Exploration Geophysics Exploration Geophysics Society
Journal of the Australian Society of Exploration Geophysicists
RESEARCH ARTICLE

A novel approach to comparing AEM inversion results with borehole conductivity logs

Niels B. Christensen 1 3 Kenneth C. Lawrie 2
+ Author Affiliations
- Author Affiliations

1 University of Aarhus, Hoegh Guldbergs Gade 2, DK8210 Aarhus C, Denmark.

2 Strategic Groundwater Science, Groundwater Branch, Environmental Geoscience Division, Geoscience Australia, Canberra, ACT 2601, Australia.

3 Corresponding author. Email: nbc@geo.au.dk

Exploration Geophysics - https://doi.org/10.1071/EG17029
Submitted: 7 March 2017  Accepted: 3 May 2017   Published online: 7 June 2017

Abstract

Borehole conductivity logs, besides being useful for identifying, interpreting and correlating geological formations, also find widespread use as auxiliary information in the inversion of airborne electromagnetic (AEM) data. One of the quality checks often applied to AEM inversion results is a comparison between the conductivity structures revealed by borehole conductivity logs in the survey area and the AEM inversion model closest to the borehole, often called an ‘FID point comparison’.

Another use of borehole conductivity logs is found in modern AEM inversion procedures, where the borehole conductivity information is included as prior information in a laterally constrained inversion. In most former and present practices, AEM layer conductivities are compared with the measured conductivity in the borehole. However, the borehole conductivity is essentially an apparent conductivity – it is a measured data value – while the AEM layer conductivities are model parameters resulting from inverting AEM data. To avoid comparing data and model parameters we suggest a conceptually clear approach based on an inversion of the borehole conductivity data to obtain a borehole conductivity model, which in turn can be compared with the AEM model. Furthermore, the AEM forward response of the borehole model can, in a consistent way, be compared with the AEM data. In both approaches, we keep track of uncertainty and define quantitative, uncertainty-normalised measures of the difference between borehole and AEM values, and we find simple functional relationships between the two. The methodology is demonstrated on the AEM data and conductivity logs of the Broken Hill Managed Aquifer Recharge (BHMAR) project.

Key words: airborne, borehole constrained inversion, borehole log, comparison, electromagnetic.


References

Auken, E., Christiansen, A. V., Westergaard, J. A., Kirkegaard, C., Foged, N., and Viezzoli, A., 2009, An integrated processing scheme for high-resolution airborne electromagnetic surveys, the SkyTEM system: Exploration Geophysics, 40, 184–192
An integrated processing scheme for high-resolution airborne electromagnetic surveys, the SkyTEM system:CrossRef |

Christensen, N. B., 2014, Sensitivity functions of transient electromagnetic methods: Geophysics, 79, E167–E182
Sensitivity functions of transient electromagnetic methods:CrossRef |

Christensen, N. B., 2016a, Strictly horizontal lateral parameter correlation for 1D inverse modelling of large data sets: Near Surface Geophysics, 14, 391–399
Strictly horizontal lateral parameter correlation for 1D inverse modelling of large data sets:CrossRef |

Christensen, N. B., 2016b, Fast approximate 1D modelling and inversion of transient electromagnetic data: Geophysical Prospecting, 64, 1620–1631
Fast approximate 1D modelling and inversion of transient electromagnetic data:CrossRef |

Christensen, N. B., and Lawrie, K. C., 2012, Resolution analyses for selecting an appropriate airborne electromagnetic (AEM) system: Exploration Geophysics, 43, 213–227

Christensen, N. B., and Lawrie, K. C., 2014, Reply to comment on the paper - selecting an appropriate AEM system: Exploration Geophysics, 43, 213–227

Christensen, N. B., and Tølbøll, R. J., 2009, A lateral model parameter correlation procedure for one-dimensional inverse modelling: Geophysical Prospecting, 57, 919–929
A lateral model parameter correlation procedure for one-dimensional inverse modelling:CrossRef |

