- Copyright © 2001 Society of Exploration Geophysicists
Knowledge of formation pore pressure is important for the successful exploration and production of hydrocarbons. During exploration, knowledge of formation pore pressure allows the hydraulic connectivity and fluid migration pathways in a region to be assessed. Thus, an increase in pore pressure below a seismic horizon may indicate the presence of a seal, while different pore pressures either side of a fault may suggest that the fault forms a barrier to flow.
In deepwater, wells are expensive, and the increased costs associated with deepwater drilling in overpressured environments demand a reliable predrill prediction of formation pore pressure. Too low a mud weight may allow formation fluids to enter the well which, in the worst case, could lead to loss of the well; on the other hand, too high a mud weight will give too low a rate of penetration and could lead to fracturing of the formation.
The use of seismic data for pore-pressure prediction is well known (Pennebaker, 1970; Eaton, 1975; Bowers, 1995), but the seismic interval velocities used have often been derived from stacking velocities, which locally average the velocity over the seismic aperture used in the analysis. These velocities may not be suitable for pore-pressure prediction in the presence of lateral variations that can arise from the presence of dipping structures, lithology variations, salt layers of variable thickness, fault blocks, or variations in compaction and pore pressure. Reflection tomography gives improved spatial resolution and thus allows a more reliable predrill pore pressure estimate to be obtained (Lee et al., 1998; Sayers et al., 2000). However, seismic velocities can be influenced by changes in lithology and fluid content, as well as by changes in pore pressure. Both P- and S-wave velocities can be obtained in the marine environment using multicomponent receivers at the seafloor (Figure 1 …