TABLE OF CONTENTS Successful petroleum exploration involves the integration of the wireline logs and geophysical surveys, described earlier in this chapter, with geological data and concepts. This section is concerned with the manipulation and presentation of subsurface geological information. It is written on the assumption that the reader is familiar with the basic principles of stratigraphy, correlation, and contour mapping. Many of the methods to be discussed are not, of course, peculiar to petroleum exploration, but have wider geological applications. Essentially, the two methods of representing geological data are cross-sections and maps. These methods are discussed in the following sections.
Vertical cross-sections are extremely important in presenting geological data. This account begins with small-scale sections and well correlations and proceeds to regional sections.
The starting point for detailed cross-section construction, as for example within a field, is consideration of well correlation. When a well has been drilled and logged, a composite log is prepared. This log correlates the geological data gathered from the well cuttings with that of the wireline logs. The formation tops then have to be picked, which is not always an easy task. The geologist, the paleontologist, and the geophysicist may all pick the top of the Cretaceous section, for example, at a different depth. The geologist may pick the top at, say, the first sand bed; the paleontologist, at the first record of a particular microfossil (which may not have thrived in the environment of the sediments in question); and...
