During the exploitation of offshore oil and gas

it is easy to form severe slugging which can cause great harm in the riser connecting wellheads and offshore platform preprocessing system.The flow pattern and pressure fluctuation of severe slugging were studied in an experimental simulation system with inner diameter of 0.051 m.It is found that severe slugging can be divided into three severe slugging regimes:regime I at low gas and liquid flow rates with large pressure fluctuation

intermittent flow of liquid and gas in the riser

and apparent cutoff of liquid phase

regime Ⅱ at high gas flow rate with non-periodic fluctuation and discontinuous liquid outflow and no gas cutoff

regime ⅡI at high liquid flow rate with degenerative pressure fluctuation in form of relatively stable bubbly or plug flow.The results indicate that severe slugging still occurs when the declination angle of pipeline is 0

and there are mainly two kinds of regimes:regime I and regime Ⅱ.As the angle increases

the formation ranges of regime I and regime ⅡI increase slightly while that of regime Ⅱ is not affected.With the increase of gas superficial velocity and liquid superficial velocity

the pressure fluctuation at the bottom of riser increases initially and then decreases.The maximum value of pressure fluctuation occurs at the transition boundary of regimes I and Ⅱ.