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

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. O...

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Bibliographic Details
Published in:Surveys in geophysics 2024-02, Vol.45 (1), p.239-276
Main Author: Yan, Liangjun
Format: Article
Language:English
Subjects:
Acoustic impedance
Adaptability
Anisotropy
Astronomy
Data acquisition
Data interpretation
Detection
Earth and Environmental Science
Earth Sciences
Geophysics/Geodesy
Heterogeneity
Hydraulic fracturing
Hydrocarbons
Induced polarization
Methods
Observations and Techniques
Parameters
Polarization
Pseudorandom binary sequences
Reservoirs
Sedimentary rocks
Seismic exploration
Shale
Shale gas
Shales
Symbiosis
Total organic carbon
Waveforms
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Summary: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.
ISSN:0169-3298
1573-0956
DOI:10.1007/s10712-023-09808-6