scholarly journals Identification of "WS" geothermal field system by analyzing TE, TM, and TE-TM of 2D magnetotelluric inversion models

2019 ◽  
Vol 1 (2) ◽  
pp. 41
Author(s):  
Triana Triana ◽  
Tony Yulianto ◽  
Udi Harmoko ◽  
Iqbal Takodama
Keyword(s):  
Geothermal Field ◽  
Reservoir Rock ◽  
High Resistivity ◽  
Geothermal System ◽  
Magnetotelluric Data ◽  
Low Resistivity ◽  
A Value ◽  
Te Mode ◽  
Tm Mode ◽  
Representative Model

Magnetotelluric data has been carried out at the "WS" geothermal field to analyze the resistivity model resulting from 2D inversion of magnetotelluric data in TE, TM and TE-TM modes. Base on the three models produced, the mode is determined to produce the most representative model to assist in the interpretation of the "WS" geothermal system. There is a step of modes separation, namely TE (Tranverse Electric) and TM (Transverse Magnetic) modes in processing MT data. Each mode produces a 2D model with different conductivity properties. The analysis results of the three modes explain that TE mode is dominated by low resistivity with a range of values of 10-35 Ωm and medium resistivity with a value range of 35-250 Ωm and a vertical resistivity contrast. The TM mode describes the high resistivity in the Southwest and the center of the track with a value of more than 470 sehinggam resulting in lateral resistivity contrast. While the TE-TM mode produces a model that is not much different from TM mode, only the distribution of the resistivity value is a combination with TE mode. This mode describes the distribution of resistivity both vertically and laterally. Based on the analysis of the three modes, it can be concluded that the TE-TM mode is the mode that produces the most representative model. Interpretation model shows that from the TE-TM mode we have a low resistivity distribution (10-35 Ωm) represent a cap rock zone, reservoir rock with a medium resistivity distribution (35-380 Ωm), resistive zone with a high resistivity distribution (more than 380 Ωm), and the existence of the three of faults structures ro be a controller system of the "WS" geothermal.

Geophysical characterization of the Menengai volcano, Central Kenya Rift from the analysis of magnetotelluric and gravity data

Geophysics ◽  
2013 ◽  
Vol 78 (4) ◽  
pp. B187-B199 ◽  
Author(s):  
Antony Munika Wamalwa ◽  
Kevin L. Mickus ◽  
Laura F. Serpa
Keyword(s):  
Gravity Data ◽  
Gravity Models ◽  
High Resistivity ◽  
Geothermal System ◽  
Low Density ◽  
Fracture Density ◽  
Density Region ◽  
Magnetotelluric Data ◽  
Low Resistivity ◽  
2D Resistivity

In this study, we qualitatively analyze detailed gravity and broadband magnetotelluric data in and surrounding the Menengai volcano of the East African rift in Kenya to assess geothermal potential of the region. Three-dimensional gravity models obtained by inverting residual gravity anomalies and 2D resistivity models obtained by inverting the transverse electric and transverse magnetic magnetotelluric modes show several common features. Our models show that a low-resistivity zone above a higher resistivity zone correlates with a low-density region located 1–4 km beneath the volcano. These zones may be related to a high temperature gradient or hydrothermally altered, fractured rocks. Additionally, a low-resistivity ([Formula: see text]) and a low-density region located approximately 4–6 km below the volcano may be related to molten material that is the source of heat for the geothermal system. The low-resistivity ([Formula: see text]) regions that correlated with a denser ([Formula: see text]) region within the caldera are bounded by high-resistivity ([Formula: see text]), high-density ([Formula: see text]) volcanic units implying that the dense and electrically resistive volcanic material is relatively cool and lacks significant fluid content that can lower resistivity. At shallow depths, 0.5–1.5 km below the caldera, a low-resistivity and low-to-moderate density region is interpreted as a zone with high fracture density that consists of clay minerals resulting from hydrothermal alteration. These results agree well with the results from previous seismic studies on the depth of the suggested molten rocks.

scholarly journals 2D Modeling of Seulawah Agam Geothermal Field Based on Magnetotelluric (MT) Data

2019 ◽  
Vol 8 (2) ◽  
pp. 61-65
Author(s):  
Irfan Putra ◽  
Nazli Ismail ◽  
Marwan Marwan
Keyword(s):  
Geothermal Field ◽  
Magnetotelluric Data ◽  
2D Modeling ◽  
Te Mode ◽  
Tm Mode ◽  
Top Soil ◽  
Resistivity Variation ◽  
2D Data ◽  
Mode Tm ◽  
2D Resistivity

