What about all that buriedorganic matter? Methods for characterization of fossil carbon Petroleum Generation Migration, leakage and remineralization Conversion.
Post on 27-Mar-2015
212 Views
Preview:
Transcript
What about all that buriedorganic matter?
‧Methods for characterization of fossil carbon
‧ Petroleum Generation
Migration, leakage and remineralization
‧ Conversion to Deep Gas
Leakage to surface; hydrate formation
‧ Uplift and Weathering Processes Microbial utilization
‧ Alternative Hypotheses ‘Myth of Fossil Fuels’
Thomas Gold
‧Hydrocarbons are primordial
‧As they upwell into the crust,
microbial life invades for a free meal
‧Hydrocarbons are not biology
‘reworked’ but , rather, geology
reworked by biology thus explaining
the presence of all those biological
signatures in oils
KEROGEN
Kerogen is the component of organic matter that is insoluble in inorganic and organic solvents (Durand, 1980). Bitumen is the soluble component. Both widely distributed in sediments; sometimes massive accumulations as in coal and oil deposits
Microscopic examination cansometimes give information on geological age, paleoenvironment, thermal history (colour)- palynology, petrography But most organic matter is amorphous and unicentifiable – need chemical means to quantify and evaluate origins………. Bulk Properties, carbon isotopes, biomarkers
Bulk Properties
Total organic carbon %TOC% Total C, H, N, O, S13C (now easily 18O, D, 15N, 34S)elemental H/C ratio (originally 1.3 → 0 for C)solid phase nmr → environment of Cie aromatic C,H vs saturate C……………..
The above give limited information on provenance
Further characterisation by pyrolysis (Rock-Eval), pyrolysis-GC, pyrolysis GC-MS and laser ablation-MS
Solvent extraction and GC, GC-MS give information on bitumen composition
OrisBulk Properties
‘An organic facies is a mappable subdivision of a stratigraphic unit, distinguished from the adjacent subdivisions on the character of its organic constituents, without regard to the inorganic aspects of the sediment’
R.W. Jones ‘Advances in Petroleum Geochemistry’(ed. J. Brooks & D. Welte) 1987
Source Controls on Organic Carbon
Sapropelic Humic
Algal + Amorphous Herbaceous Woody Coaly
Liptinite Exinite Vitrinite Inertinite
Kerogen
Macermal Alginite + Sporinite Telinite FusiniteAmorphous Cutinite Collinite Micrinite Resinite
KerogenH/CO/CORGANICSOURCEFOSSILFUELS
OrisBulk Properties
‧API gravity. USA measure related to
specific gravity
‧API = [(141.5 / SG@16°C) – 131.5]. Water has
gravity 10°API. Heavy oils <25°. Medium 25°to
35°. Light 35°to 45°. Condensates > 45
Sulfur, Nickel andVanadium
‧Sulfur: High in marine and some saline lacustrine
oils; generally decreases as a function of maturity
‧Can be a useful correlation tool where there are S-
rich petroleum systems but Australian oils
generally low in sulfur.
‧Nickel and Vanadium contents; largely exist in
porphyrin content. Generally decrease with
maturation.
HYDROCARBONSACYCLIC & MONOCYCLIC ALKANES
HYDROCARBONS
ACYCLIC ISOPRENOID ALKANES
RegularPristane C19
RegularPhytane C20
IrregularBotryococcane
HYDROCARBONS
ACYCLIC ISOPRENOID ALKANES
Irregular C20 branched Irregular C25 branched
Derived from diatoms
MONOAROMATICHYDROCARBONS
Toluene Tri-substituted alkyl benzene
PETROGENIC PAHs
PHENANTHRENEPHENANTHRENE PHENANTHRENE
NAPHTHALENERETENE
LOWMWPAHs
NAPHTHALENE ACENAPTHENE FLUORENE
PYRENE CHRYSENE BENZO(a)PYRENE
COMBUSTION PAHs
ANTHRACENE
CORONENE
PENTACENE
BIOPOLYMERIC MOLECULESANGIOSPERM RESIN
Polycadinene
BIOPOLYMERIC MOLECULESGYMNOSPERM RESIN
labdatriene polymer
“leaf resins”e.g.
phyllocladenes,pimaradienes
“resin acids”,e.g. abietic acid
Anderson’s ResinClassification Scheme
ClassⅠ
Ⅱ
polymeric labdanoid diterpenes;+ occluded sesgui-, di and triterpenoidsAgathis/Araucaria – Baltic amberHymenaea – Dominican, Mexican amber
polymeric sesquiterpenes;polycadinene+ occluded sesqui- and triterpenoidsDammar/Dipterocarpaceae – SE Asia
polystyrenenon-polymeric cedrane sesquiterpenoidsnon-polymeric abietane/pimarane diterps
Australian Coastal Resinites Resin Pedigree
Bales bay,kangarool IsNo Two Rocks SAThree Mile rocks SALake Bonney SA
Brunei resiniteGippsland resiniteKauri resinRecent dammar
Bulk Carbon Isotope Composition of Modern & Fossil Resins
‘heavier’ carbon
Plants optimise stomatal conductance to maximise access to CO2 & minimise loss of water \ water
conservative plants have isotopically
Needle leaf morphologyWater conservativeRestricted access to CO2
Discriminates less against 13Cvalues for wood typically:
Broad leaf morphologyLess water conservativeLess restricated access to CO2
Discriminates more against 13Cvalues for wood typically:
*Data from Stuiver and Braziunas,1987 for 40 latitude modem plants
Oils with conifer vs Angiosperm OMCarbon Isotopes vs Oleanane/Hopane
GippslandBasin, Oz
TaranakiBasin, NZ
Data from AGSO/GeomarkBiodegraded oils excluded
Oleanane/hopane
Affected by migrationcontamination
‧14C-Dead Living Biomass: Evidence for Microbial Assimilation of
Ancient Organic Carbon During Shale Weathering
‧ S. T. Petsch,* T. I. Eglinton, K. J. Edwards
‧ Prokaryotes have been cultured from a modern weathering profile developed on a ~365-million-year-old black shale that use macromolecular shale organic matter as their sole organic carbon source. Using natural-abundance carbon-14 analysis of membrane lipids, we show that 74 to 94% of lipid carbon in these cultures derives from assimilation of carbon-14-free organic carbon from the shale. These results reveal that microorganisms enriched from shale weathering profiles are able to use a macromolecular and putatively refractory pool of ancient organic matter. This activity may facilitate the oxidation of sedimentary organic matter to inorganic carbon when sedimentary rocks are exposed by erosion. Thus, microorganisms may play a more active role in the geochemical carbon cycle than previously recognized, with profound implications for controls on the abundance of oxygen and carbon dioxide in Earth's atmosphere over geologic time
Science, Vol. 292, Issue 5519, 1127-1131, May 11, 2001
Table 2. 14C and 13C analysis of PLFA compound classes isolated from enrichment culture grown on New Albany Shale, and calculated fraction of PLFA carbon derived from ancient kerogen.
Total mass PLFAKerogen in shale substrateModern atmospheric CO2
top related