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During oilwell cementing operations, many situations occur for which it is crucial to regulate the temperature of the cement slurry during and after its placement. Limiting the temperature increase of cement-based composite materials has been traditionally achieved by reducing the heat of hydration of the composite (e.g., through the use of supplementary cementitious materials or inert filling materials). However, the total amount of heat generated by a cement composite is primarily determined by the hydration extent of the cement, which has a strong correlation with the composite's strength development. Reducing the heat of hydration of oilwell cement through chemical means typically results in lower strength of the material, especially during early ages. This study investigates the application of a novel material, namely microencapsulated phase change materials (MPCMs), to regulate the temperature of oilwell cement using a physical method. The MPCM acts as an energy storage medium that absorbs heat when the temperature of the cement reaches the melting point of the PCM and releases heat when the temperature drops below its freezing/crystallization point. The solid polymer shell that encapsulates the PCM prevents the melted material from chemically interacting with the cement matrix. Hence, the strength development of the cement matrix is largely unaffected. Moreover, the set cement composite appears to be more elastic and less brittle because of the addition of the MPCM, which is beneficial to the long-term integrity of the cement. During this study, the heat evolution of cement slurries was investigated by both isothermal calorimetry and semiadiabatic tests. A similar amount of heat was generated by most slurries, as shown by isothermal calorimetry tests. However, results from semiadiabatic tests and compressive strength tests show that the slurry prepared with MPCM in a solid state exhibited minimal temperature increase and optimal mechanical properties (high-strength and high-strain capacity), which can be attributed to desirable properties of the PCM, including high latent heat, high specific heat capacity, as well as high elasticity. |
