A method of controlling the annular pressure in a well during a well construction operation. The operation comprises pumping a fluid down a tubing located within the well and extracting the fluid that flows back through an annulus within said well and surrounding the tubing. The method comprises defining a set pressure pref, determining a desired extraction flow rate qc of fluid from said annulus in dependence upon the set pressure pref and a pumped flow rate into the annulus, and configuring an extraction path to achieve said desired extraction flow rate.