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A decade has passed since the introduction of projective well-log interpretation, i.e., of a system of quantitative geologic well-log analysis and interpretation for the purpose of exploration for oil and gas.
Such projective techniques use well logs to investigate and map physicochemical rock modifications that may have taken place in the sedimentary geologic column as a result of the migration and accumulation of oil and gas in structural as well as in stratigraphic traps. The principles on which the individual techniques of this system rest have been reviewed in scientific and trade magazines. Many example surveys and discovery data have been published, but most survey results have remained confidential. With passing years some operators have drilled and discovered oil not knowing that such surveys have been made on their prospect areas. Some example surveys made in Florida, in the Permian basin, in the Denver-Julesburg basin, and in the Williston basin are presented in which a number of producing oil and gas wells, and fields, have now been developed in areas mapped and indicated as petroliferous long before discoveries.
One feature common to all petroliferous trends delineated by projective well-log interpretation is that the exact limits of expected production are not pinpointed nor is any claim made that the indicated petroliferous trends will be economically productive. To define economically productive limits, a much greater well density is needed. With such density all the oil fields within the explored depth would have been found, but deeper production possibilities would be indicated by projective techniques.
In the petroliferous areas indicated on the maps of areas not yet fully explored, it is suggested that electrotelluric surveys are a means of pinpointing and of delineating the actual subsurface oil and gas accumulations within the broad probable oil-bearing regions.
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