4D seismic data is used to monitor the movement of fluids in the reservoir with time and can be incorporated into the history matching process by minimizing the difference between the 4D seismic observed in the field and the 4D seismic computed from the reservoir model. Modeling 4D seismic data involves the computation of a “base” 3D seismic, which is straightforward if the reservoir has a known initial distribution of fluids, and the “time lapse” 3D seismic, which entails use of the simulated fluid distribution. The flow simulations that provide these fluid distributions are typically performed at relatively coarse scales.<br>It has been observed that fine details in the saturation distribution (although below seismic resolution) can impact the seismic response (Mavko and Mukerji, 1998; Sengupta and Mavko, 1998; Sengupta, 2000). Downscaling saturation outputs from the flow simulator may therefore be required to correctly model the 4D seismic response. In this paper we propose an approximate method for downscaling saturations where local fine scale flows are simulated to reconstruct the fine scale saturation using local boundary conditions determined from the global coarse scale two-phase flow solution. This reconstruction does not require any global fine scale computations, guarantees flux continuity across fine scale cells in neighboring coarse blocks, and accounts for subgrid heterogeneity. Using a 2D synthetic example, we demonstrate how ignoring the fine scale effects can produce erroneous 4D seismic responses. We demonstrate that our flow-based downscaling procedure improves these results significantly.<br>


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