Comprehensive Micromodel Study to Evaluate Polymer EOR in Unconsolidated Sand Reservoirs

Abstract

Abstract In this work micromodels are generated from high resolution images of unconsolidated sands and subsequently used to study polymer EOR processes. Using this approach an almost unlimited number of equal copies can be produced. Moreover, compared to cores, the micromodels enable visual access to the flooding process, facilitating a more detailed process description. Understanding the mechanisms and effects of polymer flooding is essential to avoid failures in field applications. Core studies conducted by commercial laboratories indicated very optimistic oil recovery from polymer injection; therefore, a micromodel study was proposed to investigate the recovery process in detail. The experiments were conducted at reservoir temperature. This study aims to support the design and optimization of polymer EOR projects by experimentally determining polymer performance in terms of production acceleration, incremental production and reduction of the residual oil saturation. Performance is evaluated for a variety of critical input parameters such as polymer rheology, product, and concentration for different average rock properties. The study includes complete rheological characterization of three polymers in terms of flow curves and, in specific cases, viscoelastic effects. The characterization enables the determination of suitable polymer concentrations based on three predetermined viscosity ratios. During the flooding experiment, the oil saturation changes are continuously monitored through image analysis based on which the recovery factor can be calculated. Experimental results obtained from corefloods are compared to those obtained in micromodels, focusing on the following key parameters: (1) Recovery factor, (2) injected pore volume at breakthrough time, (3) residual oil saturation. The paper illustrates how the micromodel experiments help to improve the understanding of oil recovery processes during polymer EOR.