A new method for predicting S-velocity, anisotropy and fracture parameters in horizontal transverse isotropy media

Abstract

S-velocity, anisotropy and fracture parameters are of great importance in the development of horizontal transverse isotropy (HTI) reservoirs for the fracture attribute analysis and determination of fracture location. Increasing attention is gradually being paid to the accuracy of predicting them, especially for some well logs missing these parameters. Rock physics modelling is the one of the effective tools. For complex background media, simple spherical pores are no longer applicable. Multi-types of pores, the main component of the complex isotropic background, need to be considered using effective media model. For anisotropic media, Hudson and Schoenberg models are the classic theories for HTI fractures. However, the pitfall of Hudson model resides in the restrict of small crack density assumptions, that is not useful for most fractured stratum with higher crack density. To improve the applicability and quality of Hudson model, Padé approximation, based on Hudson first and second order expansions, is introduced. With the combination of the approximation and Schoenberg model, the new relationship of the fracture parameters and stiffness matrix are derived. On basis of this relationship, S-velocity, anisotropy and fracture parameters can be calculated. Compared to the Hudson combination method, the new proposed method shows significant advantages on the accuracy and validity of the estimated parameters for the model analysis and real well data in higher crack density, which can provide favourable data support for the exploration and development of fractured reservoirs.