Petroleum Generation from the South Barents Shelf: Results from a 2d Petroleum-System Model
Janet Pitman1, Timothy Klett1, and Donald Gautier2
1U.S. Geological Survey, Denver, CO.
2U.S. Geological Survey, Menlo Park, CA.
The south Barents Shelf in the Arctic Region has significant potential for undiscovered petroleum resources in underexplored basins but petroleum occurrence in the region is poorly understood. To evaluate the petroleum system a regional 2D burial history model simulating thermal maturity and petroleum generation was developed from a series of interpreted seismic lines. The lines extend from the North Atlantic margin to the southeast flank of the South Barents Basin. Triassic shales with Type II/III kerogen and Upper Jurassic marine shales are defined as the principal source rocks in the model. Numerous unconformities occur in the stratigraphic section but the unconformity related to Pleistocene glaciation is the most significant. An important geologic factor addressed in the model is the impact of late Cenozoic erosion on the timing of source rock maturation. Burial and thermal histories were simulated using present-day heat flows and timing and magnitudes of erosion. A complex paleoheat flow model was incorporated in the simulation based on the tectonic evolution of the region and defined over a range of 50-100 mW/m2. Published estimates of erosion, from 0-1600 m, were used to approximate the extent of late Cenozoic exhumation. Amounts of erosion determined from two vitrinite reflectance profiles agree with the estimates. Model results indicate that petroleum generation on the south Barents Shelf was controlled by a combination of burial depth and paleoheat flow and was not affected by the recent and short-lived Ice Age erosion. Lower and Middle Triassic rocks that sourced much of the petroleum trapped in younger reservoir rocks in the east Barents began generating oil and gas during the Late Triassic; generation did not commence until the Late Jurassic in the west Barents. In the deeper basins there is potential for petroleum generation and migration updip from Upper Jurassic source rocks that matured in the Late Cretaceous. Generation of petroleum continued into the late Cenozoic in the region. Discoveries on the south Barents Shelf are mainly gas with no major oil accumulations. The model indicates a gas-prone system due to the predominance of terrestrial organic matter with minor oil to gas cracking. Some sequestered gas in the petroleum system may have been released due to pressure changes during glacial rebound but analysis of these effects was beyond the resolution of the model.
AAPG Search and Discover Article #90096©2009 AAPG 3-P Arctic Conference and Exhibition, Moscow, Russia