Pore-pressure Prediction Far Ahead of the Bit - Offshore Nigeria Field Study to Evaluate a New Technique

Formation pressure is one of the important subsurface properties for drilling and completion of wells. If assumed or predicted pressures are too low or too high than the actual either a kick can occur or the well could not be drilled to its target depth respectively. Current practice is to make an assessment of the formation pressures to be encountered using offset wells and other geological and seismic information. These estimates are then monitored against the while-drilling measurements. These measurements, however, are all behind the bit and they do not directly indicate what is ahead of the bit where it matters the most.

A new technique that integrates local seismic data and real-time logs providing while-drilling formation pressure estimates “ahead” of the bit has recently been published. We present a field test of this integrated approach conducted in offshore Nigeria. Results show a formation-pressure ramp over 600 m ahead of the bit is predicted and placed within 50 m of its actual location and formation pressure values are predicted within 0.05 to 0.1 g/cm3 of their post-drill prognosis.