Annular pressure build up (APB) is caused by thermal expansion of wellbore fluid enclosed in an annulus experiencing cyclic thermal loads due to production and injection. This may lead to significant damage to the cement sheath causing zonal isolation issues and may also cause casing collapse/burst. This work focuses on using an engineered approach based on finite element modeling to analyze the cement sheath response to APB loads for the life of the well. Actual field data of pressure build up and bleeding rates are used in our analysis.
The present study provides a methodology to analyze cement systems for their ability to survive APB conditions. A proper knowledge of response of wellbore materials (cement and casing) to APB can be helpful in design of better cement systems and in selection of appropriate casing materials which can withstand the APB conditions.
It has been observed from our comparative study of two cement systems that the stresses in the elastic cement are less than those in conventional cement. A parametric study has also been performed to analyze the effect of different cement properties. The results are quantified in terms of stresses experienced by cement sheath and casing.
This study is based on fundamental principles of structural mechanics, thus providing more reliable predictions. It helps in deciding the appropriate cement system for a predetermined production/injection rate or can give a recommendation of production/injection rates for a given cement system such that damage to the cement sheath can be avoided.