Calibrating Earth system models: Upper Jurassic petroleum systems
|Location||International Geological Congress,oslo 2008|
|Holding Date||08 September 2008|
The main industrial objective of Earth System Modelling is to reduce risks for frontier exploration by predicting the most likely distribution of source rocks, reservoirs and seals for selected time-slices in Earth history. The results can be a series of palaeogeography- and palaeo-climate-based predictive lithology maps. These are available in ArcGIS and can be easily integrated with other geological data to define proven as well as potential petroleum systems.
All geologic models require calibration: 3D basin models are easily calibrated with temperature and vitrinite reflectance datasets. Validating 4D Earth System Model results requires more development and innovative approaches. Climate predictions can be compared with climate-indicator sediments and fossils. Predicted lithology distributions can be evaluated against observed data in wells and outcrops.
The temporal grain (how long time is actually represented in the geologic record in an outcrop or well) and the coarse resolution of global models (grid-size of several 100 km) represent key challenges for calibration.
The Upper Jurassic time has been extensively investigated in 2007. Altogether 65 Upper Jurassic petroleum systems have been studied worldwide to understand the spatial extent and depositional setting of source rocks and working petroleum systems.
The observed thickness, extent, organic matter content, sedimentation rate and estimated paleo-water depth of known source rocks have been investigated. Selected examples from the Norwegian Barents Sea (Hekkingen Fm.), Norwegian Sea (Spekk Fm.), North Sea (Draupne Fm.), West Siberia (Bazhenov Fm.) and from Australia (Upper Dingo Fm.) will show similarities and differences in source rock development.
To accurately predict, and thus forward model source rock deposition, the geologic controls on sedimentation rate need to be investigated. Good-quality, oil-prone source rocks occur only if the sedimentation rate is low enough to preserve adequate organic richness. With higher sedimentation rate the impact of dilution decreases source rock quality.
Extension of known petroleum systems into new areas, as well as the potential for new petroleum systems in frontier basins can be identified with the use of the Earth System Model results. This work can be done by eliminating false positives, integrating well and outcrop data, highlighting areas which might have been eroded or subducted, and by investigating burial/thermal history, in order to identify sweet spots where source rock presence and maturity can lead to new exploration opportunities.
A detailed verification of the source rock predictions is always required before one can use the results to identify new petroleum systems.