An experimental study on the correlation between the elastic wave velocity and microfractures in coal rock from the Qingshui basin

In order to study the impact of microfractures on the elastic wave velocity, multi-azimuth elastic wave velocity experiments were performed with coal rock samples under a confining pressure similar to the one in the buried coal strata of the Qinshui basin. The results indicate that (1) the microfractures in coal rock reduce the elastic wave velocity. In the experiments, the velocity was increased with a confining pressure. However, when the confining pressure was increased to 10 MPa, the velocity became stable because most of the microfractures in the coal rock samples were closed. (2) The elastic wave velocity is sensitive to the microfracture orientation in coal rock. The elastic wave propagates rapidly along the microfracture direction, while it propagates slowly perpendicular to the microfracture direction. This research provides the basic data to predict microfractures in coal rock.