Preparation and characterization of expanded graphite/modified n-alkanes composite phase change material for drilling in hydrate reservoir

During the process of hydrate reservoir drilling, the heat generated by friction in a horizontal well section leads to hydrate decomposition and affects the wellbore stability. Consequently, the low-temperature environment of subsea wellbores can cause hydrate regeneration and flow obstacles. In this study, modified n-alkanes (MNA) with an appropriate phase transition temperature and acceptable latent heat were synthesised, and the thermal conductivity was improved by adding nano-Cu. A composite phase change material (PCM) was prepared using expanded graphite (EG) with adsorbing MNA, and nano-silica modification to improve its hydrophilicity and stability. Structural properties of the composite PCM were characterised via scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and nitrogen sorption. The DSC curves revealed an acceptable latent heat capacity and reliability of the prepared composite PCM. In addition, by simulating the temperature heating and cooling during the drilling process, the composite PCM exhibited a reasonable thermoregulating and hydrate decomposition inhibition performance, which can effectively inhibit hydrate decomposition in reservoirs and hydrate regeneration in wellbores. Moreover, the composite PCM exhibited a reasonable compatibility with the drilling fluid. The study results can be applied to realise intelligent temperature control and reduce the risk of drilling in hydrate reservoirs.