Seismic Wave Propagation Characteristics In Viscoelastic Anisotropic Fractured Reservoirs

Fractured reservoir is a kind of significant hydrocarbon reservoirs, which is the main target areas in seismic exploration and development. Because of matrix, filled fluid and aligned fractures, the fractured reservoirs show up as viscoelastic and anisotropic media. To exactly characterize the fractured reservoirs, the characteristics of viscosity and anisotropy should be further studied. Thus, this paper performs study on the characteristics of seismic wave propagation in viscoelastic anisotropic fractured reservoirs.In viscoelastic fractured reservoirs, aligned fractures induced by tectonic stress constitute the reservoir spaces and migration pathways of hydrocarbons, and further induce the anisotropy of such reservoirs. In addition, the viscoelasticity induced by viscoelastic matrix and reservoir fluids cause the attenuation of seismic wave. Considering the characteristics of fractured reservoirs, this paper constructs a viscoelastic anisotropic effective medium model by combining Kelvin-Voigt viscoelastic model, Linear Slip fractured model and Hudson models. In order to study the seismic wave propagation in fractured reservoirs, this paper also carries out 3D viscoelastic anisotropic numerical simulations and plane wave analysis.To perform the time-domain three-dimensional forward modeling, this paper uses rotated staggered grid finite-difference algorithm, which performs spatial difference along the diagonal directions of each finite difference cell and achieves higher accuracy and stability. And the complex frequency shift recursive integral NPML boundary condition is utilized to absorb the boundary reflection. The numerical simulation results demonstrate the attenuate and anisotropic variation of the seismic wave propagated in viscoelastic anisotropic fractured reservoirs. This paper further summarizes the wave propagation principles with the matrix Q, filled fluids, fracture density, aspect ratio, fracture dip angle, azimuth and other parameters.For viscoelastic and anisotropic fractured media, the frequency-domain plane wave analysis is performed by solving Christoffel equation to calculate the seismic wave velocity and attenuation. By analyzing the variation of wave velocity and attenuation with matrix Q value, wave propagation incidence angles, azimuth angles and saturated fluid,, this paper verifies the attenuation and anisotropy properties of the seismic wave propagated in viscoelastic fractured reservoirs and summarizes corresponding wave propagation principles.Based on the model construction and numerical experiments, this paper studies the wave propagation characteristics in viscoelastic anisotropic fractured reservoirs, and summarizes the wave propagation principles with different parameters. The above studies may help to describe the characterization of fractured reservoirs, and further provide theoretical and empirical instructions for the industrial exploration and development of fractured reservoirs.