194 Seismic Imaging effect on Vp/Vs and mimic a reflected j vs. log (Sg) trend, they proposed the use of the following relationship between porosity j, Vp/Vs and Sg: log . . . Sgm a b Vp Vs c ( ) = + ( ) + ϕ with Sg S= − ( ) 1 ϕ (7.12) where it should be noted that Sg is multiplied by m to make Sg dimensionless. In practice, the parameter Ik-Seis (Indicator (I) of permeability (k) from acoustic or seismic (Seis) data) calculated from equation (7.13) is proportional to permeability k (Mari et al., 2018; Benjumea et al. 2019). Ik-Seis = (j.δ/S)3/f = (j/SQ)3/f (7.13) with f: P-wave frequency, Q quality factor, δ: attenuation, S: specific surface and j: porosity. The processing of the seismic lines was carried out to estimate the distribution of the velocities (Vp and Vs), the distribution of densities, the instantaneous frequency, the Q-factor (equation (7.6)), the porosity from acoustic impedance (equation (7.10)), the specific surface S (equation (7.12)), and finally the Ik-Seis factor (equation (7.13)). In the domain of seismic frequencies, the Ik-Seis factor can only be seen as a relative indicator, varying from 0 for less porous and permeable bodies, up to 1 for more porous and permeable bodies. If the porosity distribution is a key point for reservoir characterization, shale content is key both for the reservoir and the seal. Gamma ray logs are a very useful tool that can be computed from seismic data to estimate shale content. After several attempts with different seismic attributes such as P or S-wave velocity, density, seismic mechanical modules such as the shear modulus m, the matrix shear modulus appeared to be the most sensitive attribute to compute a pseudo gamma ray (Yven and Mari, 2014). The matrix shear modulus mma is given by the following formula: ma B µ µ β = −1 (7.14) with Bβ being Biot’s coefficient (1956) defined as follows: 1 1 − = − ( ) B m β ϕ ϕ and mϕ ϕ = − 3 1 with j the porosity. The matrix shear modulus is corrected for the effect of porosity and can be converted into pseudo gamma ray (GR-Seis) by using an empirical relationship (polynomial function) between the gamma ray log and the matrix shear modulus established at the well locations. The proposed procedure was applied on a 3D dataset. The results shown here were obtained on the XL217 cross-line. Figure 7.15 shows the instantaneous amplitude section and its associated SQI factor in depth. The SQI factor is low which means there is good confidence in the seismic amplitude and consequently in the elastic impedance in depth. In the 700-750 m range, one can notice a significant lateral
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