Pressure Control Strategy of Coiled Tubing Blowout Preventer Control System

Hu Yaxuan WuWenxiu （School ofMechanical Engineering，Yangtze University）

Abstract：The wall of coiled tubing is relatively thin and its pressure-bearing capacity is limited.To avoid damage to coiled tubing or inabilitytoquickly nipof coiled tubing during theoperation ofthe blowout preventer，a control strategy for outlet pressure of blowout preventer control system was studied.To solve the problemof slow response and poor control accuracy inconventional PID control，fuzzy theory was combined with PID control technology to form fuzzyPIDcontrol，soas to improve the pressure controlaccuracyand response speed of thecontrol system.By means of building a mathematical model of electromagnetic relief valve- the main actuator in the control system，the MATLAB/Simulink simulations were used to obtain the step responses offuzzyPIDcontrol and conventional PID control respectively，and the results werecompared and analyzed.The study results show that the response speed of fuzzy PID control is 21.44 % faster，the accuracy is improved by 1.33% and the overshoot is reduced by 13% compared to conventional PID control，resulting in a significant improvement in control quality. The studyconclusions provide a new solution to pressure control of coiled tubing control system，making the action of the blowout preventer more reliable and faster.

Keywords： coiled tubing blowout preventer;control system；pressure control strategy；electromagnetic relief valve；PID simulation control model

0 引言

连续管带压作业一旦发生井喷事故将会带来巨大的经济损失，对环境产生不可逆的伤害，并且可能威胁现场工作人员的生命安全[]。为防止井喷事故的发生，作业时连续管须与防喷器配套使用。连续管平时卷绕在滚筒上，作业时需采用专用设备首先将其从滚筒上拉直，再经导向拱和注入头下入油井中，作业完成后又会被重新卷绕到滚筒上。由于频繁经历拉伸与卷绕，连续管容易发生低周疲劳失效。相对于常规油管，连续管管壁较薄，抗压能力相对较低[3]。随着作业井深或者作业难度的增加，连续管内部流体压力或外部地层压力也会随之增加，承受的应力更大，其结构稳定性可能遭受严重挑战。当防喷器闸板密封压力超调较大时可能导致连续管变形或破裂，进而造成井喷时不能顺利封井。为保证防喷器动作时既能快速封闭油管又不至于挤毁连续管，要求连续管防喷器控制系统必须具备较高的压力控制精度及快速的响应能力。

PID控制技术因其结构简单、稳定性好、工作可靠、调整方便而被广泛应用于各种工业控制[4]，既适用于已知数学模型的执行元件，又适合于难以获得准确数学模型的系统[5-6，但也存在响应偏慢、控制精度欠佳等问题。防喷器控制系统中压力调节与许多因素相关，仅采用PID控制器进行压力控制难以满足系统对精确性、快速性等方面的要求，由此还可能造成防喷器封井不严、无法剪断连续管、不能及时封闭油管等问题，甚至可能导致井喷等灾难事故。……