Yardley, G.1, G Couples2, A. Aplin3, Y. Yang3, R. E.
(1) Shell, Rijswijk, N/A, Netherlands
(2) Heriot-Watt Univ, N/A, United Kingdom
(3) Newcastle Univ,
(4) Durham Univ and Geopressure Technology Ltd,
ABSTRACT: Lithology-Based Pore Pressure Prediction Success: Example from a Gulf of Mexico Mini-Basin
The GeoPOP research consortium made several significant advances in understanding and predicting overpressure. One of the most important improvements was the establishment of a strong relationship between lithology (represented as log-derived “clay fraction”) and compaction behaviour. This porosity-stress-lithology relationship was integrated into a basin modelling scheme and used to predict the pore pressure history in a Gulf of Mexico mini-basin. The “Vimto” study area (anonymous location) is a rapidly-subsiding depocentre (> 6 km accumulation in 5 Ma) bounded by active salt features. The mini-basin is filled with a dominantly muddy succession of sediments with some deep-water sandstone intervals. Wells located on the margin of the mini-basin provide lithological information and subsidence history, along with measured overpressures (at approx 5 km depth). Seismic gives further information about the mini-basin. A 3D basin model was constructed to simulate the geohistory, with each layer of the model assigned compaction properties derived only from the lithology. Upscaling of mixed sand/shale sequences produced equivalent compaction properties for heterogeneous intervals. The model predicts the observed (real) pore pressures to within a few psi (or 0.04 MPa), without a calibration step. The pore pressures in this cool mini-basin are explained as the product of disequilibrium undercompaction caused by rapid burial and related lateral transfer of pore pressures. The calculated overpressures are sensitive to changes in the lateral extent and connectivity of the sandbodies, which implies that comparisons between calculated and observed pore pressures can provide constraints on the architecture of deep-marine depositional systems.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.