About This Item
Share This Item
Interpreting depositional environments by scanning electron microscope analysis of sand surface textures is a useful new technique for petroleum exploration. The method enhances the geologic interpretation of well cuttings, and is particularly attractive where no other direct geologic information may be available.
Diagnostic surface textures appear on quartz sand grains from dune, high- and low-energy littoral, glacial, glaciofluvial, and diagenetic environments. With the scanning electron microscope, dune and littoral grain textures were observed on sand in cuttings from 4 offshore Gulf Coast wells. These primary depositional textures may be preserved to depths of 14,000 ft, and consistent preservation of depositional textures is common to 10,000 ft. Grains of Pleistocene and late Pliocene sediments commonly display primary depositional textures, fairly independently of depth. Diagenetic textures normally obliterate the primary depositional textures at depths below 10,000 ft and in sediments older than late Pliocene, but a few breaks in the general pattern of increasing diagenesis with depth a low reasonably accurate environmental interpretations of scattered deep sandstones. The depositional environments as determined from grain textures closely parallel the environmental interpretations derived from paleontologic and lithologic analyses.
The recognition of distinctive types of diagenetic surfaces holds additional promise for enhancing the geologic interpretation of well cuttings. Some diagenetic textures appear independent of one another in their occurrence and stratigraphic distribution, though the causes of these variations are not presently known. The relations of diagenetic sand surface textures to cementation, chemistry of formation waters, and fluid migration currently are being studied.
End_of_Article - Last_Page 655------------