Design And Simulation Of Automatic Drilling Control System Based On Downhole Weight On Bit

With the extensive application of automatic drilling technology in the oil field,the friction and torque of drill string make the difference between downhole WOB(weight on bit)and ground WOB much different,and can not get accurate downhole WOB,Improper downhole WOB will affect the performance and life of dill bit,resulting in low drilling efficiency.In order to achieve accurate control of downhole WOB,it is particularly important to establish the mathematical model for automatic drilling.Aiming at the specific well structure.based on drill string mechanics,the hook load is iteratively calculated from the drill point according to the formula,and combined with the hydraulic disc brake and the Yangg correct mode,a three loop control strategy is formed A set of integrated automatic control system for hydraulic disc brake is established.Aiming at the shortcomings of the conventional PID controller in the nonlinear characteristics of the automatic drilling system and the limited adaptability of the fuzzy PID controller,a fuzzy immune PID controller is applied to the automatic drilling control system.The proportional coefficient of the controller is modified online by the fuzzy immune controller.The integral and differential coefficients are adjusted in real time by the adaptive fuzzy controller The immune parameters of the fuzzy immune PID controller are based on the experience trial and error method,which results in that the immune parameter selection is not necessarily the optimal value,resulting in the overshoot of the system and the slow response speed.The genetic algorithm is used to optimize the immune parameters.The conventional PID controller,fuzzy PID controller,fuzzy immune PID controller and fuzzy immune PID controller based on genetic algorithm are used to simulate the model of the automatic drilling control system respectively,to verify the dynamic performance and steady state performance of the controller in the downhole WOB 20 t.The results show that when the step response signal is 20,compared with the conventional PID controller,the fuzzy immune PID controller based on genetic algorithm can increase the response time of drilling WOB differential by 9.35 times,8.14 times and 6.21 times,and the overshoot is reduced by about 7.5%,5% and 1%,respectively,compared with the conventional PID controller and fuzzy immune PID controller.It is fully proved that the controller can significantly improve the dynamic performance and steady-state performance of the automatic drilling control system in horizontal wells.Combined with the GUI module,an automatic drilling system is built to achieve real-time input of simulation parameters and intuitive simulation process.