Miscible and Immiscible Gas Injection for Enhancing of Condensate Recovery in Fractured Gas Condensate Reservoirs

Abstract

Abstract Gas condensate reservoirs usually exhibit complex flow behaviors because of accumulation of condensate in the reservoir and two-phase flow of gas and condensate when the reservoir pressure drops below the dew-point. In some complicated geological systems like naturally fractured reservoirs, these complex behaviors will be more. In these systems, pressure drop response propagates in the fracture network and all the matrix blocks surrounded by fractures are influenced by pressure drop in the wellbore. This causes accumulation of large amount of condensate in the matrix blocks entire the reservoir when the pressure drops below the dew point. Usually, the accumulated condensate saturation in the matrix blocks of fractured reservoirs is lower than the critical condensate saturation that causes trapping of large amount of condensate in the matrix blocks. So selection of an efficient EOR scenario for recovering this trapped condensate is important. In this paper, a single matrix block surrounded by fractures is used to study the performance of a fractured gas condensate system in natural depletion, miscible and immiscible gas injection. C1, N2, CO2 and stock-tank gas composition are considered as injection gases and their miscibility with condensate is studied. Also some sensitivity analyses were performed on different parameters for more accurate investigation about the effects of different parameters on performance of the fractured system in different production scenarios. In both miscible and immiscible gas injection scenarios, the timing for injection and injection gas composition are two key parameters. In miscible gas injection case, miscibility is the main mechanism for condensate production, while in the case of immiscible gas injection scenario, vaporization of condensate by injected gas is the more efficient mechanism for condensate recovery. Gas-gas miscibility mechanism is more efficient in comparison to gas-condensate miscibility in miscible gas injection and vaporization in immiscible gas injection scenario.