Problems of Stokes’ law application in determining the settling velocity of clays

Abstract

Clay sedimentation is important for various applications including settling of drilling mud during downtime in drilling operations, and it is essential to model such processes. A widely accepted theory that explains the kinetics of dispersed particles under gravitational pull in a quiescent medium is Stokes’ law. This law is commendable and reliable for modelling the settling velocity of particles but has been reported to be inadequate for modelling the settling velocity of clays. This has prompted a re-examination of the law with regard to assumptions made in deriving it, and it was found that several factors associated with clay sedimentation were not considered in the law. These factors include particle shape, size, interactions, flocculation, salinity, pH value, concentration and hindrance velocity of settling. Hence, this paper discusses these factors and how they defy assumptions made in Stokes’ law, thereby rendering the law unsuitable for modeling clay settlement in liquids.