An analytical solution to simulate the effect of cement/formation stiffness on well integrity evaluation in carbon sequestration projects

• An analytical solution was proposed and programmed for the cement sheath integrity along the critical section of wellbore.
• Young's modulus of cement sheath is identified as a major factor that affects the sealing ability of cement sheath.
• The sealing ability of cement sheath in shale formation is higher than that in the sandstone formation.
• Weak cement has better sealing ability than strong cement.
• The critical failure point lies at the top of sandstone formation.

Cement Sheath integrity has been gain more attention due to the increase of carbon sequestration activities in the recent years. Sealing ability of cement sheath can be lost because mechanical disruption in the CO2 injection wells. Cement sheath mechanical failure can occur in the CO2 injection wells. This paper proposes an analytical solution to address this issue. Cement sheath and formation rock stiffness are considered in the proposed model to simulate the cement sheath sealing ability on different depth of the formation. Both mechanical properties of cement and formations are evaluated and analyzed. Real field example is also provided. Young's modulus of cement sheath is identified as a major factor that affects the sealing ability of cement sheath. The sealing ability of cement sheath in shale formation is better than that in sandstone formation. Weak cement has better sealing ability than strong cement. The critical failure point lies at the top of sandstone formation. This model can also be used to design and optimize the cement system of new CO2 injection wells in carbon sequestration projects.