Exploring for Geothermal Systems: Geophysical Methods

Mediate relation between electrical and thermal conductivity of soil

Geomechanics and Geophysics for Geo-Energy and Geo-Resources ◽

10.1007/s40948-020-00173-x ◽

2020 ◽

Vol 6 (3) ◽

Author(s):

Hans Schwarz ◽

David Bertermann

Keyword(s):

Thermal Conductivity ◽

Electrical Conductivity ◽

Water Content ◽

Bulk Density ◽

Geophysical Methods ◽

Heat Extraction ◽

Geothermal Systems ◽

Corrective Factor ◽

Thermal Conductivity Model

Abstract Thermal conductivity is a key parameter for many soil applications, especially for dimensioning shallow and very shallow geothermal systems based on the possible heat extraction rate and for modelling heat transfer processes around high voltage underground cables. Due to the limited purview of direct thermal conductivity measurements, for an investigation of extensive areas, usually other geophysical methods like electrical resistivity tomography measurements are applied. To derive thermal conductivity of soil from geoelectrical measurements a relation between electrical and thermal conductivity is needed. Until now only few approaches worked on a direct correlation between both conductivities. Due to the difficulties of a direct relation, within this study a modular approach of a mediate correlation between electrical and thermal conductivity was investigated. Therefore, a direct relationship between a corrected electrical conductivity and water content as well as the standard and simple thermal conductivity model of Kersten (Bull of the Univ Minnesota 28:1–227, 1949) was used. To develop this concept soil types of sand, silt loam and clay were investigated where different saturation steps and pressure loads were applied. For each configuration electrical and thermal conductivity as well as water content and bulk density was determined. To refine the results of the calculated water content a corrective factor was applied. Furthermore, bulk density as an inlet parameter of the Kersten equation was also derived based on electrical conductivity. The suggested proceeding enables the determination of thermal conductivity solely based on electrical conductivity without prior soil property information.

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La Palma island (Spain) geothermal system revealed by 3D magnetotelluric data inversion

Scientific Reports ◽

10.1038/s41598-020-75001-z ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Federico Di Paolo ◽

Juanjo Ledo ◽

Katarzyna Ślęzak ◽

David Martínez van Dorth ◽

Iván Cabrera-Pérez ◽

...

Keyword(s):

Geophysical Methods ◽

High Resistivity ◽

Geothermal System ◽

Human Consumption ◽

Geothermal Systems ◽

Magnetotelluric Data ◽

Volcanic System ◽

The North ◽

La Palma ◽

Cumbre Vieja

Abstract The study of geothermal systems is nowadays a topic of great importance because of the huge amount of energy that could be converted in electricity for human consumption from such sources. Among the various geophysical methods employed to study geothermal reservoirs, the magnetotelluric (MT) method is capable to reveal the internal structures of the subsurface and interpret the geological structures from the electrical resistivity. We present the first 3D resistivity model of La Palma (Canary archipelago, Spain) obtained from a dataset of 44 broadband magnetotelluric soundings distributed around the island. Our results highlight the presence of resistivity anomalies, spatially coinciding with density anomalies present in literature. In the north of the island, a high resistivity anomaly can be interpreted as the signature of an old intrusive body beneath the Taburiente caldera. In the south, a complex resistivity structure around the Cumbre Vieja volcanic ridge could be indicative of presence of an active geothermal system. In particular, low-resistivity anomalies, located in a high-fractured zone, have values compatible with clay alteration caps (illite and illite–smectite). Such a result suggests the presence of hot rocks, or a dike system, heating fluids in the interior of Cumbre Vieja volcanic system.

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State‐of‐the‐art geophysical exploration for geothermal resources

Geophysics ◽

10.1190/1.1441889 ◽

1985 ◽

Vol 50 (12) ◽

pp. 2666-2696 ◽

Cited By ~ 55

Author(s):

Phillip. M. Wright ◽

Stanley H. Ward ◽

Howard P. Ross ◽

Richard C. West

Keyword(s):

Hard Rock ◽

Geophysical Methods ◽

Well Logging ◽

Geothermal System ◽

Geothermal Systems ◽

Depth Of Penetration ◽

Thermal Methods ◽

Geothermal Resources ◽

Industrial Processing ◽

Stage Of Development

At the present stage of development, use of geothermal energy saves about 77 million barrels of oil per year worldwide that would otherwise be required for electrical power generation and direct heat applications. More than a dozen countries are involved in development of geothermal resources. Currently, only the moderate‐ and high‐temperature hydrothermal convective type of geothermal system can be economically used for generating electric power. Lower‐temperature resources of several types are being tapped for space heating and industrial processing. Geophysics plays important roles both in exploration for geothermal systems and in delineating, evaluating, and monitoring production from them. The thermal methods, which detect anomalous temperatures directly, and the electrical methods are probably the most useful and widely used in terms of siting drilling targets, but gravity, magnetics, seismic methods, and geophysical well logging all have important application. Advances in geophysical methods are needed to improve cost effectiveness and to enhance solutions of geologic problems. There is no wholly satisfactory electrical system from the standpoint of resolution of subsurface resistivity configuration at the required scale, depth of penetration, portability of equipment, and survey cost. The resolution of microseismic and microearthquake techniques needs improvement, and the reflection seismic technique needs substantial improvement to be cost effective in many hard‐rock environments. Well‐logging tools need to be developed and calibrated for use in corrosive wells at temperatures exceeding 200°C. Well‐log interpretation techniques need to be developed for the hard‐rock environment. Borehole geophysical techniques and geotomography are just beginning to be applied and show promise with future development.

