Polymer Induced Permeability Reduction: The Influence of Polymer Retention and Porous Medium Properties

Abstract

Polymer injection finds wide application in enhancing oil recovery (EOR) for heterogeneous reservoirs containing viscous crude. While injection of polymer effectively reduces mobility ratios toward favorable levels and enhances sweep efficiency, it necessitates consideration of potential drawbacks, notably the risk of significant permeability reduction induced by polymer injection. This reduction arises from interactions between the injected polymer and the reservoir rock, occurring either deeper in the reservoir or near the wellbore. In addition, the extent of permeability reduction is influenced by diverse factors, including rock mineral composition, oil saturation, temperature, salinity of formation brine, formation pore structure, polymer type and molecular weight, shear rates within porous media, and the quality of injection water. Accurately assessing permeability reduction holds paramount importance in polymer selection, allowing a comprehensive evaluation of the benefits of polymer flooding for specific reservoir conditions while mitigating potential losses in polymer injectivity during field operations. Severe permeability reduction induced by polymer injection may result from factors such as excessive polymer retention within the reservoir rock, fluids/rocks incompatibility, pore throat clogging due to accumulation of large polymer molecules, shear-induced thickening near the wellbore, improper polymer solution preparation. Within this study, we delve into the utilization of coreflooding data as an evaluative tool for permeability reduction due to polymer injection. A novel interpretation method is introduced, establishing a correlation between polymer retention and the resulting permeability reduction observed in coreflooding experiments. This approach effectively couples the aspects of polymer retention and the rock quality index, leading to a proficient alignment with permeability reduction trends derived from existing data, particularly concerning sandstone and carbonate rock samples. Recognizing the pivotal role of permeability reduction in the polymer selection process, this approach underscores its significance as a pivotal design parameter. While prior methodologies have been proposed, many exhibit limitations in terms of scalability. Through precise evaluation of permeability reduction utilizing empirical data, this approach facilitates a comprehensive understanding of polymer behavior within deeper reservoir layers. Furthermore, it enables the anticipation of potential injectivity challenges and contributes to the refinement of project design, thus enhancing overall operational outcomes.