A method of and device for controlling the annular pressure in a well.

During managed pressure drilling (MPD) the annulus pressure is controlled using a model predictive control (MPD)methodology. The operation comprises pumping a fluid down a tubing 1 located within the well and extracting the fluid that flows back through an annulus 10 within said well. The method comprises defining a set pressure Pset, determining a desired extraction flow rate qcontrol, of fluid from said annulus in dependence upon the set pressure Psetand a pumped flow rate into the annulus qpump, and configuring an extraction path (ie opening closing control choke 12 and using backpressure pump 14) to achieve said desired extraction flow rate.