Electromagnetic Induction Methods in Mining Geophysics from 2008 to 2012

Smith, Richard S.

doi:10.1007/s10712-013-9227-1

Cited by 71 publications

(24 citation statements)

References 155 publications

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“…For this reason, the TEM method and more generally, all induction EM methods have been intensively used for the mapping of conductive units. Hydrogeologic and resource applications of TEM include mapping clay-rich aquitards, which offer protections for aquifers (Palacky, 1987;Kirsch et al, 2003;Foged et al, 2014), seawater intrusion in coastal aquifers for water quality control and management (Kirkegaard et al, 2011;Teatini et al, 2011;Jørgensen et al, 2012) and mining exploration of highly conductive mineral deposits (Smith, 2014). Minsley et al (2012) use frequency-domain EM to map permafrost above groundwater in arctic Alaska.…”

Section: Introductionmentioning

confidence: 99%

Helicopter-borne transient electromagnetics in high-latitude environments: An application in the McMurdo Dry Valleys, Antarctica

et al. 2016

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The McMurdo Dry Valleys are a polar desert in coastal Antarctica, where glaciers, permafrost, ice-covered lakes, and ephemeral summer streams coexist. Liquid water is found at the surface only in lakes and in the temporary streams that feed them. Past geophysical exploration has yielded ambiguous results regarding the presence of subsurface water. In 2011, we used a helicopter-borne, time-domain electromagnetic (TDEM) sensor to map resistivity in the subsurface across the Dry Valleys. The airborne electromagnetic (AEM) method excels at finding subsurface liquid water in polar deserts, where water remains liquid under cold conditions if it is sufficiently saline, and therefore electrically conductive. Over the course of 26 h of helicopter time, we covered large portions of the Dry Valleys and vastly increased our geophysical understanding of the subsurface, particularly with respect to water. Our data show extensive subsurface low-resistivity layers approximately 150–250 m below the surface and beneath higher resistivity layers. We interpret the low-resistivity layers as geologic materials containing freeze-concentrated or “cryoconcentrated” hyper saline brines lying beneath glaciers and frozen permafrost. These brines appeared to be contiguous with surface lakes, subglacial regions, and the Ross Sea, which could indicate a regional-hydrogeologic system, wherein solutes might be transported between surface reservoirs by ionic diffusion and subsurface flow. The presence of such brines underneath glaciers might have implications for glacier movement. Systems such as this, where brines exist beneath glacial ice and frozen permafrost, may exist elsewhere in coastal Antarctica; AEM resistivity is an ideal tool to find and survey them. Our application of TDEM demonstrates that in polar subsurface environments containing conductive brines, such a diffusive electromagnetic method is superior to radar surveying in terms of depth of penetration and ability to differentiate hydrogeologic conditions.

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Section: Introductionmentioning

confidence: 99%

Helicopter-borne transient electromagnetics in high-latitude environments: An application in the McMurdo Dry Valleys, Antarctica

et al. 2016

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“…In particular, the need to refill liquid nitrogen or helium regularly makes SQUIDs unattractive and expensive to operate in MT measurements that last from days to weeks or months, especially when located in remote localities. Nevertheless, owing to the shorter duration of measurements, SQUID magnetometers have been in use for surface or airborne timedomain CSEM measurements for 30 years (Kalberkamp et al 1997;Chwala et al 1999;Bick et al 1999;Panaitov et al 2002;Lee et al 2002;Vallee et al 2011;Asten and Duncan 2012;Smith 2014). For borehole AMT and BHEM measurements, SQUID sensors have the advantage that they are only 2 cm in side length.…”

Section: Borehole Sensors and Conditionsmentioning

confidence: 99%

Two-Dimensional Magnetotelluric Modelling of Ore Deposits: Improvements in Model Constraints by Inclusion of Borehole Measurements

