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Hans H. Von Der Dick1, Dane A. Bosman1
(1) Chem Terra International (CTI), Ltd, Calgary, AB

Abstract: Numerical reconstruction of micro- seep gas signals in surface gases: Technique and application

The interpretation and application of surface gas surveys as a tool for oil and gas exploration usually relies on simple surface hydrocarbon gas magnitude data and their statistical evaluation. However, these basic data cannot reveal the complex origin, alteration, and fate of light hydrocarbons in near surface environments, thus typically leading to erroneous data interpretation and surface gas “anomalies” that lack a relation to specific geologic subsurface conditions.

Despite many pitfalls a large scale surface gas data body demonstrates a general, but diagnostically limited relationship of surface gas magnitudes with subsurface oil and gas pools. The reason for this limited diagnostic exploration value of most surface gas data is the extensive, variable, and unpredictable noise level in surface hydrocarbon gas data.

In this paper we apply high quality surface gas sampling and analysis coupled with advanced numerical vector analysis to reconstruct and explain soil hydrocarbon gas data in terms of gas source families. The fundamental value of this procedure, termed GEL (Geochemical Exploration Lead), is the recognition of a distinct, unique seep gas family that numerically evolves from surface gas associations of various origins and fates. The presence or absence of such a separate seep gas phase in surface gas data is a key element for improved evaluation of surface gas data. Several case studies along with data experiments, simulations and sensitivity tests illustrate this new technique and demonstrate the applicability and limitations of surface gas data for exploration.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana