Electromagnetic studies in geothermal regions

Berktold, A.

doi:10.1007/bf01454000

Cited by 37 publications

(12 citation statements)

References 98 publications

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“…These have been suggested by MAHON and KLYEN (1968), on the basis of chemical analysis, to be derived from the same deep source as the Tokaanu field. Resistivity work around the springs by BIBBY et al (1991) showed no evidence that a link of very low resistivity exists between the two areas. This is supported by the present work, although it is likely that the moderately conductive layer detected outside the Tokaanu field does extend as far as the Motuoapa Springs.…”

Section: Discussionmentioning

confidence: 92%

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Magnetotelluric Soundings and Structure of the Tokaanu Geothermal Field, New Zealand.

Ingham

Reeves

1993

J. geomagn. geoelec

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Magnetotelluric soundings have been made at 15 locations in and around the Tokaanu geothermal field in the North Island of New Zealand. Modelling and inversion of the data along two transects clearly identify the locations of the eastern and southeastern boundaries of the field. Within the field a conductive layer at variable depth is underlain by a more resistive layer. This is in turn underlain by low resistivity which persists to considerable depth. Across the field boundary a somewhat less conductive layer exists at around 0.5-1.0 km depth. This is similar to the conductivity structure associated with the Broadlands-Ohaaki geothermal field and reported by INGHAM (1991a). Additional geophysical information suggests that the total area covered by the Tokaanu field is of the order of 30 square km. The existence of low resistivity to depth is interpreted to correspond to the upwelling of geothermal fluid and associated hydrothermal alteration. No indication is obtained of any geothermal link between the Tokaanu field and the Motuoapa Springs to the northeast.

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Section: Discussionmentioning

confidence: 92%

“…ANDER et al, 1984;BERKTOLD, 1983;HUTTON et al, 1989 INGHAM (1991a) and was also of the Broadlands-Ohaaki field. This work clearly showed the correlation of an uppermost conductive layer with the known upper surface of the geothermal reservoir as determined from drill holes in the Broadlands area.…”

Section: Introductionmentioning

confidence: 99%

Magnetotelluric Soundings and Structure of the Tokaanu Geothermal Field, New Zealand.

Ingham

Reeves

1993

J. geomagn. geoelec

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“…From the above observation we see that (i) Vmax, P, H13 and THD are the variables that occur only in one of PC c (1) or PC p (1) and (ii) THD is the only variable that contributes to PC c (2) but not to PC p (2).…”

Section: Introductionmentioning

confidence: 87%

“…We learn from the literature [1], [2], [3], [4], [5] and [6] that geothermal area is most interesting field for electric power production. The transmission lines are used to transmit electric energy from geothermal power plant to a switchyard of distribution.…”

Section: Introductionmentioning

confidence: 99%

The influence of geothermal environment to the quality of porcelain insulator: A correlation analysis

Yusoff¹,

Djauhari²

2011

2011 IEEE MTT-S International Microwave Workshop Series on Innovative Wireless Power Transmission: Technologies, Systems, and A

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Abstract--It is assumed that polluted environment reduces the quality of porcelain insulator in terms of leakage current. In this paper we conduct a correlation analysis to understand to what extent the influence of geothermal area to the quality of porcelain insulator. For that purpose, first, we test the equality of two correlation matrices by using Jennrich's test. Second, in case the two correlation matrices are not equal, we use principal component analysis (PCA) to study which variables are responsible to that situation. An example will be discussed and a recommendation will be addressed.Index Term -Correlation structure, Jennrich's test, principal component analysis, scree plot I.

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“…LTS SQUIDs have the advantage of higher sensitivity as compared to HTS SQUIDs (sensor noise $ 1 fT= ffiffiffiffiffiffi Hz p versus [ 10 fT= ffiffiffiffiffiffi Hz p at 10-10,000 Hz). In the 1980s, there was an initial period of higher usage of SQUIDs in MT field campaigns (e.g., Berktold 1983;Hermance et al 1984). However, it was soon realised that the need for cryogenic cooling with liquid nitrogen or helium and the size of early SQUID sensors made them less practical for field campaigns than induction coil sensors (Chave and Booker 1987).…”

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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Electromagnetic studies in geothermal regions

Cited by 37 publications

References 98 publications

Magnetotelluric Soundings and Structure of the Tokaanu Geothermal Field, New Zealand.

Magnetotelluric Soundings and Structure of the Tokaanu Geothermal Field, New Zealand.

The influence of geothermal environment to the quality of porcelain insulator: A correlation analysis

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

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