Automatic Monitoring and Control of Annulus Bottom Hole Pressure for Safe Oil Well Drilling Operations

Smart wells and real-time analysis are research tools that significantly increase robustness and safety, during oil well drilling operations. The major objective of this paper is monitoring and controlling an experimental drilling plant, through diagnosing and implementing decision making, for a desired operational window, despite the commonly observed disturbances that produce fluctuations in the well pressure. In fact, as the well is drilled, the hydrostatic pressure increases because of the well length grow. In addition, the reservoir fluid influx changes the well flow rate and density of the well fluid mixture. Finally, the pipe connection procedure, which requires stopping and starting of the drill fluid, produce severe fluctuations in the well flow rates. At deepwater and pre-salt layer environments, complex situations frequently occur, imposing a narrow operational window as a constraint. The main objective is under-balanced drilling implementations, that is, the well pressure is lower than the reservoir pore pressure and the reservoir fluids migrate into the well annulus (kick). During a blow-out (uncontrolled kick), large amounts of the reservoir fluids penetrate the well up to the surface, which may cause accidents and severe disasters. As a result, well construction is a complex process in which annular pressures must be kept within the operational window. In this scenario, this paper presents monitoring and control methodologies for annulus bottom-hole pressure, to avoid fluctuations outside the operational window limits, in order to guarantee safe conditions during the drilling operation.