Telah dilakukan pemodelan 2D data Magnetotellurik (MT) di Gunung Api Seulawah Agam. Penelitian ini bertujuan untuk mendapatkan model konseptual lapangan panas bumi Gunung Api Seulawah Agam berdasarkan model resistivitas 2D. Data fungsi transfer MT yang digunakan yaitu dari rentang frekuensi 2,34 - 320 Hz yang terdiri dari 7 titik stasiun pengukuran. Data titik pengukuran terdiri dari nilai intensitas medan listrik dan intensitas medan magnet yang memiliki 28 frekuensi. Total panjang lintasan pengukuran yaitu sepanjang 27,7 km. Lintasan pengukuran memotong Gunung Api Seulawah Agam dari arah Selatan ke Utara. Data hasil pengukuran yaitu berupa nilai resistivitas semu dan fase yang kemudian dimodelkan menggunakan kode REBOCC. Terdapat 3 model yang dihasilkan dari proses inversi data MT menggunakan REBOCC yaitu mode TE, mode TM dan mode TE+TM. Model mode TE+TM merupakan model yang paling bagus karena menghasilkan model yang lebih jelas dan smooth bila dibandingkan dengan model pada mode TE dan mode TM. Hasil model konseptual menunjukkan bahwa pada lapisan pertama yaitu lapisan top soil (lapisan teratas) memiliki nilai resistivitas sebesar 20 - 60 Ω.m, yang terdapat pada jarak 6 - 23 km. Lapisan kedua yaitu lapisan clay/caprock dengan nilai resistivitas relatif rendah yaitu lebih kecil dari 10 Ω.m, yang berada pada jarak 6 - 27,7 km. Lapisan clay/caprock memiliki sifat impermeabel dan konduktif. Selanjutnya lapisan ketiga yaitu lapisan reservoir dengan nilai resistivitas berkisar antara 10 - 100 Ω.m. 2D modeling of magnetotelluric data has been conducted at Seulawah Agam volcano. This study aims to obtain a conceptual model of Seulawah Agam geothermal field based on 2D resistivity model. The magnetotelluric data were measured in range of frequency from 2.34 to 320 Hz at 7 stations along a profile crossing the Seulawah Agam volcano. The length of the profile is 27.7 km with a direction from north to south. The apparent resistivity and phase of magnetotelluric transfers function were used for the 2D inversion modelling of REBOCC code. The inversion was carried out using TE-mode, TM-mode and TE+TM-mode to obtain a better model. The model inverted of TE+TM-mode has resolved well, resistivity variation of subsurface of the Seulawah Agam volcano area. The inverted model shows the top later has resistivity values from 20-60 Ω.m, which is interpreted as a top soil. The second layer is a layer of clay/caprock with a relatively low resistivity values of less than 10 Ω.m. The third layer is predicted as reservoir with resistivity values ranging between 10-100 Ω.m. Keywords: magnetotelluric method, resistivity, 2D model, REBOCC code and Volcano Seulawah Agam.

Magnetotelluric observations in the western Ouachita Mountains, southeastern Oklahoma

Geophysics ◽  
1999 ◽  
Vol 64 (6) ◽  
pp. 1680-1688 ◽  
Author(s):  
Kevin L. Mickus
Keyword(s):  
Drill Hole ◽  
High Resistivity ◽  
Geologic Mapping ◽  
Gulf Coastal Plain ◽  
Ouachita Mountains ◽  
Arkoma Basin ◽  
Magnetotelluric Data ◽  
Low Resistivity ◽  
Northern Border ◽  
Seismic Reflection Profiles

The first magnetotelluric (MT) analysis of the Ouachita Mountains region is presented. Magnetotelluric data acquired at 19 sites along a 60-km profile in southeastern Oklahoma were used to image the western extension of the Ouachita Mountains and to determine the poorly known subsurface interaction between the Pennsylvanian Tishomingo‐Belton uplift and the subsurface extension of the exposed western Ouachita Mountains. Drill‐hole data, geologic mapping, seismic reflection profiles, and 1-D and 2-D MT-derived models indicate that lying beneath the low‐resistivity Gulf Coastal Plain sediments are 2–3 km of deep‐water lower Pennsylvanian (Jackfork Group) sediments and 6–8 km of Ouachita facies lithologies, mainly consisting of the Stanley Group. Beneath the profile’s northern section are 2–4 km of Atoka Formation sediments, probably deposited within the Arkoma basin, that underlie thrusted zones of the Stanley Group. The most unique feature is a high‐resistivity zone beneath stations 7–9, interpreted to be Precambrian/Cambrian granite similar to that exposed in the Tishomingo‐Belton uplift. A deep (5–6 km) low‐resistivity zone that may represent the northern border of the subsurface extension of the Broken Bow uplift is located along the Texas/Oklahoma border; however, this zone is not required by the MT data.

