Transcript Subsurface Mapping - McGill University

Subsurface Mapping
Introduction
Introduction
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Objectives of subsurface mapping
Methods
Before you start
Objectives
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Most of the Earth’s structure and
stratigraphy are hidden
Structure/stratigraphy may host
features of economic or academic
importance
Need to be able to map/interpret
the subsurface
Objectives
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Petroleum industry
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Mining
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Explore for and develop oil and
natural gas reserves
Explore for and develop minerals and
other economic deposits
Groundwater
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Explore for and develop groundwater
Objectives
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Waste disposal
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Geotechnical engineering
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Locate and map the distribution of
layers with specific properties
Academic studies
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Find suitable repositories for waste
Environmental remediation
Structure, stratigraphy
Etc.
Objectives
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This course: focus on petroleum
Why?
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Methods applicable to other fields
Best datasets
Objectives
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Develop the most reasonable
subsurface interpretation(s) for
the area being studied, even in
areas where the data are sparse or
absent
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Integration of different types of data
Interpretations used to direct
future exploration & development
Methods
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Wireline logs
Core, cuttings (“samples”)
Seismic data (2-D, 3-D)
Potential field data (gravity,
aeromag)
Ground-penetrating radar
Engineering data (fluids,
pressures, etc.)
Previous reports
Etc.
Geophysical logs used in groundwater studies
http://sofia.usgs.gov/publications/wri/94-4010/upperflaq.html
Geotechnical
borehole logs
http://www.geoprobe.com/products/tools/geotechnical/cptpro_log.htm
Tail buoy
Streamer
Air Guns
Marine seismic vessels typically tow arrays of air guns
and streamers containing hydrophones a few meters
below the surface of the water.
Messinian Salt – Mediterranean Sea
Salt
Courtesy TGS-Nopec
Vibroseis Operations - Algeria
Courtesy François Gauthier
Mapping Faults Using Dip Panels in Thrust
Regimes
•Dip panels
Waiting on 84wy314
Courtesy Anadarko
Slicing and Dicing to Extract Geologic Information
Seismic Cube
Timeslices
Methods
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Previous reports
Paper copies of data (analog)
Digital data: computer-based
interpretations
Methods
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Caveat: Without understanding
what you’re doing, you’ll get a
wrong answer.
Working with computers, you’ll get
a wrong answer at light speed (but
it may be good-looking!).
Methods
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Interpretations (maps, etc.) are
working hypotheses, never “final”
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May need to update, revise as new
data become available
Easier with digital data
Applies to ANY branch of (Earth) Science!!!
Collect Data
Interpret Data
Drill
Build
Collect pertinent
Database
data and reports
Output to
Output to
Simulator
Simulator
Scan through data
Scan through data
(quality, phase,
(quality,
phase,
geology)
geology)
Tie well and seismic
Tie well and seismic
data (vsp, synthetics,
data
(vsp, synthetics,
tops, paleo, etc.)
tops, paleo, etc.)
Pick Horizons
Pick Horizons &
& Faults
Faults
Reservoir
Reservoir
Property
Property
Prediction
Prediction
Mapping &
Mapping
Analysis
&
(Integration)
Analysis
Output
Drilling to
Simulator
Before you start…
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Need clear definition of objectives
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Structure? Stratigraphy? Exploration?
Development? Etc.
Without knowing where you’re going,
you’re unlikely to get there…
Before you start…
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Need good understanding of structural
geology, stratigraphy and other
related fields
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The more geology one knows, the more
reasonable the resulting interpretation
Need good understanding of physical
basis for any geophysical methods
being used
Prestack Depth Migration Example
Subsalt – Offshore GOM
Before you start…
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Use correct mapping techniques and
methods
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Prepare reasonable subsurface maps and
cross-sections
“Maps and cross-sections are the primary
vehicles used to organize, interpret and
present available subsurface information”
Digital products (e.g., volumes) becoming
more common
http://www.kgs.ku.edu/Workshops/IVF2000/nissan-ivf/tocnav640.html
Geocellular model:
Each cube is assigned initial
properties (porosity, permeability,
fluid saturation etc.)
3D display of georeferenced scanned images of collar locations,
geological cross-sections, integrated with drillholes displaying assay
concentrations, and magnetic and gravity modeled bodies.
www.rockware.com
Before you start…
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Need to define fault behaviour in 3-D
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Faults may have important affects on
location, movement of fluids
Show location of faults on maps, but also
map fault surfaces
May need to do structural reconstruction
to validate accuracy of fault
interpretations
A 2-D expression of a fault
Faults are 3-D features
Twiss and Moores, 1992
Fault visualization (Hart et al., 2001)
0mi
2.5mi
0km
2.5kmand Hart, in press)
Fault visualization
(Sagan
Courtesy Midland Valley
Before you start…
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All subsurface data need to be used to
develop a reasonable and accurate
subsurface interpretation
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Geologic (including paleontologic),
geophysical, engineering
Attention to resolution, accuracy of each
type
Integration of different types of data
results in more robust interpretation
Before you start…
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Need to document the work done.
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Lots of data likely to be collected and/or
generated – document in a format that
may be referenced, used, revised
People working on project may change,
may want to “revisit” work many years
after it is done
Electronic media (PowerPoint files,
hypertext documents, etc.) good vehicles
– especially when working with digital
data
Really great stuff
Fred, but how did
you generate it?
Ummm….
Summary
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Subsurface mapping of important
economic & fundamental importance
Push towards digital, computer-based
interpretation
Need to understand fundamentals –
geology, geophysics
Integration of different types of data
results in more robust interpretation