Windal Scott Bray

Improving Well Cementing Quality with an Environmentally Preferred Multifunctional Polymer

In designing an optimum cementing system for zonal isolation of wellbores, an engineer generally has to combine several different cement additives to adjust the required and complex slurry properties, such as rheology, thickening time, stability, free fluid-, fluid loss-, and gas control. To minimize environmental impacts and incompatibility issues among various chemical admixtures as well as to simplify logistics and operations, it would be ideal to reduce the loadings and number of different additives required to optimize a cement slurry design. One way to accomplish this is to use multifunctional additives that can improve several slurry properties at the same time without significant detrimental effects on other required properties. Towards this end, a modified cellulose-based polymer has been tested according to API recommended practices in various cement slurries and was identified to have multiple benefits in addition to be environmentally friendly: The test results demonstrate that this single additive controls fluid loss better than commonly used fluid loss additives at temperatures up to 80(degree)C while also controlling free fluid and performing as an extender. In addition, it was found to work as a foam stabilizer and gas control agent in cement slurries, which was not observed for any other cellulose-based polymers. Furthermore, the new polymers retarding effect on thickening time is lower than for other cellulose-based polymers. Some forms of this modified cellulose-based polymer also exhibit delayed hydration, which facilitates surface mixing and pumping of the corresponding cement slurries. This paper will describe test procedures and demonstrate that a single modified cellulose-based polymer can replace several additives in a cement system to adjust the required cement slurry performances for optimum placement and properties in the wellbore. The presented multifunctional biopolymer simplifies cement slurry design and operations contributing to higher quality cement jobs.