Importance of Proper Seismic Gather Conditioning and Low-frequency Model Building for Successful Pre-stack Simultaneous

We show an in-house seismic pre-stack simultaneous inversion workflow with the goal of predicting lithology in an AVO Class 1 clastic section. The rocks in Murzuq Basin (Libya) show elastic property contrast between the sand and shale in the target section. The workflow includes a simple but robust seismic gather conditioning sequence to increase signal-noise ratio and remove interbed multiples. In order to build a geologically valid low-frequency model, we reinterpret the seismic velocities using Swan’s theory. This method corrects the phase mismatch between AVO intercept and gradient to get flat gathers with optimal velocity values. The velocities are also interpreted to honour well data and provide realistic values; much like is done for pore pressure prediction work. In this way, the seismic velocity field gives more accuracy AVO attributes and permits to build a geological constrained low-frequency model. This model improves the inversion results by providing realistic impedance values, especially Vp/Vs. Vp/Vs has been shown by the well data to be a good predictor of lithology.