Integration of fluid replacement modeling and seismic AVO analysis towards simultaneous seismic inversion to delineate the distribution of Globigerina limestone gas reservoir

Integration of fluid replacement modelling and seismic AVO analysis towards simultaneous seismic inversion had been done to delineate the distribution of Globigerina limestone gas reservoir in Madura Strait, East Java Basin. This study was using backward modelling or well known as inversion modelling to finish the quantitative analysis. The purpose of the study is to map the distribution of Globigerina limestone gas reservoir so that in the end the final result will be used as a guidance to drill the next exploration well. It started with an optimized low frequency model building by integrating fluid substitution modelling and seismic AVO analysis. By integrating these two methods, the distorted top and bottom reservoir can be compensated, and the low frequency model will be optimized. The availability of the data includes 3D seismic data with acquisition bin size 18.75 m × 12.5 m, with two well logs. The cross plot result showed that the reservoir and non-reservoir lithology can be distinguished by Vp and Vs log. By analysing the acoustic impedance together with Vp/Vs ratio, the character of gas reservoir at surrounding F and H structures can also be delineated. The main cut off for acoustic impedance and Vp/Vs ratio were 5,500 gr/cm³∗m/s and 2.0. The final optimizing result of low frequency model showed that the target G structure, which will be the next exploration target, showed an analogue response with its neighbour F and H structures. It is concluded that by integrating both two methods, fluid replacement modelling and AVO seismic analysis, the optimizing of low frequency model can be achieved and the simultaneous seismic inversion can successfully map other gas reservoir.