25th International Meeting on Organic Geochemistry IMOG 2011

P-304
Decision-tree chemometrics of biomarker and isotope data
identifies multiple petroleum systems in the San Joaquin Basin,
California
Kenneth Peters 1 , L. Scott Ramos 2 , Leslie Magoon 3 , Paul Lillis 4 , John Zumberge 5
1 Schlumberger and Stanford University, Mill Valley, United States of America, 2 Infometrix, Inc., Bothell,
United States of America, 3 USGS Emeritus and Stanford University, Menlo Park, United States of America,
4 USGS, Denver, United States of America, 5 GeoMark Research, Ltd., Houston, United States of America
(corresponding author:kpeters2@slb.com)
Chemometric analysis of 17 source-related biomarker
and stable carbon isotope ratios was conducted on
185 oil samples from the San Joaquin Basin. The
results identify three tribes and 14 families of oils (Fig.
1), which retain the imprint of the vertical and lateral
organofacies variations in their source rocks: (1)
Eocene Kreyenhagen and Tumey formations (four
families) (2) Miocene Monterey Formation (North
depocenter, eight families), and (3) Miocene Monterey
Formation (South depocenter, two families).
Fig. 1. Automated chemometric decision-tree can be
used to classify newly collected oil samples into one
of 14 San Joaquin Basin oil families.
Tribe 1 originated in one depocenter from basal
Kreyenhagen and overlying Tumey source-rock
organofacies. Families in Tribe 1 have more negative
isotope ratios and higher diasteranes than Tribes 2 or
3. Miocene Tribes 2 and 3 originated from Upper and
Lower Monterey source rock in two depocenters.
Tribe 2 originated from the Buttonwillow depocenter,
while Tribe 3 originated from the Tejon depocenter
north and south of the Bakersfield Arch, respectively
(Fig. 2). Unlike the other six oil families in Tribe 2
generated from the Upper Monterey Formation,
Families 22 and 231 originated mainly from the Lower
Monterey Formation and have low 25,28,30trisnorhopane
and 28,30-bisnorhopane ratios.
Fig. 2. The Bakersfield Arch plays a key role in the
distribution of Miocene oil families. Tribe 2 originates
from the North (Buttonwillow) depocenter, while Tribe
3 originates from the South (Tejon) depocenter.
Tribe 3 oils from south of the Arch have higher C19/C23
tricyclic terpane, oleanane/hopane, and %C29 sterane
ratios than Tribe 2 from north of the Arch. Therefore,
the Monterey source rocks for Tribe 3 were enriched
in higher plant input compared to Tribe 2. Based on
production intervals, Families 31 and 32 are from
Upper and Lower Monterey source rock, respectively.
Family 31 has lower C19/C23 tricyclic terpane,
oleanane/hopane, and diasterane ratios and higher
steranes/hopanes, indicating a more distal source
rock with less higher plant input than Family 32.
Both the Eocene and Miocene families show little
cross-stratigraphic migration due to internal seals
within the source rocks as evidenced in outcrops at
Chico Martinez Creek and elsewhere in the basin.
These results show the value of chemometrics
applied to large petroleum databases where all
samples are analyzed using the same procedures
and instrumentation.
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