Vertical ambiguities in volumetric 4D pressure-saturation inversion resolved with time-shift assimilation

This study focuses on demonstrating the power of joint time-shift assimilation in 4D seismic inversion to estimate pressure and saturation changes. It shows the potential of time-shift data to resolve 4D amplitude ambiguities related to the vertical distribution of reservoir property changes. We use a real case example where water saturations increase due to injection and aquifer inflow from below, while directly above this, injected gas pools at the top of the reservoir. We demonstrate how very different fluid distributions can produce the same 4D amplitude signal, but their time-shift response is quite different. Then we show how jointly inverting the observed time-shift and 4D amplitudes can resolve these ambiguities and produce a more reliable estimation of the reservoir property changes across the reservoir.