Numerical simulation of the stability of hydrate layer during well cementing in deep-water region

Abstract

Well cementing aids in enhancing wellbore stability and provides zonal isolation during the exploration of oil, gas, and hydrate energy. However, cementing a well through hydrate layer is problematic. The heat generation from cement hydration leads to the dissociation of the hydrate around the wellbore, resulting in cementing operation failure or serious safety accidents. Current studies seldom focused on the stability of the hydrate layer during well cementing. Therefore, a transient thermal model of cement column is established in this study on the basis of cement hydration kinetics model. On this foundation, a coupled model between the cement column and hydrate layer is established given the interactions between temperature field, hydrate layer, and cement hydration reaction. The transient thermal model of cement column is verified through a field test and the thermal model of hydrate layer is verified by an experiment, which exhibit good agreement. Based on the simulation results conducted in this paper, the total heat generation during cement hydration reaches 198,247 kJ/m, which leads to the dissociation of 9.84×104kg hydrate. The hydrate dissociation is a significantly longer process when compared with the cement hydration process. Thus, the safety threats posed by hydrate dissociation exist during well cementing and also for a long time after well cementing. Additionally, the results suggest that the use of a casing with a higher diameter significantly reduces the hydrate dissociation. The conclusions and suggestions of the study can aid in troubleshooting problems and optimizing the cement operation in the hydrate layer.