| With the evolution of drilling industry and the requirements of high efficiency,safety,easy to main and low labor intensity in drilling process,the deep drilling equipment is being developed with the feature of modular,automatic and intelligent.According to prime mover for rotating the drill pipe,top drive system could be classified into electrical top drive and hydraulic top drive.The main transmission system of hydraulic top drive is built with a hydraulic drive source and hydraulic actuators.Hydraulic transmission/control has several advantages such as high-power density,compact size,smooth operation,safety,reliability,and easy to control by automation.Most of the present top drives are designed for oil drilling project,so it cannot be used in deep scientific drilling.Besides,none of the top drive can drill automatically completely.It is difficult to study the internal mechanism of top drive design,optimization and application,for the following reasons,the complex structure of top drive,the long design and production cycle,expensive cost,and the special application conditions.Thus,in this paper,the main transmission of a hydraulic top drive for deep continental scientific drilling is designed and studied deeply.Based on the analysis of working conditions and performance demands in deep well drilling process,this paper presents the necessary property and function of hydraulic top drive main transmission system,and puts forward an electro-hydraulic proportional closed circuit hydraulic system with variable displacement pumps and variable displacement motors for the hydraulic top drive.In order to ensure the hydraulic top drive running in the best working state during drilling process,it is necessary to improve the controllability of its output speed and torque through scientific and reasonable technical means and control strategies.In addition to the conventional speed regulation,the hydraulic top drive is also equipped with a variety of output functions,which includes constant speed control,constant torque control,constant power control,speed adaptive control,hydraulic motor overweight control and so on.The hydraulic top drive main transmission system is a fairly complex mechanical-electrical-hydraulic integration.The hydraulic transmission system is a closed circuit hydraulic system with variable displacement pumps and variable displacement motors.The closed circuit hydraulic system consists of two variable displacement pumps and four variable displacement motors connected between the prime mover and the mechanical part of this driveline.Besides,the hydraulic system possesses replenishing arrangement,overload protective arrangement,heat exchanger arrangement,and other auxiliary components.Electro-hydraulic proportional control technology is adopted in the electric control part.Electro-hydraulic proportional control is adopted to vary the top drive output speed,and the control process as follow: the displacement of hydraulic pumps and displacement of hydraulic motors are controlled by hydraulic pressure signals,which are supplied by a pressure-limited variable pump;an electro-proportional reducing valve was connected between the pressure-limited variable pump and the displacement control section of pumps and motors,and transform the current input signal into hydraulic pressure;the displacements of hydraulic pumps and motors are varied with the current signal,and then top drive speed and torque are output according to the setting value.In order to comprehensively analyze the dynamic properties and internal relationship between mechanical structure,electronic control and hydraulic transmission of the hydraulic top drive main drive system,a theoretical model is detailed for the hydraulic top drive main transmission system based on the differential equations of hydraulic components.And then a 1D+3D simulation model of the hydraulic top drive main transmission system is proposed using the AMESim platform and Virtual Lab Motion software.Based on the simulation model,the characteristics of continuous speed regulation from low-speed to low-speed working area of hydraulic top drive,constant speed regulation under fluctuating load,hydraulic motor pressure compensator override control,and output characteristics of hydraulic top drive with long pipeline,are all carried out.The results of continuous speed regulation from low-speed to low-speed working area of hydraulic top drive show that the maximum speed,the maximum torque and the maximum power of hydraulic top drive can reach to 377 rpm,65249Nm,and 701703 W respectively when the speed of hydraulic pump is 2000 rpm,and the maximum pressure of the system is 45 MPa,which meet the design requirements of high speed and high torque.The results of constant speed regulation under fluctuating load show that the load fluctuation amplitudes influenced the response rate and steady value of the hydraulic top drive output speed very little.When the fluctuation amplitude of the load was 10000 Nm,the speed fluctuation amplitude still could be remained within 3 rpm,which could satisfy the constant speed requirement of the hydraulic top drive.The results of hydraulic motor pressure compensator override(PCOR)control show when the system pressure reaches the PCOR pressure of the motor,the displacement of the hydraulic motor will be rapidly adjusted to the maximum displacement,which can reduce the speed of top drive and improve the bearing capacity of the system.Drilling experiments of the hydraulic top drive was performed on the CRUST-I drilling rig in CCSD-SK-II well site.In 2015,the hydraulic top drive swept the hole from 2800 m to 3100 m,and then drilled from 3100 m to 3628 m with coring.In 2017,no-load test and load test were carried out.In 2018,the top drive drilled from 6769.77 m to 7108.88 m,with the total footage of 339.11 m.The drilling experiment results show that the parameters of hydraulic top drive are reasonable,and it can meet the production demands for deep well drilling.Contrastive analysis is carried out to validate the theoretical model and simulation model.In the contrastive analysis,the parameters of theoretical model and simulation model are set at the same value with the top drive when drilling CCSD-SK-II from 3436.92 m to 3447.52 m.From the comparison,we see that the simulation result shows close agreement with the theoretical result and drilling experiment data.The simulation model of the main transmission system is sufficiently accurate,and it could be used to analyze the output characteristics of the hydraulic top drive shaft under other operating conditions and determine scientific control strategies.Besides,the simulation model can also be used to gain a deeper understanding of the system's performance and key influencing factors without relying on experimental data.Hydraulic system uses hydraulic oil as working medium to realize power transmission and control.Because hydraulic oil is sensitive to temperature changing,performance and stability of hydraulic system are easily affected by temperature.In this paper,a thermodynamic model of the hydraulic top drive main hydraulic system is established by using the control volume method,and a simulation model built with the use of AMESim platform.The thermodynamic characteristics of the hydraulic system are analyzed with considering the following the conditions of displacement of the hydraulic pump,displacement of the hydraulic motor,displacement of the replenishing pump,temperature of replenishing oil,the size of replenishing relief valve,the size of heat exchange relief valve,and environment temperature.Setting the initial temperature at 20 ?,when the displacement of hydraulic pump is at its maximum value and the displacement of hydraulic motor is at its minmum value,the hydraulic pump outlet temperature could reach to 46.81 ?.Setting environmental temperature at different values,the simulation results show that when environment temperature is below-10 ?,the temperature of replenishing oil should be higher than 20 ? in order to ensure the pump temperature between 30 ? to 50 ?;when the ambient temperature higher than 30 ?,cooling circle should begin to work.During drilling experiment in CCSD-SK-II,temperature of the hydraulic components was tested when the top drive ran for 42 hours continuously with the environment temperature at 21.5?.The highest temperature rise of the hydraulic top drive was 27?,and the highest temperature rise of the hydraulic pumps was 32?.,which shows that the hydraulic power station can not only meet the requirements of uninterrupted continuous operation of hydraulic top drive,but also ensure the working temperature of hydraulic components in a reasonable range.Setting the parameters of the thermodynamic simulation model at the same value the top drive when temperature tests were carried out,the pump temperature calculated in simulation model is 41.81 ?,while the pump mperature tested in drilling experiment is 49.8 ?.In the range of allowable error,the temperature of simulation model is reasonable,and the thermodynamic simulation model can be used for analysis and forecasting characteristics of the hydraulic top drive main drive hydraulic system,and obtaining the temperature control measures of the system. |
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