P-wave traveltime analysis and Thomsen parameters inversion in orthorhombic media

An orthorhombic (ORT) model is the simplest azimuthally anisotropic model used to describe realistic fractured reservoirs ( e. g., vertical cracks embedded in an anisotropic background media or orthogonal fracture systems in purely isotropic matrix). In this paper, we calculate the omnidirectional reflection traveltime of P-wave in a single orthorhombic media with a horizontal interface by using the ray trace method. The reflection P-wave traveltime-distance curves show strong azimuthal anisotropy. Using the Niche Genetic Algorithms (NGA), inversion of reflection traveltime of three common-midpoint (CMP) lines provides us with a good estimation of azimuth, P-wave vertical velocity and Thomsen anisotropic parameters.