Physiochemical Changes or Transformation of Organic Matter to Petroleum

Physiochemical Changes or Transformation of Organic Matter to Petroleum 
                                                                                                                      

Sedimentary Deposits, contains: (1) Interstitial water, (2) Organic Matter, (3) Microbial Organism and (4) Dissolved Oxygen

O.M unstable, in order to be in equilibrium reacts with O2 (along with other reactions), here, the physiochemical transformation starts.

This transformation cannot be isolated from initial condition of deposition environment to PT condition.

                                                 Stages/Process of Formation of Petroleum

Main stages are; (1) Diagenesis, (2) Catagenesis and (3) Metagenesis

Diagenesis

“Set of physiochemical changes which takes place at shallow depth after deposition”

OR

“Diagenesis is a process through which the system tends to approach equilibrium under condition of shallow burial and through which the sediments normally becomes consolidated”

e.g., porosity reduction in clay (80% to 60%)

Depth: 200m rarely up to 2000m

No significance change in pressure and temperature (no significance)

At such depths transformation is due to biological activity, carried by bacteria (aerobic or anaerobic)

The energy within system, comes through decomposition, which produces CO2, NH3 and H2O; in sand decomposition is quick rather than mud

Eh of interstitial H2O decreased, Eh= Oxidation/Redcution, PH of system would be increased

OM like Protein, Carbohydrates are soluble in water, severely transformed (more or less completely deformed), which form a compound “Polycondensed Organic Compound or geopolymer”. A geopolymer is an organic compound, which is precursor of Kerogen (if plant materia greater, then first step would be peat then bitumen).

V.R: 0.5

Humic acid produced

During close, humic acid are minimum

Catagenesis

The second stage

T: 50-150/200C, P: 300-1000 bars and rarely 1500 bars, which results in new changes

Composition, texture of mineral phase are consumed, mostly in clay fraction, e.g., water expelled, decreased the porosity and increase in salanity

OM progressively changes:

Kerogen produces:

first liquid petroleum

Wet gas (later stage)

Condensate (later stage)

Both oil and gas are associated with amounts of methane

Massive organic deposits; various rank of coal, with methane.

End of Catagenesis:

Dissappearence of aliphatic carbon chain

V.R: 2.0 (beginning of anthracite rank coal)

Further no more generation of petroleum and minor amount of methane (this point is known as natural break)

Metagenesis

The last stage, in evolution of sediments

H and T High (OM may be exposed to magma or hydrothermal effect)

Mineral severly transformed

Early metagenesis:

Only methane produced

Coal is anthracite

Late metagenesis:

Residue of Carbon

Meta anthracite, graphite schist etc.

Factor Effecting Transformation of OM into Petroleum

Starts within reducing environment, transformation requires energy and are:

Ø  Temperature and Pressure

Ø  Bacterial Activity

Ø  Catalytic Reaction

Ø  Radioactive bombardment

(1)Temperature and Pressure

T combined with P or Low T replaced with Time along with pressure

Kerogen shales: 350-400C to convert into petroleum, presence of porphyrines, indicates T never exceeds than 200C (means time is replacing Temp., enough time would be required)

By laboratory experiments it suggested that Less T required within earth than lab.

(2)Bacterial Activity

Decomposition of OM: Methane produced, through process fermentation

Bacteria produce methane, considered as agency in the formation of other petroleum Hydrocarbons.

Types of Bacteria

Aerobic: requires free O2

Anaerobic: requires combine O2

Faculative: live in presence or absence of O2, can be found in well and helps in , extent unknown.

(3)Catalytic Reaction

 Takes no part in reaction but only accelerates it: same in composition at beginning and at the end.

 May promote the conversion of Kerogen to petroleum at low temperature.

Similarly, Ni, Mo and V like catalysts are also found in Ash/residue from the Petroleum.

