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چکیده
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Fractured and karstic reservoirs, as multifaceted subsurface systems, have significant implications in hydrogeology, petroleum exploration, and environmental engineering. The inherent heterogeneity of these systems poses serious challenges for characterization due to the extreme spatial variability of porosity/permeability, multi-scale, and complex geometries. Recent advances in time-lapse monitoring, machine learning, and structure-coupled joint inversion are related to the unique problems of exploring complex karst systems. This review article provides a comprehensive assessment of research on using geophysical methods to detect and characterize fractured and karstic reservoirs, including the transition from single techniques to fully integrated multi-methods. By critically reviewing research employing 30+ geophysical methods (i.e., Electrical Resistivity Tomography, seismic methods, gravity, ground penetrating radar (GPR), and new and emerging technologies), we demonstrate the practical implications of our findings, particularly the superior utility potential of electrical methods for all aspects, especially for near-surface exploration. In this regard, five key exploratory challenges are addressed: defining the limits of a karst system, detecting structural discontinuities, determining preferential flow pathways, locating cavities, and characterizing the epikarst zone. The review indicates that site-specific attributes are crucial when choosing methods, since the performance of methods can fluctuate from the effects of overburden properties, depth, and geology. Generally, this research showed that no single geophysical method can characterize a fractured and karstic system, and that successful geophysical investigations need additional, complementary approaches based on exploration objectives and site conditions.
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