Multiscale Simulation on Using Phase Change Materials to Mitigate Natural Gas Hydrate Dissociation during Deep-Sea Well Cementing

Abstract In deep-sea natural gas hydrates (NGHs) exploitation, heat released during well cementing can cause hydrate dissociation and natural gas release into the cement slurry, potentially triggering major engineering accidents such as wellbore collapse and environmental hazards. Although microencapsulated phase change materials (MPCMs) have been widely used for thermal regulation in cementitious composites, their potential to mitigate temperature rise in realistic deep-sea well-cementing conditions remains underinvestigated. To examine the influence of MPCM-cement composites on the thermal stability of NGHs, this study develops a multiscale simulation framework that integrates equivalent medium theory, cement hydration kinetics, and PCM properties to analyze transient heat transfer between MPCM-cement composites and the NGH-bearing surrounding. An equivalent surface heat source derived from small-scale simulations enables efficient reservoir-scale thermal modeling without the need to resolve complex wellbore components. The proposed model, validated against experimental and field data, indicates that cement hydration can induce a hydrate-dissociation zone up to 15.3 m, whereas using only 5% MPCMs by volume for well cementing reduces this thickness by up to 81.7%. Key engineering parameters, including geothermal gradient, seawater depth, well geometry, and PCM properties, are systematically quantified to provide practical guidance for thermal management during deep-sea NGH well cementing.