ABSTRACT

Exploitation of oil and gas accumulations in "shoestring sands" can be aided materially by determining, with samples from even a single well, whether a sand stringer is an offshore bar deposit with a linear shape and lying parallel to the depositional trend or whether it is a river deposit cutting across the depositional trend and having a sinuous shape. The present research has disclosed textural criteria applicable to well samples which serve to distinguish between these two types of "shoestring sands."

Samples taken from rivers and from beaches along the Texas Gulf Coast indicate clear textural differences between the two environments. Compared to river sands, beach sands show an extremely restricted range of mean sizes and sorting coefficients. Furthermore, river sands with sorting coefficients equal to those of beach sands are invariably coarser than beach sands, whereas river sands of the same mean size as beach sands are more poorly sorted. Consequently, plots of mean size versus sorting yield a clear distinction between the two types of sediment.

The above information has been obtained by sieve analyses of unconsolidated sediments. Mean sizes and sorting coefficients of sandstones, however, can be approximated readily by grain counts in thin sections. In 15 minutes, or less, sufficient grains can be counted in section to enable the geologist to distinguish between the typical beach and river sands studied in the present work.