Research On The Electrical Arc Cutting Technology And Cutting Equipment For The Abandoned Offshore Platform Wellhead

As the offshore petroleum industry developed rapidly, more and more petroleum platforms are established in the ocean. Usually, the production life of platform is about 20 years. According to the related laws, platform must be decommissioned when it reaches the end of their production lives. In our country, the offshore petroleum has been developed since 1960. And a lot of platforms that reaches to their production lives must be decommissioned. The offshore platform decommissioning work in our country is mainly monopolized by several foreign oil companies. Therefore, it is an important task to research the new cutting technology and cutting device for our offshore petroleum engineering field.The decommissioning technology and device of offshore abandoned platform are investigated systematically and deeply in this paper. A new technology based on arc cutting for offshore platform decommissioning is developed firstly to overcome the shortcomings of the traditional technologies, such as low cutting efficiency, high cost. The technology explores the high temperature melting effect produced by arc discharge between tool electrode and casing to cut. The technology is not constrained by the materials hardness and solves the problems of low cutting efficiency, high cost, large cutting force, large vibration and serious tool wear for the traditional technologies.A downhole mechanical operation system based on arc cutting technology is developed. It contains the winch mechanism, rotating mechanism, supporting and locking mechanism, and tool electrode feeding and changing mechanism. The kinematic equations of supporting and locking mechanism have been established and the motion simulation has been analyzed. The results show that it runs stably and can provide enough locking force to ensure the stability of downhole mechanical operation system. The tool electrode feeding and changing mechanism has been investigated. The coaxial magnetic coupling sealing method is adopted to study the underwater motor seal. It realizes the tool electrode automatic feeding and changing during cutting process, avoids the problems of several times to trip in and off for changing knife, improves the cutting efficiency and reduces the operation cost sharply.The control system for arc cutting robot based on PMAC is developed. The hardware system, the software system, and the corresponding motion control programs are designed. It can complete the automatic control of actions and the real time detection of cutting signals during cutting process. Based on the value of arc cutting voltage and current, the control strategy of tool electrode moving is developed. And its feasibility and reliability is verified by experiments. The human machine interface is designed based on VB to realize human-computer interaction and real-time monitoring of cutting parameters.The moving arc cutting method is proposed and investigated by experiment research and theoretical analysis. It is revealed that the influence laws of working medium, electrode materials, electrode diameter, cutting current, cutting velocity and workpiece thickness on the cutting efficiency, electrode wear rate and cutting morphology. The results show that choosing these parameters reasonably can meet the casing cutting requirements and improve the cutting efficiency.A cutting parameters sensitivity analysis method based on design of experiment and Probability Design System(PDS) is proposed. The mathematical model and finite element model of initial cutting hole diameter and depth with cutting parameters is established respectively based on the response surface method. Three important parameters including cutting current, workpiece thickness, and electrode diameter are investigated the influences on the arc cutting effect. The results show that the theoretical analysis results are almost consistent with the experimental results.The simulation experiment platform of offshore abandoned wellhead is established. The casing cutting experiment is investigated. A 13-3/8inch casing with 10.92 mm wall thickness is cut in 5min using this device. The two modes of flushing liquid and gas are investigated to achieve the influence relations between cutting parameters and effect. Based on the heat conduction theory, the temperature model of electric arc cutting is established. The effects of cutting current on temperature distribution are achieved in the different working medium. The simulation results are compared with the experimental results. It is concluded that the simulation kerf width is more same with that of flushing liquid.