3D pore pressure prediction in the Columbus Basin, offshore Trinidad & Tobago

The Columbus basin contains some 20 000 ft of Plio-Pleistocene clastic sediments and a substantial number of oil and gas fields, which have been discovered by BG and other Operators. In the course of the various drilling campaigns, major overpressures have been encountered which pose a challenge to the safe and cost-effective drilling of wells (Heppard et al. 1998). In most cases the overpressure appears to be related to undercompaction of the rapidly buried shales, although other mechanisms, such as pressure transfer from deeper mobile shales, have also been identified. In the past, pore pressure prediction based on seismic data has been used in an attempt to improve upon the routine application of off-set well data. Such work was normally done in the 1D or 2D domain, and specifically targeted the local prediction of pressures at planned well locations. BG and Paradigm Geophysical have now extended this technology into the 3D domain by constructing pressure prediction cubes from 3D seismic data. Such pressure cubes allow a rapid scanning of alternative well locations, and also provide new insights in the 3D pressure distribution of the subsurface. This allows the recognition of sealing faults and may lead directly to the identification of previously unrecognized prospectivity. Figure 1 shows a sample seismic line from the 3D survey used for this project. The various sand packages (A-L) clearly stand out from the background shales.