On the stability of shale: the role of zeta potential (ζ) and Debye Hückel length (κ−1) on shale swelling

Abstract

This work utilized electrochemical potential, linear swelling and water and ions uptake tests to correlate zeta potential (ζ) measurements with swelling results when different shales interacted with NaCl, KCl and CaCl2 solutions of different concentrations (water activities). Experimental results show that shale swelling and shrinkage seems to correlate well with changes in zeta potential and Debye Hückel length (κ −1) of shale’s charged surface. I believe that reduction of zeta potential and κ −1 leads to shale shrinkage while increase in zeta potential and κ −1 translates into shale swelling. Results also show that zeta potential and κ −1 of Pierre and Arco shale depends strongly on water activity (concentration) difference between shale and aqueous solutions. It was found that the formation and break up of an ionic shield cloud determines swelling and shrinkage of shale depending on the direction of water and ions transport. Results also suggest that, for constant temperature and medium viscosity (ƞ), the term (z/r) determines the effectiveness of ions to screen particle surface charge and it represents two opposing forces (electrostatic force and viscous force). The (z/r) for NaCl equals 0.28 m−1 which is lower than that of CaCl2 (z/r = 0.46 m−1 ) and KCl (z/r = 0.303 m−1 ).