First Break - Volume 43, Issue 1, 2025

Pore pressure is regarded as an important branch of earth science. In exploration phase, pore pressure can provide information about trap integrity. During the drilling stage, the pre-drill pore pressure prediction helps in the casing and mud design. A good pre-drill pore pressure prediction will protect the well from drilling problems such as kicks and blowouts. In the production phase, it helps in the injection process, predicting reservoir compartments.

Sapphire field is part of the offshore Nile delta which is classified as a high-pressure basin. As a result, pre-drill pore pressure prediction is an important step in the well planning process for predicting abnormal pressures along the well path and avoiding drilling problems.

The paper presents a new workflow approach for the 3D pore pressure cube for the Nile Delta basin depends on four wells to generate a cube with the full set of pressure data (overburden, effective vertical stress, and formation (pore) pressure), it is built using Eaton and Bowers equations. In addition, Eaton and Bowers were optimised to fit the Nile Delta basin, compared to the Gulf of Mexico, which used the default optimisation value. The uncertainty in the density estimation is reduced as well by using the density sonic relation.

Three cubes overburden, vertical effective stress, and pore pressure prediction are the main outputs of the research. These three cubes almost match the actual pressure that was calculated using logging while drilling tools on the rig-site at the wells.

Unidentified structural features, primarily faults, are estimated to cost the coal mining industry in Australia alone $6 billion per year. Although seismic surveys are routinely used to characterise structures ahead of mining, these are often limited to 2D lines, with only the most recent being high-resolution 3D surveys. The most common approach for providing detailed structural definition is to drill a series of holes. In this paper we show a comparison between a full high-resolution 3D survey and a much smaller mini-survey over an area of particular structural complexity. The extracted surfaces, corresponding to three different coal seams, and the resulting structural interpretations, were consistent. Based on these results we are confident this approach can be used as an alternative to drilling to quickly and easily identify possible structural issues in high-priority areas. The method could also be used to accurately measure the strike of faults identified from 2D surveys.

Throughout the decades of its use, there has always been a requirement to obtain an accurate estimate of the propagating wave emitted by the vibrator mechanism. This is even more relevant in today’s recording environment of a low signal amplitude and high noise when employing a single source, single receiver, and ‘overlapping signals’ from simultaneous acquisition techniques. The ground force estimate (or its time derivative) is assumed by many to be a representation of the seismic wave (its source signature) that is transmitted into the surrounding medium. However, from published articles, many authors have questioned this assumption noting significant phase and amplitude differences between the ground force and the signal received at a remote sensor, especially at higher frequencies. Having an accurate source signature estimate at each location has significant ramifications beyond improving the quality of acquisition (and processing) that today is heavily reliant on ‘shooting blind’ into single channel nodes: it implies that the vibrator-earth model used is an accurate representation of the changing ground conditions at each shot-point whose properties can then be determined. In addition, an accurate vibrator-earth model may also lead to improvements in the design of vibrators for increased amplitude (greater signal) of the propagating wave. In this paper, we discuss the interaction between the vibrator mechanism and the surrounding media, the forces and energies generated during a sweep, re-examine the assumptions made in the ground force models and show that current source signature estimates are not an accurate representation of the propagating wavelet.