Temperature disturbance of formation during the exploitation of hydrate
DONG Jingnan, BAN Fansheng, CHE Yang, QU Shuai, WANG Zijian, LIU Zhiqiang
1 CNPC Engineering Technology R&D Company Limited, Beijing 100081, China 2 College of Petroleum Engineering, China University of Petroleum, Beijing 102249, China
The phase transition occurs during the exploitation of gas hydrate, which will reduce the strength of sediment. Moreover, the endothermic effect during the dissociation of gas hydrate will lead to the temperature disturbance. Similar to the freeze/thaw process in porous media, the temperature of phase transition in pores is no longer a fixed value but is related to the pore size according to Gibbs-Thomson equation. During the phase transition process, heat is transformed no longer in the form of specific heat but in the form of latent heat, which does not alter the temperature. Considering these characteristics, a governing equation of heat conduction with phase transition was established; and the specific heat and latent heat terms were combined into an “equivalent heat capacity” term in the model. The relationship between ice content and temperature was assessed by the pore size distribution curve which was obtained from mercury intrusion porosimetry data. Considering a convectional boundary condition, the evolution of temperature in formation was simulated according to the governing equation. The temperature evolution curve was featured by a plateau regime. That is, temperature remains quasi-constant with time. The analysis demonstrates that the position and length of this temperature plateau is associated with the pore size distribution.
Key words：
gas hydrate; temperature disturbance; phase transition; equivalent heat capacity; convection boundary
