The promises and pitfalls of integrating geodynamic with petroleum system modeling

Petroleum system modeling is a key component of the exploration workflow. A wide range of plausible maturation histories, migration scenarios, and structural evolutions are routinely investigated before exploration decisions are made. Petroleum system models (PSM) are designed to simulate multi-phase porous flow as well as the details of petroleum generation and expulsion. They are, however, not well suited for investigating the structural and thermal evolution of rift systems. In fact, PSM usually only resolve the sedimentary basin itself – all larger scale geodynamic processes need to be parameterized in terms of a basement heat flow boundary condition.

Recent advances in 2-D and 3-D lithospheric rift modeling have significantly increased our understanding of how strain is partitioned and temperature evolves during rift formation. It seems a natural way forward to integrate these new insights into the petroleum system analysis workflow by instructing PSM with information on basement heat flow extracted from lithosphere-scale models. For such a multi-model approach to work, progress has to be made in the understanding of feedbacks between shallow sedimentary and deep lithospheric processes. Here we present results of a Norwegian margin case study that illustrates how strongly the time-varying rate of sedimentation deposition affects strain partitioning, temperature, and mantle serpentinization during margin formation.

We then take these ideas further and investigate how predictions of geodynamic models can be integrated into petroleum system models. For this purpose, we have performed case studies for the Norwegian and North Sea. We find significant differences in the timing of hydrocarbon maturation and in the GORs of hydrocarbon accumulations predicted by models that do and do not resolve the interrelations between sedimentation, crustal thinning, and basement heat flow. To investigate the underlying mechanisms, we have analyzed the predictions of thermotectonostratigraphic forward models on the evolution of basement heat flow in terms of the relative contributions from tectonic and sedimentary processes. We find that sediment blanketing effects and the diminishing importance of crustal radiogenic heating during extension often dominate over the tectonic heat flow component. This implies that in terms of basement heat flow, resolving a basin’s sedimentation history is at least as important as the details of the employed rifting model. A consequence is that predictions from geodynamic models that do not resolve the sedimentation history cannot be easily transferred into basin-scale petroleum system models. We here show how such integration can be successful, which benefits are to be expected, and what kind of pitfalls should be avoided.

In conclusion, we find that strong feedbacks exist between shallow sedimentary and deep lithosphere processes. These should be considered in geodynamic and in petroleum system models. Multi-model approaches that combine both types of models are promising and have the potential for significant improvements in the quality of the thermal and structural solutions used in PSM but care must be taken that model consistency is ensured and sediment blanketing effects are accounted for.