Research On Real-time Control Of Wellbore Pressure Based On Model Prediction

As oil exploration continues to develop into complex rock formations such as ultra-deep layers and deep water layers,the safe density window during the drilling process will become narrower.At the same time,downhole faults such as overflow and leakage are difficult to detect in time,and the processing method has hysteresis,which makes control more difficult.Wellbore pressure real-time control technology can effectively solve such problems.The wellbore pressure can be controlled by adjusting the wellhead back pressure in real time.The model prediction has the advantages of better dynamic control effect and strong robustness,and can effectively overcome the problems in the control process.Uncertainty,nonlinearity and parallelism can well constrain the control relationship between wellhead back pressure and wellbore pressure.Therefore,a real-time control method of wellbore pressure based on model prediction is proposed.The establishment of the real-time calculation model of wellbore pressure is the basis for studying the real-time control of wellbore pressure.In terms of realizing the design of wellbore pressure calculation method,the influence laws of drilling fluid rheological mode,drill pipe joints,drilling fluid solid phase content,drill string eccentricity and temperature-pressure coupling on annular flow friction are fully considered;The self-adaptive extended Kalman filter algorithm is used to establish a real-time calculation state space model of wellbore pressure,and the established real-time calculation model of wellbore pressure is used to analyze the pressure calculation example,which needs to be fed back and corrected according to the real-time monitoring data of the construction site.Furthermore,by analyzing the control principle and pressure control design of managed pressure drilling,a wellhead back pressure control system model is established,and whether the pressure value calculated in real time according to the wellbore pressure is within the reasonable range of the bottom hole pressure,which is the control amount in the real-time wellbore pressure control system.Provide guidance.Since the model prediction theory has a great advantage in displaying processing constraints,the DMC control algorithm is applied to the real-time control system of wellbore pressure,and the simulation is compared with the wellbore pressure control system based on PID closed-loop feedback in the Matlab experimental environment.The research results show that the built pressure real-time calculation model is feasible and accurate.It not only solves the problem that the filtering effect decreases due to inaccurate prediction estimates,but also effectively improves the real-time calculation accuracy of wellbore pressure.Errors can be maintained within a controllable range.Following the research on the real-time control system of wellbore pressure,comparing the control models under the two algorithms,the wellbore pressure control system model based on PID closed-loop feedback can be applied to the real-time control system of wellbore pressure,but the output results are not accurate enough and the response time is slow.The DMC control model has faster convergence speed and response time,smaller control error,and higher accuracy.At the same time,the DMC control model shows strong anti-interference ability after being subjected to external additional interference,tends to be stable in a short time,and has strong anti-interference ability,robustness.