Identifying the lithologies and thicknesses of coal seam roofs and floors based on multiparameter logging of boreholes

BackgroundIn the process of coal mining, effective exploration methods for stratigraphic characteristics are crucial to underground operations. The reason is that the accurate stratigraphic characteristics of coal seams, along with the surrounding rocks of coal seam roofs and floors, facilitate the treatment of gas in coal seams, thereby ensuring safe and efficient coal mining. MethodsBased on the multiparameter logging of boreholes crossing strata in a bottom drainage roadway, this study highlighted the lowstand, upgoing borehole trajectories, as well as the variations in parameters including natural gamma rays, spontaneous potential, and resistivity. By comprehensive comparison of the trajectories, video-derived images, and logging results of multiple boreholes, this study detailed the distributions of the coal seams and surrounding rocks of the mining face and determined the accurate types and true thicknesses of various rocks. Besides, using the logging curves of boreholes and corresponding video-derived images, this study identified zones with anomalous coal structures and the water-bearing zones within coal seams. Results and conclusionsThe results indicate that the coal seam roofs and floors in the study area consist primarily of sandy mudstones, mudstones, fine-grained sandstones, and coals, which exhibit significantly different logging responses. The combination of the lithologic classification results and corresponding borehole trajectories allows for the effective definition of coal seams, as well as the horizons of the surrounding rocks of coal seam roofs and floors. Repeated logging of a single borehole can improve the accuracy of identified lithologies and thicknesses of rocks. With errors of thickness measurements within boreholes controlled at below 0.2 m, the logging results proved valid. The cross plot of spontaneous potential and resistivity curves reveals a zone with anomalous coal structures measuring 8.4 m in length and 1.1 m in thickness between the third and fourth groups of boreholes in the bottom drainage roadway. Additionally, the cross plot of natural gamma ray and resistivity curves and borehole videos suggest the presence of a water-bearing zone with a length of 3.4 m and a thickness of 0.9 m between the boreholes of the sixth group. These results align with the results obtained using the transient electromagnetic method (TEM), suggesting regionally weak water-yield properties. Overall, multiparameter logging serves as an efficient method for rapidly determining target horizons in underground drilling, demonstrating promising prospects for advancing the geological transparency of coal mines.