Petroleum Geology and Other Sciences
1. Petroleum geology is the application of geology （the study of rocks） to the exploration for and production of oil and gas. Geology itself is firmly based on chemistry, physics, and biology, involving the application of essentially abstract concepts to observed data. In the past these data were basically observation and subjective, but they are now increasingly physical and chemical, and therefore more objective. Geology, in general, and petroleum geology, in particular, still rely on value judgements based on experience and an assessment of validity among the data presented.
2. The application of chemistry to the study of rocks （geochemistry） has many uses in petroleum geology. Detailed knowledge of the mineralogical composition of rocks is important at many levels. In the early stages of exploration certain general conclusions as to the distribution and quality of potential reservoir could be made from their gross lithology. For example, the porosity of sandstones tends to be facies related, whereas in carbonate rocks this is generally not so. Detailed knowledge of the mineralogy of reservoirs enables estimates to be made of the rate at which they may lose porosity during burial, and this detailed mineralogical information is essential for the accurate interpretation of geophysical well logs through reservoirs. Knowledge of the chemistry of pore fluids and their effect on the stability of minerals can be used to predict where porosity may be destroyed by cementation, preserved in its original form, or enhanced by solution of minerals by formation waters.
3. Organic chemistry is involved both in the analysis of oil and gas and in the study of the diagenesis of the plant and animal tissues in sediments and the way in which the resultant organic compound, kerogen, generates petroleum.
4. The application of physics to the study of rocks （geophysics） is very important in petroleum geology. In its broadest application geophysics makes a major contribution to understanding the earth's crust and, especially through the application of modern plate tectonic theory, the genesis and petroleum potential of sedimentary basins. More specially, physical concepts are required to understand folds, faults, and diapirs, and hence their roles in petroleum entrapment.
5. Modern petroleum exploration is unthinkable without the aid of magnetism, gravity, and seismic surveys in finding potential petroleum traps. Nor could any finds be evaluated effectively without geophysical wireline well logs to measure the lithology, porosity, and petroleum content of a reservoir.
6. Biology is applied to geology in several ways, notably through the study of fossils （paleontology）, and is especially significant in establishing biostratigraphic zones for regional stratigraphical correlation. The shift in emphasis from the use of macrofossils to microfossils for zonation, caused by oil exploration, has already been noted. Ecology, the study of the relationship between living organisms and their environment, is also important in petroleum geology. Carbonate sediments, in general, and reefs, in particular, can only be studied profitably with the aid of a detailed knowledge of the ecology of modern marine fauna and flora. Biology, and especially biochemistry, is important in studying the transformation of plant and animal tissues into kerogen during burial and the generation of oil or gas that may be caused by this transformation.
7. Geologists, in contrast to some nongeologists, believe that knowledge of the concepts of geology can help to find petroleum and, furthermore, often think that petroleum geology and petroleum exploration are synonyms, which they are not. Theories that petroleum is not formed by the transformation of organic matter in sediments have already been noted and are examined in more detail. If the petroleum geologists' view of oil generation and migration are not accepted, then present exploration methods would need extensive modification.
8. Some petroleum explorationists still do not admit to a need for geologists to aid them in their search. In 1982 a successful oil finder from Midland, Texas, admitted to not using geologists because when his competitors hired them, all it did was to increase their costs per barrel of oil found. The South African State Oil Company （SOEKOR） is under a statutory obligation imposed by its government to put to the test every claim to an oil-finding method, be it a dowsing or some sophisticated scientific technique. These examples are not isolated cases, and it has been argued that oil may better be found by random drilling than by the appliance of scientific principles.