3D PETROLEUM SYSTEMS MODELLING OF A MATURE BASIN: THE BENEFIT OF A RIGOROUS APPROACH

Understanding particular petroleum systems may at first glance seem straightforward and variations in petroleum type and properties can conveniently be attributed to either maturity or facies variations in the source rock. A rigorous petroleum systems analysis, however, often reveal the necessity of a more complex view of the petroleum systems which in turn can improve the understanding of key observations that would otherwise have been considered peculiar.

The petroleum systems analysis presented here encompasses a detailed hydrocarbon fluid evaluation and source rock study integrated and understood by the use of 3D basin modelling. The strength of a more rigorous approach to petroleum systems analysis is in this case illustrated for a well-known and mature area where previous modelling has demonstrated the existence of just a single petroleum system.

As a result of geochemical fluid analysis, three major oil families were identified, one oil family is recognised regionally whereas the two other oil families are much restricted and geographically separate. A detailed source rock study led to the identification of four intervals with significant source potential, stratigraphically distinct and with clear differences in source rock properties. The use of 3D modelling allowed for a comprehensive integration of the data leading to the understanding of a likely relation between observed fluid types and identified source rock intervals. Moreover, a specific maturation and expulsion history given by the overall basin parameters as defined from a range of geological input parameters was established.

In the 3D modelling part, hydrocarbons generated from each of the source rock intervals were traced to the accumulations and compared to the geochemical character indicated by the analyses. As a result of the analysis, three petroleum systems were identified capable of explaining the observed differences in petroleum fluid characteristics. Fluid compositional modelling suggested all of the gas originating from the same source rock, however, there was no data available at that point in support of such hypothesis. A dedicated gas analysis programme was thus designed with the specific objective of testing this prediction and securing a reliable model capable of supporting the continued exploration effort.