The Effects of a New Phase Change Material on the Properties of Low Heat Cement Slurries

When cementing wells drilled in low temperature deep water zones, cement slurry should give off less heat during hydration process to minimize the increase of temperature of the formations with natural gas hydrate. A new phase change material has been developed for use in low heat cement slurries used to cement wells penetrating formations with gas hydrate. The heat storage performance of the phase change material and its effects on the properties of cement slurry were studied. Laboratory experimental results showed that the peak temperature at which phase change takes place was 15.5℃ for the new phase change material. This temperature sits between downhole low temperatures and ambient temperature, and the latent heat of phase change was high. At temperatures below 77.8℃, the phase change material had good thermal stability. No change to the chemical structure of the phase change material ever happened after the phase change material had undergone many times of temperature fluctuation between 0℃ and 60℃. The rheology of the cement slurry increased with an increase in the concentration of the phase change material. Increasing the concentration of the phase change material to 8% did not affect the ability of the cement slurry to satisfy the needs of well cementing. Furthermore, the new phase change material helped improve the stability of cement slurry and only slightly affected the compressive strength of the low heat cement slurries. A low heat cement slurry treated with 8% of the new phase change material had set cement with compressive strength of 8.9 MPa, and the decrease of the compressive strength was less than 5% at most. When added 2%, 4%, 6% and 8% new phase change material into a cement slurry respectively, the thickening time of the cement slurry was 15 min less than that of the cement slurry without the new phase change material (the blank cement slurry). The 72-hour heat of hydration of the four cement slurries were reduced by 5.2%, 29.1%, 35.6% and 47.6% than the blank cement slurry, respectively. This study has provided a technical support and reference to the design of low heat cement slurry for use in cementing wells penetrating formations with natural gas hydrate.