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Geophysical Prospecting for Geothermal Resources in the South of the Duero Basin (Spain)

Energies ◽

10.3390/en13205397 ◽

2020 ◽

Vol 13 (20) ◽

pp. 5397

Author(s):

Ignacio Martín Nieto ◽

Pedro Carrasco García ◽

Cristina Sáez Blázquez ◽

Arturo Farfán Martín ◽

Diego González-Aguilera ◽

...

Keyword(s):

Geophysical Methods ◽

Geothermal Gradient ◽

Geological Structure ◽

Temperature Record ◽

Thermal Activity ◽

Geothermal Systems ◽

The South ◽

Geothermal Resources ◽

Borehole Logging ◽

Duero Basin

The geothermal resources in Spain have been a source of deep research in recent years and are, in general, well-defined. However, there are some areas where the records from the National Institute for Geology and Mining show thermal activity from different sources despite no geothermal resources being registered there. This is the case of the area in the south of the Duero basin where this research was carried out. Seizing the opportunity of a deep borehole being drilled in the location, some geophysical resources were used to gather information about the geothermal properties of the area. The employed geophysical methods were time-domain electromagnetics (TDEM) and borehole logging; the first provided information about the depth of the bedrock and the general geological structure, whereas the second one gave more detail on the geological composition of the different layers and a temperature record across the whole sounding. The results allowed us to establish the geothermal gradient of the area and to discern the depth of the bedrock. Using the first 200 m of the borehole logging, the thermal conductivity of the ground for shallow geothermal systems was estimated.

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Geophysical Methods for Monitoring Temperature Changes in Shallow Low Enthalpy Geothermal Systems

Energies ◽

10.3390/en7085083 ◽

2014 ◽

Vol 7 (8) ◽

pp. 5083-5118 ◽

Cited By ~ 41

Author(s):

Thomas Hermans ◽

Frédéric Nguyen ◽

Tanguy Robert ◽

Andre Revil

Keyword(s):

Geophysical Methods ◽

Geothermal Systems ◽

Temperature Changes ◽

Monitoring Temperature

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Use of Geophysical Methods in Construction

10.1061/9780784405215 ◽

2000 ◽

Keyword(s):

Geophysical Methods

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Integration of Multi-geophysical Approaches to Identify Potential Pathways of Heavy Metals Contamination - A Case Study in Zeida, Morocco

Journal of Environmental and Engineering Geophysics ◽

10.32389/jeeg9-067 ◽

2020 ◽

Vol 25 (3) ◽

pp. 415-423

Author(s):

Ahmed Lachhab ◽

El Mehdi Benyassine ◽

Mohamed Rouai ◽

Abdelilah Dekayir ◽

Jean C. Parisot ◽

...

Keyword(s):

Heavy Metals ◽

Seismic Velocity ◽

Seismic Refraction ◽

Geophysical Methods ◽

Low Frequency ◽

Electrical Current ◽

P Wave ◽

Low Resistivity ◽

Refraction Tomography ◽

Geophysical Surveys

The tailings of Zeida's abandoned mine are found near the city of Midelt, in the middle of the high Moulouya watershed between the Middle and the High Atlas of Morocco. The tailings occupy an area of about 100 ha and are stored either in large mining pit lakes with clay-marl substratum or directly on a heavily fractured granite bedrock. The high contents of lead and arsenic in these tailings have transformed them into sources of pollution that disperse by wind, runoff, and seepage to the aquifer through faults and fractures. In this work, the main goal is to identify the pathways of contaminated water with heavy metals and arsenic to the local aquifers, water ponds, and Moulouya River. For this reason, geophysical surveys including electrical resistivity tomography (ERT), seismic refraction tomography (SRT) and very low-frequency electromagnetic (VLF-EM) methods were carried out over the tailings, and directly on the substratum outside the tailings. The result obtained from combining these methods has shown that pollutants were funneled through fractures, faults, and subsurface paleochannels and contaminated the hydrological system connecting groundwater, ponds, and the river. The ERT profiles have successfully shown the location of fractures, some of which extend throughout the upper formation to depths reaching the granite. The ERT was not successful in identifying fractures directly beneath the tailings due to their low resistivity which inhibits electrical current from propagating deeper. The seismic refraction surveys have provided valuable details on the local geology, and clearly identified the thickness of the tailings and explicitly marked the boundary between the Triassic formation and the granite. It also aided in the identification of paleochannels. The tailings materials were easily identified by both their low resistivity and low P-wave velocity values. Also, both resistivity and seismic velocity values rapidly increased beneath the tailings due to the compaction of the material and lack of moisture and have proven to be effective in identifying the upper limit of the granite. Faults were found to lie along the bottom of paleochannels, which suggest that the locations of these channels were caused by these same faults. The VLF-EM surveys have shown tilt angle anomalies over fractured areas which were also evinced by low resistivity area in ERT profiles. Finally, this study showed that the three geophysical methods were complementary and in good agreement in revealing the pathways of contamination from the tailings to the local aquifer, nearby ponds and Moulouya River.

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