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18 pages, 17328 KiB

Open AccessArticle

The Use of Multi-Geophysical Methods to Determine the Geothermal Potential: A Case Study from the Humenné Unit (The Eastern Slovak Basin)

by Stanislav Jacko, Zdenka Babicová, Alexander Dean Thiessen, Roman Farkašovský and Vladimír Budinský

Appl. Sci. 2022, 12(5), 2745; https://doi.org/10.3390/app12052745 - 7 Mar 2022

Cited by 1 | Viewed by 2263

Abstract

The exploration of the geothermal potential of a geological unit has multiple aspects. The most important elements are the geological structure, the hydrogeological conditions, and heat flow. The analysis of the above-mentioned elements attempts to help maximize the use of a geothermal aquifer’s [...] Read more.

The exploration of the geothermal potential of a geological unit has multiple aspects. The most important elements are the geological structure, the hydrogeological conditions, and heat flow. The analysis of the above-mentioned elements attempts to help maximize the use of a geothermal aquifer’s potential. When choosing the most appropriate geophysical method, it is important to consider various factors, such as basic structural parameters as well as the total cost of exploration. This is especially true for low-thermal areas. Comparison of multi-geophysical exploration methods used in the study of the carbonate aquifer of the Humenné Unit identified the advantages and weaknesses of each method. The Humenné Unit is the north basement unit of the Eastern Slovak Basin (with a heat flow value ranging from 100 to 125 mW·m⁻²), which is part of the Pannonian Basin (with a high heat flow ranging from 50 to 130 mW·m⁻²). The calculation of the geothermal potential was based on the results of several methods. Some important geophysical survey methods resulted in: (a) deep seismic cross-sections which clarified the position and overall internal structure of the aquifer (b) gravimetric measurements in the form of a map of the Complete Bouguer Anomalies (calculated for density 2.67 g·cm⁻³) which confirmed the presence of structural elevations and depressions. These elevations and depressions intensified the water yield, heat flow and raised the overall temperature (c) the use of geoelectric resistivity profiling, which is a fast and cheap method, but is limited by depth. The similar resistivities ρ: 80–360 Ωm of carbonates and andesites was a serious problem. The specific heat-energy potential has a wide range of 0.337–19.533 GJ/m². The highest values above 15 GJ/m² are reached in areas where the temperature on the surface of the Triassic carbonates exceeds 90 °C. Full article

(This article belongs to the Special Issue Seismic Exploration and Geothermal Energy)

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15 pages, 49696 KiB

Open AccessArticle

GAN-LSTM Joint Network Applied to Seismic Array Noise Signal Recognition

by Jian Li, Dongwei Hei, Gaofeng Cui, Mengmin He, Juan Wang, Zhehan Liu, Jie Shang, Xiaoming Wang and Weidong Wang

Appl. Sci. 2021, 11(21), 9987; https://doi.org/10.3390/app11219987 - 25 Oct 2021

Cited by 3 | Viewed by 2214

Abstract

The purpose of seismic data processing in nuclear explosion monitoring is to accurately and reliably detect seismic or explosion events from complex ambient noises. Accurate detection and identification of seismic phases are of great significance to the detection and parameter estimation of seismic [...] Read more.

The purpose of seismic data processing in nuclear explosion monitoring is to accurately and reliably detect seismic or explosion events from complex ambient noises. Accurate detection and identification of seismic phases are of great significance to the detection and parameter estimation of seismic events. In seismic phase identification, discriminating between noise signals and real seismic signals is essential. Accurate identification of noise signals helps reduce false detections, improves the accuracy of automatic bulletins, and relieves the workload of analysts. At the same time, in seismic exploration, the prime objective in data processing is also to enhance the signal and suppress the noises. In this study, we combined a generative adversarial network (GAN) with a long short-term memory network (LSTM) to discriminate between noise and phases in seismic waveforms recorded by the International Monitoring System (IMS) array MKAR. First, using the beamforming data of the array as the input, we obtained the signal features of seismic phases through the learning of the GAN discriminator network. Then, we input these features and trained the joint network on mixed seismic phase and noise data, and successfully classified seismic phases and noise signals with a recall of 95.28% and 97.64%, respectively. Based on this model, we established a real-time data processing method, then validated the effectiveness of this method with real 2019 data of MKAR. We also verified whether improved noise signal identification improves the quality of phase association and event detection. Full article

