Prediction Of Small Faults Based On Gas Drainage Boreholes Cross Seam Bedding Strip

It is of significance to detect and predict small concealed faults for coal mine safety. Currently, the main techniques that are used to detect and predict concealed faults in coal mines include geological analysis method, geophysical exploration and drilling method. Geological analysis method can only predict limited areas and its predicted results’ accuracy is low. Affected by the physical properties of coal and rock,the geophysical exploration method is often with multi solutions. Drilling method takes so long time and much money that it affects the mining schedule. So the technologies are still unable to meet the requirement of mine safe production. Thus,using a large number of gas pre-drainage boreholes cross seam bedding strip to detect and predict small concealed faults has great practical significance.This paper puts forward a new method to predict small concealed fault in coal seam, which uses gas pre-drainage boreholes cross seam bedding strip to get coal seam floor or roof elevations, and draws the contour map and the three-dimensional map of coal seam floor or roof.This study shows that the main factors affecting the accuracy of small concealed faults by using gas pre-drainage boreholes cross seam bedding strip include borehole spaces,concealed fault throw,drilling deviation and measuring errors. It shows that the borehole spaces and fault throw have an influence on the coal-floor contour map’s sensitivity to the fault. The smaller the borehole spaces and the larger the fault throw,the more intensive the contour lines in the abnormal area, the greater the dislocation of contour lines on both sides of the rupture range and the more obviously the fault displays. Drilling deviation and measuring errors will cause the coordinates that control the coal floor to deviate from the true values, interfere the accuracy of predicting concealed faults, even lead to false positives or false negatives. Reducing the drilling deviation and measuring errors are the basis of improving prediction accuracy.This paper summarizes five safeguard measures to ensure the accuracy of predicting and detecting small concealed faults by using gas pre-drainage boreholes cross seam bedding strip, including perfecting drilling construction records, reducingthe measuring errors, correcting and screening drilling data, preventing borehole deviation, and using gas geological information.Through establishing 3D geological models of gas-drainage cross seam bedding strip, this paper introduces the method of getting drilling parameters, illustrates the basic correction principles and conversion step, writes the MATLAB routine of drawing coal floor contour map and three-dimensional map, puts forward a method of predicting small concealed faults qualitatively and quantitatively. Through some cases,it shows that the proposed approach could achieve high detecting accuracy of concealed small faults. Through field application, it predictes a small concealed faul with 2.2 m throw, verifying the feasibility of this method.