This paper addresses the simulation of nitrogen injection in naturally fractured reservoirs through different scenarios by using a conceptual model with isotropic and anisotropic matrix blocks.

Since, in practice, nitrogen is injected under surface conditions, there is some concern about nitrogen injection breakthrough because higher density values under lower temperatures could accelerate the movement of nitrogen in the reservoir and, therefore, it could result in an early breakthrough in production wells.

By using the ECLIPSE commercial simulator, we constructed black oil and compositional simulation case studies under isothermal conditions in order to adequately represent the production conditions of the field and the monitoring field data before nitrogen injection. Simulation results indicated that injected nitrogen moves straight to the gas-oil contact because gravity forces destabilize the displacement.

Furthermore, we considered the injection of different gases (reservoir gas and methane) at the same reservoir conditions, our simulation results show that the gravity force effect under small variations of density between the injected gas and reservoir gas has a big impact on the distribution of injected gas in the gas cap and oil recovery from matrix blocks.

Subsequently, we constructed a thermal compositional case study for a dual porosity system injecting nitrogen at surface temperature conditions. Results indicated that the variation of temperature mainly occurs in the gas cap near the bottom of the gas injector wells. An analysis of nitrogen injection at higher temperatures was also performed in order to define the impact on the distribution of gas and the oil recovery from the matrix blocks.

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