Unconventional oil and gas reservoirs have become a new focus of energy development due to their wide distribution and abundant reserves. However, the exploitation of these reservoirs is often accompanied by varying temperatures, which impose higher requirements for novel material, equipment, and technology. Recently, phase change microcapsules have been attracting increasing attention in oilfield applications, because they can absorb or release considerable latent heat during the phase change process, enabling stable temperature control. Herein, the current status and future development trend of phase change microcapsules in oilfield applications are reviewed. The classification of phase change materials, including solid-solid, solid-liquid, solid-gas, and liquid-gas phase change materials, is introduced, with an emphasis on their advantages and disadvantages. Then, the microencapsulation methods for phase change materials are presented. Next, the critical thermophysical properties of phase change microcapsules relevant to oilfield applications, including melting and freezing points, latent heat capacity, thermal conductivity, and cycling stability, are discussed. Subsequently, the specific applications of phase change microcapsules in oilfields, including temperature regulation of drilling fluid, thermal management of cement paste, thermal protection of drilling equipment, and thermal insulation of submarine oil and gas pipelines, are thoroughly overviewed. Finally, the critical challenges and future perspectives are outlined. This review highlights the critical role of phase change microcapsules in advancing thermal management solutions for the efficient development of oil and gas from high- and low-temperature reservoirs, guiding future research and development efforts.

Ocean gas hydrate is a potentially efficient and clean oil and gas alternative energy resource. Wells with complex structure, such as horizontal wells, can improve the extraction efficiency; however, drilling operations face challenges such as wellbore instability and reservoir damage due to the complex interaction between drilling fluids and hydrate reservoirs. This work presents a ceramsite temporary plugging microcapsule that uses ceramsite modified by 3-aminopropyltriethoxysilane as the core material and chitosan and sodium alginate as shell materials. It exhibits high strength during drilling and excellent plugging effects. After the action of bioenzymes, it can easily be dissolved, leading to high permeability post-drilling. The analysis and performance evaluation of ceramsite microcapsules show that their particle size is generally 40 μm, which can match the pore size of the hydrate reservoir depending on the number of encapsulation layers. Bioenzyme optimization at 15 ℃ yields the best permeability recovery of 74.5% for the low-temperature composite enzyme. As the temperature rises, the permeability recovery rate of ceramic microcapsules gradually increases and the difference in permeability recovery rate between 5 and 25 ℃ becomes more significant. With a longer degradation time, the permeability recovery rate of ceramsite microcapsules gradually enhances and the difference in permeability recovery rate becomes smaller after 12 h. The microcapsules exhibit a specific inhibitory effect on the decomposition of hydrates. Utilizing bioenzyme-responsive ceramsite microcapsules as temporary plugging materials can establish an “isolation barrier” around the wellbore, effectively sealing off the interaction between the wellbore and the gas hydrate reservoir during the drilling process. Re-opening the flow path around the well by bio-enzymatic unblocking at the end of drilling proves to be effective in solving the problem of balancing the stability of the well wall and protecting the reservoir.