Research On Geophysical Response Of Deformed Coal

The deformed coals are the main influence factor of coal mining and Coal BedMethane(CBM) extraction. Coal and gas outburst accidents seriously restrict the safetyin production of coal mine. And the existence of a certain thickness of deformed coalstratification is the necessary condition of coal and gas outburst. Using geophysicaltechniques for deformed coal exploration has been still in an exploration stage so far.The study of the geophysical response of deformed coals, seismic elastic responsecharacteristics, is the physical basis for the prediction of deformed coals and has a veryimportant practical significance of safety in production of coal mine and gas control.This paper is to study the geophysical response of deformed coal. Through theelastic test of4different metamorphic kinds of deformed coals from different miningareas in the lab room temperature and atmospheric pressure, we had studied thecharacteristic of P-wave and S-wave velocity and attenuation and elastic modulus, andhad compared with the native structure of coal with the same coal rank. Ultrasonicmeasurement found that there exists a linear correlation between the P-wave andS-wave velocity and apparent density of deformed coal. The P-wave and S-wavevelocity fell a little. The calculated results of elastic parameters show that there exists alinear correlation between the P-wave and S-wave velocity and Q value of deformedcoal. Qp and Qs value are smaller than native structure of coal, which shows the strongabsorption attenuation.During the ultrasonic measurement of native structure of coal and deformed coal,the transmissive waveform is complex and it is difficult to pick up the first arrival andwaveform of P-wave and S-waves due to the mixing seismic phases. Aiming at theabove problems, using the Butterworth filter principle studying the method to pick upthe beginning of S-wave on the basis of the Matlab language and platform, which hasimproved the calculation precision of P-wave and S-wave velocity in the elasticmeasurement of native structure of coal and deformed coal and ensured the credibilityof the calculation of elastic modulus.Through the establishment of three models of deformed coal in different locationsin unformed coal seam, the PP wave and PS wave reflection coefficients of deformed coal with different location and different thickness are simulated at different frequencies.The results show that the coal seam containing deformed coal will lead to its reflectioncoefficients larger, Deformed coal seam reflection coefficients change with the locationand thickness of the interlayer, which provides a physical basis for using seismictechniques to predict the deformed coal.