Abstract: In order to study the coupling form of risk in deepwater oil and gas transport systems, evaluate them and ensure the safety of oil and gas transportation, three types in risk groups of deepwater transport system were considered,and a risk flow diagram of deepwater oil and gas transportation system was build by SD theory. Coupling relationships between the risk factors were examined, and their weights were determined by using the entropy method on the basis of the relationships, then, a nonlinear coupling model was bulit for the risks in the system . The model was used to calculate coupling degrees and the values of the risk groups. A certain deepwater oil and gas field in China was taken as an example. The results show that for the internal non-conventional flow risk system, the external environmental risk system, and the pipelines risk system,the internal non-conventional flow risk system has the highest integrated risk value,and the pipelines risk system gets the largest volatility of two-factor coupling, the risk of coupling between the pipeline risk system and internal non-conventional flow risk system is the greatest.

Key words: deepwater oil and gas transportation system, risk group, system dynamics(SD), nonlinear coupling model, coupling system