Dual simulations of fluid flow and seismic wave propagation in a fractured network: Effects of changes in pore pressure on signature of seismic waves

Abstract

Fluid flow in the Earth’s crust plays an important role in a number of geological processes, and such flow is usually believed to be controlled by open macro-fractures in at least carbonate reservoirs. The movement of fluids in the fractured media will result in changes on the pore pressure and consequently will cause changes to the effective stress, traction and elastic properties. The main purpose of this study is to examine the effect of pore pressure changes on seismic wave propagation (i.e. amplitude, frequency range). This is achieved by using a dual simulation of fluid flow and seismic propagation in a common fracture network. The flow simulation updates the pore pressure at consecutive time steps, and thus the elastic properties of the rock, for the seismic modelling. Therefore we can evaluate the possibility of inferring the changes of fluid properties directly from seismic data. Our results indicate that Pwaves are not as sensitive to pore pressure changes as Sand coda or scattered waves. The increase in pore pressure causes a shift of the energy towards lower frequencies, as shown from the spectrum (as a result of attenuation). Another important observation is that the fluid effects on the wavefield vary significantly with the source-receiver direction, i.e. the azimuth relative to the fracture orientation.