Experimental Control of Annulus Pressure While Drilling Oil Wells

Under a conventional oil well drilling task, the pore pressure (minimum limit) and the fracture pressure (maximum limit) define mud density range and pressure operational window. During oil well drilling, several disturbances affect bottom hole pressure; for example, as the length of the well increases, the annulus bottom hole pressure varies for growing hydrostatic pressure levels. In addition, the pipe connection procedure produces disturbances in well fluids flow, changing well pressure. The objective being tracked is operating under desired pressure levels, which assures process safety, also reducing costs, as drilling operation demands around U$500,000.00/day. In this scenario, control techniques are important tools for narrow operational windows, commonly observed at deepwater and pre-salt layer environments. The major objective of this paper is controlling annulus bottom hole pressure of a drilling experimental unit, using the choke opening index as the manipulated variable, in order to guarantee safe operation (target annulus bottom hole pressure), despite the inherent process disturbances and under a scenario that maximization of ROP (rate of penetration) is a target.