Formation elastic parameters by deriving S-wave velocity logs

Colin C. Potter, Darren S. Foltinek

The calculation of the elastic parameters (Poisson's ratio, Bulk modulus, Rigidity modulus, Lame's constant and Young's modulus) of a formation requires P sonic, S-sonic and density logs. Where S sonic logs do not exist, they can be derived from a Psonic log and Vp/Vs ratios for each formation. The Vp/Vs values can be interpreted from other wells by statistical analysis of the Vp/Vs ratio of the formations in the region, predetermined values from lithology and P- and S-wave velocities from other analyses. Software to perform this calculation has been developed. Formation elasticparameters were calculated for four wells in the Blackfoot field in Southern Alberta. The elastic parameters allow further interpretation of the substructure. Vp/Vs, for example, has been shown to be a good indicator of lithology, including delineation of reservoir sands and shale content.