(Influence of the molar mass of CMC in the rheological behavior and of filtration of clay suspensions)

Abstract

The carboxymethylcellulose (CMC) is a linear anionic polymer used as viscosifier agent and filtrate reducer in drilling fluids. The chemical structure and molecular weight of the polymer interfere in the complex interactions between the polymeric chains and the mineral solids in the suspension. This study aimed to evaluate the rheological behavior and filtration process of clay suspensions in function of the increase of the polymeric additive concentration with different molar masses. For this, a sample of bentonite clay, two samples of CMC with different molecular weight (CMC 1 (9.0 x 10⁴ g/mol) and CMC 2 (2.5 x 10⁵ g/mol)) and same degree of substitution (0.7) and one sample of calcite were used. The rheological properties (apparent viscosity, plastic viscosity, yield limit and gel strength, and filtration process parameters (filtrate volume, spurt loss, cake thickness and permeability, and retaining power of the clay suspensions were determined. The rheological and filtration properties of the clay suspensions prepared with polymeric additives are strongly dependent of the CMC-clay interactions and CMC-calcite and these are dependent on the viscosity grade and chain size of the polymer.

Keywords:
carboxymethylcellulose; bentonite clay; calcite; interactions; viscosity grade