Regulation mechanisms of phase change microcapsules with different shell materials on hydration and pore structure evolution in deepwater well cementing slurry

To regulate the hydration heat of deep-water well cementing slurry, phase change microcapsules (m-PCMs) with organic (PMMA) and inorganic (SiO₂) shells were prepared in this study to investigate the influence mechanism of shell properties on the cement matrix performance. The results indicated that both types of m-PCMs exhibited excellent shear stability and similar peak phase change temperatures (25.6 ℃), effectively reducing hydration exotherms. The critical difference lay in their wettability: PMMA@m-PCM was hydrophobic (116.5°), whereas SiO₂@m-PCM was strongly hydrophilic (27.3°). Micro-CT confirmed that m-PCMs at a 6 wt% dosage effectively reduced the proportion of large pores, optimizing the pore structure. Mechanical tests revealed that SiO₂@m-PCM demonstrated a significant strength enhancement effect at 3 and 7 days, while PMMA@m-PCM severely weakened the matrix strength. SEM analysis revealed that the core of this performance disparity was interfacial compatibility: the hydrophilic SiO₂ shell formed a dense interfacial transition zone (ITZ) with the matrix, whereas the hydrophobic PMMA shell caused severe interfacial debonding, creating mechanical weak points. This study demonstrates that using hydrophilic inorganic shells is key to achieving the unification of m-PCM hydration heat regulation and mechanical performance enhancement. These findings provide a new methodology for designing low-heat cement slurries, offering theoretical and technical insights for safe and sustainable deep-sea oil and gas exploitation and reducing ecological impact.