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Geochemical prospecting is, theoretically, the most direct approach to oil and gas exploration. Migration
of a minute amount of hydrocarbons to the surface should produce an abnormal content of hydrocarbons in soils, and therefore forecast the location of an oil or gas reservoir underneath.
Several major inconveniences, however, make the hypothesis very difficult to apply, mainly, (1) the exact process of migration is not fully understood, (2) "geochemical noises" due to contamination, hydrocarbons being formed in the soils, etc., are superimposed on migrating hydrocarbons, and (3) different soil lithologies have different powers of retention of hydrocarbons and, conversely, a different aptitude to release the hydrocarbons retained.
Gasmap introduces a method which, although following the basic theory, attempts to eliminate, solve, or bypass the problems, i.e., it attempts to cope with each of the known "geochemical noises." The solution attempted in Gasmap proposes a method in which sampling and desorption of the sample are done under a definite number of principles. Its originality, however, lies basically in the method of interpretation of the results. Samples are listed according to their depths, lithology, chemical markers, and hydrocarbon contents. Through use of a computer, a statistical analysis of the Gaussian type is done and a mean value and a dispersion are derived. Samples are classified in homogeneous sets and anomalous samples are derived according to a probability threshold. Results are plotted on maps for each hydrocarbon. A composite map is produced and anomalies are classified according to their chemical composition and degree of anomaly.
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