A New Non-linear Method for Thomsen Anisotropic Parameters Inversion for Fracture Media

This paper firstly analyzed the uncertainty of AVOZ inversion based on two-term Rüger equation. Then, based on three-term Rüger equation, through subtraction method among different azimuths, a new non-linear equation is derived, which includes the third term of Rüger equation and Thomsen parameters. Subsequently, the new equation is solved by non-linear method-particle swarm optimization (PSO) method, by which fracture density, Thomsen parameters and can be simultaneously obtained. Then, the fracture fluid indicator is expressed in another form by using fracture density and Thomsen parameters. The numerical model application shows that the inverted fracture density from PSO method is much closer to the theoretical value than that from AVOZ inversion and the inverted anisotropic parameters are also approximate to the theoretical value, which indicate the PSO method is reliable to solve the proposed non-linear equation; meanwhile, fracture fluid indicator on the basis of non-linear inverted results can successfully identify different fluid types.