EFFECT OF CLAY POLYMER INTERACTIONS ON SHALE STABILIZATION DURING DRILLING

Adsorption measurements were used to investigate the mechanisms of sha le stabilization by water-soluble polymers, which are commonly added t o drilling fluids to control reactive shale formations. High molecular weight (10(7)) polyacrylamides of varying ionicity were adsorbed on w ell-characterized K-smectite, from solutions of varying electrolyte co ncentration. Polymer adsorption was found to be strongly dependent on the ionicity of the polymer and on the ionic strength of the medium, d ue to charge screening effects and the salt-dependent energy of tactoi d assembly. The interaction of these polymers with a standard shale ro ck was investigated by conventional oilfield cuttings rolling tests an d in an apparatus designed to simulate wellbore conditions of pressure and flow rates. The results show that under conditions promoting adso rption of polymers, disintegration and dispersion are inhibited, altho ugh the near wellbore material still imbibes water and ions. The stabi lity of the wellbore is also dependent on the nature of the polymer-cl ay interaction; the strongly bound cationic polymer is able to limit c lay swelling.