Objective The current design of low-heat cement slurries prepared by adding microspheres with phase change materials as wall materials for well cementing in strata bearing natural gas hydrates (NGHs) fails to fully account for the impacts of the particle size and mass fraction of the microspheres on the performance of cement slurries. This leads to impaired cement slurry performance and increased costs, further inducing many problems with well cementing quality. Hence, it is significant to analyze the impacts and controlling mechanisms of the microspheres on cement slurry performance.
Methods To eliminate the interference of the heat storage effect of the core materials also made of phase change materials, this study independently developed microspheres with polymethyl methacrylate (PMMA) as the wall materials (PMMA microspheres) with varying particle sizes. It explored the impacts of the particle size and mass fraction of the PMMA microspheres on the performance of cement slurries, established Dinger-Funk Equation (DFE) models for cement slurries with different hydration ages, and revealed the mechanisms behind the control of the cement slurry performance by the PMMA microspheres.
Results and Conclusions The results indicate that compared to the mass fraction of the PMMA microspheres, their particle size exhibits more significant impacts on the fluidity and mechanical properties of cement slurries, thus warranting more attention in the design of low-heat cement slurries with PMMA microspheres. The increase in the mass fraction of the PMMA microspheres causes two distinct effects on the cement slurry system. On the one hand, the increase in bulk density enhances the mechanical strength of set cement and reduces the cement slurry fluidity. On the other hand, the inherent strength defects caused by the introduction of the PMMA microspheres decrease the strength of the set cement. The predominant role of both effects depends on the mass fraction and particle size of the PMMA microspheres. Specifically, in the case of a low mass fraction, the bulk density effect predominates in the cement slurry system, whereas the strength defect effect becomes dominant when the mass fraction exceeds 4%. Under the joint action of both effects, the uniaxial compressive strength of set cement trends upward initially and then downward. The closest packing theory (CPT)-based DFE model is strongly correlated with the fluidity and mechanical properties of cement slurries. Generally, an optimal DFE model suggests high fluidity and favorable mechanical properties of the cement slurry system. The results of this study provide a valuable reference for the design of low-heat cement slurries prepared by adding microspheres with phase change materials as wall materials for well cementing in strata susceptible to temperature changes.
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