scholarly journals Crustal Electrical Structure of the Zhaheba Complex Imaged by Magnetotelluric Data and Its Tectonic Implications

2021 ◽  
Vol 11 (21) ◽  
pp. 10013
Author(s):  
Pingchuan Zhang ◽  
Changqing Yu ◽  
Xiangzhi Zeng
Keyword(s):  
Junggar Basin ◽  
High Resistivity ◽  
Precambrian Basement ◽  
Structure And Properties ◽  
Uppermost Mantle ◽  
Magnetotelluric Data ◽  
Northern Margin ◽  
Electrical Structure ◽  
Low Resistivity ◽  
Intrusive Rocks

A Magnetotelluric profile stretching northward from the Wulungu Depression (on the northern margin of the Junggar Basin) to the Dulate arc (crossing the Zhaheba–Aermantai ophiolite belt) was carried out in an attempt to probe the crustal structure and properties of the East Junggar, NW China. Along the profile, the inversion model was used to determine the electrical structure of the crust and uppermost mantle. The results revealed that the crust of the eastern Junggar Basin is composed of the shallow low resistivity layer and underlying high resistivity bodies. There is a crustal detachment in the basement: the upper layer is a Hercynian folded basement and the lower is a Precambrian basement. The Zhaheba complex is characterized by relatively high resistivity, with a thickness of ~5 km, the bottom controlled by the Zhaheba–Aermantai fault. The crust of the Yemaquan arc is composed of the residual continental crust, characterized by stable resistance. The exposed intrusive rocks are characterized by irregular resistors. The crust of the Dulate arc is characterized by relatively low resistivity. The shallow low resistivity layers represent the Zhaheba depression composed of the Devonian-Permian volcanic and sedimentary rocks. The crustal conductive anomalies are related to the magmatism and mechanism of metal deposits in the post-collision period.

Imaging the magmatic system beneath the Krafla geothermal field, Iceland: A new 3-D electrical resistivity model from inversion of magnetotelluric data

2019 ◽  
Vol 220 (1) ◽  
pp. 541-567 ◽  
Author(s):  
Benjamin Lee ◽  
Martyn Unsworth ◽  
Knútur Árnason ◽  
Darcy Cordell
Keyword(s):  
Electrical Resistivity ◽  
Volcanic Field ◽  
Geothermal Field ◽  
Fault System ◽  
Impedance Tensor ◽  
Magnetotelluric Data ◽  
Near Surface ◽  
Low Resistivity ◽  
Rhyolite Magma ◽  
Resistivity Model

