1. Call For Proposals January 2008
Acoustic and Elastic Waves in the Strongly Scattering and Non-linear Regime
Call For Proposals
January 2008

2. NONLINEAR GEOPHYSICS: WHY?
Nonlinear effects are visible in our ‘conventional’ seismic and EM Data but we usually ignore these
However: Non-linearities may provide new information:
Fracture systems
Fluid type
In particular at greater depths

3. Current Practice Industry seismic makes two assumptions:
single reflection process;
reflection process modelled as a linear perturbation on a smooth ‘background’
Extremely successful to
Map out subsurface structure;
Compute Reflection coefficients ~ elastic constants
Identifying rock-fluid systems (brine vs hydrocabon filled sand stones)

4. Conventional Seismic Imaging is based on a single reflection assumption in a linearly elastic subsurface using a high Frequency approximation in a smoothly varying, heterogeneous background

5. Current Seismic Techniques
Colours show reservoir quality
and possible hydrocarbons

6. Reflection Amplitudes indicative of Hydrocarbons
Normal reflection
Oblique reflection

7. Innovation is Required
Deeper targets mean more scattering will happen
Older geology means tighter and more fractured rock
Hence assumptiona may be violated!
Also, the reflection process gets more frequency dependent,
rock mass acts as varying low pass filter
Non-linearities may occur
We ask for your help to understand and model these effects.

8. NONLINEAR GEOPHYSICS: OVERVIEW
What kind of nonlinearities ?
Not: “Conventional” nonlinear terms (most simple physical model: externally driven oscillator): large amplitudes
But:
Effects of unconsolidated systems, such as fractures and faults.
Hysteresis and discrete memory effects
Flow related effects (e.g. turbulent terms)
Multifluid / fluid interface effects (oil/water, macro and micro level). This includes e.g. symmetry breaking surface tension forces.  
Effects triggered by (external ?) criticality (e.g. Tidal criticality)

9. Illustration: Nonlinear acoustic spectroscopy, fracture detection by nonlinear harmonics generation

10. Illustration: Nonlinear acoustic spectroscopy, fracture detection by nonlinear wave modulation

11. Broadening due to nonlinearities: Upper and lower side bands
SCHEMATICS: Frequency Broadening due to nonlinear effects
Amplitude
Frequency
Frequency content of typical seismic sweep
Broadening due to nonlinearities:
Upper and lower side bands
“Low Frequency effects e.g. Goloshubin”, “shadows” ???
 Use band filter to generate seismic displays with reduced frequency content (lower, e.g. <10Hz, and upper sidebands); compare to ‘conventional’ section.

12. Illustration: Nonlinear acoustic spectroscopy, fracture detection by nonlinear wave modulation
Use a Parametric Seismic Array to ‘force’ nonlinear mixing:
Two Input Frequencies  difference and sum frequencies
Seismic “version”:
Dual vibroseis setup, each emitting either a constant monochromatic signal of different frequency or one or both are doing sweeps (of different frequency content).
For example (schematic only):
frequency
time
vib1
vib2

13. TARGET ZONE (RESERVOIR)
Illustration: The nonlinear seismic field experiment
Parametric Array, Field setup and downhole arrangement:
A surface to downhole (test or exploration well) experiment is desirable to clearly identify and separate shallow and deep responses. The downhole array should at least reach beyond the immediate near surface (>100m), but it does not need to go necessarily all the way down to reservoir level. A horizontal instrumented well at intermediate depth (red sketch, “virtual source type”) would be ideal to effectively get beyond mere surface nonlinearities (unconsolidated ground, water table etc.).
TARGET ZONE (RESERVOIR)
DUAL VIB SOURCE
Surface geophone lines
Horizontal downhole geophone array
Vertical downhole array

14. Spectrograms from two vibrators 33 Hz and 45 Hz above an oil reservoir at Tatarstan (Russia, after V. Korneev 2007 LBL)

15. EXPERIMENTAL RESULTS FOR
A SEISMIC PARAMETRIC ARRAY:
Zhukov et al,
GDS Ltd. Moscow,
EAGE Vienna 2006/SEG New Orleans 2006
Parametric Array Experiment

16. EXPERIMENTAL RESULTS FOR
A SEISMIC PARAMETRIC ARRAY:
Zhukov et al,
GDS Ltd. Moscow,
EAGE Vienna 2006/SEG New Orleans 2006
Parametric Array Experiment

17. Nonlinear EM / IP effects
Wave propagation causes an electric potential across a fluid film coupled to the rock matrix
Coupling is significantly different if HCs are present
Thompson et al.,
The Leading Edge April 2007

18. Nonlinear EM /Induced Polarization
Short time: inductive („EM“)
Long time: charging („IP“)
time

19. SEISMOELECTRIC EXPERIMENT
Raw SEISMICEM Field Record:
Signals detectable
Dynamite Source array
Electrodes
Geophones
650m from surface
hydrocarbon
target
shallow fluid layer,
e.g. shallow aquifer
surface
SCHOONEBEEK
SEISMOELECTRIC EXPERIMENT

20. Some Questions/Wishes
What we would like to understand:
Behavior of strongly scattering of elastic waves with small amplitudes in heterogeneous rock/fluid systems in the non-linear regime;
What mechanical coupling with Electromagnetic waves may occur/exist in this regime?
How do curved surfaces of wetting fluids give rise to non-linear seismo-electric effects?
At what scale do these effects take place and what would be the bulk behavior – can we detect these effects remotely (i,.e. from the surface)?

21. Logistics
This program is the first part of an FOM Industrial Partnership Program
Innovative Physics for Oil and Gas
Check the FOM website for a detailed description for the Call for Proposals!
This program forms an integral part of a Shell E&P R&D Program
Shell Staff involved: Fons ten Kroode/Dirk Smit
Program is lead by:
Daan Frenkel (FOM, Amsterdam)
Martin van Hecke (Univ Leiden)
Please do not hesitate to contact the Program Leaders or us at Shell if you wish more information!