Tracer dispersion in shear thinning fluid flowing inside a rough fracture

A. BOSCHAN, H. AURADOU, I. IPPOLITO, R. CHERTCOFF AND J.P. HULIN.

SANTA FE, SANTA FE

Workshop; Reunión sobre Recientes Avances en Física de Fluidos y sus Aplicaciones; 2008

&lt;!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:FR; mso-fareast-language:FR;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --&gt; We report here an experimental study of the miscible displacement of a shear-thinning fluid by another one of same rheological properties in two transparent fractures. The fracture walls have complementary self-affine geometries in both cases but have a shear displacement parallel (fracture a) or perpendicular (fracture b) to the flux. We have studied optically the concentration variation on individual pixels: it satisfies a Gaussian convection-dispersion relation characterized by a mean transit time <t(x, y)> and local dispersivity ld(x, y). The spatial distribution of <t(x, y)> shows a marked contrast: it is narrow and single piked for a whereas larger and two-piked for b. This suggests the existence of preferential flow channels for b while not for a. The variation of the dispersivity with the distance from the inlet is linearly increasing for b while constant for a. Finally, a global  ld value can be calculated for a, and shows to behave Taylor-like (diffusive regime) in contrast with the strong channelization dominated by convective behaviour in b (diffusive regime not achieved).