SUMMARY Krafla is an active volcanic field and a high-temperature geothermal system in northeast Iceland. As part of a program to produce more energy from higher temperature wells, the IDDP-1 well was drilled in 2009 to reach supercritical fluid conditions below the Krafla geothermal field. However, drilling ended prematurely when the well unexpectedly encountered rhyolite magma at a depth of 2.1 km. In this paper we re-examine the magnetotelluric (MT) data that were used to model the electrical resistivity structure at Krafla. We present a new 3-D resistivity model that differs from previous inversions due to (1) using the full impedance tensor data and (2) a finely discretized mesh with horizontal cell dimensions of 100 m by 100 m. We obtained similar resistivity models from using two different prior models: a uniform half-space, and a previously published 1-D resistivity model. Our model contains a near-surface resistive layer of unaltered basalt and a low resistivity layer of hydrothermal alteration (C1). A resistive region (R1) at 1 to 2 km depth corresponds to chlorite-epidote alteration minerals that are stable at temperatures of about 220 to 500 °C. A low resistivity feature (C2) coincides with the Hveragil fault system, a zone of increased permeability allowing interaction of aquifer fluids with magmatic fluids and gases. Our model contains a large, low resistivity zone (C3) below the northern half of the Krafla volcanic field that domes upward to a depth of about 1.6 km b.s.l. C3 is partially coincident with reported low S-wave velocity zones which could be due to partial melt or aqueous fluids. The low resistivity could also be attributed to dehydration and decomposition of chlorite and epidote that occurs above 500 °C. As opposed to previously published resistivity models, our resistivity model shows that IDDP-1 encountered rhyolite magma near the upper edge of C3, where it intersects C2. In order to assess the sensitivity of the MT data to melt at the bottom of IDDP-1, we added hypothetical magma bodies with resistivities of 0.1 to 30 Ωm to our resistivity model and compared the synthetic MT data to the original inversion response. We used two methods to compare the MT data fit: (1) the change in r.m.s. misfit and (2) an asymptotic p-value obtained from the Kolmogorov–Smirnov (K–S) statistical test on the two sets of data residuals. We determined that the MT data can only detect sills that are unrealistically large (2.25 km3) with very low resistivities (0.1 or 0.3 Ωm). Smaller magma bodies (0.125 and 1 km3) were not detected; thus the MT data are not sensitive to small rhyolite magma bodies near the bottom of IDDP-1. Our tests gave similar results when evaluating the changes in r.m.s. misfit and the K–S test p-values, but the K–S test is a more objective method than appraising a relative change in r.m.s. misfit. Our resistivity model and resolution tests are consistent with the idea of rhyolite melt forming by re-melting of hydrothermally altered basalt on the edges of a deeper magma body.

scholarly journals Resistivity Models of Pantar Island Geothermal System East Nusa Tenggara, Indonesia

2020 ◽  
Vol 5 (3) ◽  
pp. 127-132
Author(s):  
Yoqi Ali Taufan ◽  
I. Syafri ◽  
D. Risdianto ◽  
A. Zarkasyi ◽  
T. Rahadinata ◽  
...  
Keyword(s):  
Heat Source ◽  
3D Models ◽  
High Resistivity ◽  
Geothermal System ◽  
Geothermal Systems ◽  
Low Resistivity ◽  
Resistivity Method ◽  
Geological Conditions ◽  
The Difference ◽  
Clay Cover

The subsurface geological conditions of a geothermal system are vital objects to be considered in geothermal exploration. The Magnetotellurics survey was conducted to explore for geothermal potential in Pantar Island. This is to achieve deeper penetration compared to our previous study that adopted resistivity method to determine reservoir zones based on rock resistivity models. The difference in rock resistivity in geothermal systems provides subsurface geological information in the form of low resistivity that associated the clay cap zones (high conductive), the medium resistivity zones associated with the reservoir zones, and high resistivity associated with a heat source. The results of 2D and 3D models from MT data show that the low resistivity value (<20Ωm) as a clay cover zones, this layer from the surface to -1000 meters. Medium resistivity values ​​(20-100 Ωm) starting from depths -1000 meters to -2000 meters associated with reservoirs zones, high resistivity values (> 200 Ωm) starting from depths of -2000 meters are considered as heat source from the Pantar geothermal system.

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

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.

scholarly journals Identification of low resistivity layers in the “N” geothermal field using 2D magnetotelluric inversion modelling

2020 ◽  
Vol 2 (2) ◽  
pp. 85-89
Author(s):  
Nabil Bawahab ◽  
Udi Harmoko ◽  
Tony Yulianto ◽  
Irvan Ramadhan
Keyword(s):  
Time Series ◽  
Apparent Resistivity ◽  
Time Series Data ◽  
Geothermal Field ◽  
Series Data ◽  
Geothermal System ◽  
Low Resistivity ◽  
Cap Rock ◽  
Phase Data ◽  
2D Model

Magnetotelluric research in the “N” geothermal field has been carried out to see the subsurface detail in the “N” geothermal field. 2D inversion model is generated by secondary data from magnetotelluric data collection in the form of time series data to become 2D models. Magnetotellurics method is used to identify geothermal system components, especially identifying layers with low resistivity values (2 Ω.m - 10 Ω.m) or also called as the cap rock which is seen with a very contrasting color difference compared to the surrounding layers. There are manifestations on the “N” geothermal field which reinforce the assumption that there is a geothermal system in this area. This research begins by processing time series data to become apparent resistivity and phase data. Time series data processing in this study uses several processing methods to produce better apparent resistivity and phase data. The final result of this study is a 2D model that illustrates the contour of the resistivity value of rocks laterally or vertically. 2D model interpretation in this study identified the cap rock layer with low resistivity distribution (2 Ω.m - 10 Ω.m), the medium resistivity zone identified as the reservoir layer (11 Ω.m - 70 Ω.m), and the resistive zone which has high resistivity value (more than 70 Ω.m).

