CBM reservoir rock physics model and its response characteristic study

摘要

The rock physics model of coalbed methane (CBM) reservoir is signi cant for the study ofCBM content. However, because of the adsorption and dissociation of the CBM reservoir, it is dif cultto establish models. In addition, the studies on rock physics modeling of the CBM reservoir are scarce.This paper proposes the basic modeling process. First, the coal rock minerals and methane in adsorbedstate are used to calculate elastic parameters of coal rock matrix. Then, the differential equivalent mediummodel is used to get elastic parameters of the dry rock skeleton. The free methane is mixed with water,and nally the Gassmann equation is applied to obtain elastic parameters of the CBM reservoir model. Thestudy on the CBM reservoir rock physics model's response characteristics has found that there is a sensitivenegative correlation between CBM content and P-wave velocity and density. The higher CBM content goeswith larger absolute values of intercept, gradient, and seismic amplitude, because their seismic attributesare more sensitive to higher CBM content, whereas the response characteristics are opposite with the lowerCBM content. The relationship among the CBM content and absolute values of intercept, gradient, andseismic amplitude in the real data of Qinshui Basin is largely consistent with the response characteristicsof the established rock physics model, indicating that the CBM reservoir rock physics model proposed inthis paper has a certain feasibility, and the response characteristics of its intercept, gradient, and seismicamplitude are more sensitive to predicting CMB reservoirs.