(4)Radioactive Bombardment

Heat from radioactive bombardment is also possible source of energy.
Important: uranium, thorium and potassium.

e.g., fatty acid----(alpha)----paraffin hydrocarbon

cyclohexane carboxylic acid----(alpha)-----cyclohexane

Early Transformation of OM: The Diagenetic Pathway from Organisms to Geochemical Fossil and Kerogen            (Source Rock)

OM, subjected to various degree of microbial and chemical actions: as a result its composition largely changed (during sedimentation process or after sedimentation within young sediments)

By comparison, 20% of OM recoverable, rest is lost; due to degradation in nutrients, then polycondensation to form kerogen at the end

Kerogen is the main source of petroleum (by geochemists)

The whole process is known as or referred to as diagenesis: leads to biopolymers synthesized by living organisms to geopolymers (Kerogen) through fractionation.

> Diagensis: the partial destruction and rearrangement of building stones.

Diagensis can be further divided into:

Biochemical Degradation

Polycondensation

Insolubilization

1 Biochemical Degradation

As we know there are four constituents of recent sediment deposited as source of OM (i. water, ii. organic matter, iii. minerals, iv. microbial organisms: shallow depths)

> Biochemical degradation is divided into:

a). Microbial Activity:

Bacteria + Fungi; present in variety of places (water, soil and in sed).

They would decomposed OM: build up their cells: aerobic and anaerobic (with and without O2).

OM compound dissolve through enzymatic process by organism; then take for their synthesis in their molecule.

Protein + Carbohydrate          (hydrolysed)    Amino Acid +

Surgars

Lipid + Lignins           less active

> In oxidizing; all OM destroyed

In fine grain sediments:

Dissolve oxygen used in pore spaces

Established anaerobic condition: under which, OM—partly decomposed by fermentation (in which sulphates reduced to S, Iron to Fe)

Fermentation: oxidized form of OM e.g., Cellulose   Methane + CO2

b) Free or Hydrolyzable Organic Matter

Sugar and protein: degraded can be found in addition to fatty acid + H/C (Methane): this amount is quite low

About 75-90% OM not destroyed and called as “humin” or “humic acid”

> Up to certain level most of the hydrolysable and free compounds disappeared.

2 Polycondensation

Remaining “humic acid” (residue left from micro-organism) incorporated into new polymeric insoluble structures (humic compounds)

Humic acid; results from the polycondensation of Organic residue of microbial metabolism (more or less oxidizing condition)

Oxidative condensation of Phenol is important process: addition of nitrogenous compound--- occur---through random polymerization-- -of free radicle like semiquinone

Soil humic acid structure (swaim, 1963): polycondensates made of nuclei bearing reactive groups; connected by bridges

a) nuclei: simple/or condensed aromatic/naphtenic

b) bridges: oxygen, sulphur, peptide or methylene bonds

Important reactive group is OH

3 Insolubilization

Decomposition + Polycondensation: first few meters of sediments; which represents 90% of total organic matter in young sediments

With increase in depth fulvic + humic acid converted into humin (insoluble)

Insolubilization occurs during diagenesis on a wider scale w.r.t time and depth (greater time and greater depth w.r.t other two steps)

Early Transformation of OM: The Diagenetic Pathway from Organisms to Geochemical Fossil and Kerogen            (Source Rock)

OM, subjected to various degree of microbial and chemical actions: as a result its composition largely changed (during sedimentation process or after sedimentation within young sediments)

By comparison, 20% of OM recoverable, rest is lost; due to degradation in nutrients, then polycondensation to form kerogen at the end

Kerogen is the main source of petroleum (by geochemists)

The whole process is known as or referred to as diagenesis: leads to biopolymers synthesized by living organisms to geopolymers (Kerogen) through fractionation.

> Diagensis: the partial destruction and rearrangement of building stones.

Diagensis can be further divided into:

Biochemical Degradation

Polycondensation

Insolubilization

1 Biochemical Degradation

As we know there are four constituents of recent sediment deposited as source of OM (i. water, ii. organic matter, iii. minerals, iv. microbial organisms: shallow depths)

> Biochemical degradation is divided into:

a). Microbial Activity:

Bacteria + Fungi; present in variety of places (water, soil and in sed).

They would decomposed OM: build up their cells: aerobic and anaerobic (with and without O2).

