Abstract: To study formation of hydrates during deepwater oil/gas flow assurance, development data of an offshore oilfield in Angola, West Africa, are used with OLGA software to numerically simulate formation of hydrates in subsea flowline, riser and borehole. The results show that, under specific oil compositions, productivity variations and pre-determined node temperatures/pressures, the temperatures and pressures in the pipelines and boreholes are outside of the extent for formation of hydrates, implying extremely low risks related to formation of hydrates. With the increase of watercut, both internal pressure and overall pressure drop of pipeline increase, and internal temperature increases, while overall temperature drop decreases. With the increase of gas/oil ratio, internal pressure and overall pressure drop both decrease, and internal temperature decreases, while overall temperature increases. The analysis from the oil flow composition and working conditions shows high salinity in produced water of the reservoir, which inhibit formation of hydrates.