Pore Pressure Prediction Data Using Seismic Velocities and Log Data in the Offshore Nile Delta, Egypt

Abstract One of the main challenges in the deep water of the offshore Nile Delta is the ability to predict pore pressure. In this difficult environment the rig cost and risk is high requiring an accurate estimate of pore pressure for safety concern, optimizing mud weights, and casing program. Pore pressure prediction has been based in the past on after drilling results and recently while drilling using log data such as resistivity and sonic measurements. Pre-drill pore pressure estimation has been obtained from transform models using seismic interval velocities. However, the accuracy of this estimate of pore pressure is directly related to the reliability of these interval velocities and the assumptions underlying the various pore-pressure models used. The availability of the 3-D velocity data from 3-D seismic surveys can provide valuable information that can be used to produce 3-D pore pressure cube. In this paper, a feasibility study has been carried out on exploration wells in the offshore Nile Delta, Egypt, to estimate pore pressure using borehole seismic velocities. Two examples of highly pressured and normally pressured formations in the offshore Nile Delta will be presented. The first well had an unexpectedly high-pressure gradient (15.4 ppg, 1850 kg/m3) in the Pliocene formation section at depth less than 2000 m, resulting in a significant increase in the mud weight, and a well 28 days above the AFE. The second well was drilled based on similar mud weight properties as the first well but resulted in severe losses and well 15 days above the AFE. A velocity-pore pressure transform has been derived and results were applied on 2D seismic section. The ability to predict pore pressure before drilling from 3D seismic velocities provides valuable information to optimize drilling strategy and significantly reduce well cost in deep water environment.