Automatic backpressure control techniques of MPD drilling based on three-layer feedback regulation method

The automatic regulation and feedback control of wellhead pressure is fundamental for the successful application of managed pressure drilling technique (MPD). Existing wellhead backpressure control method has less consideration on the structural and circulation characteristics of the throttle valve system, which results in the problems of slow control response and poor control effect. In order to solve these problems, this paper proposed a new three-layer feedback wellhead pressure control method based on the operating characteristics of throttle valve, the electro-hydraulic proportional control principle and the feedback control method. In this method, the first control layer is opening curve bidirectional feedback control, the second layer is fast rough regulation of wellhead backpressure and the third layer is the refined feedback control of wellhead backpressure. Then, the detailed implementation process of this three-layer feedback control method was formulated and the wellhead backpressure control module was developed. Finally, its response time and accuracy were experimentally verified. It is indicated that the wellhead backpressure control accuracy is within ±0.1 MPa. This new refined wellhead backpressure control method lays the foundation for the refined control of wellbore pressure.