Preparation and performance evaluation of phase change material microcapsules for smart regulation of drilling fluid temperature for marine gas hydrate reservoirs

In the drilling process of hydrates, hydrate decomposition and regeneration can cause wellbore collapse and plugging. Herein, phase change materials (PCMs) were introduced into the drilling fluids to regulate their temperature for controlling hydrate decomposition. The binary composite PCM and polymethyl methacrylate (PMMA) were used to prepare PCM microcapsules (PCMMs) by suspension polymerization. Basic characteristics of PCMM were studied, and its temperature-regulating effect, inhibitory performance on hydrate decomposition and regeneration, strength, and compatibility with drilling fluids were systematically investigated. The phase change temperature of the binary composite PCM could be regulated from 16 to 20 °C through the optimization of the ratio of dodecanol and fatty alcohol. When the ratio of dodecanol was 90%, the phase change temperature of PCMMs was 18 °C with the enthalpy of 93.9 J⋅g −1 . In the heating process from 16 to 22 °C, 5% and 8% PCMM could smartly cool down the suspension through phase change energy storage to prolong the temperature rise time by 40% and 74%, respectively. Under the condition that the fluid temperature is from 2 °C around the seafloor to 25 °C at the bottom of the well in a simulation drilling process, in the heating period, 8% PCMM demonstrated superior efficacy compared to lecithin in prolonging the hydrate decomposition time by its cold release effect. In addition, the decrease in drilling fluid temperature was also hindered by the cold storage effect during the cooling stage, and the hydrate regeneration time was prolonged by 52.1%. Therefore, PCMM can reduce the risk of wellbore instability and plugging caused by hydrate decomposition and regeneration. Meanwhile, PCMMs exhibited good shearing strength and sealing property under alkaline conditions of drilling fluids and showed relatively minor impacts on the basic drilling fluid properties with a concentration of no more than 8%. This study offers a new method to maintain the safety of the hydrate drilling wellbore.