Natural gas hydrates are a key resource for enhancing energy security and supporting the low-carbon transition in countries along the Maritime Silk Road. During drilling in hydrate-bearing formations, heat transfer from the drilling fluid to the formation is the main factor driving reservoir hydrate dissociation and borehole wall instability. To maintain stability in hydrate-bearing formations during drilling, a treatment agent was developed to regulate the temperature of the drilling fluid in the wellbore and reduce heat transfer from the fluid to the hydrate reservoir. To meet current engineering requirements for natural gas hydrate drilling and production, a high phase-change latent heat n-alkane was chosen as the core material, while environmentally friendly sodium alginate and carboxymethyl cellulose served as shell materials. Using a physical cross-linking mechanism, microencapsulated phase-change cold-storage materials with a core–shell structure (phase-change microcapsules (PCMCs)) were produced via an electrostatic spraying technique.

This method allowed precise control of droplet formation and solidification, facilitating accurate adjustment of microcapsule size distribution. The microstructure and surface morphology of the PCMCs were analyzed by scanning electron microscopy and a focused beam reflectance measurement system, while laser particle-size analysis determined their particle-size distribution. Differential scanning calorimetry was employed to study the phase-change behavior, latent heat properties, and thermal cycling stability of the PCMCs. Additionally, a thermal conductivity analyzer and a high-pressure natural gas hydrate evaluation system—capable of simulating hydrate reservoir pressure–temperature conditions—were used to systematically assess the thermal insulation capabilities of the PCMCs and their inhibitory effect on hydrate decomposition.

Results demonstrated that the PCMCs maintained an intact spherical capsule shape with a clear core–shell interface, and had a particle size distribution ranging from 5.7 to 50.09 μm, with a median diameter of 21.26 μm, meeting the operational demands of offshore drilling. Moreover, the phase-change melting temperature was 13.88 ℃ with a latent heat of 171.51 J/g and an encapsulation efficiency of 89.5%. After 30 heating–cooling cycles, the PCMCs retained 90.6% of their initial latent heat, indicating excellent thermal reliability and suitability for repeated use during drilling, which helps lower operational costs. When added to drilling fluid, the PCMCs reduced the system’s bulk thermal conductivity by approximately 13%, extended the time to reach the target temperature by 26.3%, and decreased hydrate decomposition rates by 12.57% compared with the control fluid. Ultimately, these PCMCs effectively inhibit reservoir hydrate dissociation by lowering the thermal conductivity, slowing heat transfer from wellbore fluid to the formation, and absorbing heat during phase change to mitigate temperature increases.

This research has been applied in China’s third offshore natural gas hydrate trial production campaign, providing a theoretical basis and technical support for future development and utilization in hydrate-rich countries like Pakistan and Indonesia. It is also expected to promote further technical exchange and cooperation in gas hydrate exploration, development, and wellbore integrity among countries participating in the Belt and Road Initiative.