(This article belongs to the Special Issue Seismic Exploration and Geothermal Energy)

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13 pages, 2128 KiB

Open AccessArticle

Exploring the Dynamics of Global Plate Motion Based on the Granger Causality Test

by Lixin Ning, Chun Hui and Changxiu Cheng

Appl. Sci. 2021, 11(17), 7853; https://doi.org/10.3390/app11177853 - 26 Aug 2021

Cited by 2 | Viewed by 1561

Abstract

The geodynamic mechanism is the research focus and core issue of plate motions and plate tectonics. Analyzing the time series of earthquakes may help us understand the relationship between two plate boundaries and further explore movement mechanisms. Therefore, this paper uses earthquake event [...] Read more.

The geodynamic mechanism is the research focus and core issue of plate motions and plate tectonics. Analyzing the time series of earthquakes may help us understand the relationship between two plate boundaries and further explore movement mechanisms. Therefore, this paper uses earthquake event data and the Granger causality test method to quantitatively analyze the interaction and energy transfer relationship of plate boundaries from the viewpoint of statistics. The paper aims to explore the relationship between the pull effect and the push effect of plate motion and to provide knowledge to explore seismic energy transfer relationships, and even to predict earthquakes: (1) The directions of the global plate motion field are opposite to the directions of Granger causality between plate boundaries of the Pacific, Nazca, African, Australian, Eurasian, and Philippine plates. (2) The slab-pull force (not limited to the subduction force of the ocean plates) provides a main driving force for plate motions in the Pacific plate, Nazca plate, African plate, Australian plate, Eurasian plate, and Philippine sea plate. (3) The causality relationship and optimal lag length of energy release between plate boundaries may provide another view to forecasting earthquakes. Full article

(This article belongs to the Special Issue Seismic Exploration and Geothermal Energy)

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16 pages, 6008 KiB

Open AccessArticle

Frequency Domain Full Waveform Inversion Method of Acquiring Rock Wave Velocity in Front of Tunnels

by Kai Wang, Meiyan Guo, Qingxia Xiao, Chuanyi Ma, Lingli Zhang, Xinji Xu, Ming Li and Ningbo Li

Appl. Sci. 2021, 11(14), 6330; https://doi.org/10.3390/app11146330 - 8 Jul 2021

Cited by 3 | Viewed by 2442

Abstract

Ahead geological prospecting, which can estimate adverse geology ahead of the tunnel face, is necessary in the process of tunnel construction. Due to its long detection range and good recognition effect on the interface, the seismic method is widely used in tunnel ahead [...] Read more.

Ahead geological prospecting, which can estimate adverse geology ahead of the tunnel face, is necessary in the process of tunnel construction. Due to its long detection range and good recognition effect on the interface, the seismic method is widely used in tunnel ahead prospecting. However, the observation space in tunnels is quite narrow compared to ground seismic prospecting, which leads to some problems in the acquisition of wave velocity, including: the velocity of the direct wave is used to replace the wave velocity of the forward rock approximately; the arrival time information of seismic waves is the main factor in time-travel inversion or the tomography method, which is sufficient to provide a simple model rather than deal with complex geological conditions. In view of the above problems, the frequency domain full waveform inversion method in ground prospecting is introduced to tunnel seismic prospecting. In addition, the optimized difference format is given according to the particularity of the tunnel environment. In this method, the kinematics and dynamics of the seismic wavefield are fully used to obtain more accurate wave velocity results. Simultaneously, forward modeling and inversion simulations on tunnel samples with typical adverse geological bodies are given here, which verified the validity and reliability of the proposed method. Full article

