Abstract: Variation in the kinetic parameters for hydrocarbon generation in Upper Jurassic source rocks offshore Norway

TELNAS, NILS, ARND WILHELMS, TROND HANESAND, ELIN REIN and DAG HERMANSEN

The Upper Jurassic source rocks offshore Norway, frequently referred to as the "Kimmeridge Clay", is the source of most of the oil found in the North Sea, and they have been studied extensively.

Few reports on the variation in the kinetic parameters for these source rocks are available in the open literature. Appropriate kinetic parameters are necessary in order to predict both the timing of hydrocarbon generation using basin modeling and the composition of the generated products, and thus have a significant implication for exploration.

Kinetic parameters have been determined for a suite of approx. 40 samples of immature samples from the Upper Jurassic source rocks. The spread in temperature for 50% conversion of the organic matter with a heating rate of 3 deg. C/m.y. is more than 45 deg.C. With a typical geothermal gradient of 30 deg. C/km, this may correspond to a variation in depth to the oil window of 1.5 km. The choice of the right kinetics is thus a critical factor in trying to predict the oil and gas windows.

The variation in these parameters are studied both laterally within a source rock section, and vertically within single wells, and are correlated with results from pyrolysis-GC-MS and microscale sealed vessel pyrolysis-GC (MSSV-GC). The results indicate a strong dependence on the content of organic sulfur, while many of the analyzed samples are very rich in organic sulfur, and would be classified as Type IIS kerogens. The possible effect of sulfur on the generation of hydrocarbons in these clastic source rocks is discussed and related to the very low sulfur content of the oils in the area.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria