Permeability from Seismic in Carbonate Reservoirs – Part I: Dream or Reality?

Gregor P. Eberli¹, Jose Luis Massaferro², Ralf Weger¹, Yue-Feng Sun³, Gregor T. Baechle¹, and Guido Bracco Gartner^4
1 University of Miami, Miami, FL
² Repsol YPF, Madrid, Spain
³ Colombia University, Palisades, NY
⁴ Shell, Rijswijk, Netherlands

Estimating permeability from seismic data is often being deemed as impossible because no physical relationship exists between the acoustic and hydraulic properties. In porous media, however, both sonic velocity and permeability are largely controlled by porosity and the pore structure. By separating porosity and pore structure contributions to both hydraulic and sonic properties, an empirical relationship potentially is established between sonic velocity and permeability using the pore structure as the crucial link.

Laboratory results confirm that mathematically derived rock frame factors can indeed be a good quantitative indicator of pore types in carbonates. In particular, the pore geometry factor (PGF) derived from poroelasticity equations mimics the geometrical parameters calculated from digital image techniques. This correlation is taken as the experimental prove that the PGF captures the changes in rigidity produced by the pore structure and quantifies the scatter in velocity values at any given porosity. Thus, our results define a two-parameter velocity model for carbonates, which allows extracting pore structure information from seismic data.

The theoretical quantification of the influence of pore structure on velocity is a major step forward to better interpret permeability from seismic data. It is now possible to extract pore structure information from the impedance cube in seismic inversion. This information will help to estimate permeability from seismic data by using an empirical relationship of PGF versus permeability at a given porosity. This empirical relationship needs, however, to be established in each field because of the complex diagenetic history of carbonates.