Annular pressure buildup (APB) in high-pressure/high-temperature (HP/HT) deepwater wells can result in wellbore failure, even during drill-ahead operations. Manufactured to collapse at a specific pressure and installed on the external casing wall, syntactic foam is an economical solution to mitigate APB and protect casing strings in offshore HP/HT wells. This paper focuses on the modeling and simulation of the effects of syntactic foam deformation on APB in casing/tubing annuli.
Syntactic foam is a composite material synthesized by filling a polymer, metal, or ceramic matrix with hollow glass microspheres (HGMSs). Under increasing hydrostatic pressure (HCP), the behavior of the foam material can be described using a HCP-strain curve typically consisting of three regions: linear elastic, plateau, and densification. A multisection linear model was established to express the volumetric strain vs. HCP relationship, which significantly simplifies the APB calculation while still ensuring sufficient accuracy. Analytical correlations were developed for the elastic compressibility and collapse pressure vs. temperature, which can generate feed-in data for the multisection linear model when only limited datasets are available.
A workflow was developed for the simulation of syntactic foam effects on APB in HP/HT wells. The syntactic foam models were implemented and integrated into a commercial casing and tubing design software platform. In a simplified example well, numerical simulation results were found to be consistent with the results from analytical calculation. In a case study of an offshore HP/HT well, numerical simulation demonstrates that syntactic foam is a viable and effective option for APB management. Combined with thermal flow and APB simulators, the implementation of the syntactic foam models enables more accurate casing/tubing load analyses. APB simulation including the effects of syntactic foam can provide valuable information to assist well design engineers in the design of HP/HT deepwater wells with long-term well integrity.