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In the past 15 years organic geochemistry has evolved from an academic discipline into an important and useful tool in exploration. The development of experimental techniques for analyzing complex organic materials (such as kerogen) and multicomponent mixtures (such as crude oils) has played a critical role, and this ability to characterize organic matter in detail has led to a better understanding and documentation of the process of petroleum generation. Although the nature of the organic matter in source rocks exercises initial control over the hydrocarbons generated (oil versus gas), it is processes acting in the reservoir that most influence oil quality. Thermal maturation and bacterial alteration are well-understood and their influence on the details of oil compositi n is documented by many studies. Pyrolysis techniques have been particularly important in providing a means for analyzing small samples quickly, and their introduction onto drilling rigs has made geochemical data available at the same time as other electric log information.
Despite considerable progress, some areas of geochemistry need further development. Analytical techniques, although still capable of refinement, are in general adequate for the tasks in hand. The biggest conceptual gap is in understanding the process of migration out of source rocks. Progress is being made, but the relative importance of the various possible migration mechanisms is imperfectly understood. This is a critically important area because of its impact in recognizing source rocks, establishing time of migration and distance of migration, and in developing oil-to-source correlation methods. Quantitative models that use time-temperature relationships to establish the time of oil generation are developing rapidly and provide an important tool. Further refinement is needed, and ere parallel research on simulating generation in the laboratory will be important. Hydrous pyrolysis (which involves heating samples of immature source rocks at elevated temperatures and pressures in an aqueous medium) seems to duplicate natural generation very well and has enormous potential for investigating generating capacities of different types of organic matter under various conditions.
The biggest challenge in exploration is to extrapolate from limited well data to other locations in the basin. Geochemistry cannot function in this way without a much better understanding of the relationships among organic matter types and environments, and the processes that operate to separate organic matter types (such as different hydraulic behaviors). It is important to establish the geochemical style of each depositional environment and to extend the present concepts of organic facies. We need more "geo" in geochemistry. Also more attention should be paid to mass balance considerations within the geologic framework;
for example, how much oil can a particular source unit be expected to produce?
Organic geochemistry is developing all the signs of a mature discipline with several widely accepted textbooks and journals, increasing numbers of industry-oriented publications, and reputable service companies. An encouraging sign is the increasing number of interlaboratory standards currently being exchanged. I am very optimistic about the future applications of organic geochemistry as an exploration tool.
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