The Colloidal Interaction Of Ferrochrome Lignosulfonate With Montmorillonite In Drilling Fluid Applications

Abstract

Abstract Ferrochrome lignosulfonate thinners function by adsorbing at the clay-solution interface. During this adsorption, they increase the anionic zeta potencial and the forces of repulsion between the clay potencial and the forces of repulsion between the clay particles. This causes an increase in colloidal particles. This causes an increase in colloidal stability which is demonstrated in higher coagulation values, in lower degrees of shear thinning, and a decrease in medium and low shear rate viscosities. At lignosulfonate concentrations greater than that required for monolayer coverage, the clay remains stable and well dispersed due to sceric stabilization. Introduction The effects of dispersants on the rheology of drilling fluids are complex. A dispersant not only affects a viscosity at a particular shear rate but also the overall shear thinning behavior. The rheology, however, is an observation of a summation of colloidal phenomena. When a shear chinning disversion becomes less shear thinning in the presence of a dispersant, chat dispersant wail normally have increased the colloidal stability of the dispersion. For aqueous dispersions of particles the colloidal stability can be understood through examination of electrical phenomena at the solid-solution interface. Such electrical properties, although difficult to measure, can be of primary importance in the stability of hydrophobic colloids. For more hydrophilic colloids, the stability can depend much less on electrical properties and more on steric stabilization. properties and more on steric stabilization. This work was performed, as much as possible, an systems which could be used in the field. The goal was no elucidate on the mechanism of colloidal interaction of a ferrochrome lignosulfonate (FCL) with a drilling type clay. Previous work by Browning has pertained to lignosulfonate adsorption and effects on mud rheology, but no actual adsorption or double layer properties were ever measured. Other authors have studied the effect of lignosulfonate adsorption on the clay structure and its cation exchange capacity, but did not relate this to colloid stability or rheological properties. In addition, some workers have found properties. In addition, some workers have found that kaolinite suspensions are coagulated rather than dispersed by sodium lignosulfonates. APPARATUS AND PROCEDURES Electrokinetic phenomena were observed using a "Laser Zee" (TM) electrophoresis instrument, model 500. This instrument uses a collimated helium-neon Laser beam co illuminate the viewing plane. Deionized water was used for preparing the systems and at least 15 minutes were allowed after pH adjustment before measurements were taken. Preliminary experimentation showed that the zeta potential did not vary by more than one millivolt on a -38 millivolt system when aged from 15 to 60 minutes. Rheology measurements were made using a Baroid variable speed electronic rheometer. All drilling fluids were mixed at high shear and let sit for a similar 15 minute period. The Casson model of rheology was used according to Asbeck's relationship: (1) i.e.: A plot of the square root of the viscosity as a function of the reciprocal of the square root of the shear rate yields a straight line. For a more complete discussion of the Casson model, see. The slope "C" is used as an indication of the degree of shear thinning while n is a uniting high shear rate viscosity and gives an indication of the viscosity at bit shear rates. The clay used in these studies was of the mantmorillonite type and is representative of that which is used for drilling mud purposes. The cation exchange capacity of the clay was measured by a methylene blue technique and found to be 70 meqs/ 100 gms.