Application of three-component transient electromagnetic method in hydraulic fracturing effect evaluation of directional long borehole in hard roof

Mine hydraulic fracturing technology has been widely used in the fields of hard roof pressure relief and high-efficiency gas drainage. However, there has been a lack of ideal geophysical prospecting methods for the detection and evaluation of hydraulic fracturing effects in long boreholes. Traditional detection methods have the shortcomings of high cost, low efficiency and short detection distance. In order to achieve the goal of efficient and intuitive detection of the hydraulic fracturing effect of long directional drilling in hard roofs, a dynamic source-dynamic receiving transient electromagnetic detection method was adopted for the construction of fracturing holes in coal mines. The antenna of the detection device is composed of a minimum transmitting coil with fixed transceiver spacing and a three-component receiving probe, which moves point by point in the borehole to perform three-component receiving. In order to make up for the lack of the detection distance of the cable device, a detection device with timing synchronization outside the hole and transmission and reception inside the hole was used to detect the 40-315 m section of the No. 2 fracturing borehole in a Shendong mine before and after fracturing. Firstly, the vertical component data was preprocessed, and the horizontal component data was used to correct the influence of probe attitude change, and the pure anomaly field is extracted for analysis. Finally, the three-dimensional imaging technology of water filling cracks was realized. The test results show that there are obvious strip-shaped low-resistivity anomalies in the contour map of the pure anomaly field. By comprehensively analyzing the distribution of apparent resistivity before and after fracturing, it is considered that the strip-like low-resistivity anomalies are caused by fractures formation, and the abnormal strike is the fracture extension direction, and the abnormal extension range is the fracture extension range. The three-component transient electromagnetic detection technology is an organic combination and complementation of mine geophysical exploration, drilling and hydraulic fracturing technology. It can effectively delineate the fracture trend and extension range, and can be effectively applied to the evaluation of hydraulic fracturing effect of directional long borehole with hard roof plate.