注氮辅助蒸汽吞吐工艺过程井筒爆炸事故分析方法

Analysis method of explosion accident in the wellbore during nitrogen injection assisted steam stimulation process

在注氮气辅助蒸汽吞吐开采原油的工艺过程中,由于地层条件复杂,存在发生油井爆炸事故的风险。以某油田注氮作业过程的井筒爆炸事故为例,结合现场调研和理论计算分析了事故的爆炸性质和点火源类型。通过对物理爆炸和化学爆炸的爆炸能量和爆炸压力进行理论计算,结合本次爆炸事故的总能量及井口装置的破坏压力,确定此次井筒爆炸事故类型为化学爆炸。此外,通过对比分析3种不同类型的点火源,确定此次井筒爆炸事故的点火源为注气速度过快导致油套管相互碰撞产生的碰撞火花。通过全面分析某油田井筒爆炸事故原因和性质,形成了一种系统性的井筒爆炸事故分析方法。

In the crude oil recovery process by nitrogen injection-assisted steam stimulation,oil well explosion accidents often occur because of the complex formation conditions.To avoid similar accidents,this paper takes the wellbore explosion accident in a block of an oilfield as an example,combined with field investigation and theoretical calculation to analyze the explosion energy and ignition source type of the accident.Concretely,the explosion energy of this wellbore explosion accident is estimated to be about 101.446 MJ by investigating the wellbore explosion site and collecting the quality and position information of the flying fragments.Moreover,by analyzing the explosion energy of the physical explosion and chemical explosion,it is found that the explosion energy is higher than the estimated explosion energy.But the explosion pressure of the physical explosion is about33.24 MPa,which is much lower than the failure pressure of the wellhead device.The explosion pressure of the chemical explosion is higher than the failure pressure of the wellhead device.Therefore,it can be inferred that the wellbore explosion accident is a chemical explosion.Besides,the volume fraction of combustible gas in the wellbore is about 7.1%,which is within the flammability limit.It further proves that the wellbore explosion is a chemical explosion.Through the theoretical analysis of the external heat source,electrostatic discharge,and mechanical collision,it is found that the temperature of steam injection is much lower than the ignition temperature of methane,the high-pressure gas in the wellbore needs a high breakdown voltage and the wellbore is well-grounded.Thus,the external heat source and electrostatic discharge are excluded.By estimating the spark energy of mechanical collisions,it is found that its energy is much higher than the ignition energy of combustible gas,and it is inferred that the ignition source of this accident is the most likely impact spark produced by the mechanical collision.In this paper,a systematic approach for wellbore explosion accident analysis is developed through a comprehensive analysis of the reason and property of wellbore explosion accidents in an oilfield.