1. The Necessity of DH Logging to Integrated Interpretation of Geology and Geophysics
ASEG Downhole logging workshop
february 2015
John McGaughey

2. Integration: flavour of the month?

3. The modern exploration context
under cover, at depth, complex brownfields
ore system footprint recognition rather than anomaly recognition
multi-disciplinary interpretation in model space, not data space
courtesy Geological Survey of Queensland

4. The modern exploration context
targeting in model space, not data space
courtesy Geological Survey of Queensland

5. The modern exploration context
Common Earth Model: a single, shared, consistent earth model
a working hypothesis that can be queried, tested, modified
lithology, alteration, structure, geochemistry, mineralisation, physical properties, spatial relationships, topological relationships
Glencore, Ribago VMS district

6. Targeting Workflow
planning
data management
modelling
analysis

7. Integrated interpretation for targeting
targeting decisions are only as good as the model!
every model component that is not a direct observation from drill core or outcrop is interpretation
geophysical data provide our only means of volumetric investigation
100% of the geophysical components of the model are interpretation
3D modelling is necessarily a multi-disciplinary, interpretive, iterative process
how is the modelling planned, managed, controlled?

8. Good math, poor geoscience?
geophysical data
geophysical model
geological data
geological model
de Kemp and Jessel (2013). Challenges in 3D modelling of complex geologic objects.
33rd GOCAD Research Meeting, Nancy, France.

9. Ambiguity is everywhere
corresponding
pseudo-section
model
UBC-GIF website

10. Ambiguity is everywhere
horizontal
remanence
vertical
remanence
no remanence
Clark et al. (1992). Magnetic pertrology: application of integrated magentic and petrological techniques to geoloigcal interpretation of magnetic surveys. Exploration Geophysics, 23,

11. Ambiguity is everywhere
RBF
MQ-C250
F1 refolded by F2
RBF
MQ-C50
de Kemp and Jessel (2013). Challenges in 3D modelling of complex geologic objects.
33rd GOCAD Research Meeting, Nancy, France.
RBF R3
Great advances with implicit schemes can now allow us to explore the solution space. However we need to know each model is a single solution to a biased matrix solver which is optimized for mathematics not necessarily for geology. Need to characterize the geologic requirements for implicit tools.
The challenge now is how far can we take our implicit schemes so that the solutions become more and more geologically realistic.
Can we embed more geological content and constraints types from the entire geologic history into the matrix. Or is there a limit to what can be solved even with abundant data in geologically complex regions.

12. Interpreting geological meaning of rock properties

13. Interpreting geological meaning of rock properties
understanding the relationship between physical property distributions and geological description is the foundation of constructing a coherent model
DH logging:
in-situ logging provides the required sample populations
in theory, more meaningful than lab samples
calibration required
Victoria Project
KGHM International
courtesy
DGI Geoscience

14. Integrated interpretation is a team responsibility
Geologically
Acceptable Models
Geophysically
Acceptable Models
Petrophysically
Acceptable Models

15. Integrated interpretation is a team responsibility
Geologically
Acceptable Models
there are always many models consistent with the geological data

16. Integrated interpretation is a team responsibility
Geophysically
Acceptable Models
there are always many models consistent with the geophysical data

17. Integrated interpretation is a team responsibility
a priori density distribution
density histogram after inversion
Petrophysically
Acceptable Models
there are always many models consistent with the petrophysical data
inverted density distribution

18. Integrated interpretation is a team responsibility
Geologically
Acceptable Models
Geophysically
Acceptable Models
with modern tools, 3D geological modelling and geophysical inversion have never been easier!
Petrophysically
Acceptable Models
are the models meaningful?

19. Integrated interpretation is a team responsibility
Geologically
Acceptable Models
Geophysically
Acceptable Models
Petrophysically
Acceptable Models
Common
Earth
Model

20. Integrated interpretation is a team responsibility
Geologically
Acceptable Models
Geophysically
Acceptable Models 1 2
Petrophysically
Acceptable Models 3
Reasonable Workflow?
initial geological model
geophysical perturbation
final adjustment

21. Integrated interpretation is a team responsibility
Geologically
Acceptable Models
Geophysically
Acceptable Models
Petrophysically
Acceptable Models
this is more like it,
with a bit of luck, time, good judgement and sound geoscience!

