--> Abstract: Abstract: Incorporating Organic and Inorganic Chemical Change into Basin Models, by Lawrence M. Cathles III; #90066 (2007)

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Incorporating Organic and Inorganic Chemical Change into Basin Models

Lawrence M. Cathles III
Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY

Chemical changes in sediments and petroleum can directly reflect fluid movement in basins, and these changes can be quantitatively modeled. For example, the washing of oil by late-generated gas along migration pathways (and perhaps particularly in carrier beds just below the top of overpressure) produces a pattern in oil chromatograms that indicates both the depth at which the washing took place and the amount of gas involved in the washing (Meulbroek et al., Organic Geochemistry, 29, 1998). CO2 generated deep in a basin can fill reservoirs with high mass fractions (>0.1) of CO2 only if Ca, Mg, and Fe alumino-silicates have been titrated from the reservoir and the migration pathways connecting to it by interaction with previous migration attempts of CO2. These are just two examples of chemical changes that are related to exploration economics, but there are many others. For example, assisted by bacteria or temperature, H2S is be generated by the interaction of hydrocarbons with sulfate, but H2S levels can also be controlled by inorganic rock buffers. Pressure drops that occur as aqueous fluids are forced through seals will alter the seals, and this alteration may quantitatively measure the amount of leakage. We have developed a general framework for incorporating inorganic and organic chemical alteration within a 2D finite element basin model that runs on a PC. The framework requires that reactive components in a fluid titrate reactive components of the sediment or other fluid phase in an element before they can move into the next downstream element. Components in a fluid that are buffered enter the sediment as dictated by pressure and temperature changes between elements. Incorporation of chemistry is a work in progress, but the approach we are taking has yielded interesting results in a number of cases already, and these can be described. Predicting alteration could tie synergistically to seismic, electromagnetic, or other methods of geophysically mapping alteration, if such could be developed. The presentation will illustrate the methods I have developed for incorporating chemical change in basin models through discussion of the most current and illustrative examples.


AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands


AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands