Research Of Drill String Heave Compensation System For Float Drilling Platform

Float platform drill string heave compensation system is a vital device for offshoredrilling operation, which compensates the effect of waves heave. The heave movement offloat drilling platform caused by ocean waves transmitted to underground through drill stringmakes the drilling reciprocate vibration and causes shock against the drill bit, which affectsthe efficiency of drilling and reduces the life of drill equipment. Under wicked conditions,normal drilling can not be carried out due to heave movement of platform. Therefore, floatdrilling platforms require the equipments with heave compensation to reduce the impact onthe drill string caused by the heave movement of drilling platform.Through analysis of structure, working principle, compensation effect and energyconsumption of drill string heave compensations current used, a new kind of drill stringcompensation system with reverse cylinder mounted between travelling block and hook isdesigned. According to the research and analysis, the detail scheme based on the use ofvariable pump, the electro-hydraulic proportional directional valve and the gas-liquidaccumulator is designed, which can realize the heave motion compensation under of thecontrol of hydraulic compensation cylinder. The parameters of mechanical, hydraulic andelectrical devices are calculated. The mechanical structure, including compensation cylinder,upper frame, lower frame and locking device are designed, the hydraulic system that can meetthe needs of normal drilling and light load compensation, realize the drill stringpressure-modulation and the DCS control system using IPC and PLC can realize functions ofreal time parameters monitoring and automatic control for heave compensation system.Then in accordance with classification method, the passive, active and semi-activecompensation systems mounted between travelling block and hook are delved deeply.Mathematical and simulation models are set up and the models are simulated and calculated by the means of Simulink. The simulation results show that the passive heave compensationdevice has certain effect of compensation and the effect is relatively poor with hysteresis.Active compensation device has good compensation effect, high precision and stronganti-interference ability, but the instantaneous power is huge. The semi-active system is acombination of passive and active devices, has advantages of better compensation effect andlower energy consumption.Based on the similar theories, a heave compensation test bed of using composite cylinderis built, and the test bed can simulate heave movement、drill string load and heavecompensation experiments. The heave simulation system of test bed consists of a constantpump, an electro-hydraulic proportional direction valve and an asymmetric hydraulic cylinder.Under the control of dead-zone compensation and PID control strategy, the system achievesbetter heave simulation. The load simulation system is composed of hydraulic cylinder, a gas-hydraulic accumulator and a solenoid valve, which can realize static and dynamic load of thehook and string. The compensation system are made up of variable pump, electro-hydraulicproportional direction valve, hydraulic cylinder, gas-hydraulic accumulator and electronicmagnetic relief valve, which can achieve better control effect.In given conditions，the passive compensation、active compensation with valve control,active compensation with pump control and valve control, semi-active compensation withvalve control, and semi-active with pump control and valve control experiments are carriedout and the drilling platform heave and hook displacement data are gotten. The experimentalresult shows that the active and semi-active valve control effects are better.The energy consumption of different compensation schemes are compared. The passivecompensation system does not consume energy, the active valve control system requires hugesystem transient power and energy consumption is the largest. The active pump control andvalve control system consume a lower energy compared with active valve control for thereasons of control hydraulic pump flow. The semi-active valve control compensating systemenergy consumption is far less than the active valve control due to the compensationaccumulator stores energy for compensation, also smaller than active pump control and valvecontrol. The semi-active pump control and valve control system requires higher controlstrategy and the control effect is not as good as semi-active valve control, but consumes a little lower energy.With using the simulation test bed, the control system, the control software and thecontrol methods are examined. The experiment data is compared with the computersimulation, which is consistent with the theoretical analysis very well. The high compensationprecision is obtained for both the heave compensation theoretical model and its simulationtest system. Thus, it is proved that the scheme of the heave compensation system is correct,the design of the control system and the control method is effective, the developed controlsoftware is stable and reliable, the system can meet the requirements of drilling heavecompensation.Learned through the system simulation and experimental study on semi-active valvecontrol heave compensating system, the system has good compensation effect and low energyconsumption, is an ideal scheme.The scheme designing, parameter calculating, mathematical and simulation modeling,experiment analyzing and system controlling are finished and a series of independentintellectual property rights are described in the paper, which can improve our country’sdeep-sea technical equipment and quicken float platform drilling technology popularizationand application.