22. Uncertainty characterising uncertainty is important
deterministic computation of uncertainty is not realistic
stochastic estimation of uncertainty is also not realistic:
no assurance that you have adequately tested the model space
the “most probable” model is likely not the most interesting model
uncertainty (or confidence) is based on:
interpretive coherence with formal checkpoints
quantitative self-consistency

23. Multi-disciplinary, interpretive, iterative
Siddorn, J.P., (2010). The geological interpretation of aeromagnetic data:
A geologist’s perspective. KEGS Symposium.

24. Integrated interpretation – what we’ve learned
multi-disciplinary, interpretive at every step, iterative
geoscientific judgement is more important than computational details
the right tools are important; the right team is more important
culture change is required to break sequential workflows
formal planning is required to connect the objective to interpretive steps
“The deployment of 3D earth modelling technology in daily operational work will require changes in paradigms and work processes.”
- Garrett et al. (1997)

25. Simple case study: gravity inversion
observed gravity
terrain corrected: 2.90 g/cc
gridded at 50m
geology model
horizontal section near-surface
Slides from C:\Mira\Roundup_2015\Gravity\Gravity_inversion.pptx

26. density statistics (g/cc)
Formation
min
25th
mean
med
75th
max
02_Richard_Lake_Pluton_Ultramafic_J18
2.76
2.9
2.91
2.93
2.96
03_Chisel_Pluton_Ultramafic_P1
2.63
2.75
2.78
2.82
04_Powderhouse_Dacite_J11
2.6
2.98
3.02
3.07
4.49
05_Moore_Lake_Basalt_J10a
2.58
2.94
2.99 3
3.05
4.3
06_Edward_HTMFBX_Mafic_J8
2.97
3.03
3.17
07_Snell_Basalt_J7
3.00
4.30
08_Stroud_HTFEBX_J6
2.16
2.71
2.77
2.83
3.81
09_Threehouse_LPTF_J19bc
10_S_Balloch_Rhyolite_J12b/Ghost
2.72
3.67
11_Photo_Rhyloite_J12b
2.42
2.79
3.55
12_Threehouse_MFTF_J19a
13_Balloch_Basalt_J13
2.37
4.29
14_Snow_Creek_Basalt_J34
15_HTMFBX_J30a
16_Welch_Aphyric_Maficflow_J1a
17_Konzie_Rhyolite_J3b
18_SLP_Sneath_Qtz_J5b
19_North_Balloch_Rhyolite_J12b
2.17
2.73
3.42
20_Daly_Rhyolite_J3b
21_Quartz_Porphyry_J17ad
22_Threehouse_Basalt_J20
23_Powderhouse_Dacite_J11
24_Caboose_Andesite_J9
2.90
2.95
25_Int_Mafic_Tuff_J30c
26_Cook_Lake_Rhyolite_J12
density statistics (g/cc)
“Best information” values

27. geological units assumed homogeneous initially
starting densities derived from DGI wireline logs and other sources
observed
calculated
starting model calculated gravity
RMS misfit = 1.41 mgal
Densities referenced to 2.90 g/cc

28. residual after homogeneous unit inversion
density bounds = minimum and maximum values
RMS misfit = 0.51 mgal (stalled inversion)

29. residual after heterogeneous unit inversion
density bounds = minimum and maximum values
RMS misfit = 0.07 mgal (acceptable for 0.05 mgal s.d.)

30. Conclusion: the necessity of petrophysical logging
Geologically
Acceptable Models
Geophysically
Acceptable Models
Petrophysically
Acceptable Models

31. Acknowledgements HudBay Minerals Fullagar Geophysics DGI Geoscience
Mira Geoscience colleagues:
Dianne Mitchinson
Gervais Perron
Tim Chalke
Glenn Pears