Pore pressure estimation of the calcareous formations in the Middle Magdalena Valley Basin, Colombia

Abstract

The reliable prediction of pore pressure is essential for petroleum engineering in its different stages, with the Eaton and Bowers' methods being the most used for this purpose. However, their application in carbonate rocks still needs to be improved because carbonates do not compact uniformly with depth, as shale does. This research calculated the pore pressure using the Eaton, Bowers, and Weakley methods and well logs of a carbonate formation and found that the Weakley's approach predicts pressure more accurately. The method presented uses an acoustic impedance equation derived from the Bowers' method, whose parameters were calibrated with the Weakley's pore pressure profile. The pore pressure estimated near the borehole, via the acoustic impedance provided by the pre-stack inversion, is very close to that observed during drilling, which indicates a reliable prediction. The method was applied to a seismic line and well logs in the Middle Magdalena Valley Basin—Colombia, where the overpressured well Lizama 158 caused a significant environmental disaster in 2018. The obtained subsurface pore pressure distribution is reliable, matches overpressure in calcareous rocks near the well, and estimates anomalous pressure in zones distant from the well.