OM compound dissolve through enzymatic process by organism; then take for their synthesis in their molecule.

Protein + Carbohydrate          (hydrolysed)    Amino Acid +

Surgars

Lipid + Lignins           less active

> In oxidizing; all OM destroyed

In fine grain sediments:

Dissolve oxygen used in pore spaces

Established anaerobic condition: under which, OM—partly decomposed by fermentation (in which sulphates reduced to S, Iron to Fe)

Fermentation: oxidized form of OM e.g., Cellulose   Methane + CO2

b) Free or Hydrolyzable Organic Matter

Sugar and protein: degraded can be found in addition to fatty acid + H/C (Methane): this amount is quite low

About 75-90% OM not destroyed and called as “humin” or “humic acid”

> Up to certain level most of the hydrolysable and free compounds disappeared.

2 Polycondensation

Remaining “humic acid” (residue left from micro-organism) incorporated into new polymeric insoluble structures (humic compounds)

Humic acid; results from the polycondensation of Organic residue of microbial metabolism (more or less oxidizing condition)

Oxidative condensation of Phenol is important process: addition of nitrogenous compound--- occur---through random polymerization-- -of free radicle like semiquinone

Soil humic acid structure (swaim, 1963): polycondensates made of nuclei bearing reactive groups; connected by bridges

a) nuclei: simple/or condensed aromatic/naphtenic

b) bridges: oxygen, sulphur, peptide or methylene bonds

Important reactive group is OH

3 Insolubilization

Decomposition + Polycondensation: first few meters of sediments; which represents 90% of total organic matter in young sediments

With increase in depth fulvic + humic acid converted into humin (insoluble)

Insolubilization occurs during diagenesis on a wider scale w.r.t time and depth (greater time and greater depth w.r.t other two steps)

Early Transformation of OM: The Diagenetic Pathway from Organisms to Geochemical Fossil and Kerogen            (Source Rock)

OM, subjected to various degree of microbial and chemical actions: as a result its composition largely changed (during sedimentation process or after sedimentation within young sediments)

By comparison, 20% of OM recoverable, rest is lost; due to degradation in nutrients, then polycondensation to form kerogen at the end

Kerogen is the main source of petroleum (by geochemists)

The whole process is known as or referred to as diagenesis: leads to biopolymers synthesized by living organisms to geopolymers (Kerogen) through fractionation.

> Diagensis: the partial destruction and rearrangement of building stones.

Diagensis can be further divided into:

Biochemical Degradation

Polycondensation

Insolubilization

1 Biochemical Degradation

As we know there are four constituents of recent sediment deposited as source of OM (i. water, ii. organic matter, iii. minerals, iv. microbial organisms: shallow depths)

> Biochemical degradation is divided into:

a). Microbial Activity:

Bacteria + Fungi; present in variety of places (water, soil and in sed).

They would decomposed OM: build up their cells: aerobic and anaerobic (with and without O2).

OM compound dissolve through enzymatic process by organism; then take for their synthesis in their molecule.

Protein + Carbohydrate          (hydrolysed)    Amino Acid +

Surgars

Lipid + Lignins           less active

> In oxidizing; all OM destroyed

In fine grain sediments:

Dissolve oxygen used in pore spaces

Established anaerobic condition: under which, OM—partly decomposed by fermentation (in which sulphates reduced to S, Iron to Fe)

Fermentation: oxidized form of OM e.g., Cellulose   Methane + CO2

b) Free or Hydrolyzable Organic Matter

Sugar and protein: degraded can be found in addition to fatty acid + H/C (Methane): this amount is quite low

About 75-90% OM not destroyed and called as “humin” or “humic acid”

> Up to certain level most of the hydrolysable and free compounds disappeared.

