Effects of the mechanical properties of a cement sheath and formation on the sealing integrity of the cement-formation interface in shallow water flow in deep water

Abstract

The sealing integrity of cement sheaths is critical for the long-term stable and safe production of crude oil and natural gas. The temperature variation in wellbores may cause mechanical disturbances during production, causing the failure of the cement-formation interface (CFI) and sealing integrity. In this work, the cohesive zone method (CZM) was applied to study the effect of SWF caused by well-production disturbance on the CFI. Artificial simulation cores and traction-separation experiments were applied to acquire interface parameters required by the CZM. Based on ABAQUS, the effects of the elastic moduli and Poisson’s ratios of the cement sheath and formation and casing internal pressure on the initial failure pressure of the CFI were studied. The results showed that the initial failure pressure was important to ensure the integrity of the CFI, and once initial damage occurred in the CFI, the pressure driving the failure area to expand was much lower than the initial failure pressure. The elastic modulus and Poisson’s ratio of the shallow formation greatly influenced the initial failure of the CFI. The CFI was less likely to fail as the formation depth increased. Shallow water flow (SWF) had little effect on the cement sheath integrity after long-term curing. Furthermore, the simulation indicated that the elastic cement sheath contributed little to the resistance of the CFI to SWF.