| Oil can become bypassed during a gas injection process as a result of gravitational, viscous, and/or heterogeneity effects. Enhanced flow and mass transfer between the bypassed region and the injected gas are responsible for oil recovery from these bypassed regions. Gravity-driven, pressure-driven, and capillary-driven crossflows along with molecular diffusion and dispersion have been identified as significant mass-transfer mechanisms.; Mass-transfer experiments have been carried out to evaluate the effects of gas enrichment, mass-transfer orientation, water saturation, and wettability on these mass-transfer mechanisms. Experiments involved injecting a gas solvent across an open face of a porous sample in an effort to simulate a bypassed region.; Injected gases were first-contact miscible (FCM), multicontact miscible (MCM), or submiscible (slightly immiscible) with the bypassed oil. In addition to isolating and investigating mass-transfer mechanisms, gasfloods were conducted to evaluate gas enrichment, water saturation, and wettability effects on oil bypassing.; Results demonstrate that mass transfer increases with gas enrichment, but is reduced in the presence of water saturation under water-wet conditions. Near-miscible mass-transfer experiments are influenced more by capillarity than water saturation or wettability. Water saturation had no effect on near-miscible, vertical gasfloods. Horizontal gasfloods; revealed evidence of less gravity override in the presence of water, but still exhibited a significant amount of bypassing under water-wet conditions.; Research has also focused on the use of compositional simulations to provide further insight into experimental observations and scale up through use of effective diffusion coefficients. Compositional simulations allowed molecular diffusion coefficients and tortuosities to be determined as functions of gas enrichment and water saturation. Using effective diffusion coefficients, mass-transfer coefficients were calculated. |
