Use of rock physics for modeling the stiffness tensor of a VTI medium

Use of rock physics for modeling the stiffness tensor of a VTI medium

In this paper, I review elastic property changes in anisotropic media and propose a workflow to model the elastic stiffness tensor using conventional well logs in a vertical transverse isotropic medium. The proposed workflow uses downscaling and then upscaling of normal logs by Backus averaging and rock physics modeling, thus it couples different effective medium theories together. The choice of the rock physics model depends on the source of anisotropy in the given medium. Rock physics modeling is the main step in this workflow, and is instrumental in defining the final elastic properties of the medium. It is the place where all anisotropy information is integrated with the log information. Finally, this workflow is tested on the Duvernay shale formation in the Western Canadian sedimentary basin where log data along with the laboratory core measurements are available. The good match between modeled and measured velocity (Vp and Vs) achieved with one set of anisotropy parameters confirms the validity of this approach. This workflow is also applicable for the area with no additional information in which it is just possible to model boundaries of the anisotropic behavior. The last example in this paper shows this scenario on another well provided only with conventional well logs