Use of Distributed Buoyancy as Lateral-Buckle Mitigation in High-Pressure High-Temperature Flowlines

The use of distributed buoyancy modules as a lateral buckle mitigation device in High-Pressure High-Temperature (HPHT) flowlines requires consideration of a range of parameters to ensure a successful solution. An investigation into several of these parameters and their impacts on lateral buckling behavior is explored. Buoyancy module spacing, the submerged weight in buoyancy sections, the buoyancy section configuration and length, and soil-pipe interactions at end modules are explored via the finite-element method. Sensitivities on these parameters for a single pipe diameter are explored as they relate to the lateral buckling behavior and associated industry-imposed limit states. A rigid 8-inch HPHT production flowline is investigated for each of the parameters described. Finite-element models are used to investigate the lateral buckling behavior in virtual-anchor-spacing (VAS) models. The VAS modeling of various distributed-buoyancy system parameters provides results that confirm the importance of adequately assessing these parameters in the design process. VAS modeling demonstrates that buoyancy-module spacing, and buoyancy-section submerged weight, configuration, and length can all materially impact lateral buckling behavior and flowline integrity. It is found that each of these parameters needs to stay within a certain range for satisfactory performance, based on industry guideline VAS acceptance criteria and model stability, and going outside that range can yield unreliable and potentially risky lateral buckling behavior. Ranges for the various parameters used in the design of distributed buoyancy sections are offered that will help ensure a robust and reliable distributed buoyancy solution.