Abstract:

Fractured reservoir is a kind of fluid-bearing fracture-porous medium, and the quantitative characterization of fracture parameters plays a critical role in the exploration and development of unconventional hydrocarbon reservoirs. However, conventional reservoir prediction methods primarily based on amplitude information are limited in revealing the complex characteristics of fractured reservoirs. This paper focuses on fluid-saturated orthogonal fractured reservoirs and thoroughly analyzes the velocity dispersion and attenuation characteristics of media containing both horizontal and vertical orthogonal fractures. An anisotropic reflectivity method is employed to simulate the frequency-dependent amplitude variation with offset (AVO) response of a single-interface dispersive sandstone reservoir. Based on this, a Bayesian inversion framework driven by the responses of horizontal and vertical orthogonal fracture models is developed to achieve multi-parameter quantitative inversion of porosity, fracture density, and fracture radius in fractured reservoirs. The results demonstrate that porosity, fracture density, and fracture radius are highly sensitive to velocity dispersion. At low frequencies, the frequency-dependent PP wave reflection coefficient exhibits significant variations with both frequency and incidence angle, and the amplitude increases linearly with the incidence angle. This highlights the substantial influence of fracture parameters on the frequency-dependent AVO response. Inversion results show that the proposed method achieves high accuracy in posterior probability distributions under varying fracture parameter conditions, with particularly improved applicability and reliability in predicting fracture radius in small-scale fractured reservoirs.

Key words: fractured reservoirs')">

fractured reservoirs, horizontally and vertically orthogonal fractures, fracture parameters, frequency-dependent AVO, Bayesian inversion method