Kalscheuer

Juhojuntti

Vaittinen³

2017

Surv Geophys

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A combination of magnetotelluric (MT) measurements on the surface and in boreholes (without metal casing) can be expected to enhance resolution and reduce the ambiguity in models of electrical resistivity derived from MT surface measurements alone. In order to quantify potential improvement in inversion models and to aid design of electromagnetic (EM) borehole sensors, we considered two synthetic 2D models containing ore bodies down to 3000 m depth (the first with two dipping conductors in resistive crystalline host rock and the second with three mineralisation zones in a sedimentary succession exhibiting only moderate resistivity contrasts). We computed 2D inversion models from the forward responses based on combinations of surface impedance measurements and borehole measurements such as (1) skin-effect transfer functions relating horizontal magnetic fields at depth to those on the surface, (2) vertical magnetic transfer functions relating vertical magnetic fields at depth to horizontal magnetic fields on the surface and (3) vertical electric transfer functions relating vertical electric fields at depth to horizontal magnetic fields on the surface. Whereas skin-effect transfer functions are sensitive to the resistivity of the background medium and 2D anomalies, the vertical magnetic and electric field transfer functions have the disadvantage that they are comparatively insensitive to the resistivity of the layered background medium. This insensitivity introduces convergence problems in the inversion of data from structures with strong 2D resistivity contrasts. Hence, we adjusted the inversion approach to a three-step procedure, where (1) (2) this inversion model from surface impedances is used as the initial model for a joint inversion of surface impedances and skin-effect transfer functions and (3) the joint inversion model derived from the surface impedances and skin-effect transfer functions is used as the initial model for the inversion of the surface impedances, skin-effect transfer functions and vertical magnetic and electric transfer functions. For both synthetic examples, the inversion models resulting from surface and borehole measurements have higher similarity to the true models than models computed exclusively from surface measurements. However, the most prominent improvements were obtained for the first example, in which a deep small-sized ore body is more easily distinguished from a shallow main ore body penetrated by a borehole and the extent of the shadow zone (a conductive artefact) underneath the main conductor is strongly reduced. Formal model error and resolution analysis demonstrated that predominantly the skin-effect transfer functions improve model resolution at depth below the sensors and at distance of $ 300-1000 m laterally off a borehole, whereas the vertical electric and magnetic transfer functions improve resolution along the borehole and in its immediate vicinity. Furthermore, we studied the signal levels at depth and provided specifications of borehole magnetic and elect...

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“…In general, motion measurements are required to obtain as much wellbore information as possible. However, in this case, the borehole EM induction (EMI) system [5,6] utilizing induction coils will be greatly influenced by the magnetic background noise (MBN) due to the motion of the sensor. At present, the effects of MBN are typically reduced by decreasing the measurement rate; however, this reduces the device efficiency and leads to increased energy consumption.…”

Section: Introductionmentioning

confidence: 99%

Borehole electromagnetic induction system with noise cancelation for casing inspection

Dang

Yang

Dang

et al. 2016

IEICE Electron. Express

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A borehole electromagnetic induction (EMI) system with noise cancelation for casing inspection is presented. Based on the analysis of the model for received signal in multi-cylindrical borehole structures, we choose to utilize a receive-only channel as the reference to cancel the effect of the background noise, where a registration matrix is used to compensate for the correlation of the non-isolated reference channel. Moreover, the performance of noise cancelation is verified by applying it to an oil borehole EMI system for the inspection of oil-well casings. Field experiments are conducted and the results demonstrate the effectiveness of the proposed method.

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Electromagnetic Induction Methods in Mining Geophysics from 2008 to 2012

Cited by 71 publications

References 155 publications

Helicopter-borne transient electromagnetics in high-latitude environments: An application in the McMurdo Dry Valleys, Antarctica

Helicopter-borne transient electromagnetics in high-latitude environments: An application in the McMurdo Dry Valleys, Antarctica

Two-Dimensional Magnetotelluric Modelling of Ore Deposits: Improvements in Model Constraints by Inclusion of Borehole Measurements

Borehole electromagnetic induction system with noise cancelation for casing inspection

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