--> Abstract: “GOR-Isotopes” – A New Tool for the Quantitative Assessment of Gas Generation and Gas Typing in Petroleum Systems, by Robert L. Braun, Yongchun Tang, Steven Zhang, Geoffrey S. Ellis, and Martin Schoell; #90039 (2005)

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“GOR-Isotopes” – A New Tool for the Quantitative Assessment of Gas Generation and Gas Typing in Petroleum Systems

Robert L. Braun1, Yongchun Tang2, Steven Zhang1, Geoffrey S. Ellis2, and Martin Schoell3
1 GeoIsochem, Inc, Walnut, CA
2 California Institute of Technology, Covina, CA
3 Gas Consult International Inc, Berkeley, CA

Despite that fact that gas formation is a more complex process than oil formation, the geochemical techniques employed for natural gas exploration are still relatively rudimentary and primarily dominated by empiric models of gas formation. In contrast to oil which is generated in the so-called "thermal oil window", natural gas is generated throughout the entire thermal evolution of sedimentary basins. A new technique is now available that addresses quantitatively many issues of natural gas formation. This model is based on direct closed-system pyrolysis measurements of quantities and isotope fractionations for gases generated from specific source rocks. With the application of first principle calculations of hydrocarbon generation we can extrapolate the high-temperature pyrolysis measurements to any geologic heating rate. Using experimental data of different source rock types (Type I and II shales and Type III coal) we are able to generate output files that display the most critical properties for specific source rocks for any thermal history of a petroleum system e.g., isotope fractionation patterns, temperature and maturity of the gas source rock, gas quality (e.g., wetness), gas maturity, and the gas to oil ratio (GOR). Additionally, integration of our gas isotope model results with those of basin models allows for prediction of the geologic conditions pertaining to gas generation within a basin (e.g., time of gas formation, depth of gas kitchen, amount of gas formed in target areas, etc.) These results can provide critical information for mapping gas migration pathways, determining reservoir filling history, characterizing reservoir connectivity, and identifying multiply sourced gas.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005