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

Integration: flavour of the month?

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

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

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

Targeting Workflow planning data management modelling analysis

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?

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.

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

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, 65-68.

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.

Interpreting geological meaning of rock properties

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

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

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

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

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

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?

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

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

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!

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

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

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)

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

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

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

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

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

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

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