Structural Geology in
Petroleum Exploration
Topics:
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
Petroleum System
Traps
Exploration Methods (seismic)
Maui Field Example
Salt Tectonics
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Reading:
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1. Outline in website
2. Pdf file: Geology for Petroleum Exploration, Drilling, and
Production by Norman J. Hyne, 1984, pages 173-197.
3. Salt Structures- Ch. 19 of Fossen
Factors required to make a
conventional Oil Deposit
•
A Sedimentary Basin with:
•
•
•
•
Source rock- rich in organic matter
Burial heating  maturation
Reservoir rock- porous and permeable
Trap–
–
structural trap
stratigraphic trap
Oil Exploration Strategy:




Petroleum system
Find the Traps
The most common traps are structures
Can’t see the oil ahead of the drill
So exploration often targets the structures in
hopes of finding oil
Origin of Petroleum

Oil forms from the decay and
transformation of dead organisms (algae)
buried in sedimentary rocks
% Total Organic Content
Maturation of Organic Matter
Source Rocks


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At about 60o C transformation of kerogen begins
• Liquid hydrocarbons begin to form
 Above 140o C only gas is produced
Black organic-rich marine
shales
Organic matter is preserved
in low-oxygen water
Restricted marine basins
and zones were water rises
from the deep
Migration of oil


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Oil is less dense than water
Oil will move up by buoyancy
Oil needs a permeable bed to move
It will stop when it reaches an impermeable bed
Migration
Oil Reservoirs

Eastern
Venezuela
Western
Canada

Permeable reservoir bed
Impermeable seal
Sandstone
Porosity
Open
space!
Trap Types
Stratigraphic Traps
3D Structural Closure, Cooper Basin (Australia)
Triassic
Cooper Basin
Permian
Structural
Traps
Triassic Inerval
Toolachee Fm
Roseneath Shale
Epsilon Fm
Murteree
Fm
Carboniferous
Patchawarra
Tirrawarra Fm
Merrimelia Fm
Merrimelia Fm:
- Starts the Cooper Basin
- Waxing and waning of glacial sediments
Trap Terminology
Fault
Traps
Gullfaks
GullfaksField
FieldNorth
NorthSea
Sea
Gullfaks Field North Sea
Fossen, 2010
Map of the
Murre Field
Compressional Traps
Newfoundland
Traps in Strike-Slip settings
Positive Flower Structures
How to see in the subsurface?
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Seismic Acquisition
Drilling
Structural Interpretation
Seismic Reflection Imaging
• Send sound into the rock, and collect the
echoes
Seismic shot
gatherEvery vertical
squiggle is from
one geophone
3D Seismic Image
Salt
3D Geological Model
Offshore Platform
Maui Field, New Zealand
Major
Hydrocarbon
Provinces in
North
America
Sedimentary Basins
Gulf of
Mexico
Salt
Gulf of Mexico
Salt moves driven by buoyancy
•Salt density= 2 g/ cm3
•Salt undergoes no compaction
•Shale Density is initially 40% water
•Initial Density = 1.8 g/
Halite, NaCl
cm3
•Water expelled during compaction
• Final Density = 2.4 g/ cm3
Gypsum,
Ca(SO4).2H20
Sequential Stages
of a Salt Diapir
Salt Traps
Seismic Image of a Salt Dome
Rootless Salt- Gulf of Mexico
AAPG Explorer, 2013
3D Seismic Interpretation of Salt
Structures
Relationship between Salt Movement and
Sedimentation
Syncline
Initial
syncline
are now
anticlines
Sandbox Experiment
Relationship between diapirism and normal faulting
Extension Above Salt Diapir
Salt Domes Pierce the Strata
Fractures around Salt Domes
Ant-Tracking
displaying radial
fracture pattern
around salt domes
8km
Salt Structures vs. Tectonic
Structures
•Caused by movement of salt, not by plate boundary
stresses
•Often linked to sedimentation
•Often localized by tectonic structures
•Both upwards movement of salt and salt withdrawal
cause deformation