Nonlinear AVA Inversion Based on a Novel Quadratic Approximation for Fluid Discrimination

Abstract

Fluid discrimination plays an important role in reservoir exploration and development. At present, the fluid factors used for fluid discrimination are estimated by linear AVA inversion methods based on the linear approximations of the Zoeppritz equations. However, the Zoeppritz equations show that the relationship between prestack AVA reflection coefficients and reservoir parameters is highly nonlinear. Therefore, inversion methods based on linear approximations will seriously influence the nonuniqueness and uncertainty of inversion results. In this paper, a nonlinear inversion based on the quadratic approximation is carried out to reduce the nonuniqueness and uncertainty of fluid factor. Firstly, in order to directly invert the fluid factor, a novel quadratic approximation in terms of the fluid factor ( ρ f ), shear modulus, and density on both sides of the reflection interface is derived based on poroelasticity theory. Then, a nonlinear inversion objective function is constructed using the novel quadratic approximation in a Bayesian framework, and the Gauss-Newton method is adopted to minimize this objective function. The synthetic data example shows that the new method can obtain reasonable fluid factor inversion results even in low SNR (signal-to-noise ratio) case. Finally, the proposed method is also applied to field data which shows that it can effectively discriminate reservoir fluids.

Fluid identification by nonlinear frequency‐dependent amplitude variation with offset inversion based on scattering theory

“…As nonlinear approximation equations continue to evolve, the development of nonlinear inversion algorithms is becoming increasingly important for accurate reservoir prediction. Nonlinear Bayesian AVO/AVA inversion methods (Aune et al., 2013; Erik Rabben et al., 2008; Zhou et al., 2020), nonlinear optimization algorithms (Poli et al., 2007; Rutenbar, 1989; Růžek et al., 2009) etc. have been widely used in the inversion process.…”

Seismic Response Models and the AVO Simulation of Coal-Bearing Reservoirs

“…AVO analysis is often conducted to analyse and invert the subsurface's lithological structure by evaluating how the characteristics of reflection amplitudes vary with offset to describe and detect oil and gas reservoirs [27,28]. Different stratigraphic structures and lithological combinations correspond to different AVO types.…”