dr. tabari 1 introduction to petroleum geochemistry unit one
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Dr. TabariDr. Tabari1
Introduction to PetroleumGeochemistry
Introduction to PetroleumGeochemistry
Unit ONEUnit ONE
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Preservation or Productivity ? Preservation or Productivity ?
The quantity and quality of organic matter preserved during digenesis is controlled by a number of factors, notably the oxygen content of the water column and sediments, water circulation, organic matter productivity, and sedimentation.Preservation: anoxia (reducing environment) is the main cause for enhanced preservation of organic matter leading to the formation of organic rich source rocks. Under oxic conditions, organic matter is rapidly degraded even though the rate of productivity may be high, leading to sediments with low organic carbon contents.Productivity: it is the driving force behind the accumulation of organic rich rocks rather than preservation. Their argument is based on laboratory experiments that show rate of destruction is similar under oxic and anoxic conditions, and the fact that anoxic Black Sea sediments show not high organic matter content.
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Depositional Environment of Organic Rich Source Rocks
Depositional Environment of Organic Rich Source Rocks
Large anoxic lakes.Anoxic silled basins.Areas of coastal upwelling.Anoxic zones of the open oceans.
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Origin of Fossil Fuels Origin of Fossil Fuels Fossil fuels result from the accumulation, preservation, and burial of organic matter in various types of sedimentary environment. Over a long period of time and with increasing temperature, this organic matter will be subsequently degraded by diagenetic reactions and later by thermal reactions, which ultimately lead to the production of liquid hydrocarbons.
IMMATURE
OIL
WET GAS
DRY GAS
DIAGENESIS
CATAGENESIS
METAGENESIS
~~~~~~~
Land Plants
Aquatic PlantsOxic
Anoxic
Potential
Source Bed
Burial and HeatOil Trap
Oil and GasMigration
Oil
OilSource
Bed
Heat
Evolution of Organic Matter in Sedimentary Rocks
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
0
1
2
3
4
5
Dep
th (
km)
Products
Biogenic Gas
Thermogenic Gas
Oil
Bio
mar
kers
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Origin of Fossil FuelsOrigin of Fossil FuelsThe starting point for the production of organic matter is the photosynthetic cycle.Higher plants on land and phytoplankton in the oceans are the major primary producers.They assimilate CO2 from the atmosphere incorporating carbon into compounds that become part of these living systems. Carbohydrate is the main form in which organic matter is stored in living cells.The reverse process of photosynthesis is respiration, which typically occurs at night in the absence of sunlight. The majority of the photosynthetically fixed organic carbon (99.9%) is relatively rapidly recycled back into the atmosphere with only a small amount (0.1%) escaping from the photosynthetic cycle and being incorporated into the sedimentary record.
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Origin of Fossil FuelsOrigin of Fossil Fuels
An even smaller fraction of this trapped organic carbon may ultimately become part of some type of fossil fuel.
Atmospheric CO2
PhotosynthesisPlants-Bacteria
Dead & DecayingPlants, Animals,
Bacteria
SedimentaryOrganic Material
Incorporation
DAYS-YEARS~3.0X1012 Tone Organic Carbon
MAJOR CYCLE
CO2
Combustion ofFossil Fuels
Oil, Gas
Bitumen
Shale, CoalKerogen
MILLION YEARS6.5X1015 Tone Organic Carbon
MINOR CYCLE
Leakage(0.01-0.1%
Total OrganicCarbon)
Oxidation
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Composition of Organic Matter Composition of Organic Matter Naturally occurring organic matter is composed of varying proportions of six major classes of organic compounds namely proteins, carbohydrates, essential oils, resins, lipids and pigments.Lipids constitute the precursors of many classes of compounds found in crude oils and source rock extracts.
SubstanceElemental Composition in Weight Percent
C H S N OCarbohydrates 44 6 - - 50
Lignin 63 5 0.1 0.3 31.6Proteins 53 7 1 17 22Lipids 76 12 - - 12
Petroleum 85 13 1 0.5 0.5
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Methods of quantifying maturity in source Rock:
Vitrinite reflection (Ro)Thermal alteration Index (TAI)C.P.IRatio of hydrogen to carbon (H/C)Elemental compositionTmaxTime temptation index (TTI)Spore & pollenRock Eval pyrolysisBiomarker Guide
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Composition of Organic MatterComposition of Organic Matter
H
H
24-Ethytcholeatane
H 10.4 ppm
49 ppm
C28TA-Steroid
H
H
H 145 ppm17(H)-Hopane
3.8 ppm
C29MA-Steroid
Triaromatic Steroids
Monoaromatic Steroids
17(H)-Hopanes
Steranes
Saturates
Aromatics
Whole Oil
The compounds derived from the lipid precursors and occurring in crude oils, typically known as biomarkers.
