Investigation of multi-field coupling mechanisms during well cement through gas hydrate layer in horizontal well

Exploitation of natural gas hydrates from horizontal wells can significantly improve the production rate and final recovery. However, the long interaction surfaces of horizontal wells may easily disturb the hydrate reservoir. Cement hydration in wellbore is an exothermic reaction, which may lead to the premature dissociation of hydrate, thereby threatening the wellbore integrity. In the present study, experimental and numerical investigations are carried out to analyze the cement hydration in a wide range of temperatures. Then, a coupled model is established considering the multi-field coupling mechanisms between horizontal wells and the hydrate reservoir during well cementing. In the proposed model, the cement hydration, phase change of hydrate, and the multiphase flow in porous hydrate layer are considered. The cement hydration process, transient temperature and pressure distributions, and the hydrate phase change are analyzed by numerical simulations. Results show that the temperature of wellbore and hydrate increases rapidly. The saturation of the hydrate layer within the region 3 times of wellbore diameter decreases significantly. The pressure at the wellbore-hydrate layer interface increases significantly, which may lead to gas penetration into the wellbore. Moreover, threats imposed by the premature dissociation of hydrate last even for a long period after well cementing.