Quantitative Dynamic Stratigraphy: A Workshop, A Philosophy, A Methodology

Timothy A. Cross, John W. Harbaugh

Quantitative Dynamic Stratigraphy (QDS) is the application of mathematical/quantitative procedures to analysis of stratigraphic, geodynamic, and hydraulic attributes of sedimentary basins, treating them as features produced by the interactions of dynamic processes operating on physical configurations of the earth at specific times and places. Although QDS normally requires the construction of computer models that attempt, through simplification of the real world, to represent processes in terms of natural laws and/or empirical generalizations, it is a philosophically much broader and coherent approach to analysis of sedimentary basins. QDS allows more complete and effective integration of knowledge from previously separate disciplines; it requires more accurate definition of the variables involved in and their operations upon (within specified boundary conditions) the geologic system being simulated; it assesses or measures the degree of confidence in descriptions and predictions made by models; it may lead to new intuition by revealing interdependencies and feedback mechanisms among process variables and responses that are otherwise obscure or unnoticed; through real-time graphic simulations, it allows users to visualize and more completely understand interactions among processes and the products produced by their interactions; and it reduces time and effort constraints that manual manipulation of data impose on scientists such that more hypotheses may be developed and tested and more insights gained about complex geologic systems.

About 70 participants attended an international workshop on Quantitative Dynamic Stratigraphy, co-sponsored by AAPG, DOE, GRI, NSF, and USGS, in February 1988. The goals of this workshop were to summarize the state of the art in quantitative approaches to stratigraphic analysis; to identify major areas in which empirical geological information is required for construction and verification of quantitative models; and to define research directions that will significantly enhance capabilities to predict temporal and spatial relations of facies elements, fluid movement, and diagenetic changes in subsurface strata. Workshop participants presented a variety of QDS models that ranged over 10 orders of magnitude in temporal and spatial scales and that had been applied to problems ranging from geodynamics of basin formation, to genesis and prediction of stratal architecture and lithofacies distributions, to methods for increasing temporal resolution of the stratigraphic record, to fluid flow and rock/fluid interactions. The participants made specific recommendations, some of which are recounted in this talk.

Of all the positive attributes of QDS, one of the least commonly recognized, but most important, is the impact that QDS models have on decision-making. In a recently completed study of the variables and their relative strengths that are incorporated into decisions about geological risks for petroleum exploration, it was found that predictions lacking quantitative assessments produced no impact on the decision. For example, a prediction (negative or positive) about the occurrence of a reservoir-quality facies reached through application of a nonquantitative facies model, regardless of whether the study was complete and conducted by a qualified specialist, caused no change in the outcome of the decision. By contrast, the same prediction resulting from a QDS model, if accompanied by quantitative statements about the level of confidence, ambiguities in the data se and data analysis, and degree of applicability to the specific conditions of interest, had a major impact on the decision-making process.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.