Simulation of Nitrogen Injection into Naturally Fractured Reservoirs

摘要

This paper addresses the simulation of nitrogen injection inrnnaturally fractured reservoirs through different scenarios byrnusing a conceptual model with isotropic and anisotropicrnmatrix blocks.rnSince, in practice, nitrogen is injected under surfacernconditions, there is some concern about nitrogen injectionrnbreakthrough because higher density values under lowerrntemperatures could accelerate the movement of nitrogen in thernreservoir and, therefore, it could result in an earlyrnbreakthrough in production wells.rnBy using the ECLIPSE commercial simulator, wernconstructed black oil and compositional simulation casernstudies under isothermal conditions in order to adequatelyrnrepresent the production conditions of the field and thernmonitoring field data before nitrogen injection. Simulationrnresults indicated that injected nitrogen moves straight to therngas-oil contact because gravity forces destabilize therndisplacement.rnFurthermore, we considered the injection of different gasesrn(reservoir gas and methane) at the same reservoir conditions,rnour simulation results show that the gravity force effect underrnsmall variations of density between the injected gas andrnreservoir gas has a big impact on the distribution of injectedrngas in the gas cap and oil recovery from matrix blocks.rnSubsequently, we constructed a thermal compositional casernstudy for a dual porosity system injecting nitrogen at surfacerntemperature conditions. Results indicated that the variation ofrntemperature mainly occurs in the gas cap near the bottom ofrnthe gas injector wells. An analysis of nitrogen injection atrnhigher temperatures was also performed in order to define thernimpact on the distribution of gas and the oil recovery from thernmatrix blocks.