Study On Speed Control And Pressure Management Of Subsea Pump For Riserless Hydrate Drilling

Although the reserves of marine hydrate are abundant,due to the harsh burial environment,exploration and development of marine hydrate face the dual challenges of deepwater drilling and hydrate drilling,which seriously affects the application of conventional drilling technology in marine hydrate drilling and limits the development of marine hydrate.Riserless drilling as a dual gradient drilling technology can well solve the problems faced by marine hydrate drilling and realize safe and efficient marine hydrate drilling.In this paper,on the basis of the research of subsea mudlift drilling technology in our research group,the study on speed control and pressure management of subsea pump for riserless hydrate drilling was carried out.This thesis is mainly focused on following aspects:(1)Riserless pressure management drilling for marine hydrateIn terms of the marine hydrate accumulation environment,difficulties faced by marine hydrate drilling were analyzed,and the methods of marine hydrate drilling were studyed.Combined with marine hydrate drilling technology and dual gradient drilling technology,the safety drilling technologies which can be used in marine hydrate drilling were compared to optimize marine hydrate drilling mode,the scheme of riserless pressure management drilling for marine hydrate was proposed.Aiming at the deep water operation environment,the structure of suction module,the key equipment of drilling system,was optimized.According to the equipment characteristics of drilling system for riserless drilling,the installation process of drilling system was proposed.(2)Study on configuration and layout of subsea pump moduleBased on the power-law fluid rheological model,the pipeline characteristic equation of mud return system was derived,the calculation method of configuration parameters for subsea pump module was proposed.In terms of the working condition of 1500 m water depth,the configuration scheme of subsea pump module was determined.Based on the mechanical energy equation of solid-liquid mixture,the maximum installation height of the upper subsea pump unit was solved.The method for optimizing installation height was proposed,which comprehensively considering the pressure characteristics and mechanical characteristics of mud return system.The structure of the key equipment for mud return system was designed,the layout scheme and anchoring scheme of mud return system were determined through the analysis of mechanical properties.(3)Study on speed regulation technology of series subsea pumpsThe speed regulation model based on proportion law and the speed regulation model based on dimensionless flow-head characteristics were established.Based on the speed regulation experiment of subsea pump,the speed regulation accuracy of two models was compared,the best speed regulation model for subsea pump was determined.The numerical solution method for speed regulation of series pumps was proposed,through the analysis of speed regulation performance,work efficiency and energy saving effect of subsea pump module,the speed regulation scheme of subsea pump module was determined.The speed regulation simulation model of subsea pump module was established,through the simulation of variable speed flow regulation,the superiority of speed regulation scheme of subsea pump module was verified.(4)Early overflow monitoring and well control decision for normal drilling conditionBased on the analysis of normal drilling condition of riserless drilling,the variation characteristics of drilling parameters in early overflow were studied,the identification signals of early overflow were determined.The calculation model of gas-liquid two-phase flow in wellbore was established to reveal the variation law of drilling parameters in early overflow,the early overflow monitoring parameters were optimized,and the early overflow monitoring scheme was developed.Based on fluid flow equation in wellbore annulus,the early overflow control method for riserless drilling was studied,and automatic control decision-making process for early overflow was proposed according to the overflow treatment capacity of different well control measures.