Preparation of boron nitride reinforced epoxy phase change microcapsules for the cementing of natural gas hydrate layers
Xiaohua Li, Miaomiao Hu, Qiang Wang, Ming Liu, Jianwei Wang, Yongxu Xie, Jintang Guo
Abstract
Phase change microcapsules can reduce the exothermic hydration of cement paste and avoid natural gas hydrates decomposition during cementing in deepwater fields. Phase change microcapsules with low heat storage efficiency can lead to excessive reduction in the early compressive strength of cement stones due to the high mass fractions and the huge difference in strength with cement. Phase change microcapsules (MBPCM) with high thermal storage efficiency were prepared by emulsion polymerization process using epoxy resin as the shell. Introducing hydrophobically modified boron nitride (BNVT) can improve the energy storage efficiency of microcapsules. The produced MBPCM had a typical core-shell structure with an average particle size of around 716 nm and a shell thickness of about 23 nm. According to the experimental findings, the phase change enthalpy of the microcapsules was 185 J/g. The supercooling temperature of MBPCM containing 5 wt% BNVT was only 0.70°C, and the thermal conductivity was improved by about 131.0 %. The incorporation of 7 % MBPCM into cement resulted in a notable reduction of 12.23°C in the hydration temperature of the cement, alongside a substantial decrease of 46.9 % in the exothermic heat of hydration. Moreover, MBPCM improves the dispersion of the cement paste and reduces the porosity of the cement stone, resulting in a 6 % increase in the compressive strength of the cement. The prepared microcapsules effectively reduced the exothermic heat of cement hydration, avoided the decomposition of natural gas hydrates, and improved the safety of extraction.