2012 Honorary LecturerSponsored by Shell

South & East Asia

Sam Z. Sun

China University of Petroleum, Beijing, China

The cheapest elastic information: How rock physics models and amplitude processing affect prestack PP inversion


Sam Z. Sun

Reservoir characterization and fluid prediction often require elastic information such as P- and S-wave impedance or Vp/Vs. This information can be obtained from 3C data but they are quite often not available. PP-wave prestack inversion is the cheapest way to obtain elastic information, and it is widely available. Because of high acquisition costs, prestack PP-wave data should be worked harder and employed more often to extract elastic information for reservoir and fluid mapping. But, implementing proper prestack inversion requires integration of a rock physics model with amplitude processing that includes amplitude-preserved migration into the prestack inversion. There are many different rock physics models. But, they must be employed properly. Often, people are not aware of the application conditions or prerequisites needed to use a certain model. Amplitude-preserved prestack migration is not critical for prestack inversion of flat reflectors. But today, amplitude-preserved prestack migration for CRP gather extraction has become routine. It is not only because almost all reflectors are structurally related but also because the CRP gather is better for determining the Fresnel zone.

This presentation will focus on three key factors of prestack inversion: rock physics, amplitude processing, and inversion algorithms. The talk will illustrate how to define a better or best rock physics model. It will cover existing and  newly developed rock physics models, including the time-average equation, Gassmann equation, Kuster-Toksoz model, Xu-White model, AS-Xu-White model (3D Xu-White model), and DEM-Gassmann model. Berryman (1992) proposed a differential effective medium (DEM) model, in which pores are incrementally added into the matrix, satisfying the demand of "dilute pores," DEM-Gassmann model is a dispersion-corrected Kuster-Toksoz model and has wide application for characterizing reservoirs with sophisticated pore structure and geometry. The talk will also cover amplitude processing, including Kirchhoff and RTM algorithms. Different inversion algorithms will also be analyzed. The talk will include many field examples and case studies.