2 Polycondensation

Remaining “humic acid” (residue left from micro-organism) incorporated into new polymeric insoluble structures (humic compounds)

Humic acid; results from the polycondensation of Organic residue of microbial metabolism (more or less oxidizing condition)

Oxidative condensation of Phenol is important process: addition of nitrogenous compound--- occur---through random polymerization-- -of free radicle like semiquinone

Soil humic acid structure (swaim, 1963): polycondensates made of nuclei bearing reactive groups; connected by bridges

a) nuclei: simple/or condensed aromatic/naphtenic

b) bridges: oxygen, sulphur, peptide or methylene bonds

Important reactive group is OH

3 Insolubilization

Decomposition + Polycondensation: first few meters of sediments; which represents 90% of total organic matter in young sediments

With increase in depth fulvic + humic acid converted into humin (insoluble)

Insolubilization occurs during diagenesis on a wider scale w.r.t time and depth (greater time and greater depth w.r.t other two steps)

Early Transformation of OM: The Diagenetic Pathway from Organisms to Geochemical Fossil and Kerogen            (Source Rock)

OM, subjected to various degree of microbial and chemical actions: as a result its composition largely changed (during sedimentation process or after sedimentation within young sediments)

By comparison, 20% of OM recoverable, rest is lost; due to degradation in nutrients, then polycondensation to form kerogen at the end

Kerogen is the main source of petroleum (by geochemists)

The whole process is known as or referred to as diagenesis: leads to biopolymers synthesized by living organisms to geopolymers (Kerogen) through fractionation.

> Diagensis: the partial destruction and rearrangement of building stones.

Diagensis can be further divided into:

Biochemical Degradation

Polycondensation

Insolubilization

1 Biochemical Degradation

As we know there are four constituents of recent sediment deposited as source of OM (i. water, ii. organic matter, iii. minerals, iv. microbial organisms: shallow depths)

> Biochemical degradation is divided into:

a). Microbial Activity:

Bacteria + Fungi; present in variety of places (water, soil and in sed).

They would decomposed OM: build up their cells: aerobic and anaerobic (with and without O2).

OM compound dissolve through enzymatic process by organism; then take for their synthesis in their molecule.

Protein + Carbohydrate          (hydrolysed)    Amino Acid +

Surgars

Lipid + Lignins           less active

> In oxidizing; all OM destroyed

In fine grain sediments:

Dissolve oxygen used in pore spaces

Established anaerobic condition: under which, OM—partly decomposed by fermentation (in which sulphates reduced to S, Iron to Fe)

Fermentation: oxidized form of OM e.g., Cellulose   Methane + CO2

b) Free or Hydrolyzable Organic Matter

Sugar and protein: degraded can be found in addition to fatty acid + H/C (Methane): this amount is quite low

About 75-90% OM not destroyed and called as “humin” or “humic acid”

> Up to certain level most of the hydrolysable and free compounds disappeared.

2 Polycondensation

Remaining “humic acid” (residue left from micro-organism) incorporated into new polymeric insoluble structures (humic compounds)

Humic acid; results from the polycondensation of Organic residue of microbial metabolism (more or less oxidizing condition)

Oxidative condensation of Phenol is important process: addition of nitrogenous compound--- occur---through random polymerization-- -of free radicle like semiquinone

Soil humic acid structure (swaim, 1963): polycondensates made of nuclei bearing reactive groups; connected by bridges

a) nuclei: simple/or condensed aromatic/naphtenic

b) bridges: oxygen, sulphur, peptide or methylene bonds

Important reactive group is OH

3 Insolubilization

Decomposition + Polycondensation: first few meters of sediments; which represents 90% of total organic matter in young sediments

With increase in depth fulvic + humic acid converted into humin (insoluble)

Insolubilization occurs during diagenesis on a wider scale w.r.t time and depth (greater time and greater depth w.r.t other two steps)

Early Transformation of OM: The Diagenetic Pathway from Organisms to Geochemical Fossil and Kerogen            (Source Rock)

OM, subjected to various degree of microbial and chemical actions: as a result its composition largely changed (during sedimentation process or after sedimentation within young sediments)

By comparison, 20% of OM recoverable, rest is lost; due to degradation in nutrients, then polycondensation to form kerogen at the end

Kerogen is the main source of petroleum (by geochemists)

The whole process is known as or referred to as diagenesis: leads to biopolymers synthesized by living organisms to geopolymers (Kerogen) through fractionation.

> Diagensis: the partial destruction and rearrangement of building stones.

