| Coal elasticity is one of the important mechanical parameters reflecting the material composition and structure of coal.Ultrasonic testing technology is used to obtain the ultrasonic elastic parameters of coal samples to understand the physical and mechanical properties and structural characteristics of coal.It has a good sense of direction,strong directivity and wear.At the same time,under the constraints of drilling and logging,the in-situ seismic wave test is used to obtain the seismic elastic characteristics of the coal seam to reflect its physical properties.For coal and gas outburst danger prediction and coalbed methane reservoir evaluation and development has important theoretical and engineering guiding significance.At present,the indoor coal rock ultrasonic experiment is mainly for the development of single-phase solid coal rock.Therefore,the research on the ultrasonic elastic characteristics of gas-solid coupling two-phase medium with gas is carried out,and the in-situ seismic wave contrast test of outburst coal is carried out in the outburst coal seam roadway where the coal sample collection site is located,which has important theoretical and practical guidance value.In this paper,theoretical analysis,petrophysical experiments and field tests are taken as the research methods.The ultrasonic elastic parameters of gas-containing coal samples and the in-situ seismic wave elastic parameters of coal bodies are obtained.The main research results are as follows:(1)The time of reaching the equilibrium state of gas adsorption was determined for three kinds of coal samples,8 #,9 # and 15 #,Xinjing Coal Mine,Yangquan Coal Mine.Through the study on the influence of different adsorption time on the elastic parameters of coal samples under 1 MPa gas pressure of 8 #,9 # and 15 #,it was determined that the time for 8 #,9 #,15 # coal samples to reach adsorption equilibrium was 16 hours.(2)The characteristics of ultrasonic elasticity and the variation of wave velocity anisotropy of coal samples of 8 #,9 # and 15 # under different gas pressures are revealed.With the increase of gas pressure,the longitudinal and shear wave velocities of the three coal samples show the trend of first rising and then decreasing,while the velocity ratio and Poisson's ratio show the trend of first decreasing and then rising.The difference is that the pressure turning point of the change trend of the four elastic parameters of 8# coal appears at0.6Mpa,while the two coal samples of 9# and 15# appear at 0.2MPa.At the same time,the four elastic parameters are between strike,trend and vertical direction.The anisotropy of longitudinal wave velocity is larger than that of shear wave,which indicates that theanisotropy of longitudinal wave velocity is more sensitive to the change of gas pressure.(3)The variation of seismic wave elasticity,gas parameters and firmness coefficient of coal body in roadway where coal samples are collected are revealed.With the increase of desorption index K1,the P-S wave velocity shows a downward trend;There is a good positive correlation between the P-S wave velocity and the hardness coefficient of coal roadways in each coal seam,while there is a good negative correlation between the P-S wave velocity ratio and the hardness coefficient of coal.The variation law of seismic wave characteristics in in-situ test of outburst coal body is consistent with that of ultrasonic elasticity characteristics of gas-bearing coal sample.The variation law of coal body firmness coefficient,gas concentration and longitudinal and shear wave velocity in in-situ seismic wave test can provide some guidance for the discussion and explanation of the variation law of ultrasonic elasticity characteristics of gas-bearing coal at the mechanism level.The existence of gas leads to the decrease of coal strength,which ultimately leads to the decrease of elastic parameters such as longitudinal and shear waves of coal. |
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