Incorporation of Hydroxyethylcellulose-Functionalized Halloysite as a Means of Decreasing the Thermal Conductivity of Oilwell Cement.
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abstract
The significant heat loss and severe thermal fluctuations inherent in steam-assisted gravity drainage (SAGD) and cyclic steam stimulation (CSS) impose considerable constraints on well cementing. In order to obtain better energy efficiency and mechanical robustness, there is considerable interest in the development of low-thermal-conductivity cement that can provide a combination of enhanced thermal insulation and mechanical resilience upon thermal cycling. However, the current palette of thermal cements is exceedingly sparse. In this article, we illustrate a method for decreasing the thermal conductivity of cement by inclusion of hydroxyethylcellulose-functionalized halloysite nanotubes. Halloysite/hydroxyethylcellulose inclusions offer an abundance of disparate interfaces and void space that can effectively scatter phonons, thereby bringing about a pronounced reduction of thermal conductivity. The microstructure of the nanocomposite cementitious matrix is strongly modified even as the compositional profile remains essentially unaltered. Modified cement nanocomposites incorporating halloysite nanotubes along with hydroxyethylcellulose in a 8:1 ratio with an overall loading of 2 wt.% exhibit the lowest measured thermal conductivity of 0.2120.003W/m.K, which is substantially reduced from the thermal conductivity of unmodified cement (1.252W/m.K). The ability to substantially decrease thermal conductivity without deleterious modification of mechanical properties through alteration of microstructure, inclusion of encapsulated void spaces, and introduction of multiple phonon-scattering interfaces suggests an entirely new approach to oilwell cementing based on the design of tailored nanocomposites.
