Abstract:
The rock physics model of coalbed methane (CBM) reservoir is signi cant for the study of
CBM content. However, because of the adsorption and dissociation of the CBM reservoir, it is dif cult
to 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 adsorbed
state are used to calculate elastic parameters of coal rock matrix. Then, the differential equivalent medium
model 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. The
study on the CBM reservoir rock physics model's response characteristics has found that there is a sensitive
negative correlation between CBM content and P-wave velocity and density. The higher CBM content goes
with larger absolute values of intercept, gradient, and seismic amplitude, because their seismic attributes
are more sensitive to higher CBM content, whereas the response characteristics are opposite with the lower
CBM content. The relationship among the CBM content and absolute values of intercept, gradient, and
seismic amplitude in the real data of Qinshui Basin is largely consistent with the response characteristics
of the established rock physics model, indicating that the CBM reservoir rock physics model proposed in
this paper has a certain feasibility, and the response characteristics of its intercept, gradient, and seismic
amplitude are more sensitive to predicting CMB reservoirs.
