Modeling And Analysis Of Seismic Wave AVO Responses From Fractured Reservoirs

As an important hydrocarbon restore space and migration channel, fracture has drawn more and more attentions in petroleum exploration field. Meanwhile, it has developed many seismic exploration methods to explore fractured reservoirs, and some of them have been used in industrial exploration, which have gain well application effect. Fracture is a set of surface of discontinuity, caused by tectonic deformation or Physical and chemical diagenesis. The filling of fractures is different from the original rock, which changes the wave impedance and Poisson’s ratio of the rock, as well as seismic wave propagation characteristics. Modeling and analyzing seismic wave responses from fractured reservoirs is the fundamental of understanding the seismic reflection of fractured reservoirs, and the fundamental of developing inversion algorithm to recognize and illustrate the fractures. So, it has great significance.There are two parts of modeling seismic responses from fractured reservoirs. The first is using rock physics models to model fractured reservoirs, and the second is using seismic forward modeling method to model the response of the model. In this article, we focus on those fractures which are directional alignment. The most obvious characteristic of these fractured reservoirs are having significant anisotropic characteristics. Combining previous research results, we model horizontal fractured reservoir, vertical fractured reservoir, reservoir with VTI background and vertical fractures and viscoelastic fractured reservoir, and analyze the variation of velocity when containing fractures.Secondly, we calculate AVO responses of horizontal fractured reservoir and vertical fractured reservoir. We use reflectivity method to model the response form fractured reflector, instead of modeling the response form the single surface, which considers less wave field propagation effects. And it is better than wave equation methods as it has no limit form grid spacing and computational efficiency. We using propagation matrix method to model horizontal fractured reservoir and analysis its AVO response. And we use Schoenberg reflectivity method to model AVO response from a vertical fractured reservoir. And the comparison is made between Rüger’s method and Schoenberg reflectivity method. We also study the influence of VTI background and viscoelasticity in a fractured reservoir. Results indicate that, for the entire reservoir, the dynamic information from its seismic response includes the difference of wave impedance and Poisson’s ratio form the interfaces, the interval anisotropic propagation, and tuning of response form top and bottom interface, as well as tuning of converted wave. We consider the entire reservoir as a unit when calculating its AVO response, which is more accurate compared to Rüger’s method. The existence of horizontal fractures increased anisotropy of the reservoir, and its AVO effect is more apparent. Moreover, vertical fracture makes azimuthal anisotropy apparent. In large incidence angle, the PP wave reflected from bottom interface changes obviously as the azimuth angle changes, and in large azimuth angle, the Amplitude of converted P wave is increased, which makes the entre wave longer. In addition, the azimuthal anisotropy of AVO response is decreased when the reservoir contains thin-interlay or vertical bedding, as well as when the reservoir is elastico-viscous.In the end, aimed at practical application, rock physics methods are used to modeling fractured reservoir, and we use well logging data to invert fractured parameters. Thus, the model of actual formation is built to compute its synthetic seismogram, which is used in oil exploration industry.