The aim of this work is to evaluate the micro-displacement mechanisms associated with heavy oil recovery by water and chemical flooding in a non-linear system (2D Model). To evaluate the effect of sweep efficiency improvements with no local pore level trapping of fluids, a 2D neutral water wet Hele-Shaw cell is used to visualize the dominant mechanisms of surfactant, polymer and their combinations to enhance heavy oil recovery. Waterfloods were conducted as a base line, and compared to surfactant, polymer and SP floods at different injection stages (secondary and tertiary) and under variable injection rates. Post-breakthrough oil recovery and pressure drop during the water flood and chemical flood were evaluated with the analysis of images which show the distribution of the fluids in the cell.
The results demonstrated that in waterflooding, oil pinches off the pre-formed water fingers and allows the formation of snap-off which divert further water to un-swept zones. Oil is produced discontinuously because of snap-off effects, with production of oil related to small pressure spikes in the system. This mechanism was also observed in polymer displacements. This observation can explain viscous flow of oil and discontinuous oil and water production after breakthrough in a heavy oil waterflood. Oil stripping and zones of low IFT, in the form of O/W emulsions were mechanisms observed in surfactant and SP flooding. Such emulsions are present in secondary fingers that then propagate and sweep new areas of the cell. The synergy between polymer and surfactant leads to a slightly better sweep efficiency in the cell by stripping oil and stabilizing the flood front compared to surfactant or polymer alone. Injection rate has also an impact in the flow stability and formation and flow of emulsions. At higher injection rates, flow is more unstable and leads to a less oil recovery. Multiple tests under the same conditions revealed the reproducibility levels of each displacement process.
The novelty of this study is that it provides insights into fluid flow behavior in diverging flow paths as observed in 2D systems, as opposed to linear core floods that have limited flow pathways. In particular, these visual observations help to illustrate the role that surfactants can play in heavy oil systems, with and without the addition of polymer.