Study On Induced Polarization Characteristics Of Tectonically Deformed Coal Under Coal Mine

Tectonically deformed coal(TDC)is an outstanding risk coal of coal and gas.Predicting the development range of TDC in coal seam is one of the important bases for evaluating the risk of gas outburst.However,there are few reports on the evaluation of TDC in the mine by traditional geophysical exploration methods.In view of the physical characteristics of TDC,the surface induced polarization method is introduced into the underground to carry out the mine induced polarization method in the roadway and borehole for small-scale tectonic coal detection and research,which is of great practical demand.Based on the development of TDC sampling method and rock sample test,this paper studies the distribution law of full space induced electric field under the condition of tectonic coal distribution,clarifies the characteristics of induced electrical response on TDC,explores the observation method of underground detection of TDC and applies this method to underground detection test of TDC.The main research contents and achievements are as follows:(1)According to the characteristics of TDC and the problems of sample-making on tectonic coal,the tectonic coal sampling drilling tool is designed and processed on the basis of single dynamic and double layer pipe drilling tool.The drilling tool saves the tectonic coal sample directly in the built-in sample tank on the basis of reducing sampling disturbance,and accomplish the test of sample in approximate situ.(2)Based on the analysis of the spectral characteristics of the real part,the imaginary part,the phase and the amplitude of Cole-Cole model,the sample measurement method is used to test the complex electrical properties of two kinds of coal samples:broken coal and mylonite coal,which are easily protruding structural coal and primary structural coal.Then the electrical properties of different coal bodies are analyzed.It turned out that the impedance and polarizability of primary structural coal and structural coal are obviously different in the tested samples,despite the disparity of time constant which can almost be ignored.This test provides a reference for distinguishing primary structural coal from structural coal.(3)By using numerical simulation method,the distribution of Percent Frequency Effect(PFE or F_s)under the condition of point electric field source,cube model,plate model and different IP parameters are studied.(1)The results showed that there was a process of transition from negative value to positive value between the upper boundary and the lower boundary of the abnormal body,no matter it was the cube polarization model or the plate polarization model,and no matter it was the low resistance polarization model or the high resistance polarization model,there always had a process from negative value to positive value between the upper boundary and the lower boundary of the abnormal body,and the PEF value at the lower boundary of the abnormal body reaches the maximum value.Through the PFE value,the distribution position and range could both be reflected very accurately on the abnormal polarization depth.(2)For cube polarization model,the response of low resistance polarization model is stronger than that of high resistance polarization model under the same conditions.For the plate model,the distribution of the PFE is related to the distribution of the plate.For the vertical plate,the distribution of the PFE is consistent with that of the cube model.For the inclined plate model,the distribution of the PFE can reflect the inclined direction of the inclined plate,and the inclined direction of the contour of the PFE of the low resistance inclined plate and the inclination direction of the abnormal body is the same,the inclination direction of the contour of the PFE of the high resistance inclined plate body is perpendicular to the inclination direction of the abnormal body;for the horizontal plate model,the response of the abnormal body with high resistance polarization is more obvious than that of the abnormal body with low resistance polarization.(3)The parameters of the Cole-Cole model and the power supply frequency have certain influence on the variation of the PFE,and the polarization parameter m reflects the polarization property of the abnormal body,which is positive to the value of the PFE Correlation;time constant and correlation coefficient c have no significant positive and negative correlation with the apparent frequency;the influence of power supply frequency on the apparent frequency is mainly reflected in the characteristic frequency corresponding to the peak value of the apparent frequency,in which time constant has significant influence on the characteristic frequency,Polarizability parameter m has little influence on the characteristic frequency,and correlation coefficient c has little influence on the characteristic frequency.(4)To the observation system,the detection effect of different factors,such as device form,surrounding rock resistivity,coal seam thickness,measurement polar distance,abnormal body size and so on,is analyzed in detail.The results show that the pole-dipole observation device has the best effect in dividing the structural coal electricity interface in the construction and working face;the difference of electricity between the surrounding rock and the abnormal body is the primary condition for detection;when the difference between the surrounding rock and the abnormal body is large,the abnormal response is clearer and the detection effect is more obvious;the thickness of the coal seam has a certain impact on the detection effect of the coal seam along the coal seam,and the detection method of the coal seam along the coal seam wall has a certain impact on the thin seam The detection effect of coal seam is better than that of thick coal seam.When the coal seam is thick,a larger power supply polar distance is needed.The measurement polar distance has certain influence on the detection effect of abnormal body.In actual work,it is necessary to comprehensively consider the influence of measurement electrode on apparent resistivity and apparent amplitude frequency as well as work efficiency,and reasonably arrange electrodes.(5)In this paper,the effects of borehole array observation,tunnel-borehole array observation and borehole-tunnel array observation are studied.Among them,the borehole array observation can find the extension range of structural coal in depth and the development of structural coal in a certain depth along the borehole direction in the coal seam,which has a high resolution for the detection of different depth ranges along the borehole.The tunnel-borehole array observation mode not only can determine the depth of the abnormal body,and has a high resolution in the horizontal direction,which has a good detection effect for the structural coal depth in the coal seam and the orientation relative to the borehole;the borehole-tunnel array observation method has a relationship between the position of the power supply electrode and the relative position of the abnormal body,which is convenient for comprehensive interpretation and analysis.(6)Based on the dual-mode network parallel electrical method technology,the IP detection test of small-scale structural coal in the mine is completed,and the development position and range of structural coal are preliminarily determined.The test results are consistent with the data provided by the mine side,which proves the feasibility of this method to detect the development area of structural coal in a small range.This paper has 82 figures,4 tables and 115 references.