Magnetotelluric transect of Long Valley caldera: Resistivity cross‐section, structural implications, and the limits of a 2-D analysis

Geophysics ◽  
1991 ◽  
Vol 56 (7) ◽  
pp. 926-940 ◽  
Author(s):  
P. E. Wannamaker ◽  
P. M. Wright ◽  
Zhou Zi‐xing ◽  
Li Xing‐bin ◽  
Zhao Jing‐xiang
Keyword(s):  
Apparent Resistivity ◽  
Transverse Electric ◽  
Hydrothermal Fluids ◽  
Bishop Tuff ◽  
Long Valley Caldera ◽  
Low Resistivity ◽  
Te Mode ◽  
Tm Mode ◽  
Long Valley ◽  
North And South

Twenty‐four magnetotelluric (MT) soundings have been collected in an east‐west profile across the center of Long Valley caldera. The average station spacing is approximately 1 km and appears adequate to sample the important features of the upper crustal and deeper resistivity structures. Additional control on the shallowest resistivity is provided by a continuous profile of time domain electromagnetic soundings coincident with the western portion of the MT line. Our MT data set reveals numerous resistivity structures which illuminate the evolution and present state of the Long Valley system. Many of these have been quantified through two‐dimensional (2-D) finite element modeling emphasizing the transverse magnetic (TM) mode. Important structural components include low‐resistivity layers 0.5–1.5 km deep under the eastern half of the caldera, beneath the axial graben of the resurgent dome, and under the west caldera moat. Most of this layering appears to lie in post‐caldera Early Rhyolite tuffs, and the uppermost unwelded Bishop Tuff. These rhyolite units have been observed to be porous and highly altered and to commonly contain Pleistocene intercalated lacustrine clays. The remainder and majority of the Bishop Tuff appears highly resistive. A low resistivity layer also occurs below the axial graben near the base of the Bishop Tuff (1.5 km). Hydrothermal fluids or alteration in precaldera volcanic strata or, less likely, carbonaceous metasediments may be the cause of this. Resistive, probably crystalline basement at high levels is apparent beneath the center of resurgence. Low resistivities are modeled at a depth around 5 km below the entire west moat and central graben and may represent a zone of hydrothermal fluids released from magma crystallization, with potential magmatic contributions at greater depths. The correspondence between this low resistivity and teleseismic delay and low density zones found in other studies is quite striking. A subtle anomaly in the transverse electric (TE) mode impedance is weakly suggestive of a midcrustal conductive axis centered beneath the central graben and resurgent dome. However, it cannot be simulated by two‐dimensional transverse electric calculations and requires a full three‐dimensional evaluation to ensure that the anomaly does not represent resistivity complexity in just the upper few kilometers. A fundamental, caldera‐wide 3-D effect is documented by comparison of observed and computed TE impedance and vertical magnetic field data. The abrupt termination of conductive caldera sediments less than 10 km north and south of our profile greatly depresses the observed TE apparent resistivity and vertical magnetic field relative to the model calculations for periods greater than 0.3 s for the central and eastern caldera. Analysis of the TE mode data also suggests that a similar finite‐strike effect lies in the response at periods greater than 3 s due to the mid‐crustal west moat conductor. The TM mode measurements are judged to also contain some large‐scale departure from the 2-D assumption related to horizontal current gathering from the north and south. This inflates the apparent resistivity and decreases the phase somewhat around 10 s over the central portion of the caldera relative to the 2-D model response. The regional profile of resistivity for the data at hand can be modeled with a 40 ohm‐m basal half‐space beneath 30 km of crust of 1000 ohm‐m or more. Although stations outside the caldera are very desirable to constrain this deep profile better, there is no evidence for a discrete low‐resistivity layer deep below Long Valley in contrast to our interpretation in the northeastern Basin and Range.

Subsurface geoelectrical structure from 3-d inversion of magnetotelluric data of Gisenyi geothermal field, western part of Rwanda

2021 ◽  
Vol 186 ◽  
pp. 104277
Author(s):  
Jean d'Amour Uwiduhaye ◽  
Gaetan Sakindi ◽  
Hakim Saibi ◽  
Biruk Abera Cherkose
Keyword(s):  
Geothermal Field ◽  
Magnetotelluric Data ◽  
Geoelectrical Structure
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