Gas hydrate dissociation would damage the cementing quality seriously due to the hydration exothermic of cement slurry. Therefore, the well cement slurry with low hydration exothermic is necessary.
The design of well cement slurry with low hydration heat mainly includes three steps. First, high-strength metakaolin-based hollow-core microspheres (HMHM) were prepared. Second, phase change materials (PCM) was applied for encapsulating HMHM to form energy storage microsphere (ESM). Finally, the hydration heat of well cement with different dosage of ESM were tested, and the strength, rheological property, sedimentation stability and other basic properties were also evaluated.
Hydrate reservoirs with high pressure and low temperature are distributed in offshore deep-water areas (Ravi, 1999; Armstrong, 2002). In the process of deep-water cementing, the temperature around the wellbore increases due to the heat release of cement slurry hydration, which destroys the stability of natural gas hydrate (Wang, 2019). The decomposition of natural gas hydrate will seriously damage the cementing quality (Xu, 2005). Paraffin is a phase change materials, which can effectively reduce the hydration heat release of cement, but paraffin can not be directly added to cement. Therefore, HMHM were introduced as new energy storage microspheres to carry PCM to avoid its directcontact with the cement slurry.
The hollow microspheres were prepared by inverse suspension polymerization, which regarded metakaolin as raw material and regarded alkali solution as activator. Metakaolin was provided by Yukun Mineral Company, Jiaozuo, China. Sodium hydroxide and sodium silicate were provided by Xilong Science and Technology Co. Ltd. and Guangzhou Julan Chemical Co. Ltd. PCM-30 (variation range of phase transition temperature: 15-40 °C) is a thermally stable and reliable oily hydrocarbon (No degradation occurring below 100 °C and continuous melting and freezing cycle shown), which has high phase transformation latent heat storage capacity (189 J / g). Its latent heat and temperature remain unchanged after multiple endothermic and exothermic processes, and there is no phase separation and corrosivity. Waterborne bisphenol A epoxy resin (ER) and waterborne polyamine epoxy curing agent are produced by Shanghai Hanzhong Coatings Co. Ltd., China. Class G oil well cement (600 mesh) is produced by Sichuan Jiahua Special Cement Co. Ltd. The specific surface area of Class G oil well cement is 332 m2 / kg, and the density of cement powder is 3.1g/m3. Micro silicon (1000 mesh) was provided by Po Ken International Trading Company, Shandong province, China, and floating beads (6000 mesh) from Maanshan Institute of Mining Research, Anhui province, China. Fluid loss additive (polycarboxylic acids) and dispersant (sulfonated aldehydes and ketones) were provided by BO-XING engineering science and technology company of CNPC, Tianjin, China.