29%
24%
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Chemical Structures and Nomenclature Chemical Structures and Nomenclature
It is the building block of biomarkers.The end closer to the methyl branch (-CH3) is called the “head”, and the other end is the “tail”.Monoterpane: two isoprene units joined head- to- tail.Diterpane: four isoprene units or two monoterpanes.Triterpane: six isoprene units or three monoterpanes.
Monoterpane
Isoprene
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BiomarkersBiomarkers
H
H
24-Ethytcholeatane
H 10.4 ppm
49 ppm
C28TA-Steroid
H
H
H 145 ppm
17(H)-Hopane
3.8 ppm
C29MA-Steroid
Triaromatic Steroids
Monoaromatic Steroids
17(H)-Hopanes
Steranes
Saturates
Aromatics
Whole Oil
Complex organic compounds composed of carbon, hydrogen, and other elements which are found in oil, bitumen, rocks, and show little or no change in structure from their parent organic molecules in living organisms.
They are very useful in determining the source and diagenesis, and the maturity of organic matter as well as the reservoir transformations.
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Examples of BiomarkersExamples of Biomarkers
Steranes
Four rings A, B, C and D.D-ring contains only “5C” atoms.Triterpanes
3-6 rings.5-rings are the most common (hopanes) in which E-ring contains only “5C atoms”.Gammacerane: 5-rings with “6 C atoms” in E-ring.
A B
C D
Cholestane Diacholestane
STERANES
A B
CD
E
A-Tricyclic Terpane
De-A-Lupane Hopane
Gammacerane
TRITERPANE
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Numbering System Numbering System
The precise number of carbon atoms depends on: Source material. Diagenesis. Thermal maturity. Biodegradation.
The numbering system indicates where side chains are attached to the ring system.
1
STERANES
2
34
5
19
910 8
67
1211
1713 16
1514
18
21
2022
2324
25
26
29
28
TRITERPANES1
2
34
5
25
910 8
67
1211
2813 16
1514
18
26
19 20
21 34
3522
27
30
32
33
29
31
19
23 24
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Nomenclature of BiomarkersNomenclature of Biomarkers
Nor-
Prefix meaning without, indicating that a methyl group has been lost from the base compound (parent molecule) of the biomarker at the position indicated by the preceding number. Thus, 28,30-bisnorhopanes lack the C28 and C30 methyl groups found in hopanes.Homo-
Prefix referring to additional carbon atom on the structure of the parent molecule.
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StereochemistryStereochemistry
It refers to the spatial relationship of atoms in a molecule.Whenever two rings are joined, each of the atoms at the junction is attached to three other carbon atoms in the ring structure.Its fourth bond (H2 or CH3-) can point either up or down with respect to the plane of the ring.
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A
StereochemistryStereochemistry
Alpha (α) position:Alpha (α) position:refers to substituents that attachedrefers to substituents that attachedbelow the plane of the ring structure.below the plane of the ring structure.Beta (ß) position:Beta (ß) position:refers to substituents that attachedrefers to substituents that attachedabove the plane of the ring structure.above the plane of the ring structure.
Two Systems of PresentationTwo Systems of PresentationWedgesWedges Solid wedges indicate Beta (ß) position.Solid wedges indicate Beta (ß) position. Dashed or dotted wedges indicate Alpha (α) position.Dashed or dotted wedges indicate Alpha (α) position.
CirclesCircles Solid (dark) circles indicate Beta (ß) position.Solid (dark) circles indicate Beta (ß) position. Open circles indicate Alpha (α) position.Open circles indicate Alpha (α) position.
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StereochemistryStereochemistryChirality or Asym.carbon atoms:
If four different substituents are attached to a particular carbon atom (e.g. C22 in hopanes or C20 in steranes), the atom is called an asymmetric or chiral carbon atom.In a molecule containing more than one asymmetric center, inversion of all the centers leads to the enantiomer (mirror image). Inversion of only one center yields an epimer. Inversion of more than one or less than all yields a diastromer.
d
c
ab
d
c
ba
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StereochemistryStereochemistryR (right or rectus) epimerIt indicates that the rank of the different four groups bonded to an asymmetric carbon atom decreases in the clockwise direction.S (left or sinister) epimerIt indicates that the rank of the different four groups bonded to an asymmetric carbon atom decreases in the counterclockwise direction.
X
H22
22R
X
H22
22S
H
CC
I-C3H7 C2H5
n-C4H9
C20H35
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