Dynamic monitoring of roof fracturing fissure and water enrichment anomaly based on multi-source geophysical prospecting technology

Combining the multi-source geophysical technologies of microseismic monitoring and mine audio-frequency electrical penetration, we monitored the microseismic signals and apparent resistivity changes generated during the fracture of surrounding rock, and obtained key information such as the deformation and fracture of overlying rock in coal seam roof and water hazard risks through microseismic source location and apparent resistivity imaging. Taking the 4106 working face of Wenjiapo Mining Area as the research object, this paper systematically analyzed 2185 valid microseismic events monitored from January to October 2023, The results show that microseismic events are more concentrated in the goaf and on the side of the return air gateway in the plane; in the vertical direction, the closer the microseismic event energy is to the roof, the higher the energy proportion, which is mainly concentrated in the range of 0-60 m from the roof. Microseismic events induced by the caving of overlying strata in the goaf roof are dominated by medium-energy events, while those in the upper part are dominated by small-energy events generated by fracture development. The energy intensity, vertical propagation range and lateral influence range basically follow a cycle of two square spans. When the cumulative mining footage exceeds 2100 m, affected by the large undulation of the working face strike and upward mining operation, the energy distribution on the goaf side is more concentrated and the influence range is larger than other areas. The height of the caving zone in the The roof of the working face measures 40-60 m, the height of the water-conducting fracture zone ranges from 140 to 240 m, and the fracture-mining ratio is 13-23.5. The development height of the water-conducting fracture zone does not reach the Yijun-Luohe Formation while mining. The resistivity imaging results of mine audio-frequency electrical penetration show that under the action of mining stress in the working face, an obvious low-resistivity water-rich anomaly zone appears in the fractured zone of the roof overlying rock, with the apparent resistivity ranging from 430 to 460 Ω·m, which is 8%～12% lower than the background value, and the anomaly zone extends to the goaf and the section coal pillar side. Joint interpretation of the microseismic-electrical method results show that the microseismic energy concentration zones and the electrical method low-resistivity anomaly zones present a significant spatial coupling characteristic, and the mechanical process of fracture development directly aggravates the enhancement of regional fracture water-richness. The coupling of the two can clarify the mechanical causes of water-rich anomalies and accurately determine the water-bearing state of fracture development zones. The combined monitoring technology of microseismic monitoring and mine audio-frequency electrical penetration has constructed a technical method of "dynamic monitoring-static imaging-joint interpretation", which can provide technical support for the risk early warning of roof overlying rock deformation, fracture and water inrush disasters, and offer important data support and technical foundation for the construction of transparent working faces.