Diagensis can be further divided into:

Biochemical Degradation

Polycondensation

Insolubilization

1 Biochemical Degradation

As we know there are four constituents of recent sediment deposited as source of OM (i. water, ii. organic matter, iii. minerals, iv. microbial organisms: shallow depths)

> Biochemical degradation is divided into:

a). Microbial Activity:

Bacteria + Fungi; present in variety of places (water, soil and in sed).

They would decomposed OM: build up their cells: aerobic and anaerobic (with and without O2).

OM compound dissolve through enzymatic process by organism; then take for their synthesis in their molecule.

Protein + Carbohydrate          (hydrolysed)    Amino Acid +

Surgars

Lipid + Lignins           less active

> In oxidizing; all OM destroyed

In fine grain sediments:

Dissolve oxygen used in pore spaces

Established anaerobic condition: under which, OM—partly decomposed by fermentation (in which sulphates reduced to S, Iron to Fe)

Fermentation: oxidized form of OM e.g., Cellulose   Methane + CO2

b) Free or Hydrolyzable Organic Matter

Sugar and protein: degraded can be found in addition to fatty acid + H/C (Methane): this amount is quite low

About 75-90% OM not destroyed and called as “humin” or “humic acid”

> Up to certain level most of the hydrolysable and free compounds disappeared.

2 Polycondensation

Remaining “humic acid” (residue left from micro-organism) incorporated into new polymeric insoluble structures (humic compounds)

Humic acid; results from the polycondensation of Organic residue of microbial metabolism (more or less oxidizing condition)

Oxidative condensation of Phenol is important process: addition of nitrogenous compound--- occur---through random polymerization-- -of free radicle like semiquinone

Soil humic acid structure (swaim, 1963): polycondensates made of nuclei bearing reactive groups; connected by bridges

a) nuclei: simple/or condensed aromatic/naphtenic

b) bridges: oxygen, sulphur, peptide or methylene bonds

Important reactive group is OH

3 Insolubilization

Decomposition + Polycondensation: first few meters of sediments; which represents 90% of total organic matter in young sediments

With increase in depth fulvic + humic acid converted into humin (insoluble)

Insolubilization occurs during diagenesis on a wider scale w.r.t time and depth (greater time and greater depth w.r.t other two steps)

Early Transformation of OM: The Diagenetic Pathway from Organisms to Geochemical Fossil and Kerogen            (Source Rock)

OM, subjected to various degree of microbial and chemical actions: as a result its composition largely changed (during sedimentation process or after sedimentation within young sediments)

By comparison, 20% of OM recoverable, rest is lost; due to degradation in nutrients, then polycondensation to form kerogen at the end

Kerogen is the main source of petroleum (by geochemists)

The whole process is known as or referred to as diagenesis: leads to biopolymers synthesized by living organisms to geopolymers (Kerogen) through fractionation.

> Diagensis: the partial destruction and rearrangement of building stones.

Diagensis can be further divided into:

Biochemical Degradation

Polycondensation

Insolubilization

1 Biochemical Degradation

As we know there are four constituents of recent sediment deposited as source of OM (i. water, ii. organic matter, iii. minerals, iv. microbial organisms: shallow depths)

> Biochemical degradation is divided into:

a). Microbial Activity:

Bacteria + Fungi; present in variety of places (water, soil and in sed).

They would decomposed OM: build up their cells: aerobic and anaerobic (with and without O2).

OM compound dissolve through enzymatic process by organism; then take for their synthesis in their molecule.

Protein + Carbohydrate          (hydrolysed)    Amino Acid +

Surgars

Lipid + Lignins           less active

> In oxidizing; all OM destroyed

In fine grain sediments:

Dissolve oxygen used in pore spaces

Established anaerobic condition: under which, OM—partly decomposed by fermentation (in which sulphates reduced to S, Iron to Fe)

Fermentation: oxidized form of OM e.g., Cellulose   Methane + CO2

b) Free or Hydrolyzable Organic Matter

Sugar and protein: degraded can be found in addition to fatty acid + H/C (Methane): this amount is quite low

About 75-90% OM not destroyed and called as “humin” or “humic acid”

> Up to certain level most of the hydrolysable and free compounds disappeared.

