Evolution of Clay Smears and Associated Changes in Fault Transmissibility Using a New Direct Shear Fluid Cell

A new type of fluid cell has been developed to allow for direct shear deformation of very large and cohesive rock samples under sealed conditions. Rock samples consist of a low-permeability clay or shale layer, which is embedded in porous quartz sandstone to mimic a reservoir-seal pair. The cell is specifically designed to monitor changes of fault permeability, both across and along the evolving rupture surface, to displacements equivalent to several times the thickness of the argillaceous layer (i.e. SSF>6, c.f. Lindsay et al., 1993), and under stress conditions typical for burial depths of up to 2000 m. We present the general concept of the new testing equipment, and provide structural and flow data of evolving clay smear structures at controlled physical conditions. The results of the analogue experiments are integrated into a numerical modelling study (cf. companion paper by Ter Heege et al.) in an attempt to upscale our findings to reservoir conditions.