Gernot Paulus
Department of Geology and Paleontology, University of Salzburg
Salzburg, Austria

ABSTRACT

Subsurface fluid migration is a multi-parameter process depending on many different components (e.g., tectonics, facies, lithology, hydrochemistry, and hydraulics). Knowledge of subsurface fluid migration is critical to the success of petroleum and geothermal exploration, and to petroleum production in sedimentary basins. A geographical information system (GIS) has been used for the present study to integrate different data sets related to subsurface fluid migration and to perform spatial analysis on the resulting comprehensive database. The discussion illustrates the reliance on geographic location as the common frame of reference during the integration phase. The area of investigation is the Molasse Basin in Upper Austria, which is a typical asymmetric, compressional foreland basin at the northern margin of the Alps. Due to petroleum exploration and production, an excellent data set exists with more than 500 wells ranging in depth from 1000 to 4000 m. Three different fault systems have been active at different times from pre-Tertiary until the present and have a large impact on hydrocarbon migration and fluid flow. There are two components to the fluid migration modeled in this study: (1) a north-directed migration of hydrocarbons and (2) an east-directed fluid flow of deep groundwater at basin scale in a Jurassic carbonate aquifer. The aquifer is the main target for geothermal exploration in this area. The datasets used in the spatial analysis contain well data, subsurface fault data, and hydrocarbon reservoir data. Applications and examples of various spatial GIS analysis techniques are presented here, including (1) investigation of the spatial relationship between subsurface faults and well locations using buffer zones and topological overlay, (2) calculation of fault density and assessing its implication on subsurface fluid flow, (3) modeling of fault-related fluid flow using cost surfaces, and (4) spatial overlay of hydrocarbon reservoir information and fault-related permeability distributions. These examples provide a comprehensive overview of how to use the unique capabilities of a GIS in subsurface geologic analysis.