Effect of Fluid Loss Polymers Architecture on Cement Slurry Rheology : Impact of Adsorption and Microstructure

Several polymer technologies are commonly used as fluid loss control additives. Working mechanisms were studied by Plank et al. (Plank et al. 2009) and most of the time these can be classified into 2 categories: adsorbing polymers and pore plugging "microgel" like systems. In addition, these polymers have a strong influence on the cement slurry rheology and are also often expected to play a role on cement particle suspension, cement sheath homogeneity and to prevent settling. The scope of this paper is to investigate the impact of several types of fluid loss polymers on cement slurry stability. Then, an effort is made to correlate the working mechanism of the fluid loss additive with cement slurry rheological behavior and its ability to prevent segregation or settling. On top of conventional tests on fluid loss and flow rheology, refined evaluations of the rheological behavior are performed in oscillatory rheometry at very-low strain. This technique allows some insight into the microscopic interactions at stake in cement slurries. In particular a "yield stress model" is applied to formulated oil well cement slurries at 90°C providing additional insight on the impact of adsorbing or non-adsorbing polymers. From this study it can be confirmed that adsorbing polymers have a strong impact on rheological properties with a surprisingly lower yield stress combined with improved slurry stability. On the other hand non adsorbing polymers of either linear or μgel form have a very limited impact on slurry yield stress and a variable impact on slurry stability through either viscosification of the interstitial fluid for linear polymers or enhanced settling hindrance from μgels.