The effect of fluid chemistry on wetting textures in novaculite

We have performed two suites of experiments at 600°C and 200 MPa on samples of Arkansas Novaculite to investigate the effect of fluid chemistry on the local distribution of fluids amid grains of solid rock under crustal conditions. Analysis of texture before and after these experiments indicates that fluid chemistry has an effect on both equilibrium wetting angles and the degree of fluid connectivity along triple junctions. The first suite of experiments shows that triple grain junctions in low‐porosity (ϕ < 1%) novaculite have dihedral angles (Θ) less than 60° in the presence of 1 m MgCl 2 , 3 m KCl, and 3 m , 4 m , or 6 m NaCl solutions. In these samples wetted triple junctions observed under a scanning electron microscope in polished section were approximately 0.15 μm from corner to corner. In fracture surfaces the triple junctions appear to form an interconnected network of very fine tubules. Novaculite in the presence of CaCl 2 solutions also contains wetted triple junctions with Θ < 60° but appears to be less wetting than the previous fluids. Novaculite in the presence of H 2 O and CO 2 ‐H 2 O equilibrates to nonwetting textures (Θ ≥ 60°) and lacks interconnected tubules as observed in fracture surfaces. In the second set of experiments samples were equilibrated sequentially in two different fluids. After this treatment, samples exhibited textures characteristic of the second pore fluid, attesting to the reversibility of the textural equilibration process and suggesting that reversion of textures occurs rapidly (<24 hours) under these conditions.