Investigations on the Thixotropy of Bentonite Suspensions

Abstract

The thixotropic behavior of water bentonite suspensions has been investigated using Wyoming and Zenith bentonites at 5.0% and 6.42% concentrations with 0.0 M, 0.01 M, and 0.1 M NaCl following API preparation protocols. Rheological data was collected with a Couette 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. The Herschel-Bulkley model describes very well all experimental data. Yield stresses did not vary, but variations of flow consistency and of flow behavior indices were detected for the three curves. All suspensions with no salt and 0.01 M salt exhibited anti-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. The mechanisms of thixotropy and implications on drilling fluid performance are discussed.

Keywords:

• bentonite
• drilling fluids
• Herschel-Bulkley
• rheology
• suspensions
• thixotropy

Acknowledgment

Experimental data has been collected by Mrs. C. Tsamantaki.