INFLUENCE OF FLUID RHEOLOGY ON TRANSPORT IN FRACTURES

H. AURADOU, A.BOSCHAN, M.V. D’ANGELO AND J-P. HULIN

Soultz sous Forets (France)

Congreso; Phase II Scientific Meeting, 2006 Annual International Meeting of the Cooperative European Program SES6-CT-2003-502706 STREP-Pilot Plant (Soultz sous Forets Geothermal Facility) by the European Hot Dry Rock Association.; 2006

European Hot Dry Rock Association

Miscible displacement experiments using Newtonian and shear thinning fluids are realized in two types of transparent model fractures : these models represent respectively gouge filled fractures with contact points and open fractures with complementary rough walls of self affine geometry sheared perpendicular to the flow direction. An optical absorption technique is used to determine the concentration distribution and the displacement front geometry during the experiments. In both cases the width of the displacement front increases with the shear thinning properties of the fluids and the stability of the displacement is enhanced with respect to buoyancy driven effects due to small density contrasts between the fluids. For the square network of channels of random aperture modeling a fracture with contact points, front spreading is dispersive while, for the open fracture with self affine walls, the mean width σ of the front parallel to the flow increases linearly with distance from the initial injection line. In this latter case, front spreading is shown to be strongly influenced by the structuration of the flow field in channels with a long correlation length in the direction perpendicular to the relative shear displacement of the two wall surfaces (and parallel to the mean flow). A simple model based on this channelization effect is discussed and allows to predict the variation of the width σ with the rheological properties of the fluids and the flow rate.