Patent attributes
A method for controlling a managed pressure drilling system including a drillstring located in a borehole, a pump that delivers drilling fluid, and a choke that controls the flow of the drilling fluid from an annulus formed between the drillstring and the wall of the borehole. During drilling, the drilling fluid flows downwardly through the drillstring from the pump and through a drill bit, and returns through the annulus to the choke. The method includes determining a correction ΔVcorr in the volume of the fluid in the annulus to achieve a target pressure in the fluid; calculating a choke flow rate correction term Δqcorr by dividing ΔVcorr by a factor related to the acoustic travel time ta of a pressure wave in the fluid travelling the length of the annulus; and determining a flow demand from the choke on the basis of the flow rate correction term Δqcorr.
