Roy D. Nurmi, 1987. "Section 8 Use of Well Logs in Evaporite Sequences", Marine Evaporites, Walter E. Dean, B. Charlotte Schreiber, Walter E. Dean, Gerald M. Friedman, Robert J. Hite, Roy D. Nurmi, Omer B. Raup, B. Charlotte Schreiber, Douglas J. Shearman
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Nearly two decades ago, Marshall Kay (in Grabau, 1960) wrote an interesting prefatory note to the paperback version of Grabau’s (1913) remarkable compendium concerning the
lithogenesis of sedimentary rocks - Principles of Stratigraphy. Kay indicated that since Grabeau’s book was written, much had been learned because of the increased depths and numbers of wells drilled by the petroleum industry. “The knowledge gained from rock cores, the analysis of sediments and microfossils, and the varied geophysical probes [well logs] in such borings, as well as those relating to greater depths, have vastly increased our understanding of sedimentary rocks in three dimensions”, stated Kay. And since Kay’s statement, many thousands of wells have been drilled, cored, sampled and logged with wireline well logs.
The sedimentological and geochemial techniques and principles thus far described in these short course notes are most appropriate to the direct examination of rock. Clearly, subsurface studies should utilize drill cores for chemical, paleontological, and detailed sedimentological analyses. However, the vulnerability of evaporite deposits to dissolution, deformation, and complex diagenesis necessitates the use of all subsurface data available.
Well logs and samples of cuttings provide the two most abundant records of subsurface geology. Unfortunately, since the introduction of well logs there has been a somewhat decreased concern regarding the sampling of well cuttings that has lessened the contribution of this important resource of subsurface data. Well cuttings and many well logs have sampling problems such as the influence of poor borehole conditions (Misk and others, 1977) and lack of
Figures & Tables
Evaporites were classified on the basis of their environmental relationships, particularly with respect to the under- and over-lying sedimentary sequences. The scope of knowledge that went into establishing this classification was limited to deposits developed in cratonic (continental crust) areas of the world. The advent of the concept of sea-floor spreading, together with new data collected by the Deep Sea Drilling Project and extensive submarine seismic surveys, both on the continental margins and in the deep-sea, enables us to classify evaporitic sediments on the basis of tectonic settings as well as sediment affinities. The various divisions are in a sense artificial; the one classification readily overlaps with the other, and each of the groupings may grade through time and space.