Christensen, N. B., Reid, J. E., and Halkjaer, M., 2009, Fast, laterally smooth inversion of airborne transient electromagnetic data: Near Surface Geophysics, 7, 599–612
Fast, laterally smooth inversion of airborne transient electromagnetic data:CrossRef |

Christiansen, A. V., Auken, E., and Viezzoli, A., 2011, Quantification of modeling errors in airborne TEM caused by inaccurate system description: Geophysics, 76, F43–F52
Quantification of modeling errors in airborne TEM caused by inaccurate system description:CrossRef |

Foged, N., Auken, E., Christiansen, A. V., and Sørensen, K. I., 2013, Test site calibration and validation of airborne and ground based TEM systems: Geophysics, 78, E95–E106
Test site calibration and validation of airborne and ground based TEM systems:CrossRef |

Foged, N., Marker, P. A., Christiansen, A. V., Bauer-Gottwein, P., Jørgensen, F., Høyer, A.-S., and Auken, E., 2014, Large scale 3D-modeling by integration of resistivity models and borehole data through inversion: Hydrology and Earth System Sciences, 18, 4349–4362
Large scale 3D-modeling by integration of resistivity models and borehole data through inversion:CrossRef |

Inman, J. R., Ryu, J., and Ward, S. H., 1973, Resistivity inversion: Geophysics, 38, 1088–1108
Resistivity inversion:CrossRef |

Kellog, Brown and Root Pty Ltd (KBR), 2010, Ord East Kimberley Expansion Project Weaber Plains Groundwater Modelling Report - Stage 2 results. Report for WA Landcorp. February 2010.

Kellog, Brown and Root Pty Ltd (KBR), 2011, Weaber Plains Groundwater Modelling Report -Final. Report for WA Landcorp, May 2011.

Lane, R., Heislers, D., and McDonald, P., 2001, Filling in the gaps - validation and integration of airborne EM data with surface and subsurface observations for catchment management - an example from Bendigo, Victoria, Australia: Exploration Geophysics, 32, 225–235
Filling in the gaps - validation and integration of airborne EM data with surface and subsurface observations for catchment management - an example from Bendigo, Victoria, Australia:CrossRef |

Lawrie, K. C., Munday, T. J., Dent, D. L., Gibson, D. L., Brodie, R. C., Wilford, J., Reilly, N. S., Chan, R. A., and Baker, P., 2000, A ‘Geological Systems’ approach to understanding the processes involved in land and water salinisation in areas of complex regolith - the Gilmore Project, central-west NSW: AGSO Research Newsletter, 32, 13–32

Lawrie, K. C., Tan, K. P., Halas, L., Cullen, K., Pain, C. F., Brodie, R. C., Apps, H., Wong, V., Reid, M., Clarke, J. C., and Gibson, D., 2009, River Murray Corridor (RMC) salinity mapping and interpretation project. Report on the Barr Creek to Gunbower Island region: Geoscience Australia Professional Opinion 2009/13, 186 pp.

Lawrie, K. C., Tan, K. P., Clarke, J. C., Munday, T. J., Fitzpatrick, A., Brodie, R. S., Pain, C. F., Apps, H., Cullen, K., Halas, L., Kuske, T. J., Cahill, K., and Davis, A. 2010, Utilising time domain airborne electromagnetics (AEM) to map aquifer systems and salinity hazard in the Ord Valley, Western Australia: Geoscience Australia Professional Opinion 2010, 400 pp.

Lawrie, K. C., Brodie, R. S., Tan, K. P., Gibson, D., Magee, J., Clarke, J. D. A., Halas, L., Gow, L., Somerville, P., Apps, H. E., Christensen, N. B., Brodie, R. C., Abraham, J., Smith, M., Page, D., Dillon, P., Vanderzalm, J., Miotlinski, K., Hostetler, S., Davis, A., Ley-Cooper, A. Y., Schoning, G., Barry, K., and Levett, K., 2012a, BHMAR Project: data acquisition, processing, analysis and interpretation methods: Geoscience Australia Record 2012/11. Geocat 73819. 782 pp.

