Laws of Hydration Heat of Cement and Hydrate Stabilization in Shallow Formations of Deep Seawater.

When cementing is required in marine deepwater hydrate formations, the heat released from the hydration process of oil well cement can easily lead to hydrate decomposition. It is necessary to clarify the initial phase transition temperature of the hydrate layer under the influence of cement waiting for setting so that it can meet the stability of the hydrate layer during cementing. In this paper, based on the actual conditions of offshore deepwater cementing, the coupled temperature field model of cement sheath hydration heat source-well wall hydrate decomposition is established by considering the hydration heat release during the cement waiting process and the phase change heat absorption of the well wall hydrate. Combined with the established model, the hydrate formation in the deepwater region of the ocean was selected and matched with suitable oil well cement for simulation. Through simulation, the critical temperature range (291-295 K) for the initial phase transition of the hydrate layer at 10-15 MPa was clarified and the relationship between the critical values of cement hydration heat release to maintain hydrate stability at different initial temperatures of the formation was established. The phase stability law of hydrates in the formation under cement sheath hydration heat release was revealed, providing a theoretical basis and guidance for the development of low-hydration heat release cement slurry systems.