Topic 8 Geochemical Correlation
Crude oil is generated by the action of heat on the organic matter in source rocks and subsequently migrates to a reservoir. Because migration is such an inefficient process most of the generated bitumens remain in the source rock and this suggests that the extractable organic matter left in the rock and the crude oil in the reservoir may show similarities in their chemical compositions. Also, crude oils generated by the same source rock but reservoired in different traps should show similarities. On the other hand, crudes which were derived from different source rocks will have distinct compositions. The techniques used to relate crude oils to each other and to the source rocks which produced them consitute geochemical correlation.
Correlation is important in exploration. When an oil is correlated to its source rock the migration path is established and structures along it become important exploration targets. In the early stages of basin evaluation the presence of two unrelated crudes would indicate the presence of two source rocks. Any area with multiple source rocks is attractive. Similarly, if an oil and a source rock cannot be correlated, there must be another source rock for the crude oil and the first source may have produced other oils. Such a basin would be more attractive than one with only a single source rock.
Techniques for correlating normal crude oils are well established and are used routinely, but when one (or more) of the oils is degraded correlation becomes more difficult and special procedures
Figures & Tables
Organic geochemistry can be a useful addition to the range of techniques available to the exploration geologist. This publication introduces the fundamental ideas of organic geochemistry with four main objectives: what organic geochemistry can and cannot do; provide an understanding of the language of organic geochemistry; provide some insights into general concepts such as minimum time and temperature, maximum temperature, and minimum organic matter content for source rock; and provide inforamtion on the techniques available for knowing things such as whether two oils are related.