Topic 2 Review of Fundamentals
The terminology of organic geochemistry is, in a very real sense, the language of organic chemistry. The following outline provides a brief review of the basic terminology necessary for understanding the application of organic geochemistry in exploration. The treatment is not meant to be comprehensive. In particular, it should be noted that the system used for naming organic compounds is a simplified and abridged form of several more comprehensive ones.*
The simplest organic compound is methane in which one carbon atom is linked tetrahedrally to four hydrogen atoms (Figure 2.1). The linkages, or bonds, are fixed in direction and length and are covalent in character. Even in more complex organic compounds carbon always forms four bonds and these commonly link the carbon to hydrogen, oxygen, sulfur or to other carbon atoms. This ability to form carbon-carbon bonds results in large groups of linked carbon atoms and leads to the enormous number and variety of organic compounds. Representing these structures presents problems because even the simplest hydrocarbon, methane, is three-dimensional and must be shown by a perspective drawing or be drawn in two dimensions according to some convention. Many different methods are in use and some of the more common ones are illustrated in Figure 2.1 using the branched 7-carbon compound (“2-methylhexane”) as an example.
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.