The Forward Modeling for Surface-borehole Observation Responses of Polarized Target

Surface-hole induced polarization method is a typical deep resource exploration technology, which plays an important role in the mineral survey. The traditional surface-hole induced polarization method is mainly to observe a single polarized secondary field. At present, the time spectrum observation of polarization fields is becoming more and more popular, which greatly enriches the interpretation technology of induced polarization data. In this work, the time spectrum induced polarization method is expounded, the decay polarization fields were numerical calculated and analyzed for the typical 2-dimensional geoelectric model. The results show that for a single polarized target, the time spectrum obtained from different azimuth observation responses are basically the same, which can effectively reflect the time-varying characteristics of the polarized fields. The observation responses of polarized target at different depths can still reflect the time spectrum of decay fields. The main change of the observed response of the polarized target closer to the borehole is the response amplitude. The conclusions and simulations of this study can provide working mode for relevant research and reference for similar work.

An Approximate Inversion Scheme for Surface-Borehole EM in the Presence of Steel Casing. 1D Implementation

An approximate inversion scheme for Surface-Borehole EM data is proposed. The method aims at reducing the computational burden arising by the fine discretization required to accurately solve for the field distribution in the full complexity of the borehole system together with the reservoir medium. I first analyze numerical simulations of the surface-borehole response performed for a 1D layered earth, incorporating also realistic complexity of the borehole system. The analysis brings useful insight on the requirement of incorporating fluid and mud/cement electrical properties when implementing an inversion by numerically simulating the full complexity of the system. Subsequently, the synthetic dataset was used to test an inversion method which uses the data dominated by the casing effect to approximately describe the casing secondary fields. A scaling factor is then introduced to account for the the current induced in the well as the exciting source is placed further below the casing shoe. The method is found to recover fairly well the known 1D resistivity strata, still some bias is expected for the resistivity close below the casing shoe, where the data is anticipated to be most distorted by the casing effect.

Review of Geophysical Exploration on Mined-out Areas and Water Abundance

With the increase in mining depth, the presence of goafs has become increasingly severe in mine safety. The accurate and effective detection of underground goafs and their water abundance is the key to ensure the safety of mine production. On the basis of the relevant research, this paper defines different goaf types from the perspective of geophysical exploration and discusses the geophysical prerequisites for goaf detection. DC methods, electromagnetic methods, seismic methods, and other geophysical methods on the ground and in the subsurface are reviewed and summarized using the method's principle, research status, and technical features. Research progress on the geophysical methods in goafs and their water abundance detection are introduced, including the electrical source short-offset transient electromagnetic method (SOTEM), the wave-field transformation and synthetic aperture of the transient electromagnetic method, and comprehensive detection. At the end of the paper, a direction for the development of coal mined-out areas and their water abundance detection is put forward, including information fusion technology, ground-airborne electromagnetic methods, magnetic resonance sounding (MRS), surface-borehole transient electromagnetic method, surface-borehole seismic methods, and seismic while tunneling technology. The application prospects of these methods are discussed, and the results of this study are expected to considerably improve the location precision and resolution of the goaf detection on the basis of the implications of these techniques.