The effect of system variables on in situ sweep-efficiency improvements via viscosity modification

Laboratory experiments and numerical simulations were performed to critically evaluate the utility of viscosity modification as a technique to improve injected fluid sweep efficiencies within texturally heterogeneous geomedia. The objective of this technique is to improve the subsurface distribution of fluids by mitigating the potential for preferential flow and bypassing of lower permeability media that can limit the effectiveness of in situ remediation applications. The results of two-dimensional sand tank experiments and numerical simulations demonstrate that viscosity modification, via polymer amendment, can improve sweep efficiencies within layered heterogeneous structures by up to 90%, relative to the no-polymer case. The amount of sweep efficiency improvement depended on a number of system variables, including: the degree of layering, the relative positioning of layers within the system, the permeability contrast between layers, fluid viscosity, and the rheological character of the fluid utilized. Although significant sweep-efficiency improvement was observed, achieving 100% sweep in one pore volume was only possible when the permeability contrast was less than a factor of four, regardless of the viscosity and the rheological character of the fluid.