2 Polycondensation

Remaining “humic acid” (residue left from micro-organism) incorporated into new polymeric insoluble structures (humic compounds)

Humic acid; results from the polycondensation of Organic residue of microbial metabolism (more or less oxidizing condition)

Oxidative condensation of Phenol is important process: addition of nitrogenous compound--- occur---through random polymerization-- -of free radicle like semiquinone

Soil humic acid structure (swaim, 1963): polycondensates made of nuclei bearing reactive groups; connected by bridges

a) nuclei: simple/or condensed aromatic/naphtenic

b) bridges: oxygen, sulphur, peptide or methylene bonds

Important reactive group is OH

3 Insolubilization

Decomposition + Polycondensation: first few meters of sediments; which represents 90% of total organic matter in young sediments

With increase in depth fulvic + humic acid converted into humin (insoluble)

Insolubilization occurs during diagenesis on a wider scale w.r.t time and depth (greater time and greater depth w.r.t other two steps)

Early Transformation of OM: The Diagenetic Pathway from Organisms to Geochemical Fossil and Kerogen            (Source Rock)

OM, subjected to various degree of microbial and chemical actions: as a result its composition largely changed (during sedimentation process or after sedimentation within young sediments)

By comparison, 20% of OM recoverable, rest is lost; due to degradation in nutrients, then polycondensation to form kerogen at the end

Kerogen is the main source of petroleum (by geochemists)

The whole process is known as or referred to as diagenesis: leads to biopolymers synthesized by living organisms to geopolymers (Kerogen) through fractionation.

> Diagensis: the partial destruction and rearrangement of building stones.

Diagensis can be further divided into:

Biochemical Degradation

Polycondensation

Insolubilization

1 Biochemical Degradation

As we know there are four constituents of recent sediment deposited as source of OM (i. water, ii. organic matter, iii. minerals, iv. microbial organisms: shallow depths)

> Biochemical degradation is divided into:

a). Microbial Activity:

Bacteria + Fungi; present in variety of places (water, soil and in sed).

They would decomposed OM: build up their cells: aerobic and anaerobic (with and without O2).

OM compound dissolve through enzymatic process by organism; then take for their synthesis in their molecule.

Protein + Carbohydrate          (hydrolysed)    Amino Acid +

Surgars

Lipid + Lignins           less active

> In oxidizing; all OM destroyed

In fine grain sediments:

Dissolve oxygen used in pore spaces

Established anaerobic condition: under which, OM—partly decomposed by fermentation (in which sulphates reduced to S, Iron to Fe)

Fermentation: oxidized form of OM e.g., Cellulose   Methane + CO2

b) Free or Hydrolyzable Organic Matter

Sugar and protein: degraded can be found in addition to fatty acid + H/C (Methane): this amount is quite low

About 75-90% OM not destroyed and called as “humin” or “humic acid”

> Up to certain level most of the hydrolysable and free compounds disappeared.

2 Polycondensation

Remaining “humic acid” (residue left from micro-organism) incorporated into new polymeric insoluble structures (humic compounds)

Humic acid; results from the polycondensation of Organic residue of microbial metabolism (more or less oxidizing condition)

Oxidative condensation of Phenol is important process: addition of nitrogenous compound--- occur---through random polymerization-- -of free radicle like semiquinone

Soil humic acid structure (swaim, 1963): polycondensates made of nuclei bearing reactive groups; connected by bridges

a) nuclei: simple/or condensed aromatic/naphtenic

b) bridges: oxygen, sulphur, peptide or methylene bonds

Important reactive group is OH

3 Insolubilization

Decomposition + Polycondensation: first few meters of sediments; which represents 90% of total organic matter in young sediments

With increase in depth fulvic + humic acid converted into humin (insoluble)

Insolubilization occurs during diagenesis on a wider scale w.r.t time and depth (greater time and greater depth w.r.t other two steps)

Early Transformation of OM: The Diagenetic Pathway from Organisms to Geochemical Fossil and Kerogen            (Source Rock)

OM, subjected to various degree of microbial and chemical actions: as a result its composition largely changed (during sedimentation process or after sedimentation within young sediments)

By comparison, 20% of OM recoverable, rest is lost; due to degradation in nutrients, then polycondensation to form kerogen at the end

Kerogen is the main source of petroleum (by geochemists)

The whole process is known as or referred to as diagenesis: leads to biopolymers synthesized by living organisms to geopolymers (Kerogen) through fractionation.

