Abstract
Oil and gas plays are continuing to move into increasingly hostile drilling environments, including near and/or sub-salt proximities. The ability to reduce the risk and uncertainly involved in drilling operations in unconventional geologic settings starts with improving the techniques for pore pressure modeling. Nearly all of the modern day pore pressure prediction methods utilize interval velocities from seismic surveys to detect abnormal pressure along a proposed wellbore trajectory. Seismic interval velocities have long been known as being sensitive to formation properties such as lithology and porosity which may give way to erroneous pore pressure values; additionally, salt intrusions have proven to be a significant hindrance when predicting pore pressure from seismic interval velocities. A relatively new approach, which predicts pore pressure by way of seismic frequencies, has addressed the pitfalls seen in seismic interval velocity applications. With the goal of offering a valid seismic-based alternative to pore pressure prediction, a study has been conducted in a near-salt field in deepwater Gulf of Mexico that will compare and analyze the accuracy of seismic frequency versus seismic interval velocity based methodologies for pore pressure prediction. For the first time in the literature, the outputs between the two seismic models will be quantitatively assessed for accuracy. Accuracy standards will be based on the agreement of the seismic outputs to pressure data obtained while drilling and petrophysically based pore pressure outputs for each well. The results will show significantly higher accuracy for the seismic frequency based approach in wells that were in near/sub-salt environments and higher overall accuracy for all of the wells in the study as a whole.
