Geological prior information, and its applications to geoscientific problems

Geological information can be used to solve many practical and theoretical problems, both within and outside of the discipline of geology. These include analysis of ground stability, predicting sub-surface water or hydrocarbon reserves, and assessment of risk due to natural hazards. In many cases, geological information is provided as an a priori component of the solution (that is, information that existed before the solution was formed and which is incorporated into the solution). Such information is termed ‘geological prior information’. The key to the successful solution of such problems is to use only reliable geological information. In turn this requires that (a) multiple geological experts are consulted and any conflicting views reconciled, (b) all prior information includes measures of confidence or uncertainty (without which their reliability and worth is unknown), and (c) as much information as possible is quantitative, and qualitative information or assumptions are clearly defined so that uncertainty or risk in the final result can be evaluated. This paper discusses each of these components, and proposes a probabilistic framework for the use and understanding of prior information We demonstrate the methodology implicit within this framework with an example: this shows how prior information about typical sequence stacking patterns allows aspects of 2-D platform architecture to be derived from 1-D geological data alone, such as that obtained from an outcrop section or vertical well. This example establishes how the extraction of quantitative, multi-dimensional, geological interpretations is possible using lower dimensional data. The final probabilistic description of the multi-dimensional architecture could then be used as prior information sequentially for a subsequent problem using exactly the same method.