Reflection Of Elastic Waves In Layered Media With A Patchy Saturated Porous Layer

The layer is not simple media which contains oil and gas and water resource under the Earth surface, and that is multiphase porous media composed of solid frame and the fluids in it. The study of the problems that refraction and reflection of elastic wave at an interface of fluid-saturated porous media, not only can provide useful information about the internal composition of the stratum better but also provide a favorable help to detect the valuable resources underground such as oil, natural gas and water.The theory about porous media has been going on for many years, Biot formulated the dynamical equations and constitutive relations for a fluid saturated porous elastic solid and established the mechanics theory which to be called Biot theory.The Biot theory is used the most widely about the study of porous media. But when porous media saturated by biphasic fluids,the patchy saturation theory can explain the wave dispersion and attenuation better than the Biot theory at mesoscopic scales.In the process of the present and the formation and the development of the patchy saturation theory,three patchy models which are White patchy model, Johnson patchy model and Pride patchy model appeared successively. Pride patchy theory is easier to apply in framework of the Biot theory, this paper will focuses on the reflection of elastic waves by patchy saturated porous media inclusion in layered media based on Pride patchy saturation theory.In order to understand the propagation characteristics of elastic wave in patchy saturated porous medium, first the basic theories of White patchy model and Johnson patchy model are introduced briefly,the velocity dispersion and attenuation of the P-wave are calculated and analyzed of two models, and the differences between the two models are compared.Then this paper present the Pride patchy theory and calculate the velocity dispersion and attenuation of the fast P wave,slow P wave and S wave for low and high water saturation in gas-water and oil-water systems and compare the similarities and differences between both systems.When we research the reflection of elastic wave in layered media with patchy saturated porous layer,two kind of stratification situations are considered: one is water and patchy saturated porous media configuration,the other one is watet-patchy saturated porous media-elastic solid configuration which is closer to the actual situation. The paper establishes theoretical models, uses Helmholtz decomposition, deduces the basic field quantities and acoustic field expressions in each of the layer by introducing potential functions and then uses the boundary conditions to calculate the reflection coefficients. Using numerical calculation, the reflection coefficients that the elastic wave is incident to the interface of patchy saturated porous medium from water with varying excitation frequencies, water saturations, and porous media depths are discussed. The results show that the type and content of fluids in patchy saturated porous media have an significant effect on reflection coefficients.With the increasing demand for oil and gas resources, people pay more attention to inhomogeneous saturated porous medium with oil, gas and water this study will help to understand reflection of elastic waves in patchy saturated porous media further, and also provide help to explore oil and natural gas resources theoretically in porous sediment or in other geological conditions.