Eagle Ford outcrops in Lozier Canyon, located in eastern Terrell County in West Texas, provide the opportunity to examine an unconventional carbonate mudstone reservoir at various scales across an area extending over 50 square miles. In Lozier Canyon and its tributaries, tens of cutbank outcrops provide panoramic views of the entire Eagle Ford Group in exposures hundreds of feet high and thousands of feet long. Furthermore, some localities display laterally extensive exposures of individual bedding planes and key stratal surfaces to allow for the 3-dimensional view of sedimentary structures, biogenic debris beds, and trace fossils. Whereas unconventional mudstone reservoirs like the Eagle Ford are commonly portrayed as being homogenous reservoirs, our work to date reveals a vertically heterogeneous facies and TOC succession with variability at the bed-, bedset-, parasequence-, sequence-, and sequence-set scale. Within the study area, lateral variations in the thickness, lithofacies, and bedding continuity within the various defined members and sequences is observed. The Eagle Ford outcrops in West Texas offer a unique 3-D perspective to document, understand, and predict the vertical and lateral heterogeneities that occur at a variety of scales within unconventional mudstones reservoirs, like the Eagle Ford in the subsurface of South Texas, and similar reservoirs elsewhere.
The Upper Cretaceous (Cenomanian to Coniacian) Eagle Ford Group is a prolific unconventional mudstone reservoir in the Gulf of Mexico Coastal Plain of South Texas (Figure 1). More often than not, unconventional reservoirs like the Eagle Ford are often conveyed as monotonously uniform and homogenous, with the connotation being that these they are simple " resource plays", which require limited geologic analysis beyond predicting product type. This perception quickly changes, however, when resource exploitation reveals a range of well rates across the play fairway, suggesting underlying geologic variability.