Revisiting Well Design and Formation Pressure Prediction: Study from Gulf of Mexico

Improving well design has and always will be the primary goal in drilling operations in the oil and gas industry. To address this issue, an analysis of wellbore stability and well design improvement has been conducted. This study will show a systematic approach to well design by focusing on best practices for mudweight window projection for a field in Mississippi Canyon, Gulf of Mexico. The field includes depleted reservoirs and is in close proximity of salt intrusions. Analysis of offset wells has been conducted in the interest of developing an accurate picture of the subsurface environment by making connections between depth, non-productive time (NPT) events, and mudweights used. Commonly practiced petrophysical methods of pore pressure, fracture pressure, and shear failure gradient prediction have been applied to key offset wells in order to enhance the well design for a proposed well. For the first time in the literature, the accuracy of the commonly accepted, seismic interval velocity based and the relatively new, seismic frequency based methodologies for pore pressure prediction are compared. Each of these methods is compared to the petrophysically derived mudweight windows for the key offset wells and the proposed well in this field, showing higher reliability in the frequency based approach. Additionally, the interval velocity method yielded erroneous results in a fast-rock-velocity channel zone and the near salt proximity environments, whereas the frequency Based method appeared unaffected by either of these factors.