In this study a numerical reservoir model has been built using synthetic reservoir and fluid characteristics which can reflect realistic conditions in a field scale process. The miscibility conditions are considered to be fulfilled. The model has been implemented to investigate the behavior of up-dip water-miscible gas injection in terms of volumetric sweep efficiency.
The phenomenon of up-dip water-miscible gas injection has been analyzed using analytical methods to check the accuracy of computed segregation distance. To be able to use an analytical method for estimating complete segregation distance, the relative mobility of gas and water in the mixed zone versus water-gas ratio has been calculated using Buckley-Leverett theory. The resulting volumetric sweep in a dipping model is also compared to a horizontal model with the same properties to verify the analytical results which show the up-dip water-miscible gas injection can have a good volumetric sweep, even better than a horizontal model. Afterwards, a sensitivity analysis has been carried out to check if the nature of the phenomenon is similar to that for horizontal models. The extent of the gas-water mixed zone, the permeability pattern, layering and anisotropy in permeability, WAG ratio, total injection rate and prior gas injection are the parameters that have been studied for this part.
Even though stable up-dip miscible gas injection gives an inspiring volumetric sweep, common heterogeneities in the reservoirs which can result in viscous tonguing and fingering frequently prohibit this to happen. However, up-dip water-miscible gas injection may be an alternative method that is quite efficient and economical as compared with miscible-gas injection.