Polymer Screening Criteria for EOR Application - A Rheological Characterization Approach

Abstract

Abstract Polymer flooding has been the most widely used enhanced oil recovery technique in both sandstone and carbonate reservoirs. Ample polymer flooding projects have been conducted with different level of success ever since the technique was introduced 50 years ago. It is a usual practice to select a polymer based on viscosity range, concentration and molecular weight without getting into rheological characterization and its effect on oil recovery. However, in recent times the application of polymer flood has gained critical mechanistic insight with advancement in understanding the role of elasticity on sweep efficiency. Therefore, selecting the type of polymer and understanding how its fluid rheology affects oil recovery are probably among the most critical factors involved in designing a successful polymer flood job. To deal with this, a systematic approach for screening a polymer based on rheological characterization was adapted. Three different polymers, partially hydrolyzed polyacrylamide (HPAM) and Polyoxyethylene (PEO) were first used for fluid rheology study using a cone and plate rheometer and then for oil recovery through a special core holder designed to simulate radial flow through a sand pack – saturated with mineral oil. Effects of various rheological parameters such as; a) Newtonian vs. non-Newtonian rheology (constant shear viscosity vs. shear thinning), b) shear viscosity vs. elasticity, and c) average molecular weight vs. molecular weight distribution (polydispersivity) on oil recovery were investigated. Finally, a parametric characterization study was performed to develop a screening criteria and to correlate oil recovery prediction. The approach could lead to a successful screening process of polymer based on various characteristic parameters such as average molecular weight, polydispersity and Trouton ratio.