Evaluation of the submarine debris-flow hazard risks to planned subsea pipeline systems: a case study in the Qiongdongnan Basin, South China Sea

The ever-increasing deepwater oil and gas development in the Qiongdongnan Basin, South China Sea has initiated the need to evaluate submarine debris-flow hazard risks to seafloor infrastructures. This paper presents a case study on evaluating the debris-flow hazard risks to the planned pipeline systems in this region. We used a numerical model to perform simulations to support this quantitative evaluation. First, one relict failure interpreted across the development site was simulated. The back-analysis modeling was used to validate the applicability of the rheological parameters. Then, this model was applied to forecast the runout behaviors of future debris flows originating from the unstable upslope regions considered to be the most critical to the pipeline systems surrounding the Manifolds A and B. The model results showed that the potential debris-flow hazard risks rely on the location of structures and the selection of rheological parameters. For the Manifold B and connected pipeline systems, because of their remote distances away from unstable canyon flanks, the potential debris flows impose few risks. However, the pipeline systems around the Manifold A are exposed to significant hazard risks from future debris flows with selected rheological parameters. These results are beneficial for the design of a more resilient pipeline route in consideration of future debris-flow hazard risks.