Dynamic characterization of viscoelasticity during polymer flooding: A two-phase numerical well test model and field study

Abstract

Polymer flooding is an important means of improving oil recovery and is widely used in Daqing, Xinjiang, and Shengli oilfields, China. Different from conventional injection media such as water and gas, viscoelastic polymer solutions exhibit non-Newtonian and nonlinear flow behavior including shear thinning and shear thickening, polymer convection, diffusion, adsorption, retention, inaccessible pore volume, and reduced effective permeability. However, available well test model of polymer flooding wells generally simplifies these characteristics on pressure transient response, which may lead to inaccurate results. This work proposes a novel two-phase numerical well test model to better describe the polymer viscoelasticity and nonlinear flow behavior. Different influence factors that related to near-well blockage during polymer flooding process, including the degree of blockage (inner zone permeability), the extent of blockage (composite radius), and polymer flooding front radius are explored to investigate these impacts on bottom hole pressure responses. Results show that polymer viscoelasticity has a significant impact on the transitional flow segment of type curves, and the effects of near-well formation blockage and polymer concentration distribution on well test curves are very similar. Thus, to accurately interpret the degree of near-well blockage in injection wells, it is essential to first eliminate the influence of polymer viscoelasticity. Finally, a field case is comprehensively analyzed and discussed to illustrate the applicability of the proposed model.