4D Effect from Saturation Variation Due to Fluid Movement Using 4D Seismic Acoustic Impedance Inversion Methods for Reservoir Monitoring

Abstract

Inversion method is the process of extracting the acoustic impedance (AI) profile for each seismic trace. The AI property is related to the layer properties of the reservoir-density and velocity. Meanwhile, velocity and density data can be obtained from well logs. Therefore the impedance inversion relates the seismic data with the well log data. The purpose of this study is to understand the changes in reservoir properties that could be predicted from the changes in P-impedance between the two surveys (base and monitor) and to obtain a time-lapse impedance model that can predict changes in fluid distribution that is due to production of hydrocarbons and also due to water injection (EOR) over the well X. All inversion algorithms suffer from non-uniqueness because there could be more than one possible geological model consistent with the seismic data. However, we can include the low frequency model (LFM) to constrain the final result and give a reliable and accurate inversion output. Low frequency information can be derived from well logs information or from the stacking velocities. The benefits of seismic inversion are numerous such as the broader bandwidth of the impedance data maximizes the vertical resolution and minimizes the tuning effects, interpreting volumes rather than surfaces is geologically more meaningful, removes the effects of the wavelet from the seismic bandwidth, reservoir properties are separated from the overburden, may provide quantitative predictions on the reservoir properties and possibility of extending the layer features beyond the seismic bandwidth.