Abstract
The Pore Pressure is a critical point of any drilling project, once it influences the definition of the mud weight, casing setting depths, casing design, riser safety margin (RSM), etc. During the design stage of offshore and shallow water wells, safety factors (ranging normally from 0.5 to 1.0 ppg) are introduced to compensate the lack of accuracy in pore pressure evaluation. However, this may impose a limit in deepwater drilling operations. In such environment, as the water depth increases, the formations tend to show lower fracture gradients, which makes the difference between the pore pressure and the fracture gradient curves quite small, complicating the project.
In this work the methods employed by Petrobras to evaluate the formation pressure are reviewed. Next, a procedure, employing statistical analysis, to evaluate the uncertainty in the pore pressure determination in the offshore portion of Campos Basin - Brazil, is presented. For that, a DST (drill stem test) and RFT (repeat formation test) database collected along the years in this area is employed. As a result, the safety factor applied over the Pore Pressure could be reduced, simplifying deepwater well projects.
