Grimbeek2: First Successful Application Polymer Flooding in Multilayer Reservoir at YPF. Interpretation of Polymer Flooding Response

Abstract

Abstract Here we report the key success factors of the first polymer pilot at YPF in the south of Argentina and the consensus shifting strategy for polymer expansion in the current oil price context. We calculated water flow velocities in the reservoir using three multiscale history matched simulation models. We found that more than 80% of water velocities across the complete field are below1ft/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 ratio in the high permeability streaks possibly located in the channel bars. This is very important because low end point water permeability (<0.09) could explain the success of water flooding in friable formation with viscous oil. This challenges the common assumption of poor performance because adverse mobility ration (> > 10). High permeability streaks (above 10 Darcy) are not characterised because they are often lost during coring or they are not suitable for coreflooding experiments. Instead, stochastic history matching supports the idea of greater water end point permeability (>0.2) in the high perm streaks. Then, the target resistance factor for polymer could be underestimated (underestimation of polymer concentration) and polymer injection might not perform as expected. Simulation-based analysis of flows in the pilot zone strongly suggests that one of the key success factors was pattern confinement. The pilot configuration is five-spot with 4 injectors, 1 confined producer and 9 offsets producer wells. After injecting 0.15 pore volumes of 2500/3000ppm polymer we recovered more than 11% ooip incremental oil above waterflooding from the central pattern and more than 6% 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. Water cut reduction and therefore the oil response is greater than best pilots in the literature. This can be explained because of the cross flow between fluvial layers in the inter-well region. Our simulations indicated that there was no out-flow of the central pattern. The very good performance in terms of low utility factor obtained so far (2.9 kg per incremental barrel of oil above water flooding) supports the hypothesis of the good confinement. The accurate simulation model allowed us to conceptualise a pattern rolling strategy for the polymer expansion that makes this technology economic for this low oil price context.