Abstract
A considerable portion of world reserves are located in mature and viscous oil reservoirs having thickness less than 15 m. Polymer flooding is a mature technology and is the most important EOR method based on full field case histories. Accurate assessment of injectibility of viscous polymer solutions into these reservoirs without induced fractures is a major challenge. Therefore, the objective of this study is to experimentally investigate and model polymer injectivity in porous media using unfiltered partially hydrolyzed polyacrylamide (HPAM) solutions for wide range of polymer concentrations (125–5000 ppm) and salinities (5–20 g/L) in high permeability sandstones. Data from rheological measurements and single phase linear core flood studies carried out as a part of this study were utilized for understanding the key microscopic (pore level) mechanisms and for quantifying the injectivity.
Based on the experimental analyses, it was found that viscous nature of polymer solutions and their retention in porous media were the main mechanisms for loss in injectivity. Data obtained from the experiments were used to validate and fine tune the model. Subsequently, with the help of the Langmuir adsorption isotherm, filtration theory, permeability reduction model, Non-Newtonian viscosity and Darcy laws numerical modeling was performed for predicting the injectivity losses during polymer injection. A good quality match was obtained with experimental data. Finally, sensitivity of polymer concentration and salinity on injectivity was studied. Further, the results from this study, will serve as an auxiliary input for field scale simulations, will help operators in the selection, design and execution of the field projects and will stand as guidelines for extending the polymer flooding technology for heavy oil reservoirs.
