Comparison of Numerical Simulations and Laboratory Waterfloods with In-Situ Saturation Imaging of Fractured Blocks of Reservoir Rocks at Different Wettabilities

摘要

Iterative comparison between experiments and numericalrnsimulation has been used to predict oil recovery mechanismsrnin fractured chalk as a function of wettability. Selectivernalteration of wettability, by aging in crude oil at elevatedrntemperature, produced chalk blocks which were stronglywater-rnwet and moderately-water-wet, but with similar porerngeometry and mineralogy. Larger scale, nuclear-tracer, 2Dimagingrnexperiments monitored fluid distributions whilernwaterflooding blocks of chalk, first whole then fractured.rnThis data provided in-situ fluid saturation development forrnvalidating numerical simulation and evaluating capillaryrnpressure- and relative permeability input data used in thernsimulations. Capillary pressure and relative permeability atrneach given wettability were experimentally measured and usedrnas input for the simulations. Optimization of either Pc-data orrnkr-curves gave indications of which of these input data couldrnbe more trusted. History matching both the production profilernand the in-situ saturation distribution development gave higherrnconfidence in the simulation. Labelling the injection waterrndifferently from the in-situ water made it possible to determinernthe degree of water mixing during the waterfloods. Mixing ofrninjection water and in-situ water during waterfloodng wasrndetermined for both unfractured and fractured blocks.rnReduced water wettability resulted in less oil recovery byrnspontaneous imbibition. Interconnected fractures did notrnsignificantly impact the final oil production when thernpermeability increase after fracturing was low, for bothrnstrongly-water-wet and moderately-water-wet conditions.rnHowever, in-situ saturation distributions were significantlyrnaffected by the wettability conditions. For higher permeabilityrnincrease after fracturing significant reduction in oil recoveryrnwas experienced at less water wet conditions, while oilrnrecovery at strongly-water-wet conditions was not reduced,rneven at high permeability increase after fracturing. The overallrnbest match between the simulations and the experiments wasrnobtained using the experimentally obtained capillary pressurerncurves and optimizing the experimentally measured relativernpermeabilities.