Automatic Coordinated Control of Pump Rates and Choke Valve for Compensating Pressure Fluctuations during Surge and Swab Operations

摘要

In this paper we present new methods for coordinated con- trol of pump rates and choke valve for compensating pres-sure fluctuations during surge and swab operations. In hydrocarbon well drilling, automatic control of the choke valve improves the control of the bottom-hole pres- sure. This has made it possible to drill wells where it previously was not possible to reach total depth, due to narrow pressure margins in the reservoir. This concept is developed further in this paper, to also include automatic control of pump rates, coordinated with the choke valve control. In configurations where the choke valve is fitted with a flow rate controllable annulus back-pressure pump, the sit- uation calls for structured methods for automatic and coor- inated control of the main mud pump, the back-pressure pump and the annulus return choke valve. In this paper, well known methods for multivariable control are applied to the drilling process. These meth- ods are based on identification of coupling and interaction between system input (controllable variables), e.g. pump rates and choke valve settings, and output (measured or estimated variables), e.g. pressure at given depths. It is shown how the well pressure profile can be kept within tight margins, subject to disturbances such as drillstring ovement in surge and swab operations. Automatic coordinated control is shown through nu- merical simulations on a detailed, space-discretized well model. Comparisons are made with the case of complete manual control and the intermediate case where only the annulus return choke line pump is automated, using a sim- ple linear controller. The results with automatic coordinated control of pump rates and choke valve are very promising - the perfor- mance of such a solution, measured by variance in pressure fluctuations, is improved - compared to both the case of manual control and the case of only automated choke line pump control.