Evaluating the chain of uncertainties in the 3D geological modelling workflow

Geological models are used for a range of applications relevant for engineering geology and the demands for reliable geological models with realistic uncertainty assessments are therefore increasing. The geological modelling workflow is divided into multiple steps, each associated with uncertainties. Often however, many of these sources of uncertainty are overlooked, which may lead to an underestimation of the uncertainties of the final model. The main reason is that most of the steps in the geological modelling workflow are subjective to some degree. Thus, the possible sources of uncertainty in geological modelling are theoretically infinite, and without a trustworthy conceptual model to outline the expected geological structures and lithologies, the uncertainty assessment of the resulting model will likewise be unreliable. In this paper, we describe the chain of uncertainties in the geological modelling workflow and showcase some of the most important sources of uncertainties through practical modelling examples from two different model areas. The paper also presents and discuss a method to conduct qualitative uncertainty assessment, which is conducted by the modeler and based on expert evaluation and prioritization of the different sources of uncertainty. The practical use of the uncertainty assessment method is exemplified in the last two examples, representing a local-scale and a large-scale model, respectively. All four examples are from Danish geological models that have been constructed as interpretation-based layer-models. However, the considerations regarding the uncertainties in the chain of the geological modelling workflow are useful regardless of the modelling method.