A fluid-solid coupling model of wellbore stability for hydrate bearing sediments

Wellbore stability decides the success or failure and the cost of oil or gas drilling. It is more complicated for gas hydrate bearing sediments (HBS) because of the special properties of gas hydrates. Considering the key influence factors of wellbore stability, such as heat conduction and convection, hydrates decomposition, the variation of physical and mechanical parameters, and the coupling effect among them, the mathematical model of wellbore stability for HBS was established. The finite element solution was obtained. Taking a hydrate formation of Gulf of Mexico as an example, the influence of drilling fluid temperature on hydrates decomposition, formation mechanical properties and wellbore stability was studied. Analysis shows that formation mechanics properties become worse sharply with the thermal decomposition of hydrates, and this easily results in the instability of the formation. Choosing low temperature drilling fluid can do help to wellbore stability of HBS, and to realize safe drilling.