Unconventional reservoirs are becoming an important source of hydrocarbons around the world. For many years, detailed studies of mudrocks were not conducted largely due to the pervasive view that muds, being the result of fine-grained settling within a quiet water column, were ‘uneventful’. Recent research, however, indicates that mudrocks are internally more complex than previously thought and mostly likely deposited under dynamic conditions. Recognition of the complexity of mudrocks has led to a desire to more fully describe finegrained cores with attention to textural variations. From an exploitation point of view, understanding the fine-scale structure of mudstones is a key part to building a framework with which to better predict reservoir vertical and lateral variability. The Cenomanian-Turonian Cretaceous Eagle Ford Formation of the Texas Gulf Coast is a dark grey marl that functions as both source and reservoir. From multiple cores within both the oil and gas-condensate windows, a database of core descriptions, thin sections, high-resolution helical computed tomography (CT) scans, and SEM images of ion-milled surfaces was built. Observations from these data were used to create an interpretation of the Eagle Ford’s texture and fabric. In particular, the CT data was fund to be very helpful for understanding the internal fabric and was used to initially break the rock into fabric units. An outcome of this work was an understanding of why a ‘universal’ electrofacies model was elusive. Tying these observations to larger scale cycles seen in well logs and outcrops created a predictive model for reservoir quality.


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