‘Earth–ionosphere’ mode controlled source electromagnetic method

Li, Diquan; Di, Qingyun; Wang, Miaoyue; Nobes, David C.

doi:10.1093/gji/ggv256

Cited by 14 publications

(10 citation statements)

References 15 publications

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“…To illustrate the general behavior of the EM fields generated by artificial sources in the Earth-ionosphere cavity and to study the feasibility of the WEM for large-scale mineral exploration, the field components |Hϕ| of the spherical 1D Earth model were compared to controlled source audio-frequency magnetotelluric (CSAMT) and flat "Earth-ionosphere" models [24]. The calculations are based upon the Earth conductivities of 2.8 × 10 −4 S•m at 45 Hz and 3.2 × 10 −4 S•m at 75 Hz [13], with the conductivity of the atmosphere being 10 −14 Ω•m, and the conductivity of ionosphere being 10 −5 S•m.…”

Section: Comparison Of Csamt and Wem Methodsmentioning

confidence: 99%

“…However, it needs to be pointed out that the algorithm cannot be employed to calculate the near field. Since the interest of this paper is to expand the application range of the WEM, and there are mature algorithms [24,31] for the calculation of near field, therefore, this algorithm is applicable to the problems discussed in this paper.…”

Section: Convergence Of Spherical Harmonic Seriesmentioning

confidence: 99%

“…There are two methods to solve this problem: the first one is assuming that atmospheric and Earth layers are relatively flat; the other is to consider the spherical atmosphere and the Earth, and thus obtain a spherical harmonics series solution in a spherical coordinate system [10]. Since the pioneering works of J. R. Wait [11], J. Galejs [12], Bannister [13], J. P. Casey [14], and Pan and Li [15], many theoretical studies on ELF electromagnetic waves have been performed for different fields, such as communication [14,16], earthquake monitoring [17][18][19], geophysical exploration [20][21][22][23][24], and so on. It is clear that the ELF-EM method is an effective tool for probing the deep underground in a variety of geologic settings [20].…”

Section: Introductionmentioning

confidence: 99%

“…Since the wavelength of the ELF-EM waves is comparable to the perimeter of the Earth, it is inevitable to incorporate the effects of the ionosphere and the curvature of the Earth. To reduce the mathematical complexities associated with the propagation of ELF waves over the spherical Earth, Li [24] and Fu [31] introduced an Earth-flattening approximation and established a fully coupled theory of the lithosphere, atmosphere, and ionosphere, and some important findings are included in the book Study on the Propagation Characteristics of Electromagnetic Waves in the "Earth-Ionosphere" Mode by Di et al [32]. For an offset on the order of a few hundred kilometers, a plane model has been proved to be adequate [31,33].…”

Section: Introductionmentioning

confidence: 99%

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A Spherical “Earth–Ionosphere” Model for Deep Resource Exploration Using Artificial ELF-EM Field

Zheng

2022

Remote Sensing

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Fully coupled lithosphere, atmosphere, and ionosphere theory has demonstrated that extremely low-frequency electromagnetic (ELF-EM) fields present a broad application prospect in deep resource exploration, but previous studies have ignored the contribution of the Earth’s curvature. This study extends the theory of ELF-EM over a stratified Earth to the case where the Earth’s curvature must be taken into account, and presents an analytical solution of the ELF-EM field excited by a grounded horizontal antenna in a spherical Earth–ionosphere model, whose theoretical approach and solution method are notably different from the flat Earth–ionosphere model. Additionally, the Earth is treated as a concentric-layered sphere rather than an ideal homogeneous sphere. We aim to investigate the effects of the Earth’s curvature on the surface field, so as to broaden the coverage of the ELF wave in resource exploration. The solution is mathematically accurate and physically reasonable, since it reflects the sphericity and radially stratified structure of the Earth. We first verify the correctness and reliability of the proposed method by comparing the results with FDTD in a full-space spherical model. Additionally, we then compared the spherical results with the conventional controlled-source electromagnetic method and flat Earth–ionosphere results. The results show that when the distance between the transmitter and the receiver is comparable to the Earth radius, the spherical model better reflects the resonance of the wave in the cavity, suggesting that the effect of the Earth’s curvature is not negligible. Then, the numerical simulations conducted to investigate the properties of the EM fields and their sensitivities to the conductivity at depth in the Earth are discussed. Finally, the EM responses of some simple electrical conductivity structures models are modeled to illustrate their prospects in future resource exploration.

