Numerical Analysis Of Seismic Response Characteristic In Fluid-saturated Porous Medium

Seismic data contains abundant information reflecting the characteristics of the subsurface medium, especially the seismic attenuation and velocity dispersion existed in the fluid-saturated porous medium. Therefore, using reasonable method to simulate the seismic response of subsurface medium, explore the relations between abnormal characteristics and seismic response of the subsurface media are of great import to oil and gas exploration. Seismic wave transmitting in the fluid-saturated porous media will have a significant velocity dispersion and attenuation, which exists frequency dependent characteristics, is close related to the fluid porosity, permeability, pore structure and pore fluid type. However, the conventional convolution method and the finite difference method numerically simulating seismic response in time domain, do not consider frequency dependent velocity characteristic and are difficult to describe the inherent frequency dispersion and attenuation of seismic wave propagating in porous media.In this paper, we propose a stably extended screen propagation operator which can adapt to lateral variation of multi-physical parameters, and we use it to implement frequency-dependent simulation based on diffusive-viscous equation(DVWE). The operator calculated in frequency domain can naturally combine with frequency-dependent phase velocity, so when we use the screen propagation operator to perform simulation by taking account the velocity dispersion and attenuation, we can get the dispersion and attenuation characteristics of seismic wave propagating in fluid-saturated porous medium. While DVWE considering the fluid viscosity and diffusion in porous media, is very suitable for simulating of attenuation caused by fluid flow, it differs from the conventional scalar acoustic wave equation. When using the DVWE we should not only deal with the lateral variation of the velocity, but also the lateral variation of viscosity and dispersion coefficient. According to the Born approximation and scattering theory, in this paper we divide velocity, viscosity and diffusion into horizontal homogeneous background field and heterogeneous disturbed field, and deduce a DVWE based screen propagation operator adapt to lateral variation of velocity, viscosity and diffusion.In this paper, we calculate the frequency-dependent compressional wave velocity corresponding to different permeability, fluid saturation and geometrical parameters according to the improved patchy saturation model by Rubino. We first use the dual-domain screen propagation operator to simulate frequency-dependent seismic response of horizontal stratified model, and analyse the role of permeability on seismic response. Then, we calculate the seismic response of the braided river geological model based on DVWE and AWE, respectively. The results show that there exists distinct energy loss, travel time pull-down and phase distortion in the seismic reflection form the hydrocarbon reservoir or layers below it. So the DVWE based screen propagation operator proposed in this paper can depict inherent attenuation and dispersion of the hydrocarbon reservoir, which can contribute to understanding the effect of reservoir pore fluid on the seismic response, and guiding reservoir prediction in frequency domain. The simulation method in this paper has important theoretical and practical significance for the studying the seismic response and improving the detection accuracy of complex reservoirs.