Seismic Solutions for Drilling - Real-time Pore-pressure Estimation Ahead of the Bit

Overpressure is one of the important drilling hazards seen globally. Estimates of overpressured zone locations and overpressure magnitudes have a direct impact on well drilling and completion. Formation pressures in a drilling location are estimated from seismic velocities by using rock-physics-based transforms that map formation velocities to pore pressures. Consequently, the accuracy of the estimated pore pressures depends both on the accuracy of the velocities and the transforms. We present a method that makes optimum use of seismic data and information obtained from the well being drilled to provide pore-pressure estimates ahead of the drill bit in real time. During the drilling process, adjustments are made to the rock-physics model based on Logging While Drilling (LWD) data calibrating the model to local overburden geology. Furthermore, we show that by using while-drilling checkshot information, integrated with surface seismic data, we can improve the velocity estimates ahead of the bit. Field study results from a Gulf of Mexico well show that combining these two measurements provides a significantly better pore-pressure estimate ahead of the bit compared with pre-drill predictions.