impossible, since kerogen must form in diagenesis before it can be cracked to hydrocarbons.

Q: ................. of kerogen is the principal stage of oil formation.

The principal stage of oil formation from kerogen is catagenesis.Organic matter matures in three stages. During diagenesis, at shallow depth and low temperature, organic matter is converted into kerogen and biogenic methane. During catagenesis, at roughly 50-150 °C, the kerogen is thermally cracked and generates most of the oil and wet gas: this is the 'oil window'. During metagenesis, at still higher temperature, only dry gas (methane) is produced and the residue turns to graphite-like carbon.Metamorphosis is a biological term for a change of body form and is not a stage of kerogen maturation.

Q: Thermal maturation of sedimentary organic matter to hydrocarbons is driven by :

Thermal maturation is driven by both temperature and time.Kerogen breaks down into oil and gas through chemical reactions whose rates rise steeply with temperature but which also need geological time to proceed. A source rock can reach the oil window either by being heated strongly for a short time or moderately for a long time, which is the basis of Lopatin's time-temperature index (TTI) and of modern basin models.Temperature alone or time alone ignores this trade-off, and pressure has only a minor effect on the reactions compared with temperature.

Petroleum is formed from oceanic organisms that have large component of.................and therefore less oxygen per carbon than the C₆H₁₀O₅ of carbohydrates found as three major component of land plants :

A.pepofine
B.lipid
C.fulvic acids
D.amino acids

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: B

The missing component is lipid.

Marine plankton and algae are rich in lipids (fats, oils and waxes), which are long hydrocarbon chains with very little oxygen. That hydrogen-rich, oxygen-poor organic matter is what generates oil, whereas land plants are dominated by carbohydrates such as cellulose, built of C₆H₁₀O₅ units with one oxygen for every carbon or so, which tend to form coal and gas.

Fulvic acids are soil humic substances and amino acids are the building blocks of proteins; neither explains the low oxygen content of petroleum. 'Pepofine' is not a recognised constituent.

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The correct order of the three stages of transformation of organic matter into hydrocarbons.

A.Catagenesis - diagenesis - metagenesis
B.diagenesis - catagenesis - metagenesis
C.Catagenesis - metagenesis - diagenesis
D.Diagenesis - metagenesis - catagenesis

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: B

The correct order is diagenesis - catagenesis - metagenesis.

In diagenesis, at shallow depth and low temperature, organic matter is altered by bacteria and chemical reactions into kerogen, with some biogenic methane. In catagenesis, at greater depth and about 50-150°C, kerogen is thermally cracked to oil and then wet gas: this is the oil window. In metagenesis, at still higher temperature, the remaining material yields only dry gas (methane) and residual carbon.

The other orders put catagenesis or metagenesis first, which is impossible, since kerogen must form in diagenesis before it can be cracked to hydrocarbons.

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................. of kerogen is the principal stage of oil formation.

A.Diagenesis
B.Metagenesis
C.Metamorphosis
D.Catagenesis

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: D

The principal stage of oil formation from kerogen is catagenesis.

Organic matter matures in three stages. During diagenesis, at shallow depth and low temperature, organic matter is converted into kerogen and biogenic methane. During catagenesis, at roughly 50-150 °C, the kerogen is thermally cracked and generates most of the oil and wet gas: this is the 'oil window'. During metagenesis, at still higher temperature, only dry gas (methane) is produced and the residue turns to graphite-like carbon.

Metamorphosis is a biological term for a change of body form and is not a stage of kerogen maturation.

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..................... is the movement of petroleum from non-reservoir rocks to reservoir rocks.

A.Seepage
B.Primary migration
C.Secondary migration
D.Tertiary migration

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: B

The movement of petroleum from non-reservoir (source) rocks into reservoir rocks is primary migration.

Oil and gas generated in a fine-grained source rock such as shale are first expelled out of it into an adjacent permeable carrier or reservoir bed. Secondary migration is the later movement through the carrier and reservoir rocks, driven by buoyancy, until the hydrocarbons are held in a trap.

Seepage is the escape of hydrocarbons to the surface, and 'tertiary migration' is used, where at all, for the remigration of oil out of an existing trap, so neither describes expulsion from the source rock.

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Thermal maturation of sedimentary organic matter to hydrocarbons is driven by :

A.Temperature only
B.Time only
C.Both temperature and time
D.Temperature and pressure

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: C

Thermal maturation is driven by both temperature and time.

Kerogen breaks down into oil and gas through chemical reactions whose rates rise steeply with temperature but which also need geological time to proceed. A source rock can reach the oil window either by being heated strongly for a short time or moderately for a long time, which is the basis of Lopatin's time-temperature index (TTI) and of modern basin models.

Temperature alone or time alone ignores this trade-off, and pressure has only a minor effect on the reactions compared with temperature.

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