ABSTRACT
An accurate prediction of formation pore pressures prior to drilling a well can significantly improve drilling performance, reduce the number of costly drilling problems encountered, and in many instances, can be the determining factor in successfully reaching objectives. This is particularly true when dealing with exploratory wells. The fact that we are going to penetrate the same stratigraphies as offset wells does not equate to being in the same pore pressure environment. In fact, when dealing with exploratory wells, there is a high percentage of the time when this is not the case.
This approach to predicting formation pore pressures utilizes offset log information, and velocity information from surface seismic data. All surface seismic data has velocity information built into it in the way of stacking velocities. From these stacking velocities, estimates of interval velocities can be made. We have developed a quantitative technique for determining formation pore pressures from the relative changes in these velocities.
From the stacking velocity data, we develop curves we refer to as ITT (Interval Transit Time) curves. ITT curves are generated at offset locations as well as the proposed drilling location. Actual offset well pore pressures are determined from the logs and the ITT curves at these offsets are calibrated to the known pressures. After this calibration process, the ITT at the proposed location can be interpreted to predict formation pore pressures to be encountered.
The combination of these tools yields a reliable pore pressure scenario from which to plan a drilling program and execute the operations. This procedure has been utilized on numerous wells throughout the Gulf of Mexico as well as a number of wells around the world. The technique will be illustrated with figures as a step by step analysis is done. Results of the use of this methodology will also be illustrated.
