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Page 1: A brief Introduction · A brief Introduction Chapter 1 in textbook. 1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion 2. Passive

A brief Introduction

Chapter 1 in textbook

Page 2: A brief Introduction · A brief Introduction Chapter 1 in textbook. 1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion 2. Passive

1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion

2. Passive techniques - detect a naturally occurring signal - example: variations in gravity over a buried object

Geophysical exploration techniques

GEOPHYSICS 224 1. Seismic exploration (reflection and refraction)

2. Gravity exploration

3. Magnetic exploration

Common Applications - oil and gas exploration - mineral exploration - diamond exploration (kimberlites) - hydrogeology - geotechnical and engineering studies - tectonic studies - earthquake hazard assessment - archaeology

Page 3: A brief Introduction · A brief Introduction Chapter 1 in textbook. 1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion 2. Passive

(active or passive) (passive) (passive)

Page 4: A brief Introduction · A brief Introduction Chapter 1 in textbook. 1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion 2. Passive

from wikipedia based on CIA Factbook

Key Target: 1. Hydrocarbons

Page 5: A brief Introduction · A brief Introduction Chapter 1 in textbook. 1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion 2. Passive

!5

178 billion barrels (Wikipedia)Traditional: 40% in Alberta, then 27-28% each in Newfoundland & Saskatchewan If factor in oil sands: Alberta =98% (today = 95%, 3rd to Venezuela & Saudi Arabia)

Page 6: A brief Introduction · A brief Introduction Chapter 1 in textbook. 1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion 2. Passive

!6from Eccles, AGS Open File Report 65, 2011 (not highly economical)

Key Target: 2. minerals

Page 7: A brief Introduction · A brief Introduction Chapter 1 in textbook. 1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion 2. Passive

Crustal Structure of Alberta

(Pilkington et al., 2000; Hope and Eaton, 2002)

• Archean and Proterozoic basement covered by WCSB

• basement domains identified using geophysical data and rocks from oil wells

MAGNETIC DATAGRAVITY DATA

Key target: 3.Tectonics

SEISMIC DATA

Page 8: A brief Introduction · A brief Introduction Chapter 1 in textbook. 1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion 2. Passive

Geophysical measurements

- indirect observations of subsurface geology

- surface measurements of natural or artificial signals that travel through the Earth

- surveys are regional: 10s of km up to the entire Earth

- generally resolution is 1 m or more – but can be higher for near-surface studies with sensitive instruments

General Assessment

Page 9: A brief Introduction · A brief Introduction Chapter 1 in textbook. 1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion 2. Passive

Interpretation of geophysical data is often non-unique ! several different rock types and geometries may give the same

observation

It is important to use additional information ! borehole data, knowledge of local geology, other types of

geophysical data

- geophysics and geology are complementary

Geophysics and Geology

Geophysical observation

Material property

Subsurface geology

Page 10: A brief Introduction · A brief Introduction Chapter 1 in textbook. 1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion 2. Passive

Validation

Validation of geophysical exploration methods

A. Geological mapping - detailed information about rocks exposed at surface - limited information about deeper structures (need areas that have undergone uplift, faulting, erosion)

B. Borehole studies - extensive information about one location (rock types, thicknesses, etc.) - point measurement, expensive, few km deep

Most of the techniques are Interpretive, based on modeled/inverted outcomes

Page 11: A brief Introduction · A brief Introduction Chapter 1 in textbook. 1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion 2. Passive

Kola Superdeep Borehole (NW Russia, 1989) - 12,262 m depth in 19 years - drilling stopped due to high temperatures (>180C)

Al Shaheen oil well (Persian Gulf, 2008): - 12,290 m in 36 days

Sakhalin-I Odoptu OP-11 well (offshore eastern Russia, 2011) - 12,345 m in 60 days - horizontal distance of 11,475 m

(www.geo.uni-bonn.de/members/schulze)

Deepest Boreholes

(http://stratoil.wikispaces.com/Sakhalin)Yastreb drilling rig

(52 m tall)

FOR COMPARISON: - avg. continental crust = 35 km thick - avg. radius of Earth = 6371 km

Page 12: A brief Introduction · A brief Introduction Chapter 1 in textbook. 1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion 2. Passive

!12Corine Prieto, IGC Footnote Series, Integrated Geophys. Corp.

Where seismics may not be as effective…

Page 13: A brief Introduction · A brief Introduction Chapter 1 in textbook. 1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion 2. Passive

These methods are complementary

Seismic reflection data from northern Germany! layers of sediments that have been perturbed by a salt diapir

! salt structure coincides with an area of low gravity

Gravity data !

(Oezsen, 2004)

Seismic data

Page 14: A brief Introduction · A brief Introduction Chapter 1 in textbook. 1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion 2. Passive

Simulated ‘ground roll’ near Antipode

Get me out of here, faaaaaassstttt…..!!

Methods of our focus (basin/crust) have far reaching applications, not just in prospecting

Global Example

Page 15: A brief Introduction · A brief Introduction Chapter 1 in textbook. 1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion 2. Passive

Example 2: megahertz scale studies of bones (ultrasound imaging)

Page 16: A brief Introduction · A brief Introduction Chapter 1 in textbook. 1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion 2. Passive

Waveform Fitting Using Best 1D ModelThe nature of these pulses on the ultrasound records are:

P wave in top CB

P-S conversions in top CB

S wave in top CB

Surface wave in top CB

Marrow P and S multiples

Black ---- data Red ---- synthetics

(Le, Gu, Li & Chen 2010, APL)

Page 17: A brief Introduction · A brief Introduction Chapter 1 in textbook. 1. Active techniques - a signal must be generated - example: seismic waves are generated by an explosion 2. Passive

Main goal: to develop an understanding of: - the physical basis for 3 geophysical techniques - how each technique is applied (data collection, processing,

interpretation) - advantages & limitations of each technique (resolution, non-uniqueness)

Mathematics will be used in this class - you are not expected to memorize equations (equation sheet provided) - must know how to use equations in data analysis and interpretation - bring your calculator to classes, labs, and exams

Feel free to ask questions! - provide feedback on the level of course material (math, geology, etc.)

1.3 General Comments


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