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Section: Comparison Of Csamt and Wem Methodsmentioning

confidence: 99%

Section: Convergence Of Spherical Harmonic Seriesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Spherical “Earth–Ionosphere” Model for Deep Resource Exploration Using Artificial ELF-EM Field

Zheng

2022

Remote Sensing

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“…We derive the planar full-model skywave theory by expanding the half-space CSAMT model to include ionosphere and lithosphere. The solution is achieved by the integral equation method based on the Green's function, and derived using the R-function and layer-matrix method [ 37 , 38 ].…”

Section: Theory and Equipmentmentioning

confidence: 99%

Insight into skywave theory and breakthrough applications in resource exploration

Xue

et al. 2021

National Science Review

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Skywave refers to the electromagnetic wave reflected or refracted from the ionosphere and propagate in the form of a guided wave between the ionosphere and the Earth's surface. Since the skywave can propagate over large distances, it has been widely used in long-distance communication. This paper explores and demonstrates the feasibility of skywave for deep resource and energy exploration at depths up to 10 km. Theoretical and technical advancements were accomplished in furthering the skywave applications. A new solution method based on Green's function has been developed to study skywave propagation in a fully coupled lithosphere-air-ionosphere full space model. The model allows one, for the first time, to study skywave distribution characteristics in the lithosphere containing inhomogeneity such as ore deposits or oil and gas reservoirs. This model also lays a foundation for skywave data processing and interpretation. On a parallel line, we have developed a multi-channel, broadband, low-noise, portable data acquisition system suitable for receiving skywave signals. Using the skywave field excited by a high-power fixed source located in the central China, actual field surveys have been carried out in some areas in China including the Biyang depression of Henan Province. The initial results appear encouraging – The interpreted resistivity models prove to be consistent with those of seismic exploration and known geological information, and the exploration cost is only about 1/4 to 1/10 of seismic surveys. These initial successful applications of the skywave theory lay a solid foundation for further verification of the new method.

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Advancements in Controlled Source Electromagnetic Methods for Prospecting Unconventional Hydrocarbon Resources in China

Yan

2023

Surv Geophys

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Globally, unconventional hydrocarbons, known for the symbiosis of their hydrocarbon source and reservoir, pose significant seismic exploration challenges due to their confined target regions, extensive burial depth, minimal acoustic impedance variation, marked heterogeneity, and strong anisotropy. Over the past decade, electromagnetic (EM) exploration has evolved markedly, improving resolution and reliability, thus becoming indispensable in unconventional hydrocarbon exploration. Focusing on China's application of the controlled source electromagnetic method (CSEM), this review examines the geological and electrical attributes of these reservoirs, notably the low resistivity, high polarization and strong electrical anisotropy of shale gas reservoirs. Despite the demonstrated positive correlation between induced polarization (IP) parameters and reservoir parameters, current methodologies emphasize the IP effect, inadvertently neglecting electrical anisotropy, which affects data precision. Moreover, single-source CSEM methodologies limit the observational components, acquisition density, and exploration area, impacting the accuracy and efficacy of data interpretation. Recently developed CSEM techniques in China, namely wide-frequency electromagnetic method (WFEM), time–frequency electromagnetic method (TFEM), long offset transient electromagnetic method (LOTEM), and wireless electromagnetic method (WEM), harness high-power pseudo-random binary sequence (PRBS) waveforms, reference observation and processing technology, hybrid inversion, and enhancing operational efficiency and adaptability despite the pressing need for multi-functional software for data acquisition. Case studies detail these methods' applications in shale gas sweet spot detection and continuous hydraulic fracturing monitoring, highlighting the immense potential of EM methods in unconventional hydrocarbon sweet spot detection and total organic content (TOC) predication. However, challenges persist in suppressing EM noise, streamlining 3D inversion processes, and improving the detection and evaluation of sweet spots.

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‘Earth–ionosphere’ mode controlled source electromagnetic method

Cited by 14 publications

References 15 publications

A Spherical “Earth–Ionosphere” Model for Deep Resource Exploration Using Artificial ELF-EM Field

A Spherical “Earth–Ionosphere” Model for Deep Resource Exploration Using Artificial ELF-EM Field

Insight into skywave theory and breakthrough applications in resource exploration

Advancements in Controlled Source Electromagnetic Methods for Prospecting Unconventional Hydrocarbon Resources in China

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