New Dimensionless Numbers Characterising Viscous Crossflow During Chemical Flooding in Layered Reservoirs

Reservoirs are often layered due to depositional processes and this affects the sweeping efficiency of chemical flooding. The traditional dimensionless numbers of viscous crossflow may fail to predict the impact of crossflow under these circumstances. In this work, we have derived new dimensionless numbers to take into account mobility modification that occurs as a result of chemical flooding. We considered models of viscous dominated chemical flooding. In such systems, the formation waterfront was formed and followed by a second chemical waterfront. We also took into account models where there was a rarefaction wave of a gradual increase in water saturation behind the second waterfront. We began by deriving analytical solutions in noncommunicating layers. Then, we used these solutions to obtain dimensionless numbers that described the relationship between fluid flow and the heterogeneity between layers. We considered models where each layer was contrasted from the other by porosity, permeability, initial and final fluid saturation, relative permeability, viscosity and retardation factor. We compared the predictability of these numbers against the numerical results for models under low salinity and polymer flooding. The new analysis shows that a group of four dimensionless number can be used to quantify the effect of viscous crossflow. While two of these numbers are new, the others have been modified to extend previous work. The current study shows that mobility modification due to chemical flooding is a significant parameter and should be included, whereas this was not considered previously. We also introduce a modified longitudinal heterogeneity ratio as a new dimensionless number that grouping the contrast of porosity, permeability, saturation change, and harmonic average of total mobility of displacing front. This new term is more descriptive than having a dimensionless number of each individual property as previously suggested. Also, for the first time, we report the role of fractional flow contrast where it should be considered as an individual dimensionless number in chemical flooding and as associated parameter within the longitudinal heterogeneity ratio for both chemical and traditional flooding. This newly derived group is very important for EOR processes in layered models where mobility changes occur, and mobility modification, fractional flow and saturation change are accurately presented.