Seismic modelling study of CO2 effects on P-wave amplitude

Abstract

The presence of carbon dioxide (CO2) in the pores of rocks can cause changes in the amplitude of a propagating seismic wave. These changes in turn can be used to estimate the degree of saturation of this greenhouse gas in the rocks. In this paper, we examine the effects of CO2 on P-wave amplitude in a layered medium through seismic modelling. Our hypothetical model consists of four isotropic layers. The third layer, which is our target layer, is modelled as a fully poro-elastic medium saturated with brine and CO2 with varying crack densities. The CO2 and brine saturations in the third layer range from 0 to 100% with crack densities of 0.01, 0.02 and 0.03, respectively. We analysed the reflection amplitudes from the top and bottom of the target layer for the case of no fluid saturation and varying degrees of saturation, respectively, in the layer. The P-wave amplitude is shown to be sensitive to the degree of CO2 saturation and crack density. At a given crack density, the amplitude change increases with decreasing percentage of CO2 saturation and reaches a maximum value at 5% saturation with sharp variations between 5 and 30%. The amplitude change also increases with crack density. These findings provide more valuable insights into the use of P-wave amplitude as a potential tool to obtain valuable information on reservoir fluid properties.