(This article belongs to the Special Issue Seismic Exploration and Geothermal Energy)

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17 pages, 9506 KiB

Open AccessArticle

Analysis of Seismic Wavefield Characteristics in 3D Tunnel Models Based on the 3D Staggered-Grid Finite-Difference Scheme in the Cylindrical Coordinate System

by Zhiwu Zuo, Duo Li, Pengfei Zhou, Chunjin Lin, Zhichao Yang, Xinji Xu, Lingli Zhang and Jiansen Wang

Appl. Sci. 2021, 11(13), 5854; https://doi.org/10.3390/app11135854 - 24 Jun 2021

Cited by 5 | Viewed by 1761

Abstract

The accurate prediction of the geological conditions ahead of a tunnel plays an important role in tunnel construction. Among all forward geological prospecting methods, the seismic detection method is widely applied. However, due to the characteristics of the tunnel and the complexity of [...] Read more.

The accurate prediction of the geological conditions ahead of a tunnel plays an important role in tunnel construction. Among all forward geological prospecting methods, the seismic detection method is widely applied. However, due to the characteristics of the tunnel and the complexity of the geological conditions, the seismic wavefield is complicated. Carrying out a more realistic forward modeling method is vital for fully understanding the law of seismic wave propagation and the characteristics of seismic wavefield in the tunnel. In this paper, the 3D staggered-grid finite-difference scheme in the cylindrical coordinate system based on the decoupled nonconversion elastic wave equation is used to carry out the numerical simulation. This method can avoid the diffraction interferences produced at the edges of the tunnel face in the Cartesian coordinate system. Based on this forward modeling method, the characteristics of wavefield and propagation laws of seismic waves under three kinds of common typical unfavorable geological models were explored, which can provide theoretical guidance to seismic data interpretation of tunnel seismic forward prospecting in practice. Full article

(This article belongs to the Special Issue Seismic Exploration and Geothermal Energy)

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30 pages, 6928 KiB

Open AccessArticle

Seismic Velocity Characterisation of Geothermal Reservoir Rocks for CO₂ Storage Performance Assessment

by Martijn T. G. Janssen, Auke Barnhoorn, Deyan Draganov, Karl-Heinz A. A. Wolf and Sevket Durucan

Appl. Sci. 2021, 11(8), 3641; https://doi.org/10.3390/app11083641 - 18 Apr 2021

Cited by 7 | Viewed by 3294

Abstract

As part of a seismic monitoring project in a geothermal field, where the feasibility of re-injection and storage of produced CO₂ is being investigated, a P- and S-wave seismic velocity characterisation study was carried out. The effect of axial (up to 95 [...] Read more.

As part of a seismic monitoring project in a geothermal field, where the feasibility of re-injection and storage of produced CO₂ is being investigated, a P- and S-wave seismic velocity characterisation study was carried out. The effect of axial (up to 95 MPa) and radial (up to 60 MPa) stress on the seismic velocity was studied in the laboratory for a broad range of dry sedimentary and metamorphic rocks that make up the Kızıldere geothermal system in Turkey. Thin section texture analyses conducted on the main reservoir formations, i.e., marble and calcschist, confirm the importance of the presence of fractures in the reservoir: 2D permeability increases roughly by a factor 10 when fractures are present. Controlled acoustic-assisted unconfined and confined compressive strength experiments revealed the stress-dependence of seismic velocities related to the several rock formations. For each test performed, a sharp increase in velocity was observed at relatively low absolute stress levels, as a result of the closure of microcracks, yielding an increased mineral-to-mineral contact area, thus velocity. A change in radial stress appeared to have a negligible impact on the resulting P-wave velocity, as long as it exceeds atmospheric pressure. The bulk of the rock formations studied showed reducing P-wave velocities as function of increasing temperature due to thermal expansion of the constituting minerals. This effect was most profound for the marble and calcschist samples investigated. Full article

