Pre-alarming method, control method and control system for harmful flow pattern in oil and gas pipeline-riser system

A pre-alarming method for a harmful flow pattern in an oil and gas pipeline-riser system, comprising steps of:

• (1), through at least three pressure difference signals on the pipeline-riser system, continuously and rapidly identifying an overall flow pattern in the pipeline-riser system, and acquiring a non-dimensional mean value of each pressure difference signal;
• wherein:
• the pressure difference signals comprise at least one seabed pipeline pressure difference DP1 and at least two riser pressure differences;
• the riser pressure differences comprise a total riser pressure difference DP2 and a local riser pressure difference DP3;
• (2), with a seabed pipeline liquid slug formation mechanism and a first liquid slug formation position parameter, training a first support vector machine;
• and, with a riser bottom liquid slug formation mechanism and a second liquid slug formation position parameter, training a second support vector machine;
• and
• (3), if a non-dimensional mean value of the total riser pressure difference DP2 is smaller than 0.4, inputting at least three pressure difference signals into the first support vector machine and judging;
• if at least one sample is judged as an unstable flow pattern by the first support vector machine, issuing a pre-alarm and judging that a liquid slug is formed in a seabed pipeline;
• otherwise, not issuing the pre-alarm;
• if the non-dimensional mean value of the total riser pressure difference DP2 is larger than 0.4, inputting at least three pressure difference signals into the second support vector machine and judging;
• if one sample is judged as an unstable flow pattern by the second support vector machine, identifying three consecutive samples thereafter;
• if the three consecutive samples are all identified as unstable flow patterns, issuing the pre-alarm, and judging that a liquid slug is formed at a bottom of a riser;
• otherwise, not issuing the pre-alarm.