Numerical Simulation of Interfacial Sealing Failure at Cement/Formation Bonding Caused by Heterogeneous Filter Cake on Wellbore Wall

Summary The filter cake remaining on the wellbore wall during cementing can significantly compromise the sealing integrity at the second interface between the cement sheath and the formation, potentially leading to annular flow and wellbore integrity failure. To elucidate the mechanical mechanisms underlying this failure, we developed a 3D finite element model of a casing/cement-sheath/filter-cake/formation composite system. Based on the bilinear cohesive zone method, this model utilizes Python for the secondary development of Abaqus and for the first time constructs the filter cake as an independent heterogeneous layer with randomness. Simulation results indicate that the heterogeneous filter cake alters the stress distribution within the cement sheath, leading to stress concentration and localized interface damage. When the filter-cake thickness exceeds 2 mm, full interface debonding and asymmetric microannulus propagation along the maximum horizontal principal stress direction are likely to occur. The introduction of specific additives forms a cured interfacial layer with low elastic modulus and high yield strength, effectively reducing interface damage and microannulus size. Enhancing the bonding strength between the filter cake and the cement sheath maintains interface integrity even under internal pressures of up to 90 MPa. This study provides a valuable theoretical basis for optimizing the preflush fluid system—especially through filter-cake thinning and modification—laying a foundation for ensuring the long-term sealing performance of oil and gas wells.