25th International Meeting on Organic Geochemistry IMOG 2011

P-031
New techniques for understanding and mapping high-maturity
petroleum systems. Examples from the San Joaquin Basin, San
Juan Basin, and US Gulf Coast
David Zinniker, J. Michael Moldowan, Jeremy Dahl, Peter Denisevich
Stanford University, Stanford, United States of America (corresponding
author:dzinniker@stanfordalumni.org)
While high-maturity petroleum systems play an
increasingly important role in exploration, the
geochemical tools available for their characterization
remain limited. Traditional organic geochemical
analyses focusing on easily-cracked components like
biomarkers are blind to high-maturity contributions
and other analyses (i.e. light hydrocarbon analysis
and diamondoid abundance) hint at their presence but
do not narrow down the geological source, thermal
maturity, or expulsion, migration, or degradation
processes important in its history.
Our work focuses on new analytical techniques for
quantifying and isotopically characterizing a range of
persistent compounds that can survive the extreme
processes involved in the formation of high-maturity
hydrocarbons. Compounds studied include simple
and higher diamondoids, volatile hydrocarbons,
persistent aromatic compounds, and ―high-stability
biomarkers‖ formed from traditional biomarkers by
rearrangement or cracking.
These techniques are showing promise for
fingerprinting the sources of high-maturity liquids and
thermogenic gas – and for identifying and mapping
the contribution of high-maturity liquids to conduits,
reservoirs, and seeps. The work also points toward
important signatures that may help us decipher
evaporative fractionation, cracking, expulsion and
retention in tight source rocks, migration, and catalytic
degradation.
Novel aspects of this research include the routine
extenstion of quantitative diamondoid analysis to
higher diamondoids with four to seven cages, the
extension of diamondoid carbon isotope analysis to
trimantanes and tetramantanes, isotopic
measurement of diverse mono-, di-, tri-, and tetra-
aromatic hydrocarbons, and isotopic measurement of
low ppm / high ppb concentrations of ―high-stability
biomarkers‖.
Model systems with vertically stacked source rocks
were explored to test the utility of these new
techniques. These include Tertiary and Mesozoic
systems in the San Joaquin Basin, Paleozoic and
Mesozoic systems in the San Juan Basin, and
Mesozoic systems along the United States Gulf
Coast.
These new techniques show potential for identifying,
mapping, and understanding high-maturity petroleum
systems. Their utility extends to many petroleum
mixtures because high-maturity contributions will be
the dominant source of ultra-stable compounds
across a broad range of dilutions.
Diamondoid Carbon IsotopeValue,‰
Diamondoid Relative Abundance
-16
-20
-23
-27
10
1
0.1
0.01
0.001
0.0001
0.00001
Adamantane
Smackover
Tuscaloosa
1 2 3 4 5 6 7 8 9 10 11 12
Compound #, adamantane and alkyladamantanes
Diamantane
Triamantane
Tuscaloosa
Smackover
Tetramantane 1
Tetramantane 2
Tetramantane 3
Pentamantane 2
Figure 1. CSIA-D and extended diamondoid profiles
easily distinguish Smackover- and Tuscaloosasourced
petroleum samples from the US Gulf Coast.
The set includes uncracked, cracked, and TSRaltered
samples.
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