The Effect of Particle Size Distribution and Exchange Cation on Gel Properties of Fractionated Bentonite Suspensions

Abstract

Published in Petroleum Transactions, AIME, Volume 216, 1959, pages 455–459. Introduction The plastic flow characteristics of clay water suspensions were first recognized by Bingham in 1916 and further studied by Ambrose and Loomis in 1931–1932. Many physical and chemical properties of clay suspensions are deeply influenced by particle size distribution as well as by the exchange cation. Separation of a number of fractions is particularly helpful in making a detailed study of a suspension. A limited amount of work has been conducted on the effects of particle size on specific properties of mud drilling fluids. A knowledge of particle size distribution is essential for a better understanding of fundamental properties of clay suspensions, particularly viscosity and gel strength. The purpose of this investigation was to study the effect of particle size on the viscosity and gel properties of clay suspensions and to determine any changes in mineral composition accompanying variation in size. Experimental Procedure Numerous methods may be used to fractionate a poly-dispersed clay suspension into nearly mono-dispersed systems. Particles larger than 44 micron (325-mesh) may be obtained by wet screening. For sizes from 44 to 1 micron, the fractionation may be accomplished by sedimentation, elutriation plus microscopy, or turbidimetry. When dealing with systems which contain a major portion of particles below 1-micron size, slit ultramicroscopy, centrifuge methods of Svedberg, Beams, and McBain, and X-ray methods may be employed. The Sharples super centrifuge has been proved suitable for the economical separation of suspended particles of submicron range. Three-hundred and forty-five gal of 1 per cent by weight Aquagel suspension was mixed in a high-speed 5-gallon mud mixer and the suspension was allowed to stand in 5-gal glass bottles for 30 days to assure full hydration. All particles larger than 44 microns were removed by wet screening. Five fractions in the range of 44 to 1 micron were obtained by sedimentation.