Analysis of influence factors of coal elastic parameters andits AVO response characteristics

The study of the influence factors of coal elastic parameters can reveal the physical meaning of the AVO response of coalbed,which is beneficial to guide the exploration of coalbed methane in complex geological conditions. The 60 coal samples from the No.3 coalbed in the Sihe coalmine of the Qinshui Basin were used for the study. According to the industrial composition analysis,mineral composition analysis and logging data of the coal,various different fluid-saturated rock physics models of coalbed methane(CBM)reservoir were constructed based on the BET multilayer adsorption theory and self-consistent model. These models mainly consider three types of fluids,one is completely water-saturated,and the other two are multiphase mixed fluids with different water contents,adsorbed gas and free gas. Using the models,the authors analyzed the comprehensive effects of CBM reservoir characteristics such as coal matrix composition,porosity and fluid type on the elastic parameters of coal,and further analyzed the seismic AVO response characteristics of coalbed under different porosity and fluid types. In the research area,the porosity of coal is the main influencing factor for the change of P-wave and S-wave velocity of coal and bulk modulus of multiphase fluid-saturated coal. And the increase of porosity causes a significant change in the bulk modulus of multiphase fluidsaturated coal. Compared with the porosity, the effect of different coal matrix composition on the bulk modulus and density of completely water-saturated coal is more significant. In addition, the change of elastic parameters of coal caused by different fluid types is small compared to porosity and coal matrix composition. By analyzing the AVO response characteristics of coalbed,it can be found that the porosity has a certain linear relationship with the AVO attributes,and the water saturation has a certain nonlinear relationship with the AVO attributes. The S-wave impedance attribute responds most significantly in different porosity and different fluid saturation conditions.