Abstract The geological conditions of deep mines are highly complex, with coal and gas outbursts occurring frequently. Among the contributing factors, small geological structures are the most likely to induce such gas outbursts. Traditional mine geophysical prospecting technologies suffer from limited resolution, resulting in significant blind spots when identifying small geological structures. To address this issue, a new method for the precise detection of small geological structures in coal seams using horizontal borehole acoustic reflection imaging is proposed. A realistic three-dimensional geological model of the working face is constructed based on point cloud data from cross-seam boreholes. Three small geological structures—coal seam thickening zones, minor folds, and inclined coal seams—are selected from the model’s pre-mined roadway belt area for finite element simulations of horizontal borehole acoustic reflection imaging. The simulation results are then compared to the original model. The key findings of the study are as follows: The arrival times of the reflected waves, as they vary with the source coordinates, effectively capture the morphological characteristics of the coal seam’s upper and lower boundaries. The greater the fluctuation in these boundaries, the more complex the reflected wave characteristics in both the t - x and f - k domains. Inversion of the reflected acoustic wave data allows for the imaging of small geological structures. The imaging slices reveal that in region 1, a coal seam thickening zone exists, where the coal thickness increases from 7 m to 12 m. In region 2, a continuous fold of a thin coal seam is present, with the thinnest part measuring around 2.2 m. In region 3, there is an inclined coal seam with a thickness of about 5 m and a dip angle of about 15°. The errors in the coal seam roof interface, floor interface, and coal seam thickness compared to the original model are less than 0.9 m, 0.6 m, and 1.1 m, respectively. Finally, by stacking the imaging slices, a three-dimensional geological model of the three regions is reconstructed, and the positions and morphological characteristics of the small geological structures in the working face are clearly identified. The results of the acoustic reflection imaging detection are consistent with the original three-dimensional geological model, demonstrating the method’s effectiveness in detecting small geological structures in coal seams. This study advances the transparency of small geological structures in coal seams and provides a crucial technique for the three-dimensional fine geological modeling of mines.
Xu et al. (Mon,) studied this question.
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