Last Time
UNIVERSITY OF SOUTH ALABAMA
Petroleum Geology (ON LINE)
GY 305: Geophysics
Lecture 4:
Petroleum Part 1:
•
•
•
Introduction
Subsurface fluids (origin of petroleum)
Migration of petroleum
Reservoirs, Trapping Mechanisms, Porosity
Subsurface Fluids
Rocks in the subsurface generally contain fluids:
Water: the most common fluid and as important to the petroleum
geologist as it is to hydrologists like Connors.
Subsurface Fluids-Petroleum
Petroleum: A natural substance
that occurs as semi-solids, liquids
or gases and mutual solutions of
these)
1) Crude Oil: leaves a residue of
crap on distillation
2) Gas Condensate: leaves no
residue on distillation
A crude oil spa in Azerbaijan
http://www.lindsayfincher.com/2006/12/a_barrel_of_your_finest_crude.html
http://www.andrill.org/iceberg/blogs/luann/images/porewater-in-ss.jpg
Subsurface Fluids-Petroleum
Subsurface Fluids-Petroleum
Grades of Petroleum
Crude oil composition
varies widely from area to
area, field to field and even
reservoir to reservoir in one
field, but elemental
composition varies little.
Condensate: > 55° API
Light oil: 31-55° API; viscosity <100 cP
Medium oil: 22-31° API
Heavy oil: 10-22° API; viscosity >100 cP
Extra-heavy oil : <10° API
Tar Sands: viscosity > 10,000 cP
C: 83 to 87%
H: 12 to 15%
NSO: <5%
*centipoise =cP
Chapman, R.E., 1983. Petroleum Geology. Developments in Petroleum Science
16. Elsevier, Amsterdam, 415p.
1
Petroleum Formation
Type 1 Kerogen: derived from organic
material with lipids (dominantly marine)
with H/C ratios >1.5. Few aromatic
compounds. Good source for oil/gas.
Petroleum Formation
Organic maturity is
controlled by
temperature and possibly
pressure…
Type II Kerogen: also derived from marine
organic material but with H/C ratios <1.5
and dominated by aromatic rings. A “quite
good” source for oil/gas.
http://www.uni-tuebingen.de/geo/gpi/ag-luterbacher/mitarbeiter/ Liguis/seiten/bild-6.JPG
Type III Kerogen: derived from terrestrial
plant organic material. H/C ratios <1.0 and
dominated by aromatic rings. Not a good
source for liquid petroleum, may generate
gas.
http://www.humble-inc.com/wafr_sr_stdy.htm
Petroleum Formation
Today’s Agenda
… which is ultimately depth-related
Petroleum Geology Part 2
•
•
•
•
Migration of petroleum (continued from Monday)
Reservoirs
Trapping Mechanisms
Porosity
http://openlearn.open.ac.uk/file.php/2292/S278_1_001i.jpg
Migration of Petroleum
Primary Migration
Oil Phase Migration
Need to consider primary
and secondary modes of
petroleum migration.
•Secondary migration is important
for reservoir development and will
be the subject for the next lecture.
http://www.geo.wvu.edu/~jtoro/Petroleum/petroleum_figs/review2/source_rx.jpg
•In high TOC rocks, the kerogen can form
connected bands.
•The fluid pressure of the oil within the black
shales can become high enough to produce
microfractures in the rock.
•Once the microfractures form, the oil is
squeezed out and the source rock collapses.
•Primary migration can be viewed as a second
episode of compaction.
•Microfractures of this type can be seen in most
productive source rocks and they are often
filled with remnants of oil.
•Most hydrocarbons probably are expelled
from the source rock as liquids.
http://www.geo.wvu.edu/~jtoro/Petroleum
2
Petroleum Reservoirs
Petroleum Reservoirs
Petroleum reservoirs are rock units that contain recoverable quantities of crude oil,
distillate and/or natural gas.
Petroleum reservoirs are rock units that contain recoverable quantities of crude oil,
distillate and/or natural gas.
•Almost always sedimentary in nature
•Almost always sedimentary in nature
•Must be both porous and permeable
http://www-rohan.sdsu.edu/~rhmiller/sedimentaryrocks/oildeposit1.jpg
http://www.indiana.edu/~librcsd/etext/hoosier/image/og-13.jpg
Trapping
Mechanisms
Trapping
Mechanisms
Come in different “flavors”
Come in different “flavors”
1) Stratigraphic (e.g., pinchouts)
2) Structural (e.g., anticlines)
1) Stratigraphic (e.g., pinchouts)
2) Structural (e.g., anticlines)
3) Sedimentary (e.g., facies and/or
porosity changes)
http://www.geo.wvu.edu/~jtoro/Petroleum/petroleum_figs/review2/traps/strat_traps.jpg
http://bcartifacts.50megs.com/RodGallery/SSMapping/AppendixCStructuralandStratmaps.jpg
Trapping
Mechanisms
Porosity
Also comes in many flavors:
Come in different “flavors”
1) Primary (depositional):
a) interparticle
b) framework
c) fenestral
1) Stratigraphic (e.g., pinchouts)
2) Structural (e.g., anticlines)
3) Sedimentary (e.g., facies and/or
porosity changes)
4) Combinations of any of the above
2) Secondary:
a) dissolution (moldic, oomoldic, vuggy)
b) intraparticle/intracrystalline/intercrystalline
b) fracture
http://www.geomore.com/images/TRAPS.jpg
3
Porosity
Porosity
Two different sandstones viewed in thin-section
Two different sandstones viewed in thin-section
Porous
1 mm
Plan polarized light
Porosity
1 mm
0.5 mm
crossed Nichols
Non-porous
Plan polarized light
0.5 mm
crossed Nichols
Porosity
Primary (Interparticle)
Primary (Intraparticle)
Porosity
Porosity
Primary (fenestral)
Primary (Intraparticle)
4
Porosity
Secondary (moldic)
Porosity
Secondary (moldic)
Porosity
Porosity
Secondary (oomoldic)
Secondary (fracture)
Porosity
Upcoming Stuff
Thursday Lab:
Left over mathematics (bring calculator)
Porosity in thin sections
Monday Lecture
Sp Logs
Secondary (vuggy)
5