3D Pore Pressure Prediction in the Columbus Basin, Offshore Trinidad and Tobago

Abstract

The overburden pressure, hydrostatic pressure and normally compacted shale velocity are theoretical values or empirically derived from relevant well data, whereas the interval velocity is derived from seismic processing velocities using the Dix formula. Modelled input cubesParadigm's software was used for the manipulation of the various input cubes into the pressure prediction. A 3D overburden pressure vs. depth model was derived from a modelled porosity cube. This (shale) porosity cube was generated using a compaction curve below sea bottom (to allow for variable water depths), and was subsequently transformed into a density cube using a density-porosity relation empirically derived from well data. Integration of the density cube over depth resulted in the overburden pressure cube P ob . The hydrostatic pressure cube P hyd was made using an assumed hydrostatic gradient of 0.45 psi/ft and depth from MSL.The normal velocity cube V n was based on Wyllie's Time-Average equation for sonic rocks, which establishes a connection between transit time for the rock (∆T norm ) and transit time for the matrix (∆T matrix ) and fluid (∆T fluid ):

Research Note: Overpressure prediction from C‐wave seismic data

“…Drilling safety demands the prediction of anomalous pressure cells and pressure gradients across prior to drilling (Snijder et al 2002). To accomplish this, Eaton (1969) recognizes the advantageous areal extent of reflection seismic data and relates formation pressure gradient and traveltime (obtained from seismic) through the ratio of normally‐pressured traveltime Δ t n and observed traveltime Δ t 0 .…”

Occurrence and Nature of Overpressure in the Sedimentary Section of the South Caspian Basin, Azerbaijan

“…Evidence of abnormal high pore / reservoir pressures (hereinafter "overpressures") has been encountered in many basins of the world (Dickinson, 1953;Berry, 1973;Bigelow, 1994;Chiarelli and Duffaud, 1980;Chapman, 1994;Bradley and Powley, 1994;Ward, 1995;Audet, 1996;Belonin and Slavin, 1998;Kan et al, 1999;Snijder et al, 2001;Sun and Püttmann, 2001) and, in certain cases, the pore pressure gradient reaches the lithostatic pressure. Such greatly complicates drilling and has often caused accidents and the abandoning of wells.…”