Application of Pre-stack Poisson Impedance Inversion in the Prediction of Igneous Rocks

The carbonate reservoir is complicated by igneous rocks in Block M of Santos Basin. Igneous rocks have weak - strong amplitude, low-high frequency, and chaotic-continuous seismic reflection features, which is similar to seismic features of reservoir. It is difficult to effectively identify them using conventional seismic attributes of post-stack and pre-stack data. The sensitivity analysis of logging data shows that pre-stack Poisson impedance can well distinguish igneous and carbonate rocks. Therefore, simultaneous pre-stack inversion is carried out on the basis of petro-physical analysis. Firstly, the Poisson impedance is calculated by the P and S-impedance. Secondly, the probability of igneous rock and carbonate rock is analyzed by probability density function analysis, and then spatial probability distribution of different lithology is calculated by Bayesian fuzzy discriminant analysis, and the qualitative and quantitative prediction of igneous rock is finally realized. The results show that igneous rocks are mainly distributed around growth faults and have dual effects of destruction and construction, which can not only occupy the development space of carbonate rocks, but also change the paleo-geomorphology in low-lying areas to facilitate the development of carbonate rocks. Drilling data has confirmed that the prediction coincidence rate of igneous rock has reached 80%. The identification and prediction of igneous rock improved the drilling ratio, greatly improved the drilling success rate, and strongly supported the optimal deployment of well locations.