Research and development of compressible foam for pressure management in casing annulus of deepwater wells

Casing annulus pressure build-up owing to fluid thermal expansion in sealed annuli severely threaten the casing safety and wellbore integrity of deepwater wells. To mitigate the annular pressure with stronger effect and lower cost, a new type of syntactic foam with high compression ratio, which consists of hollow glass microspheres and a resin matrix system, was developed in this study. It can provide extra space for the annular fluid to expand when the annular pressure exceeds the specific foam crush pressure, allowing the foam to collapse and consequently, mitigate the annular pressure. The foam compression behavior is divided into three stages according to a hydrostatic compression test, and the annular pressure is mainly influenced by the microspheres volume and temperature. To optimize the parameters of the compressible foam, a novel model considering fluid thermal expansion, casing elastic deformation, and foam compression behavior in multi-annuli is established. The results indicate that the compressible foam can reduce the trapped annular pressure effectively and permanently. In a case study well, the annular pressure no longer exceeds the maximum acceptable annular pressure in each annulus with optimized design of the foam wraps and a suitable number of installed foam casing joints.