Coalbed methane fracturing effectiveness test using bore-hole transient electromagnetic method

Coalbed methane hydraulic fracturing technology is an effective way for enhancing the output ratio of underground coal mine coalbed methane resources,but there has been a lack of ideal method to test and assess the effectiveness of hydraulic fracturing. The traditional way of monitoring and measuring hydraulic pressure or medium aquosity is high cost,low efficiency and not intuitive. In order to solve the problem in assessing the effectiveness of hydraulic fracturing efficiently and visually,a dynamic source and reception TEM detection method was proposed to apply in underground coal mine fracturing borehole. This method uses the R-T unit,composed of the position relatively fixed minimal transmitting coil and receiving probe,to conduct three-component measurement along the bore-hole point by point,and then realize a high-precision detection for the tiny geological anomalous bodies around borehole’s radial direction. This method is sensitive to the parameter of the R-T unit,thus numerous physical modelling experiments were designed to analyze the characteristics of single curve and multichannel abnormal responses. After that,the most suitable R-T unit parameters was selected,such as the number of turns of transmit coil and its wire diameter,transmit current magnitude,the number of turns of receive coil and its wire diameter,the length of magnet core and so on,then formed the ideal single-hole TEM unit. Compared the vertical component observation curve of single-hole TEM with traditional coal mine TEM curve,a data preprocessing and processing method for vertical component data was proposed. A rectification method for horizontal component data caused by probe attitude was proposed,using trend-surface extract technology realized pure anomalous field extraction of horizontal component data. The abnormal body’s center azimuth was located by analyzing the relation of abnormal body space form combination and its amplitude. Considering the particularity of fracturing cracks,a 3D imaging technology,adopting the function of Suffer and Voxler software,was developed. The results from the comparison on the radius of radial investigation of roadway-borehole TEM with single borehole TEM in underground field experimentation verified that the radial detection capacity of single borehole TEM was half of the roadway-borehole TEM. Combined with engineering practice in Hancheng Mining Industry Corporation,the method’ spracticability and availability for fine detecting the cracks’characteristic,form and scale,which were formed by coalbed methane hydraulic fracturing,were tested. The research shows that the single-hole dynamic source and reception TEM detection method is an effective combination and mutual complementation of underground geophysical exploration technology,drilling technology and coalbed methane hydraulic fracturing technology,can meet the requirements of testing and evaluating the effectiveness of hydraulic fracturing.