Pipeline bundle system mainly consisting of carrier pipe, sleeve pipe, internal flowlines, bulkheads and towheads offers innovative solution for the transportation of oil and gas especially at higher pressure and high temperature (HP/HT). The pipeline bundle system resting on uneven seabed, crossing existing pipelines and terminating at rockdumped towheads introduces free spans, and seabed intervention design will be required. This paper presents the seabed intervention design methodology based on Finite Element Analysis (FEA). This gives the designer to exploit more opportunities to design the pipeline bundle both safe and cost effective. Pipeline bundle system is introduced first. Different seabed intervention strategies are addressed secondly. The in-situ behavior of the bundle system at rockdumped towheads and on uneven seabed is simulated over its through-life with focus on operating condition. Nonlinear FEA model for such a system is established in a realistic way using ABAQUS (HKS, 1999). Dynamic effect due to trawl board impact is investigated though the simulation. To demonstrate FEA based seabed intervention design methodology for pipeline bundle system, a practical example is given for a real life case. Based on the ABAQUS simulation results, seabed intervention design is carried out, design check against the acceptance criteria is performed. It is concluded that the FEA based seabed intervention can provide safe and cost effective solutions.
Pipeline bundle system has been in use for nearly two decades. This concept is currently finding favor in several HP/HT fields development, such as in North Sea and Gulf of Mexico. The main feature of such system is that multiple flowlines can be bundled together providing unique advantages including excellent thermal performance compared to conventional pipelines. The internal flowlines carry production fluids and are insulated to achieve better thermal performance. Outer pipe provides required buoyancy, mechanical and corrosion protection.
