177 7. Integrated seismic study density) and a relationship between the two variables exists. The Gardner’s relation (Gardner et al., 1974) given by the following equation ρ α β = Vp is often used. The logging data (sonic and density logs) recorded at well Est433 (see map location, Figure 7.3) have been used to compare acoustic impedance Ip and velocity Vp logs and the relationship given by equation (7.4) has been checked: Log Vp Av.Log Ip Bv ( ) = ( ) + (7.4) The coefficients Av and Bv have been computed in a root mean square sense, between the Vp and Ip logs. The results of the minimization have shown that the Vp log and the predicted P-wave velocity from the acoustic impedance log are strongly correlated (Figure 7.11, left). The correlation coefficient and the Taner-Kohler coefficients between the two velocity logs are very high (> 0.98) and a single law can be used whatever the range of acoustic impedance and whatever the geological unit to obtain a high-resolution velocity model in time Vp given by equation (7.4). Consequently a density log can be easily obtained by the ratio Ip to Vp. The velocity model was integrated in time to obtain a time-depth conversion model (Figure 7.11, right). The time-depth conversion model was used to convert in depth any type of time-seismic sections such as amplitude, instantaneous frequency, Ip and Is, and consequently Vp, Vs and density. Figure 7.11 Predicted P-wave velocity model and time-to-depth conversion model.
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