Interpreting Shoreline Sands Using Borehole Images - A Case Study of The Cretaceous Ferron Sands in Utah

Xu, Chunming¹ (1) Shell, Houston, TX

To establish borehole image interpretation guidelines in siliciclastic shoreline environment, this study utilized the unique data in the Ferron Sandstone members in Utah, where several core holes were drilled next to the outcrop cliff and logged with the electrical borehole images. The guidelines include three main components, 1) differentiating depositional elements based on borehole image textures; 2) multi-well correlation for regional stratigraphy; 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 fluvial, tidal, bay fill and shoreface elements were differentiated in each well based on a list of depositional textures and sequence characteristics revealed by the images and conventional logs. Differentiating hummocky cross stratification from channel cross bedding is critical to identify the shoreface sands. The shoreline pinchout lines and progradation directions are drawn through the multi well sequence correlation 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 marginal marine environments and eroded into the strand plain shoreface sands in most of the regression cycles. In the northern study area, the latest borehole image data revealed the south- to eastward delta plains fluvial channels following the southeastward prograding shoreline. The integrated study supports the regional V-shaped Ferron shoreline and oblique delta progradation within the regional eastward transportation into the Mancos Sea.