Many cutting operations are necessary for tubular structures and the wellhead during platform decommission. Electric arc cutting technology for casing and wellhead inner cutting is presented in this study. The electric arc cutting system eliminates the plasma gas system and focuses only on high cutting efficiency given that this cutting operation has no requirements on dimensional accuracy. An arc ignition circuit that is different from traditional arc cutting power is introduced. This study aims to explore cutting performance, such as cutting efficiency and electrode wear. Several cutting parameters, including the working medium, electrode material, electrode diameter, cutting current, and workpiece thickness, are investigated by a series of experiments to analyze cutting performance. Cutting time and electrode wear rate are obtained to evaluate the cutting performance. The morphological features of the experimental results are also investigated. Results show that electric arc cutting technology can be employed to cut a workpiece effectively in sea water with a 4mm tungsten electrode. Cutting performance is affected significantly by cutting current and velocity. A 13 3/8inch casing is cut within 5min in the laboratory with optimal machining parameters, which allow for a good cutting effect.

Better exclusion of debris from the machined kerf is very important to obtain a stable machining performance in the EDM process. This research investigates the working fluid velocity and debris movement for the pipe cutting tool based on EDM. A computational fluid dynamics (CFD) model is developed to predict the working fluid field in the cutting kerf. The flow velocity at the transverse cross-section and longitudinal cross-section are all analysed and the debris moving trajectories are achieved. By using the CFD analysis, machining conditions, such as rotating speed, tool electrode width and tool electrode thickness will be analysed for more effective debris exclusion and high performance EDM. A series of experiments are executed to verify the CFD analysis results. And the results show that CFD results are reasonable and instructive for the actual pipe cutting process.

The effectiveness of a submarine casing cutting robot is mainly influenced not only by its operational but also by its reliability and safety. In this paper, fault diagnosis research of this cutting robot is evaluated using the Bayesian network. A methodology of transforming the fault tree model into Bayesian network model is used. The fault tree model is established simply and conveniently. Bayesian network can address interesting questions allowing both forward and backward analysis. Combining the merits of two methods, the causes of failures, the occurrence probabilities and the importance of various components are analyzed based on the Netica software. The results show that the robot has high reliability and should be paid attentions to the research of feeding mechanism and the discharge gap detection circuits.

The paper designs and develops a casing cutting robot for the platform decommission. This robot can achieve the sea-bottom casing reclamation duties required by the environment protection acts related to decommissioning of offshore oil plants. The objective of this research work was to investigate and explore the casing cutting robot model for the platform decommission. A 2-linear axis cutting robot is prototyped and a test bench is designed in the laboratory for the research. A surface control system provides remote control functionalities for the operator to command signals and automatic sequences. The robot control system based on Programmable Multi-Axis Controller (PMAC), which makes it easier to be operated. Moreover a Human Machine Interface (HMI) is developed to monitor and control the cutting process conveniently. The laboratory test results show that the robot system developed is very usable and it is working satisfactory for the casing cutting.

In view of the oil field by the use of the rod production equipment of intermittent oil caused by the low utilization rate of equipment,high power consumption,up and down stroke sucker rod in alternating load operation is not smooth etc.An efficient bidirectional pumping units and supporting the oil well pump was developed.For realizing wellhead continuous delivery,this pimping unit synchronously drives two sets of downhole pump backward movement in the up and down stroke.One pump is in oil pumping condition,another pump in oil absorption state in a cycle working period.Through the two sets of downhole pump synchronous backward movement,pumping unit work load smooth,continuous sucker small type large stroke,balance suction load improve work efficiency and equipment utilization purpose were achieved.Efficient double beam pumping unit and downhole supporting pump test prototype was made,through test,the reasonability and feasibility of the design were proven.

In order to develop the mobile robot for removing the plug oil well, the robot was designed based on the wheel-type and leg-type robot mechanism. A well functioning prototype has been manufactured. To demonstrate the validity and the benefit of the mobile robot, supporting mechanism and guiding rod were chosen to design based on the FEM. The mathematical model of the supporting mechanism is established and the mechanical property is analyzed using the FEM. The deformation and stress of some components of the supporting mechanism and the guiding rod is investigated. The results show that the supporting mechanism and the guiding rod have excellent performance with little displacement and small stress under working condition. The strength and rigidity of supporting mechanism and the guiding rod are good enough to ensure the reliability of the whole robot mechanism.

The deepwater electromagnetic valve directly controls the startup of the deepwater blowout preventer(BOP) stack in offshore deepwater drilling.It is the key equipment which ensures the safety and reliability of deepwater drilling.The high pressure of deepwater requires the valve to have desirable performance of high pressure resistance and sealing.The embedded design method was adopted to design a kind of electromagnetic valve which can properly work in over 3 000 m deepwater high-pressure environment.The deepwater electromagnetic control valve is designed within the main control valve and it does not contact seawater directly,which solves the problems such as high pressure resistance and sealing.In addition the design of the iron core and valve core has been integrated,improving the response speed of the valve.The electromagnetic valve of the deepwater BOP stack has been produced according to the design scheme and it has been verified by initial tests.The findings show that the valve can satisfy the requirement of application.

The mobile robot for removing the plug oil well is developed. And the robot has the merits of the wheel-type and crawling-type mechanism and can adapt to different oil pipe sizes. A well functioning prototype has been designed and manufactured. The mathematical model is established for the supporting mechanism which is one of important components of the robot. The deformation and stress of some components of the supporting mechanism is investigated by using the FEM. The components show excellent performance with little displacement and small stress under working condition. The strength and rigid of supporting mechanism is good enough to ensure the reliability of the whole robot mechanism.

Pipe cutting technology plays an important role in the process of offshore platforms decommissioning, as many devices such as tubing, drill pipe, and casing need to be decommissioned. In this study, a novel cutting pipe technology based on electro-discharge machining (EDM) is proposed, and a cutting pipe mechanism is developed to cut the pipes for decommissioning offshore platforms. The machining principles and characteristics of the technique are described. The effects of machining parameters, including tool polarity, dielectric fluid, electrode material and width, pulse on-time, pulse off-time, peak voltage, and electrode rotation speed to machining performance, are investigated. The material removal rate (MRR) of the machined casing and tool electrode wear ratio (EWR) is obtained based on the calculation of the percentage of mass loss per machining time. The experimental results show that a better cutting performance can be obtained with negative tool polarity at the conditions of dielectric fluid of emulsion, pulse on-time of 500 μs, pulse off-time of 200 μs, peak voltage of 70 V, copper electrode width of 28 mm, and electrode rotation speed of 250 rpm is a better choice. Additionally, the cutting slots surface has been investigated by the means of SEM. The cutting slots machined by the rotary EDM are clean and smooth.

分析了现阶段应用于海洋平台拆除的多种深海套管切割技术,主要包括聚能切割、化学切割、金刚石切割绳技术、磨料水射流技术和机械切割。介绍了几种典型的套管切割工具,即ND-S114型套管内割刀、井下电动切割工具、高聚能镁粉火炬切割系列工具、水力自旋式可控磨料射流切割装置以及深水井口头切割回收工具,并指出我国深海套管切割装置与国外技术存在的差距。对我国深海套管切割技术的发展提出了如下建议:引进新的切割技术、研制新型套管切割装置和实现切割工具的智能化。