Issues Faced while Calculating Overburden Gradient and Picking Shale Zones to Predict Pore Pressure 8th February 2022 – Posted in: Geo Pressure
1st EAGE Workshop in Pore Pressure Prediction, Pau, France, Mar 19-21, 2017
Over-pressure is one of the important drilling hazards seen globally. Estimates of over-pressured zones/locations and over-pressure magnitudes have a direct impact on well drilling and completion. Overburden gradient (OBG), Pore pressure (PP) and Fracture Gradient (FG) are the three basic outputs of any pore pressure analysis. OBG is calculated from density (RHOB) log data. As density log data does not start from surface/seabed, we use several equations to compute shallow section pseudo-RHOB and integrate it with LWD/wireline RHOB log data. This article discusses the issues with various ways to fill the data gap of shallow section density. PP is normally predicted against shale zones and then calibrated with the most reliable and direct pressure measurements against sands and log data from adjoining shales. This paper also addresses the various issues faced while picking shale points to predict pore pressure.