(This article belongs to the Special Issue Seismic Exploration and Geothermal Energy)

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15 pages, 88342 KiB

Open AccessArticle

Travel-Time Inversion Method of Converted Shear Waves Using RayInvr Algorithm

by Genggeng Wen, Kuiyuan Wan, Shaohong Xia, Huilong Xu, Chaoyan Fan and Jinghe Cao

Appl. Sci. 2021, 11(8), 3571; https://doi.org/10.3390/app11083571 - 16 Apr 2021

Cited by 2 | Viewed by 2175

Abstract

The detailed studies of converted S-waves recorded on the Ocean Bottom Seismometer (OBS) can provide evidence for constraining lithology and geophysical properties. However, the research of converted S-waves remains a weakness, especially the S-waves’ inversion. In this study, we applied a travel-time inversion [...] Read more.

The detailed studies of converted S-waves recorded on the Ocean Bottom Seismometer (OBS) can provide evidence for constraining lithology and geophysical properties. However, the research of converted S-waves remains a weakness, especially the S-waves’ inversion. In this study, we applied a travel-time inversion method of converted S-waves to obtain the crustal S-wave velocity along the profile NS5. The velocities of the crust are determined by the following four aspects: (1) modelling the P-wave velocity, (2) constrained sediments Vp/Vs ratios and S-wave velocity using PPS phases, (3) the correction of PSS phases’ travel-time, and (4) appropriate parameters and initial model are selected for inversion. Our results show that the vs. and Vp/Vs of the crust are 3.0–4.4 km/s and 1.71–1.80, respectively. The inversion model has a similar trend in velocity and Vp/Vs ratios with the forward model, due to a small difference with ∆Vs of 0.1 km/s and ∆Vp/Vs of 0.03 between two models. In addition, the high-resolution inversion model has revealed many details of the crustal structures, including magma conduits, which further supports our method as feasible. Full article

(This article belongs to the Special Issue Seismic Exploration and Geothermal Energy)

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14 pages, 5358 KiB

Open AccessArticle

Magmatic Geothermal Genesis Model in the Huailai Area Based on the Constraints of the Crust–Mantle-Scale Geoelectric Structure

by Meng Fanwen, Han Jiangtao, Liu Wenyu and Liu Lijia

Appl. Sci. 2021, 11(5), 2086; https://doi.org/10.3390/app11052086 - 26 Feb 2021

Cited by 3 | Viewed by 2246

Abstract

The Huailai area is rich in geothermal resources, but the formation mechanism of its deep heat source is still unclear. In this paper, based on 16 broadband magnetotelluric sounding points, the two-dimensional electrical structure of the crust and mantle in the Huailai area [...] Read more.

The Huailai area is rich in geothermal resources, but the formation mechanism of its deep heat source is still unclear. In this paper, based on 16 broadband magnetotelluric sounding points, the two-dimensional electrical structure of the crust and mantle in the Huailai area was obtained. Combined with deep seismic reflection and P-wave seismic tomography, the geophysical characteristics of deep heat sources and reservoirs in the Huailai area are described. The Huailai area is characterized by low resistivity and layered reflection above 2 km in depth, which shows the distribution of the Cenozoic sedimentary cover layer. The upper crust is characterized by high resistivity without an obvious reflector, corresponding to the crystalline basement of the basin, whose main lithology is Archean gneiss. There is a highly conductive and bright-spot-reflective structure under the basement, which extends to 100 km, indicating the upwelling of mantle-derived material. Combined with the results of helium isotope tracing, a magma-type geothermal model in the Huailai area is proposed. The upwelling mantle-derived magma material is enriched under the basement to form a heat source. The heat is transferred to the upper crust through heat conduction along the crystalline basement. Then, groundwater circulation brings deep heat to the surface, forming hydrothermal resources. Full article

(This article belongs to the Special Issue Seismic Exploration and Geothermal Energy)

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