Effectiveness of Polycarboxylate Dispersants in Enhancing the Fluid Loss Performance of Cellulose Ethers

Abstract

Abstract This paper investigates the performance of different kinds of polycarboxylate (PCE) dispersants in combination with cellulose ethers as fluid loss additives and presents their influence on the fluid loss. The objective was to find out whether PCEs can better enhance the fluid loss performance of HECs than the currently applied acetone-based dispersant (AFS). Two different polycarboxylates were synthesized via free radical copolymerization using either methacrylate ester or isoprenyl ether as macromonomers and tested. The AFS polycondensate and the hydroxyethyl cellulose (HEC) were commercial samples. The impact of the PCE and AFS dispersants on the fluid loss of cement slurries achieved from hydroxyethyl cellulose was investigated via static fluid loss and rheology measurements. All PCE polymers improved the fluid loss performance of HEC significantly more than AFS; i.e. they required considerably lower dosages than AFS to achieve the same volume of fluid loss. For example, at 27 °C the addition of 0.1 % bwoc PCE to 0.4 % HEC improved the fluid loss from 250 mL/30 min to 50 mL/30 min. For the same effect, 0.4 % of AFS were needed. Most important, such low fluid loss values were achieved at very thin filter cakes, indicating that although the PCEs reduced slurry rheology considerably, no sedimentation had occurred which can also lead to low fluid loss, but is highly undesirable. Furthermore, a linear correlation between cement slurry rheology and fluid loss was observed: The stronger the dispersing effect of the PCE, the better is the fluid loss control. Among the PCEs tested, the isoprenol ether-based copolymer stood out as performing best. Dynamic light-scattering measurements revealed that the presence of PCEs strongly enhances the association of the HEC molecules, thus improving their ability to plug cement filter cake pores.