The presence of vugs in a naturally fractured reservoir can bea significant source of reserves. These vugs can be connectedto the fracture system or be isolated in matrix material whichconstitutes a triple porosity system. The modeling of thedisplacement of oil from the vugs can not be made withconventional dual porosity reservoir simulators since tripleporosity system “isolated vugs” are not part of theformulation.The simulation of oil production from triple porosityreservoirs requires the development of composite porosity,composite relative permeabilities and composite capillarypressure relationships. These composite curves can begenerated from properly designed laboratory experiments onrepresentative cores or by history matching fine grid singleporosity simulations. Kossack, et al1 discussed this for wateroilsystems. Since the displacement of oil from vugs by gasinvolves very different mechanisms from water-oil systemsand is very complex, the simulation of this process must bestudied separately.This paper describes a numerical scale-up technique toprovide the composite properties and curves to be used in gasoildisplacements in triple porosity systems. Displacements indual and triple porosity gas-oil systems are dependent on themagnitude of gravity and viscous forces, capillary pressure inthe matrix rock, composition of the injection gas, and rate ofcomponent diffusion in the porous media. Fine grid singleporosity simulations are made with a compositional simulatorto determine the rate of oil recovery from the fractures, matrixrock, and vugs. These results are then matched with dualporosity compositional simulations, which create thecomposite matrix properties.These composite properties can then be used in full field dualporosity simulations of fractured and vuggy reservoirs tocorrectly predict the oil recovery. The process described canbe applied to any triple porosity reservoir where gas isinvading the fracture-matrix system.
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