Lawrie, K. C., Brodie, R. S., Dillon, P., Tan, K. P., Gibson, D., Magee, J., Clarke, J. D. A., Somerville, P., Gow, L., Halas, L., Apps, H. E., Page, D., Vanderzalm, J., Abraham, J., Hostetler, S., Christensen, N. B., Miotlinski, K., Brodie, R. C., Smith, M., and Schoning, G., 2012b, BHMAR Project: assessment of conjunctive water supply options to enhance the drought security of Broken Hill, regional communities and industries - summary report: Geoscience Australia Record 2012/16, 213 pp.

Lawrie, K., Christensen, N. B., Brodie, R. S., Abraham, J., Halas, L., Tan, K. P., Brodie, R. C., and Magee, J., 2015, Optimizing airborne electromagnetic (AEM) inversions for hydrogeological investigations using a transdisciplinary approach: 24th ASEG-PESA International Geophysical Conference and Exhibition, 4 pp.

Ley-Cooper Y., and Davis A., 2010, Can a borehole conductivity log discredit a whole AEM survey? ASEG Extended Abstracts 2010, 1, 1–5.

Menke, W., 1989, Geophysical data analysis: discrete inverse theory: Academic Press Inc.

Moran, J., and Kunz, K., 1962, Basic theory of induction logging and application to study of two-coil sondes: Geophysics, 27, 829–858
Basic theory of induction logging and application to study of two-coil sondes:CrossRef |

Munday, T., Green, A., Brodie, R., Lane, R., Sattel, D., Barnett, S., Cook, P., and Walker, G., 2003, Developing recharge reduction strategies in the Riverland of South Australia using airborne electromagnetic data – a case study in tailoring airborne geophysics given a particular target and a desired set of outcomes: 16th ASEG Conference, Adelaide, 1–4.

Schamper, C., Jørgensen, F., Auken, E., and Effersø, F., 2014, Assessment of near-surface mapping capabilities by airborne transient electromagnetic data - an extensive comparison to conventional borehole data: Geophysics, 79, B187–B199
Assessment of near-surface mapping capabilities by airborne transient electromagnetic data - an extensive comparison to conventional borehole data:CrossRef |

Serban, D. Z., and Jacobsen, B. H., 2001, The use of broadband prior covariance for inverse palaeoclimate estimation: Geophysical Journal International, 147, 29–40
The use of broadband prior covariance for inverse palaeoclimate estimation:CrossRef |

Smiarowski, A., and Mulè, S., 2014, Comments on: Christensen, N., and Lawrie, K., 2012, Resolution analyses for selecting an appropriate airborne electromagnetic (AEM) system: Exploration Geophysics, 43, 213–227

Sørensen, K. I., and Auken, E., 2004, SkyTEM - a new high-resolution helicopter transient electromagnetic system: Exploration Geophysics, 35, 191–199

Spies, B., and Woodgate, P., 2005, Salinity mapping methods in the Australian context. Department of the Environment and Heritage, and Agriculture Fisheries and Forestry, June 2005, 236 pp.

Strategen, 2014, Ord Project- groundwater management plan - updated January 2014. Report to WA Landcorp, 25 pp. (published).

Taboga, M., 2012, Lectures on probability theory and mathematical statistics (2nd edition): CreateSpace Independent Publishing Platform.

Walker, G., Cresswell, R., Munday, T., and Liddicoat, C., 2004, South Australian Salinity Mapping and Management Support Project: final report (overall project summary report): South Australia. Department of Water, Land and Biodiversity Conservation. Report, DLWBC 2004/39.

Ward, S. H., and Hohmann, G. W., 1987, Electromagnetic theory for geophysical applications, in M. N. Nabighian, ed., Electromagnetic methods in applied geophysics: investigations in Geophysics 3: Society of Exploration Geophysicists, 131–311.

York, D., Evensen, N., Martinez, M., and Delgado, J., 2004, Unified equations for the slope, intercept, and standard errors of the best straight line: American Journal of Physics, 72, 367
Unified equations for the slope, intercept, and standard errors of the best straight line:CrossRef |



Export Citation