1887

Abstract

Summary

Previous core flood investigation of acrylamide-based polymers with associative thickening properties indicated in-situ flow resistance factors (RF) significantly higher than experienced with non-associative polymers having similar bulk rheological properties. Here we propose a novel model for associative polymers which handles the formation of an in-situ polymer network and captures its properties in different flow regimes and at various polymer concentrations. The model is implemented in an in-house black-oil simulator and will allow more robust core-to-field scaling of laboratory results.

The modeling is validated by simulating a set of core experiments conducted with the same polymer but with different concentrations.

In the experimental study the polymer was injected at variable flow rates into dual serial mounted cores with 100 % water saturation. The results are compared with results obtained with a non-associative polymer with similar bulk rheological properties. The increased flow resistance due to injected polymer was observed to propagate as two fronts. The first front had flow resistance consistent with measured bulk viscosity and a velocity typical for non-associative polymer, while the second front had up to two order of magnitude higher RF and the velocity was lower and dependent on the injected polymer concentration. Another characteristic observed for these types of polymer is the moderate sensitivity of the steady-state pressure drop to changes in the flow rate.

In the proposed model, the associative polymer is treated as a mixed polymer system consisting of a smaller fraction rich in hydrophobic groups and a larger fraction with properties like a regular synthetic polymer. For both fractions, we include typical rheological behavior observed for regular synthetic polymers in flow regimes; shear thinning, shear thickening (elongational flow) and mechanical degradation when going from low to high shear rate. The formation of a pore filling network is modelled as a shear rate dependent retention of the smaller hydrophobic fraction and its additional flow resistance is obtained using a Carman-Kozeny approach.

Simulations of the experiments conducted with 100 % Sw demonstrate that the model can reproduce observed effects like pressure front velocities at different polymer concentrations and responses in RF to rate variations. The model was also applied to two-phase experiments. Effect of water saturation was included in appropriate terms and the RF in presence of oil is captured. Finally, we demonstrate how temperature dependent associative behavior can be utilized at the field scale in a simple large-scale model.

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2019-04-08
2024-03-29
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