The Elimination Methods And Control Technology Of Subsea Severe Slugging

During the process of the offshore oil and gas exploration, inclined pipeline-riser system is needed to transport the mixer of oil and gas to the center processing platform. The severe slugging will appear at the low speed of oil and gas velocity. This flow pattern will lead to a lot of problems to the design of the gathering system and production. This paper did the research of the characteristics, control strategy and elimination methods of severe slugging.Propose a new method to distinguish the flow patterns of severe slugging using the difference of the pressure fluctuation curve. The typical severe slugging includes four phases, but the inordinate severe slugging will blow out as soon as the slug reaching the top of the riser without the phase of slug flowing out. The amplitude of the pressure fluctuation is related to the minimal pressure, one eliminates and the other replaces it. The blow-out velocity of severe slugging could reach 23-35 times of the inlet velocity. During the blowing out of the slug, the pressure curve of the middle of the riser will sharply rise up, then rapidly drop down. There are two necessary conditions for this phenomenon, one is that there must be plenty space for the gas accumulation; the other is that the slug has reached a high speed, but the tail of the slug does not pass the pressure tap.Establish a quantitative description between the opening of the valve and the process of severe slugging. Indicate that the volume of the separator is related to the property and the adjustment of the valve. It is very effective to select the appropriate valve to decrease the separator volume. Provide a model of the valve selecting. A dynamic model for control of separator liquid level and pressure using classical control techniques is developed in this paper. This model is very necessary for the operation under severe slugging conditions. Detailed analysis of the dynamic model showed that the system stability and transient response could be ensured by appropriately designing the controller and control valve characteristics. A control valve in the gas outlet for any inflow condition could achieve separator pressure control. Based on the proposed linear control system model, a sample control system design is developed and the system transient response is simulated using suitable software. Finally a design framework for implementation of separator control system using a simulator is presented.Auto-Pumping method was proposed to eliminate severe slugging. Severe slugging could be eliminated virtually by the new method, and the range becomes smaller. This method could not only reduce the fluctuation of pressure, but also decrease the pressure of the pipeline system at low speed, so the pressure of the well head will decreased too. This will lead to the result that increasing the efficiency and product more oil and gas in a shortest time. The self-priming of the pump will greatly influence the efficiency of the method. Propose that the submersible pump could be used in the oilfield.