Enhanced Understanding of Coastal Plain Aquifers

Origin of Petroleum
Results of 2005 AAPG Research
Presentations at Conference
L. Anissimov – LUKOIL-VolgogradNIPImorneft
C. Barker* – University of Tulsa
A. A. Brown* – Independent Consultant
J. L. Charlou – Geosciences Marines, Institut Francais de recherche pour l’exploitation de la mer
W. G. Dow* – Chief Geochemist, EOG Resources, Inc.
M. Hovland* – Statoil
C. W. Hunt – Independent Consultant
B. J. Katz* – Chevron
S. B. Keith – MagmaChem, LLC
A. A. Kitchka – Centre For Aerospace Research of the Earth (CASRE), Nat’l Acad. Sci. Ukraine
M. R. Mello*– High Resolution Technology and Petroleum Institution
J. Seewald – Woods Hole Oceanographic Institution
P. Szatmari – Petrobras Research Center (CENPES/GEOTEC)
B. M. Valyaev – Oil and Gas Problems Institute, Russian Academy of Sciences
*= Presentation supporting organic origin of petroleum
Summary of Katz et al. (2008)
1. Organic (Biogenic) Formation of Petroleum
2. Inorganic (Abiogenic) Formation of Hydrocarbons
a. Mantle Degassing (Deep Hydrocarbon Degassing)
b. Serpentization & Fischer-Tropsch Reactions
3. Importance of Fluid Flow in Hydrocarbon Migration
Organic (Biogenic) Origin of
At the AAPG Research Conference, presenters in
support of an organic origin provided a single and
uniform model in which sedimentary organic matter is
thermally converted to oil and gas.
Inorganic (Abiogenic) Origin of
1. At the AAPG Research Conference, some
presenters in support of an inorganic origin provided
a model based on mantle degassing associated with
the polymerization of low molecular weight
compounds (deep hydrocarbon degassing).
2. Some presenters advocated serpentization of
ultramafic rocks coupled with Fischer-Tropsch
catalyzed reactions in which carbon monoxide and
hydrogen are converted into hydrocarbons.
Organic Formation of Petroleum
1. Principal school of thought of petroleum geoscientists
is that the origin of petroleum is by organic means.
2. Organic formation of petroleum is the assumed origin
of oil and gas for this class.
3. Exploration strategies discussed in this class are
based on an organic origin of petroleum.
What is Petroleum (Petra=Rock,
1. Organic origin.
2. Non-renewable resource.
3. Crude oil comprised of hydrocarbons (H, C) and nonhydrocarbons, including nitrogen, sulfur and oxygen
4. Occurs naturally as gas (methane), liquid
(petroleum), semisolid (bitumen), and solid (asphalt).
Criteria for Optimal Occurrence
1. Rapid deposition of fine grain sediments and
associated organic matter in aqueous reducing
2. Compaction and chemical change of organic matter
due to thermal alteration resulting in generation of
3. Expulsion and primary migration of oil and gas from
source rock to reservoir rock associated with seal.
4. Secondary migration in reservoir rock and
accumulation in trap.
Limiting Conditions for Occurrence
1. Aqueous Reducing Sedimentary Environment
(Marine or Non-marine)
2. Depth of Burial (Geothermal Gradient, Heat Flow)
3. Temperature (150-350 degrees F for Liquid HC and
350-450 degrees F for Thermogenic Gas)
4. Length of Cooking Time (estimated 1-2 million years
5. Type of Organic Matter (Oil or Gas Prone)
Chemistry of Petroleum
1. Paraffins (Straight or Branched Chains)
2. Naphthenes (Saturated Ring Structures)
3. Aromatics (Benezene Ring with Double Bonds)
4. More Hydrogen Rich, More Oil Prone
5. Non-hydrocarbons (Asphaltenes and Residins)
API Gravity
1. American Petroleum Institute (API) Gravity
2. 141.5/Specific Gravity at 60 degrees F minus 131.5
3. Low Gravity (10 to <20 degrees)
4. Intermediate Gravity (20 to 40 degrees)
5. High Gravity (41 to >50 degrees)
Types of Organic Matter (Kerogen)
1. Algal (Phytoplankton)
2. Herbaceous (Spores, Pollen, Leaf Cuticle)
3. Woody
4. Coaly
5. Amorphous (Altered Algal or Herbaceous, Enriched
in Hydrogen through Biological Processes)
HC in Present Day Sediments
1. Odd Carbon Numbers Dominant
2. High Percent of Heavy HC and Non-hydrocarbons
3. Biogenic not Thermogenic Methane
4. Low Percent of C2 to C6
5. Light HC (C12-14) Absent
Methods for Determining Thermal
1. Thermal Alteration Index (TAI, Visual Kerogen, Color)
2. Vitrinite Reflectance (% Ro)
3. Weight Percent of C in Kerogen
4. Fixed C Index
5. Coal Index
Source Rock Criteria
1. Maturation State
2. State of Hydrocarbons
3. Type of Organic Matter (Kerogen)
4. Color of Shale is not a Reliable Criterion
Quality Source Rock Characteristics
1. Contact with Reservoir Rock
2. Shale Richness (2 to 4 plus % TOC, Average
Shale=1% TOC)
3. Carbonate Mudstone Richness (0.5 to 1 plus % TOC)
4. Type of Organic Matter (Algal and Amorphous for Oil)
5. Sufficient Saturation Level (HC to C Ratio) to Support
Expulsion and Migration
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