Analysis of Polymer Injectivity in Porous Media
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- Department of Chemistry 
Polymers are chemical substances that occur both naturally or synthesized and consist of large macromolecules. They are created by the process of polymerization of many smaller molecules also known as monomers. Due to their unique properties, there are tremendous number of daily life applications that involve polymers, from basic food and clothing industries to the manufacturing of advanced machineries. One of the applications of polymers in the oil industry is in the method known as polymer flooding, which is one of the most successful and widely applied chemical enhanced oil recovery techniques. The recovery of oil from subsurface reservoirs usually involves injection of water to improve oil sweep and maintain pressure. In some cases, however, the mobility ratio between displacing water and displaced oil is unfavorably large which results in significant amount of bypassed oil. Therefore, Polymer is added to injection water to enhance waterflooding sweep efficiency by increasing injected water viscosity and reducing its mobility. Although polymer flooding is a relatively mature and widely discussed method in the literature, many flow mechanisms and phenomena of polymer flow in porous media are yet to be fully understood. Among these topics is the non-Newtonian shear dependent in-situ rheology of polymer solutions at reservoir conditions, and its impact on polymer injectivity. Another example is the modelling of immiscible viscous fingering observed in the preconditioning waterflooding in heavy oil reservoirs. Accurate modelling of this phenomenon is essential as it provides better understanding of fluids distribution in the reservoir prior to polymer flooding. In this thesis, numerical simulation studies were conducted to investigate several issues related to polymer injectivity in porous media. The main topics discussed are (1) modelling immiscible viscous fingering of water flooding at adverse mobility conditions, (2) optimizing field polymer injectivity test design by investigating the impact of polymer in-situ rheology on injection bottom-hole pressure data, and (3) analyzing the data of actual field polymer injectivity test conducted in a high temperature high salinity carbonate reservoir in Abu Dhabi, UAE. Viscous fingering observed in unstable displacement 2D waterflooding experiments were matched using a novel approach that resolves the issue from both physical and engineering perspective. The approach depends mainly on choosing a modified fractional flow function to increase the shock front saturation within established fingers. By combining this concept with a dispersivity-optimized grid sizing and a randomly correlated permeability field representative of micro heterogeneity, four waterflooding experiments at four different heavy oil viscosities were matched adequately for both observed fingering patterns and production data. Radial lab experiments on HPAM polymer revealed significant deviation in polymer shear dependent viscosity behavior from the one observed in linear experiments. The main difference is seen in the lower magnitude and delayed onset of shear thickening in radial geometry compared to linear. Lab scale simulation studies proved the robustness of utilizing injection pressure data to estimate polymer rheological behavior. Upscaled field simulation models were used to investigate the signature of Newtonian behavior compared to possible non-Newtonian behaviors in near wellbore region. Results have shown that each of shear thickening, shear thinning, and the combined effect rheology behaviors could be distinguished from the injector bottomhole pressure data. For instance, a viscosity profile that increases towards the wellbore (shear thickening) reflects an increasing slope on pressure versus rate plots, and vice versa for shear thinning. Besides, transient pressure behavior exhibits distinctively sharper trends for Newtonian and shear thickening compared to shear thinning. General guidelines on optimizing polymer injectivity test design were suggested based on observations from several generic simulation studies on homogeneous and vertically heterogenous models. The two main recommendations with regard to the test design are the essential inclusion of rate stepping, besides the importance of injecting for a sufficient time of at least 0.001 pore volumes of the near wellbore region. Analysis of polymer injectivity test data from a field application in Abu Dhabi have further confirmed the practicality of using bottomhole pressure data to predict polymer in-situ rheology. Sensitivity studies showed a more gradual impact of concentration stepping on the bottomhole pressure response compared to rate stepping. Besides, average weighted residual resistance factor was found equivalent to using permeability dependent RRF correlations. Polymer degradation from pre-shearing prior to injection can be included in the model by inputting modified concentration values that account for degradation percentage. Consequently, by utilizing pressure data and modified concentrations, reliable in-situ rheology curve can be constructed to history match polymer injectivity test data.
Has partsPaper 1: Jacobsen, J. G., Alzaabi, M. Skauge, T., Sorbie, K & Skauge, A. (2019): Analysis and Simulation of Polymer Injectivity. Presented at the 20th European Symposium on Improved Oil Recovery, Pau, France, 8-11 April. The article is not available in BORA due to publisher restrictions. The published version is available at: https://doi.org/10.3997/2214-4609.201900115
Paper 2: Alzaabi, M. A., Jacobsen, J. G., Sumaiti, A. A., Masalmeh, S, Pettersen, Ø. & Skauge, A. (2020): Polymer Injectivity Test Design Using Numerical Simulation, Polymers, Vol. 12(4): 801. The article is available at: https://hdl.handle.net/11250/2760612
Paper 3: Alzaabi, M. A., Hinestrosa, J., Skauge, A. & Masalmeh, S. (2021): Analysis and Simulation of Polymer Injectivity Test in a High Temperature High Salinity Carbonate Reservoir. Polymers, Vol. 13(11): 1765. The article is available at: https://hdl.handle.net/11250/2760739
Paper 4: Salmo, I., Alzaabi, M. A., Sorbie, K., Skauge, A. (2021): Modelling Immiscible Viscous Fingering: History Match of Water Flood at Adverse Mobility Ratio.The article is not available in BORA.