Development law of cracks in a thick and hard sandstone roof with narrow coal pillars after burst-prevention weakening
To clarify the uncertainty of fracturing effect due to the insufficient research on the law of fracture evolution and burst-prevention cracks under hard roof engineering conditions,No.3106 working face of Menkeqing Coal Mine was selected as the research background.Starting with long hole hydraulic fracturing research of the high,thick hard sandstone roof,drilling leakage rate and transient electromagnetic technology were used to study the evolution of drilling leakage rate and transient electromagnetic resistivity in different layers of rock strata fissures before and after fracturing.The development law and expansion range of overlying rock fractures before and after the weakening of hard roofs were verified,which provided theoretical guidance for evaluating the law of hydraulic fracturing evolution and the influence range of hydraulic fracturing.The results indicate that when the borehole is in undeveloped fissure area,the drilling leakage rate in the fracturing layer shows a significant increase before and after fracturing.This confirms the fracture extension range in the fractured layer area from the perspective of drilling leakage.The reliability of the fracture development range was verified by the phenomenon that the resistance of transient electromagnetism reduced with the increase of water content in rock fractures.It provides theoretical guidance for studying the evolution and impact range of hydraulic fracturing and offers a new method for evaluating the effectiveness of hydraulic fracturing under hard roofs.
fracturing expansion rangethick and hard sandstonerock burstlaw of fracture evolutiondrilling leakage rate
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