EFFECTS OF PH AND SOLID CONCENTRATION ON THE RHEOLOGY OF DRILLING FLUIDS COMPOSED BY NATURAL CLAY, WATER, AND NaCMC

The functions of drilling fluids depend directly on the fluid’s physical, chemical, and rheological properties. The selection and control of fluid composition is crucial to obtain the best performance in the process of drilling oil. The presence of solid particulate material and viscosifying agents contributes to the maintenance of the rheological behavior of these fluids. The pH variation during the drilling may affect rheological properties leading to poor well cleaning and drill string imprisonment. This work aims to evaluate the influence of solid concentration and pH variation in the rheological behavior of carboxymethyl cellulose and natural clay dispersions. Results indicated that solid concentration increased the apparent viscosity of dispersions due to chemical interactions between the polymer and the particles of natural clay. Dispersions at a pH lower than five presented lower values of yield stress and apparent viscosity than dispersions with higher pH values. The protonation of the carboxylic groups of the NaCMC resulted in a hydrophobicity increase of NaCMC and in a subsequent reduction of natural clay wettability. The formation of natural clay aggregates caused a decrease in dispersion viscosity.