Iterative comparison between experiments and numerical simulation has been used to predict oil recovery mechanisms in fractured chalk as a function of wettability. Selective alteration of wettability, by aging in crude oil at elevated temperature, produced chalk blocks which were strongly-water-wet and moderately-water-wet, but with similar pore geometry and mineralogy. Larger scale, nuclear-tracer, 2D-imaging experiments monitored fluid distributions while waterflooding blocks of chalk, first whole then fractured. This data provided in-situ fluid saturation development for validating numerical simulation and evaluating capillary pressure- and relative permeability input data used in the simulations. Capillary pressure and relative permeability at each given wettability were experimentally measured and used as input for the simulations. Optimization of either Pc-data or kr-curves gave indications of which of these input data could be more trusted. History matching both the production profile and the in-situ saturation distribution development gave higher confidence in the simulation. Labelling the injection water differently from the in-situ water made it possible to determine the degree of water mixing during the waterfloods. Mixing of injection water and in-situ water during waterfloodng was determined for both unfractured and fractured blocks. Reduced water wettability resulted in less oil recovery by spontaneous imbibition. Interconnected fractures did not significantly impact the final oil production when the permeability increase after fracturing was low, for both strongly-water-wet and moderately-water-wet conditions. However, in-situ saturation distributions were significantly affected by the wettability conditions. For higher permeability increase after fracturing significant reduction in oil recovery was experienced at less water wet conditions, while oil recovery at strongly-water-wet conditions was not reduced, even at high permeability increase after fracturing. The overall best match between the simulations and the experiments was obtained using the experimentally obtained capillary pressure curves and optimizing the experimentally measured relative permeabilities.

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