Study on prediction on seismic wave velocity in coalbed methane reservoir based on dual pore structure

In order to solve the difficult prediction of the seismic wave velocity in the coal reservoir caused by the adsorption occurrence and the crack development features of the coal reservoir based on the detail analysis on the coalbed methane base and the velocity influences, in combination with the dual pore structure and the expansion and shrink effect in consideration of the saturation gas, the gas was mainly adsorbed in the micro pores and the large pores would mainly store water. The coalbed methane was taken as the matrix minerals in order to have the average elastic modulus and the average density of the coalbed methane to replace the rock modulus and density, a Gassmann Equation was applied to the fluid replacement. Thus a prediction methane of the seismic wave velocity in the coalbed methane reservoir was established. The calculation results of the core data showed that the method could improve the prediction accuracy of the velocity in the coalbed methane reservoir. The gas difference of the coalbed methane reservoir could cause a high variation of the seismic wave velocity and thus could cause the response difference of the seismic information.