Grimbeek -120 cp Oil in a Multilayer Heterogeneous Fluvial Reservoir. First Successful Application Polymer Flooding at YPF

Very low water effective permeability could explain the success of water flooding and polymer flooding into friable formation with viscous oil. This challenges the common assumption of poor performance because very adverse mobility ration. In this type of reservoirs, high permeability zones (above 8-10 Darcy) are not well characterised because they are often lost during coring or they are not suitable for coreflooding experiments. Then, the target resistance factor could be underestimated and polymer injection might not perform as expected. Multilayer fluvial reservoirs hinder vertical conformance and affect the efficiency of polymer flooding. Here we report the results of the ongoing polymer pilot. After injecting 0.3 pore volumes of polymer solution we recovered 10% ooip incremental oil above water flooding from the central pattern and 5% of the ooip from offset producers in contacted zone. The water cut reduced from 90% to 45% in the confined producer and from 87% to 67% in the offset producers. We calculated water flow velocities in the reservoir using three history matched simulation models constructed at different scales (full field, sector model coarse and fine) and we found that more than 90% of water velocities across the complete field are below 1ft/day [normally assumed reservoir water velocity for calculating the resistance factor in laboratory experiments]. We increased polymer concentration in 10 to 30% to ensure good mobility ration in the high permeability streaks possibly located in the channel bars. Simulation based analyses of the flows in the pilot zone strongly suggest that one of the key success factors was pattern confinement. There was no out flow of the central pattern. The very good performance in terms of low utility factor obtained so far [0.31 kg per incremental barrel of oil above water flooding] supports the hypothesis of the good confinement. This allows us to design a pattern rolling strategy for the polymer expansion that makes this technology economic for this low oil price context.