Defining Uncertainty in Earth System Based Process Models of Source, Reservoir and Seal Facies

Markwick, P.J.¹, P.J. Valdes² (1) Petroleum Systems Evaluation Group, GETECH, University of Leeds, Leeds, United Kingdom (2) University of Bristol, Bristol, United Kingdom

The use of Earth System models to predict the past distribution and quality of source, reservoir and seal facies, has gained considerable interest over the past 10 years. But, such models are experiments that must be continually tested against observations, and so an important part of any application of models must be a systematic, quantitative assessment of uncertainty. This can then be added to the overall risking used by explorationists.

Here, we present some results for source facies predictions using a series of sensitivity experiments designed to examine the response of predictions to changes in the model boundary conditions, in this case atmospheric CO2. The full matrix of potential uncertainties is extremely large, and includes not only sensitivity experiments for changing boundary conditions (including plate tectonic and palaeogeographic variability, atmospheric chemistry, surface vegetation, orbital parameters), but also postulated intrinsic model issues (inter-computer processing variability, missing (or equivocal) dynamic processes), and uncertainties associated with our current understanding and representation of the processes responsible for source, reservoir and seal depositional facies. We consider both marine and terrestrial systems.

The results clearly indicate that different variables respond in different ways to model variability, and this then has similarly complicated response in terms of uncertainty. For example, marine productivity systems based on gross ocean circulation patterns are relatively robust, but changes in local geography (and especially bathymetry) can modify this pattern and especially its magnitude and seasonality, which in turn dictates how much of this productivity is then converted to export POC (particulate organic carbon).

Earth Systems models provide a powerful tool for explorationists, but only when applied through an understanding of process and uncertainty.