A Calculation Model for the Temperature Field of the Shallow Submarine Strata Considering the Heat of Hydration of Cement Slurry

Abstract

Abstract During offshore oil and gas resource exploration, the large amount of heat generated by cement hydration will cause the hydrates around the wellbore to decompose, leading to cementing operation failure or more serious types of accidents. Therefore, the influence of the heat on temperature of hydrate layer, overlying and underlying strata during the cementing process is studied in this paper. A calculation model for the temperature field of deep-water hydrate layer cementing is established. The model considers the influence of cement slurry hydration heat release, hydrate decomposition, and heat transfer between hydrate layer, overlying and underlying strata on temperature distribution of the hydrate layer, overlying and underlying strata. Using MATLAB language programming, the partial differential equations were solved by the difference method, and numerical simulations were carried out through simulated wells. The temperature distribution of drilling fluid, cement slurry, hydrate layer and strata during the deep-water cementing process is calculated. Through analysis, the following conclusions are obtained: 1. The cement hydration in the cementing process generates a lot of heat, which severely destroys the stable temperature and pressure conditions of the hydrate layer and causes a large amount of decomposition of the hydrate; 2. The decomposition of hydrate is a long-term process comparing with the cement hydration process. Therefore, the decomposition of hydrate during the cementing operation and for a period of time after completion will bring safety threats to the drilling and completion operations; 3. Considering the heat transfer between hydrate layer, overlying and underlying strata is more accurate to reflect the temperature change of the hydrate layer during the cementing process than only considering the heat exchange between the cement column and the hydrate layer; 4. Reducing the volume of the annulus between the conductor casing and the surface casing can effectively reduce the heat of hydration of the cement slurry, which is beneficial in order to reduce the impact of hydrate decomposition, so it is recommended to use a casing combination with a smaller annulus in the cementing through the hydrate layer. The models studied in this paper can more accurately predict the deep-water cementing temperature field of hydrate layers, provide safety guidance for cementing design in deep-water hydrate layer cementing operations, and lay a foundation for deep-water drilling stability studies.