Background High-precision and long-distance exploration of geological conditions is required for coal extraction and disaster prevention in coal mines. However, traditional drilling and geophysical prospecting methods face technical bottlenecks such as insufficient exploration accuracy and limited exploration ranges. Borehole geophysical prospecting technology integrates the reliable and straightforward axial results of drilling with the high-resolution transverse results of geophysical prospecting, providing technical support for safe, efficient, and intelligent coal mining. Based on the construction spaces, this study categorizes borehole geophysical prospecting technology into four types: i.e., intra-borehole, inter-borehole, borehole-surface, and borehole-roadway. Furthermore, it presents the primary advances and applicable conditions of the former three types from the perspective of basic principles, technological advances, and application examples.

Progress For intra-borehole geophysical technology, high-frequency (HF) reflection radar within a near-horizontal borehole in coal mines allows for the coal-rock interface exploration and geological structure identification within a radial distance range of 0 to 10 m. The three-component transient electromagnetic technology deployed within a borehole can pinpoint low-resistance anomalous zones within a radial range of 30 m. Meanwhile, borehole 3D laser scanning assists in reconstructing underground goaves with centimeter-level precision. For inter-borehole geophysical prospecting technology, inter-borehole CT imaging based on electromagnetic or seismic waves enables precise delineation of anomalous bodies including faults, collapse pillars, and burnt areas through trans-borehole tomography. Using inter-borehole seismic and electromagnetic wave joint perspective, combined with velocity and resistivity interpretations, the properties of inter-borehole geological anomalous bodies can be inferred. Regarding borehole-surface geophysical prospecting technology, the reverse vertical seismic profile (RVSP) method, which adopts seismic excitation in a borehole and geophones on the surface, enables high-precision spatial positioning of goaves. The borehole-surface charging method assists in estimating the static water reserves of goaves by delineating the distribution range of the electric fields of low-resistance conductors.

Prospects  Future research and development efforts in borehole geophysical prospecting technology should focus on directional exploration while drilling, far-field radial exploration, and dynamic monitoring based on multiple fields and parameters. Furthermore, it is necessary to establish an integrated borehole geophysical prospecting technical chain that incorporates exploration, detection, and monitoring and construct a 3D, transparent geological model driven by cluster borehole data. These will provide a transparent geological guarantee for safe, efficient, and intelligent coal mining.