A Study on the Thixotropy of Egyptian Bentonite Suspensions

Abstract

The rheology behavior of water bentonite suspensions has been studied through recording the viscosity measurements to study the thixotropy of the suspensions using local Egyptian bentonite at 5.0%, 6.40%, and 7.5.0% concentrations in the a presence of different salt concentration as 0.0 M, 0.01 M, and 0.1 M NaCl according to API stander, rheological data was calculated by viscometer, deriving first the D0 curve, from 600 to 3 rpm, followed by a typical thixotropic loop, getting the U curve from 3 to 600 rpm, and then the D curve from 600 to 3 rpm. Three rheograms have been derived for each suspension after intensive preshearing, from high to low, from low to high, and from high to low shear rates. Positive thixotropy is observed for all suspensions at 0.0 M and 0.01 M but not at 0.1 M salt concentrations. Thixotropic indexes computed from the normal thixotropic loop, low to high to low shear rates, have been computed and vary from positive to negative. The higher the bentonite concentration, the higher the index for the suspensions with no salt, while in the presence of salt, variations of the thixotropy index are obtained with the degree of variation dependent on bentonite concentration and salt concentration The suspension with no salt and 0.01 M salt exhibited thixotropy, estimated from the D0-U curves, while the 0.1-M suspensions showed no thixotropy. Thixotropy indices vary and depend on bentonite type and concentration and on the presence and amount of salt.

Keywords:

• drilling fluids
• Egyptian bentonite
• rheology
• salts
• shear rate
• shear stress
• suspensions
• thixotropic
• viscosity
• yield point