Interpreting shoreline sands using borehole images: A case study of the Cretaceous Ferron Sandstone Member in Utah

Abstract

To establish borehole image interpretation guidelines in a siliciclastic shoreline environment, this study used unique data from the Ferron Sandstone Member in Utah, where several core holes were drilled next to the outcrop cliff and logged with electrical borehole images. The guidelines include three main components: (1) differentiating depositional elements based on borehole image textures, (2) multiwell stratigraphic correlation and depositional architectures, and (3) ambiguity and data limitations. The stratigraphic interpretation of the image logs is closely correlated with the cores and the outcrops to evaluate the interpretation methodology. The sandstones of upper shoreface, middle shoreface, and channels are differentiated in each well based on a list of depositional textures and sequence characteristics revealed by the images and open-hole logs. The coals, carbonaceous shales, bay fill, and transgression lag deposits are identified as important elements in building the stratigraphic framework. Channels eroding into the shoreface and shoreface pinch-out into delta plains are recognized based on the facies classification and stratigraphic framework. The shoreface progradation directions are drawn through multiwell sequence correlation, paleoflow, and seaward facies transition analysis. In the Muddy Canyon area, the progradation directions of the shoreface parasequences vary from north to east with dominance to the northeast. The complex channel systems with diverse flow directions amalgamated in the delta plains and eroded into the strand-plain shoreface sandstones in most of the regression cycles. In the northern study area, the latest borehole image data revealed the south- or southeastward-prograding Ferron shorelines and the cyclic Blue Gate Member shoreline sequences. The integrated study supports the regional V-shaped Ferron shoreline with oblique delta progradations within the regional eastward transportation into the Mancos Sea.