> Diagensis: the partial destruction and rearrangement of building stones.

Diagensis can be further divided into:

Biochemical Degradation

Polycondensation

Insolubilization

1 Biochemical Degradation

As we know there are four constituents of recent sediment deposited as source of OM (i. water, ii. organic matter, iii. minerals, iv. microbial organisms: shallow depths)

> Biochemical degradation is divided into:

a). Microbial Activity:

Bacteria + Fungi; present in variety of places (water, soil and in sed).

They would decomposed OM: build up their cells: aerobic and anaerobic (with and without O2).

OM compound dissolve through enzymatic process by organism; then take for their synthesis in their molecule.

Protein + Carbohydrate          (hydrolysed)    Amino Acid +

Surgars

Lipid + Lignins           less active

> In oxidizing; all OM destroyed

In fine grain sediments:

Dissolve oxygen used in pore spaces

Established anaerobic condition: under which, OM—partly decomposed by fermentation (in which sulphates reduced to S, Iron to Fe)

Fermentation: oxidized form of OM e.g., Cellulose   Methane + CO2

b) Free or Hydrolyzable Organic Matter

Sugar and protein: degraded can be found in addition to fatty acid + H/C (Methane): this amount is quite low

About 75-90% OM not destroyed and called as “humin” or “humic acid”

> Up to certain level most of the hydrolysable and free compounds disappeared.

2 Polycondensation

Remaining “humic acid” (residue left from micro-organism) incorporated into new polymeric insoluble structures (humic compounds)

Humic acid; results from the polycondensation of Organic residue of microbial metabolism (more or less oxidizing condition)

Oxidative condensation of Phenol is important process: addition of nitrogenous compound--- occur---through random polymerization-- -of free radicle like semiquinone

Soil humic acid structure (swaim, 1963): polycondensates made of nuclei bearing reactive groups; connected by bridges

a) nuclei: simple/or condensed aromatic/naphtenic

b) bridges: oxygen, sulphur, peptide or methylene bonds

Important reactive group is OH

3 Insolubilization

Decomposition + Polycondensation: first few meters of sediments; which represents 90% of total organic matter in young sediments

With increase in depth fulvic + humic acid converted into humin (insoluble)

Insolubilization occurs during diagenesis on a wider scale w.r.t time and depth (greater time and greater depth w.r.t other two steps)

Two stages: 1st Initial Stage

 First 10m: humic acid fraction

Shows loss of peptide bonds

Decrease of hydrolyzable nitrogen and N/C ratio: elimination of N from solid organic phase (expulsion of N): thus amonia increases in pore water

Result: during same interval: carboxylic and aliphatic group increases

2nd Step  10m-100m

Over this interval: oxygen content reduced

O/C ratio ranges from 0.3-0.6 in young humic acid sediments to

1-0.2 in kerogen: related to elimination of carboxylic acid group.

Source Rock:

“sedimentary rock in which organic material under pressure, heat and time is transferred into liquid/gas hydrocarbons” usually shales and limestone.

Result and Sumary of Diagenesis

OM present within water and sediments degraded by organisms and used in metabolism.

Even in fine mud, part of OM has been consumed

Other part used in constituents of organism cell and enter to biological cycle. The OM lost is about 15-50% of Original by decay

The residue left polymerized or condensed into new form insoluble kerogen. This reaction takes place under mild T and P

Besides kerogen, OM still comparises at the end of diagenesis a minor amount of free hydrocarbons and related compounds, which are synthesized by organism and incorporated into sediments with no or little change, called as geochemical fossils (witnessing the depositional environment).