Design And Control Strategy Research Of Ocean Drilling Drawworks Heave Compensation System

Heave compensation equipment is an important device of offshore floating drilling system.It is used to mitigate the adverse effect of platform heave movement on drilling operation.The research of heave compensation system started early at abroad,so foreign countries have monopolized on this technology for a long time.Several universities and research institutes at home are still at the stage of theoretical research,analog simulation,prototype development and experimental study.According to the way of power supply,heave compensation system can be divided into passive,active and semi-active compensator.According to the installation position and working principle,heave compensation system can be divided into compensator mounted between travelling block and hook,crown block compensator and drawworks heave compensator.Compared with other compensation ways,active drawworks heave compensation system developed overseas in recent years has the features of high efficiency,simple transmission,compact structure,low center of gravity,less platform load,less space occupation and unrestricted compensation stroke.As a result,it's highly valued in oil machinery industry and relevant enterprises at home have begun to study the darwworks heave compensation technology.Based on the analysis and summaries of foreign advanced technology,a new type of semi-active drawworks heave compensation system program is put forward in this thesis.Through comparative evaluation,theoretical analysis,computer simulation,experimental research and other ways,this paper conducted an in-depth study of this program,so that it can simplify the offshore drilling rig structure,improve compensation accuracy,reduce compensation energy consumption,improve system adaptability to different sea conditions and working conditions,and accelerate the localization process of drawworks heave compensation device.In the developed offshore floating drilling semi-active drawworks heave compensation system,2K-H type differential planetary gear train with characteristics of dual power input, single-output of are used to control outer ring gear and sun gear to achieve heave compensation motion and automatic bit-feeding motion.The planet carrier drives the drawworks to achieve heave compensation motion and automatic bit-feeding motion at the same time.So hardware decoupling control is realized.The electro-hydraulic hybrid drive is used.Passive hydraulic motors balance rig static load with liquid gas storage devices,recycle and release load gravitational potential energy periodically.Vector inverter motors overcome the remaining load of compensation process.So energy saving by hydraulic accumulator is achieved on the premise of ensuring compensation accuracy.Semi-active drawworks heave compensation system needs to meet the requirements of working conditions including heave compensation,automatic bit-feeding and empty hook operation,moreover,the system can response to sudden accidents such as rupture,dropout of drill string and pipeline.Take the well depth of 10000 m,compensation load of 350 t,compensation displacement of 7.62 m,heave motion cycle of 12s as design parameters and technical indicators,the power and energy consumption of compensation system is analyzed.Key structure parameters and electro-hydraulic compound dirve program is optimized by considering factors including motor power,energy consumption,structural strength and wireline life.The new type of semi-active drawworks has obvious energy saving effect compared to active heave compensation.The key structure of semi-active drawworks including drawworks,differential planetary gear reducer,hydraulic motor circuit is designed.The active compensation motors and passive hydraulic motors are connected to outer ring gear input shafts of differential planetary gear reducer,achieve the heave compensation and pipe tripping motion.The bit-feeding motors are connected to sun gear input shafts of differential planetary gear reducer through double stage cycloid reducer with large reduction ratio,achieve automatic bit-feeding motion and emergency lifting for derrick and drill string.The drawworks meets the requirements of hardness and stiffness.The differential planetary gear reducer meets the requirements of transmission ratio,strength and installation.The hydraulic motor can switch freely in a variety of operating conditions including heave compensation,tripping,self locking and floating.The layout of compensation drawworks is symmetrical,the structure is compact,the safety and reliability is strong,so the drawworks meets the requirements of drilling operation.The movement decoupling control strategy of semi-active drawworks is designed,the research of system modeling and simulation is carried out.Heave compensation control employs double control scheme,which includes hook displacement closed loop in the outer loop and motor speed closed loop in the inner loop.Automatic bit-feeding control employs double control scheme,which includes bit weight closed loop in the outer loop and motor speed closed loop in the inner loop.Mathematical model of each part and Simulink/AMESim combined simulation model is built.The research results indicate that the passive compensation system has no effect.The compensation rate of active and semi-acitve system is above 95%.Compared to active compensation,the energy saving rate of semi-active compensation is 22.1%-52.3%.The energy saving effect is more obvious as the drilling depth increases.The bit pressure is steady with the movement of automatic bit-feeding.The control effect meets the requirement of floating drilling.Studies on control algorithm of heave compensation are being carried out.Internal model control,a novel control strategy based on mathematical model of the controlled target,has the advantages that dynamic performance and robustness of the system can be adjusted only by adjusting time constant of filter.When the built model and actual system model is matching,the internal model algorithm adjusts PID parameters conveniently and accurately.When the built model and actual system model is mismatching,the fixed time constant have a severe adverse effect on control performance.The fuzzy algorithm based on engineering experience reduces the accuracy of control,but the robustness and anti-interference ability of which is raised.The fuzzy internal model controller is designed base on comparing of many kinds of control algorithm.Fuzzy inference system of filter time constant is built to realize parameters tuning online.The fuzzy internal model controller has the advantages of convenient parameters tuning,strong robustness and anti-interference ability.The heave compensation drawworks principle prototype and experimental system is designed and built,experimental investigations are carried out.The test results show that the control effect of heave compensation and automatic bit-feeding is good,energy saving effect of semi-active compensation drawworks is obvious compared to active heave compensation,verify feasibility of the system,lay the foundations for practical engineering prototype.