Wavefield Propagation Characteristics In Anisotropic Double-porosity Medium Induced By Fractures

Nowadays, fractured hydrocarbon reservoir as one type of subtle pools is taking more and more important role in the geophysical exploration of our country. With developments of seismic wave propagation theories, people realize that the existence of geo-fluid and rock anisotropy in fractured hydrocarbon reservoir affects the transmission of seismic waves markedly. Meanwhile, various effective media models have been built, which are becoming increasingly close to the actual subsurface media. However, among those models, double-porosity models describing fractured hydrocarbon reservoirs are reported rarely. Therefore , in this paper, the wave-field propagation characteristics in anisotropic double-porosity medium induced by fractures are studied.Basing on the theories of fracture-induced anisotropy media and two-phase media, constitutive equations in the medium of horizontal transverse isotropic (HTI) double-porosity induced by fracture are derived. Using the concept of continuous percolation, combining two sets of porosity and permeability, the equivalent porosity and permeability of two-porosity medium are given, after which we obtain motion equations. Finally, wave-field controlling equations are gained and degenerated to different classical media. Moreover, numerical simulations, basing on single-order velocity-stress equations in HTI two-porosity medium and its simplified media, are carried by the method of 2D high-order staggered-grid finite-difference. Comparing and analyzing the results, we get that the existence of two systems, fractures and matrix pores systems, in HTI double-porous media causes anisotropy and two-phase of the medium. This conclusion will lay a foundation of further studies on seismic wave propagation in actual earth layers. Besides, the identification of multi waves in the modeling results of double layers will contribute to further studies on fractured reservoir using multi-wave data.