High Temperature Cementing: Fluid Loss Control Polymers Performance and Limitations

Abstract

Abstract Oil well cementing is a technically critical job and requires a well controlled placement along the wellbore and an even fill of the annular volume. As a consequence fluid loss control additives, preventing water from filtering into the formation are key ingredients of cement designs. These additives are often based on synthetic high molecular weight sulfonated copolymers. The mechanism of action of these polymers has been studied recently and it was demonstrated that adsorption onto the cement surface is key to the achieve product performance. Unfortunately this adsorption yield is generally limited and typically performance decreases significantly as temperature increases. In order to overcome that loss, formulators typically increase loading to regain acceptable performance. Due to the high molecular weight nature of these AMPS copolymers, the subsequent drawback of increased loading is also an increase in cement slurry viscosity. In addition, as higher density slurries are typically used when downhole temperature increases, the problem is exacerbated and these limitations highlight the need for alternative technologies. In this study we investigated the use of block copolymers comprising first a strong adsorbing block, then a long second hydrophilic block providing filtration control. This technology has already demonstrated to be very effective in preventing performance losses in presence of competitive formulation additives such as dispersant or retarders (see SPE173758). In this work, the behavior of such fluid loss additive is investigated in several cement grades and at elevated temperature. Thanks to systematic methodology combining adsorption quantification with a standard HP/HT filtration, it is possible to quantify fluid loss polymer adsorption. This methodology using steric exclusion chromatography applies even in the case of complex formulations comprising retarders. This work focuses on the analysis of the adsorption of fluid loss polymers on several cement grades and at elevated temperature. Comparison of conventional copolymers and diblock copolymers show that conventional systems are very sensitive to cement grades even at moderate temperatures and gets very difficult to use above 100°C. On the other hand diblock copolymers are consistently performing at moderate temperature. Some potential performance limitation of this additive may occur at very high temperature if sulfate/aluminate balance of cement is such that ettringite thermal degradation can take place.