Research on Hydrate Risk Prediction in Deepwater Submarine Natural Gas Transmission Pipelines

Hydrates generation-blockage in submarine natural gas pipelines has always been related to the safety of deepwater natural gas production and transportation. However, the current hydrate formation risk prediction in subsea pipelines is still immature. In this paper, a model for evaluating the risk of hydrate formation in submarine natural gas pipelines has been established. The model has been applied and the sensitivity analysis of typical factors has been carried out. The results show that: (a) owing to the low temperature of the seabed, hydrate formation region (HFR) often exists in submarine pipelines. Avoiding HFR by injecting inhibitors is the key to ensure the safe transmission. (b) the decrease of gas temperature in the pipeline is determined by the heat loss of gas from inside to outside of the pipe. At a lower gas transport rate, the decrease of gas temperature is more significantly affected by the heat exchange rate. (c) at the same gas transport pressure and temperature, the pressure drop increases with the increase of gas transmission rate, while the temperature drop and the length of HFR decrease with the increase of gas transmission rate. (d) at the same gas transport rate and pressure, the pressure drop in the submarine pipeline is not significantly affected by the gas transport temperature, but the gas temperature at the end of the pipeline increases with the increase of the gas transport temperature and and the length of HFR decreases with the increase of gas transport temperature. (e) at the same gas transport rate and temperature, the temperature drop and HFR in the submarine pipeline is not significantly affected by the gas transport pressure, but the pressure drop loss decreases gradually with the increase of gas transport pressure. (f) reasonable setting of gas transport temperature and gas transport rate can help to reduce the hydrate risk and consumption of inhibitors in the submarine natural gas transportation. Accurate prediction of hydrate risk in deepwater submarine pipelines is essential for safe gas transportation. The research provides the theoretical guidance for safe and efficient natural gas resources development and transportation.