Theoretical And Experimental Study Of Drilling Cuttings Weight Based On Effective Stress

Coal and rock composite dynamic disaster is the most serious natural disaster in coal mine,drilling cuttings bits index method is the main method for the prediction of Coal and rock composite dynamic disaster in the field.Under the condition of deep mining,the horizontal stress can not be ignored,the average effective stress was introduced,and the model of the plane strain around the borehole was established.A new cuttings formula was derived by the Mohr-Coulomb criterion,analyzing the relationship between drilling cuttings bits and the effective stress,coal mechanical parameters.The method of judging drilling cuttings weight by the effective stress was put forward.On this basis,Sunjiawan coal mine in Fuxin is a typical high gassy mine as example,coal drilling cuttings weight test device of three-dimensional stress was home-made,which can change axial pressure to simulate vertical crustal stress,confining pressure to simulate vertical crustal stress and pore pressure to simulate gas pressure.The experiments of drilling cuttings weight were carried out in the laboratory,and the effects of effective stress,coal seam depth,gas pressure,drilling speed and drilling diameter on the drilling cuttings weight were studied.The results show that drilling cuttings bits are linear increasing with the coal seam depth,bulk density and Poisson's ratio,and exponential increasing with elastic modulus of coal.And the drilling cuttings weight increases linearly with effective stress,and the test value is slightly larger than the theoretical value,the average error deviation is 7.9%,which is consistent with the previous conclusions.the drilling cuttings weight increases linearly with the depth of coal seam.With the increase of drilling depth,the drilling cuttings weight firstly decreases,then increases,and finally decreases slowly.With the increase of gas pressure,the drilling cuttings weight is increasing in the form of exponential functions.The value of drilling cuttings weight with the drilling velocity increased increases,and a power function law of increasing,increased amplitudes decrease gradually;drilling cuttings weight with the increase of the diameter of the drill rod increases and exhibits exponential function law of increasing amplitude increases with the increasing.The experimental results are in good agreement with the field and theoretical formulas.The conclusions have important reference value for the prediction and control of Coal and rock composite dynamic disaster in coal mines.